Subway and Underground Structures - MTA · 2020. 8. 13. · ASCE 37 2.1 Dead Loads Dead Loads (D)...

DG 452A

Structural Design Guidelines

Subway and Underground Structures

Issue No. 3

November 24, 2015

Approved By:

Frank Mondello, P.E., Chief Civil/Structural Engineer

Issue Record

No. Date Description of Change Prepared By Formal Review

Intermediate Review

0 July 31, 2002 Original Issue S. Sengupta x

1 Dec. 29, 2004 General Revision S. Sengupta x

2 Dec. 29, 2006 Chapter 12 - added Chapter 9 - Substantially revised Other Chapters - minor revisions

S. Sengupta x

3 Nov. 24, 2015 Complete Review H. Lakhani x

Division of Engineering Services

Alok Saha, P.E.

Vice President and Deputy Chief Engineer



Table of Content

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STRUCTURAL DESIGN GUIDELINES

SUBWAY AND UNDERGROUND STRUCTURES

DG 452A



Table of Contents

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Acknowledgements:

Contributions of the following Engineers from CPM are recognized.

Madan Naik, P.E., Chief Civil/Structural Engineer. Dr. Ajit Kumar Shah, Senior Geologist

Also acknowledged are the contributions of Subal Sarkar, PhD and Arman Farajollahi of PB Americas, Inc. for reviewing and commenting on the Chapter 9 - Tunneling Structures

Sanjay Sengupta, P.E.

Preparer



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TABLE OF CONTENTS

Chapter Topic Page

1 Introduction 3

2 Loads 6

3 Load Combinations 21

4 Geotechnical 27

5 Materials 32

6 Cut-And-Cover Structures 37

7 Foundations 86

8 Construction Induced Movements and Settlements – Cut-and-Cover

88

9 Tunnel Structures 98

10 Construction Induced Movements and Settlements – Tunneling

134

11 Underpinning 145

12 Seismic Design Requirement for Architectural, Electrical and Mechanical components

148

Appendix 9A, 9B

Evaluation of Liner Capacity 9A-1 9B-1



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Introduction

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Chapter 1

Introduction

Table of Contents

Section Item Page

1.0 Scope 4

1.1 Design Life 4

1.2 Guiding Documents 4



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CHAPTER 1

Introduction

General

1.0 Scope

The scope of this document is to provide Structural Design Guidelines on the following new structures and facilities:

1. Cut and Cover Structures. 2. Mined Tunnel in Rock and Mixed Soil. 3. Bored Tunnels in Rock. 4. Cavern Structures in Rock. 5. Station Structures. 6. Other Underground Structures such as:

Ventilation Fan Plants Pump Rooms Substations

This document also provides design guidelines on evaluations of ground movements and settlements due to excavations and tunneling and the means to mitigate them.

1.1 Design Life

The structures shall be designed for 100 years. Assurance of this criterion shall be primarily through:

Crack Width and Crack Control Concrete Composition Waterproofing Corrosion Control of Rebars and Structural Steel

1.2 Guiding Documents

Codes, Standard, Manuals, and Guidelines shall be the most current ones.

1.2.1 Codes and Standards

1. American Concrete Institute (ACI). ACI 318 Building Code Requirements for Structural Concrete.

2. American National Standards Institute (ANSI)

3. American Society for Testing and Materials (ASTM).

4. American Welding Society (AWS). Structural Welding Code (AWS D1.1).

5. National Fire Protection Association (NFPA). Standards and Guidelines NFPA 130.

6. National Earthquake Hazard Reduction Program (NEHRP). NEHRP Requirements, Latest version.



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7. New York City. New York City Building Code (NYCBC).

8. New York City. Department of Buildings. Rules of the City of New York Title 1.

9. New York City. Department of Transportation (NYCDOT).

10. New York City Transit. NYCT DG 453 Field Design Standards.

11. New York City Transit. NYCT DG 452 Structural Design Guidelines.

12. New York State. Building Code of New York State (NYSBC).

13. New York State. Codes, Rules and Regulations of the State of New York (NYCRR)

14. New York State. Department of Transportation (NYSDOT)

1.2.2 Manuals and Guidelines

The pertinent manuals and guidelines are listed in the relevant chapter.



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Chapter 2

Loads

Table of Contents

Section Item Page


2.1 Dead Loads 7

2.2 Train Axle Loads 7

2.3 Impact 11

2.4 Centrifugal Force 11

2.5 Wind Loads 12

2.6 Thermal Loads 12

2.7 Live Loads 13

2.8 Platform Loads 13

2.9 Sidewalk and Roadway Loads 14

2.10 Existing Buildings and New Construction 15

2.11 Lateral Pressure 15

2.12 Seismic Loads 16

2.13 Miscellaneous Loads 17



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CHAPTER 2

Loads



Refer to Chapter 1, Section 1.2.1.


1. American Society of Civil Engineers (ASCE). Minimum Design Loads for Buildings and Other Structures. ASCE 7.

2. American Society of Civil Engineers (ASCE). Design Loads on Structures During Construction. ASCE 37

2.1 Dead Loads

Dead Loads (D) consist of the actual weight of the structure plus superimposed dead loads, such as earth, water, permanently installed track work, partitions, finishes, service walks, pipes, conduits, utilities, services, and all other permanent construction and fixtures. Since dead load stresses are always present, the structure shall be designed to support all dead loads at all times without reduction.

The weight of materials shall be estimated as follows:

MATERIAL WEIGHT (PCF) Steel................................................................................................................490 Cast Iron .........................................................................................................450 Reinforced Concrete(Normal Weight) ...........................................................150 Stone Or Asphalt Concrete (Plain) ................................................................144 Earth, Dry .......................................................................................................100 Earth, Saturated ..............................................................................................125 Brick Masonry ...............................................................................................120 Stone Masonry ...............................................................................................150 Crushed Stone, Gravel ...................................................................................110 Water .............................................................................................................62.4

Other design unit weights shall be based on the Geotechnical Engineer’s recommendation.

2.2 Train Axle Loads

a. The train load on subway tracks shall be taken as a continuous train of cars with axle loads of the amounts and spacing given in Figures 2.1A to 2.1C. For maximum values of shear, moment and floor beam reaction, see Table 2.1A for “A” Division (IRT) loading and Table 2.1B for “B” Division (IND/BMT) loading.



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b. In designing structural members, the effect of dead load and impact shall be added to the values given in Tables 2.1A and 2.1B.

c. The train axle loads shown in Figures 2.1A, 2.1B, and 2.1C were utilized as the standard design loading for New York City Transit Structures. The cars for which these loadings were developed are in most cases no longer in service. However, current and all future non-revenue and passenger car designs must be restrained in the magnitude and spacing of maximum axle loads so that the shears, moments and floor beam reactions produced by these loads in subway structures do not exceed the values produced by the standard design loading.

d. Where the structure supports other railroad trains, the design shall be in accordance with the requirements of the railroad company concerned, provided those of New York City Transit are not more severe.

e. Intermediate track floors in subways with beams placed transversely shall be designed for a live load of 1100 psf static equivalent, applied over a width of 10 feet symmetrical to the centerline of track, in addition to the dead load, as shown in Figure 2.2. The direct compression due to side pressure shall be considered in designing track floor and other intermediate beams. Special track floor construction at crossings, with rail supports placed longitudinally, shall be designed in accordance with Tables 2.1 and 2.2.



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TABLE 2.1A “A” DIVISION (IRT) CAR LOADING

Shears, Bending Moments And Floor Beam Reactions (FBR) For Stringers On Straight Track Due To Train Load On One Rail

(Impact Not Included)

SPAN FT.

SHEAR KIP

MOMENT FT.-KIP

FBR* KIP

SPAN FT.

SHEAR KIP

MOMENTFT.-KIP

FBR* KIP

6 15.13 22.69 15.13 46 46.04 470.07 53.91 8 17.65 30.26 17.65 48 46.64 500.07 55.61 10 20.17 37.83 22.18 50 47.20 530.09 57.17 12 21.85 47.33 26.05 52 47.73 560.13 59.07 14 23.05 61.46 28.81 54 48.62 590.19 61.37 16 24.58 75.84 31.51 56 49.45 620.26 63.51 18 26.89 90.39 34.73 58 50.34 650.35 65.50 20 28.74 111.16 37.31 60 51.44 680.44 67.85 22 30.25 133.83 39.42 62 52.46 710.55 70.55 24 32.77 156.50 41.18 64 53.43 740.67 73.08 26 34.90 179.18 42.67 66 54.33 770.79 75.45 28 36.73 201.86 43.94 68 55.48 800.93 77.98 30 38.32 231.28 45.05 70 56.70 831.07 80.51 32 39.71 260.95 46.01 75 59.82 908.93 86.25 34 40.93 290.69 46.87 80 63.18 1000.85 91.27 36 42.02 320.48 47.63 85 66.14 1104.07 95.69 38 42.99 350.33 48.73 90 68.77 1207.38 99.89 40 43.87 380.21 49.89 95 71.13 1322.22 104.19 42 44.66 410.14 50.93 100 73.25 1458.94 108.83 44 45.38 440.09 52.38

* For two adjacent spans of equal length.

ADJACENT SPANS

FT.

FBR KIP

ADJACENT SPANS

FT.

FBR KIP

30 and 35 46.78 35 and 35 47.26 30 and 40 48.07 35 and 40 48.59 30 and 45 49.08 35 and 45 50.76 30 and 50 51.25 35 and 50 52.97 30 and 55 54.06 35 and 55 55.79 30 and 60 57.25 35 and 60 58.98 30 and 65 60.65 35 and 65 62.38 30 and 70 63.56 35 and 70 65.29 30 and 75 66.09 35 and 75 67.82 30 and 80 68.30 35 and 80 70.03 30 and 85 70.50 35 and 85 71.98 30 and 90 72.70 35 and 90 73.97 30 and 95 74.67 35 and 95 76.29

30 and 100 77.04 35 and 100 78.77



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TABLE 2.1B “B” DIVISION (IND/BMT) CAR LOADING

Shears, Bending Moments And Floor Beam Reactions (FBR) For Stringers On Straight Track Due To Train Load On One Rail

(Impact Not Included) SPAN

FT. SHEAR

KIP MOMENT

FT.-KIP FBR* KIP

SPAN FT.

SHEAR KIP

MOMENTFT.-KIP

FBR* KIP

6 20.50 30.75 20.50 46 51.00 517.48 57.62 8 23.00 41.00 23.00 48 51.71 551.17 59.99 10 26.50 51.25 26.50 50 52.36 584.89 61.89 12 28.83 61.58 28.83 52 52.96 618.62 63.64 14 30.50 80.39 31.57 54 53.52 652.37 65.81 16 31.75 99.56 34.00 56 54.04 686.15 68.04 18 32.72 118.97 37.78 58 54.52 719.94 70.45 20 33.50 138.55 40.80 60 54.97 753.74 73.03 22 34.14 158.25 43.27 62 55.69 787.55 75.45 24 35.42 178.04 45.33 64 56.68 821.38 77.72 26 37.92 197.90 47.08 66 58.22 855.22 79.85 28 40.07 221.20 48.57 68 59.67 889.06 81.85 30 41.93 249.48 49.87 70 61.04 922.92 83.74 32 43.56 282.76 51.00 75 64.13 1007.59 88.03 34 45.00 316.13 52.00 80 66.84 1092.30 91.78 36 46.28 349.56 52.89 85 69.24 1177.05 96.21 38 47.42 383.06 53.86 90 71.36 1304.72 101.53 40 48.45 416.61 54.40 95 74.27 1436.33 106.29 42 49.38 450.20 55.05 100 77.06 1568.22 111.49 44 50.23 483.82 55.84

* For two adjacent spans of equal length.

ADJACENT SPANS

FT.

FBR KIP

ADJACENT SPANS

FT.

FBR KIP

30 and 35 51.89 35 and 35 52.46 30 and 40 53.41 35 and 40 53.98 30 and 45 54.59 35 and 45 55.16 30 and 50 55.53 35 and 50 56.95 30 and 55 58.20 35 and 55 60.37 30 and 60 61.05 35 and 60 63.21 30 and 65 63.46 35 and 65 65.62 30 and 70 66.12 35 and 70 67.69 30 and 75 68.61 35 and 75 69.48 30 and 80 70.80 35 and 80 72.37 30 and 85 73.06 35 and 85 75.04 30 and 90 76.00 35 and 90 77.42 30 and 95 78.63 35 and 95 79.55

30 and 100 81.00 35 and 100 82.00



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2.3 Impact

a. Impact shall be considered for trains only. For subways, the train loads specified in Section 2.2 shall be increased by a percentage I, as given by the following formula:

I = )L450(

100)]6/L(150[

(1)

Where: I = increase in percent of the live load on a single track. L = length of span in feet.

b. For members supporting several tracks, such as cross girders and columns,

L = length of adjacent spans for one track only. See Table 2.2 for values of I.

c. Where a member supports more than one track, the number of tracks assumed loaded shall be such as will produce the maximum stress in the member, but the impact increase shall be applied only to that track which, when loaded, contributes most to the live load stress.

TABLE 2.2

Impact Increases (%) For Train Loads As Determined from Formula (1)

L I L I L I 5 33 40 29 100 24 10 32 50 28 150 21 15 32 60 28 200 18 20 31 70 27 250 16 25 31 80 26 300 14 30 30 90 25 350 12

2.4 Centrifugal Force

Where proper super elevation is provided, the centrifugal force shall be considered as stressing columns (in bending only), bracing and steel column bases, and shall be assumed to act at the level of the base of rail in the direction outward and radial to the curve. In this case, only its horizontal effects need be considered.

Where no super elevation is provided, the centrifugal force shall be assumed to act 5 feet above the base of rail and the resulting vertical forces shall be taken into account in designing stringers and columns.



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In computing stresses, assume trains on all tracks and use the following formula:

F = CW (2)

where: F = centrifugal force (kips) C = coefficient depending on degree of curvature, as per Table 2.3 W = weight of train, assumed as 2 klf of each track measured between

centerlines of spans.

TABLE 2.3

DEGREE OF CURVATURE

RADIUS FT.

C DEGREE OFCURVATURE

RADIUS FT.

C

1 5730 0.020 11 522 0.132 2 2865 0.040 12 478 0.132 3 1910 0.060 13 442 0.130 4 1433 0.076 14 410 0.126 5 1146 0.090 15 383 0.120 6 955 0.102 16 359 0.112 7 819 0.112 17 338 0.102 8 717 0.120 18 320 0.090 9 637 0.126 19 303 0.076 10 574 0.130 20 288 0.060

Centrifugal force shall be neglected for curves of less than 1 degree, while for curves exceeding 20 degrees, the value of C shall be taken as 0.060.

2.5 Wind Loads

Wind loading, where applicable, shall be as per the BCNYS, which in turn references ASCE 7. The basic wind speed, per Section 1609, with V3s=110 mph (3 second gust speed). In no case shall the wind load be less than 15 psf.

2.6 Thermal Loads

a. Coefficient of thermal expansion:

In the design and analysis of structures, provision shall be made for the stresses or movements resulting from a variation in temperature from –10 to + 110 degrees Fahrenheit. The coefficients of linear expansion for common materials are provided in Table 2.4.

TABLE 2.4

Material Coefficient Of Linear Expansion Per Unit Of Length, Per Degree F

Steel, Mild (Structural) 6.5 x 10-6 Steel, Stainless 9.6 x 10-6 Iron, Cast, Gray 6.0 x 10-6

Concrete, Normal Weight 5.5 to 7.0 x 10-6



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2.7 Live Loads

Structural floor and roof members shall be designed to resist the distributed and/or concentrated loads given in Table 2.5.

All equipment loads shall be verified from the vendor’s information during the final design.

Table 2.5: Design Live Loads

U = Uniform Load in psf and C = Concentrated Load in kips NO. Description U C NOTE

1 Service Walk 150 0 1 2 Stairs, on horizontal projection 150 0 1 3 Platforms & Mezzanines 150 0 1 4 Chiller Room 150 15 1 5 Air Cooling Unit Room 150 1 1 6 Fan Area 150 5 1, 2 7 Control Room 150 0 1 8 Elevator Machine Room 150 - 3 9 Elevator Pit 150 - 3 10 Escalator Machine Room 150 2 1, 4 11 Escalator Pit 150 0 4 12 Ejector Room 150 1 1 13 Pump Room 250 2 1 14 Sumps - - 5 15 Circuit Breaker House 200 2 1 16 Electrical Distribution Room 250 5 1 17 Electrical Panel Room 150 0 1 18 Relay Room 150 1 1 19 Central Instrument Room 150 1 1 20 Signal Tower Control Room 150 1 1 21 Communication Room 150 0 1 22 Telephone Compartment Room 150 0 1 23 Compressor Room 150 0 1 24 Substation

Transformer Area 300 15 1 Circuit Breaker Platform 300 6 1

25 Track Lubrication Room 150 0 1 26 Various Quarters 150 0 6 27 Subway Storage Spaces 400 0 1 28 Maintenance Service Rooms & Duct Manholes 150 0 1 29 Passageways 150 0 7



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Notes on table 2.5:

1a. In designing floor slabs (one-way or two-way) or floor beams, use the uniformly distributed live load over the entire floor area plus the concentrated live load located so as to produce: (1) maximum shear, and (2) maximum moment. For one-way slabs, apply the distributed live load plus the concentrated live load to a slab with a width that is twice the effective depth.

1b. In the design of columns, use only the uniformly distributed live load.

2. This loading is to be used for under platform exhaust fan rooms, fan chambers, fan work areas, and any other areas supporting similar size fans.

3. A minimum uniformly distributed live load of 150 psf shall be used on all floors.

4. Design live loads given are for escalators with a maximum rise of 33 feet. For longer escalators, note 3 applies.

5. Design live loads must be determined on the basis of maximum hydrostatic pressure (and external earth pressure, where applicable).

6. This design live load applies to quarters of the following personnel, including tool rooms, workshops and "light" storage rooms.

a. Foreman b. Dispatchers c. Trainmen d. Motormen e. 3rd Railmen f. Trackmen

7. Passageways and other areas on which equipment is to be temporarily supported must be designed for the design live loads of the appropriate rooms.

2.8 Platform Loads

Design live load for platforms shall be 150 psf.

An additional allowance of 40 psf minimum shall be assumed for 3” finishes (either initial or future), and a minimum of 70 psf for 5½” finishes.

Additional loads such as continuous cement masonry unit (CMU) walls over the platform shall be considered in conjunction with appropriate replacement of the prescribed uniform live loading.

Escalator point loads shall be included.

2.9 Sidewalk and Roadway Loads

Vehicle loading shall be per AASHTO HS-25 loading and 15 cu yd concrete truck. See Figure 2.3.

Impact need not be considered for structures having 3 or more feet of cover. Follow AASHTO Section 3 where impact is required to be considered.



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Loads shall be assumed to transmit through fill per AASHTO Distribution of Wheel Loads Through Earth Fills.

Sidewalk loading shall be designed to support a minimum, uniformly distributed load of 600 psf for areas inaccessible to trucks. However, sidewalk gratings and hatch covers shall be designed for AASHTO HS 25.

Table 2.6 Sidewalk and Roadway Live Load Over Subways (ksf)

COVER FT.

LIVE LOAD

SIDEWALK ROADWAY

2 0.6 1.14 3 0.6 0.82 4 0.6 0.69 5 0.6 0.60 6 0.6 0.60 7 0.6 0.60 8 0.6 0.60 9 0.6 0.60 10 0.6 0.60 11 0.6 0.60 12 0.6 0.60 13 0.6 0.60 14 0.6 0.60 15 0.5 0.50 16 0.4 0.40 17 0.3 0.30 18 0.2 0.20 19 0.2 0.20 20 0.2 0.20

2.10 Existing Buildings and New Construction

When existing private property falls within the zone of influence of new underground construction, a thorough evaluation of construction-induced settlement/deformations and their impact on the existing structures shall be made. See Chapters 8 and 10.

2.11 Lateral Pressure

a. Lateral pressure is due to one or more of the following conditions:

Earth abutting against a vertical plane, flush with back of wall. Water producing hydrostatic pressure. Pressures produced by loads within the influence line of the structure.

b. In establishing lateral pressure, the following general rules are utilized:

The lateral pressure shall at no point be taken at less than 200 psf.



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Rock Pressure shall be as per Geotechnical Engineer’s recommendation.

c. For purposes of including lateral pressures due to surcharge loads within the influence line of the structure:

Lateral pressures due to live loads shall be considered as part of the Live Load L. Lateral pressures due to adjacent buildings or facilities, both existing and new

construction, shall be considered as part of the permanent surcharge loading in H.

2.12 Seismic Loads

2.12.1 Basic Seismic Loads

a. Two levels of Earthquake shall be considered:

1. Maximum Design Earthquake (MDE) - 2% probability of exceedance within a 50-year period - return period 2500 years.

2. Operating Design Earthquake (ODE) - 10% probability of exceedance within a 50-year period – return period 500 years.

b. The Design Response Spectra as well as two sets of hard rock time history motions or each design earthquake hazard level (as a minimum) as specified in the report to the NYCDOT, Seismic Design Criteria Guidelines, dated December 30,1998 shall be used unless otherwise specified. These design spectra and ground motion time histories are based on the 84% hazard curves derived in 1998 NYCDOT study.

c. Effects of liquefaction and foundation settlement shall be evaluated.

d. Effects of faults, if any shall be taken into consideration.



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2.12.2 Performance Requirements for Design Earthquake Loads

a. Performance Requirements under Maximum Design Earthquake (MDE) : Since it is of high intensity and low probability of occurrence , the following criteria of design shall be met:

No catastrophic collapse failure Structure shall be designed with adequate strength and ductility to survive loads and

deformations imposed on the structure thereby preventing collapse and maintaining life safety.

Any structural damage shall be controlled and limited to elements that are accessible and can be repaired. Local yielding of steel and cracking of concrete may be permitted as long as it is detectable and repairable. .

Interruption of the rail service and operation resulting from damage is permitted provided that life safety of passengers is maintained.

The structure may not remain elastic during the earthquake.

b. Performance Requirements under Operating Design Earthquake (ODE) : Since it is of low intensity and high probability of occurrence , the following criteria of design shall be met:

Structure is expected to sustain little or minimal damage and be able to continue to serve its function with minimal interruption.

Higher than the usual stress level will be permitted.

2.12.3 Seismic Design Loads to Be Considered

The following loads shall be considered in seismic design:

Effects of soil overburden and/or weathered rock (i.e. site effects) on ground motions Effects of soil-structure and/or soil-foundation interactions shall be considered.

2.13 Miscellaneous Loads

2.13.1 Collision Forces

Structures, such as columns, walls and other supports, situated less than 10 feet from the edge of platforms shall be designed to withstand a horizontal static force of 225 kips applied at the most critical height, unless protected with suitable barriers. This force is applied on the support element at an angle of 10 degrees from the direction of the rail traffic. This condition occurs with the dead load of the structure, but need not be applied concurrently with other loadings.

The collision force shall be multiplied by a load factor of 1.6 for strength design.

2.13.2 Construction Loads

The loads on structures during construction shall be as per ASCE Standard SEI/ASCE 37.



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Figure 2.1

2.IC

2.IB

2.IA



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Figure 2.2



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HS 25 Truck 6 wheels Total= 90 kips

Concrete Truck 6 wheels total = 100 kips

Figure 2.3

5 kips 20 kips

5 kips 20 kips 20 kips

6'-0"

varies 14'-0" to 30'-0"14'-0"

20 kips

20 kips

20 kips

20 kips

6'-0"

14'-0" 4'-6"

10 kips

10 kips

20 kips



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Chapter 3

Load Combinations

Table of Contents

Section Item Page

3.0 Scope 22


3.2 Load Combination Tables – Notes and Definitions

22

3.3 Reinforced Concrete Design 23

3.4 Structural Steel Design 24

3.5 Seismic Loading Combinations 25

3.6 Flow Chart for Seismic Analysis 25

3.7 Construction Loading Combinations 26

3.8 Criteria to be Satisfied 26



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Chapter 3

Load Combinations

3.0 Scope

All Subway and Underground Structures shall be designed with the following load combinations along with the criteria specified in Section 3.8 and sections detailing acceptance criteria for seismic design in Sections 6.12 and 9.9.





1. American Institute of Steel Construction (AISC), Manual of Steel Construction – 9th Edition – Allowable Stress Design

2. American Society of Civil Engineers (ASCE). Minimum Design Loads for Buildings and Other Structures. ASCE 7.

3.2 Load Combinations – Notes and Definitions

Symbol Definitions

D = Dead Load E = Combined effect of horizontal and vertical earthquake-induced forces F = Load due to fluids with well defined pressures and maximum heights Fa = Flood load H = Load due to lateral earth pressure, groundwater pressure, or pressure of bulk material L = Live load Lr = Roof live load R = Rain load S = Snow load T = Self straining force W = Wind load

Notes for Reinforced Concrete and Steel Load Combination Tables:

1. Per NYSBC, where a particular loading or combination is not defined, its load and combination shall be derived from ASCE 7.

2. The applicable loading is the loading to be used in the design.

3. f1 and f2 shall be as defined in NYSBC.



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3.3 Reinforced Concrete Design

Applicable Codes Applicable Loading

NYSBC ASCE 7 Load Combination

I 1.4D (16-1) 1.4D

II 1. 1.4 (D+F) 1.4(D+F)

III 2. 1.2(D+F+T)+1.6(L+H)+ 0.5(Lr or S or R)

1.2(D+F+T)+1.6(L+H)+

0.5(Lr or S or R)

IV 1.2D+1.6L+ 0.5(Lr or S or R) (16-2)

1.2D+1.6L+0.5(Lr or S or R)

V 1.2D+1.6(Lr or S or R)+ (f1L or 0.8W ) (16-3)

3. 1.2D+1.6 (Lr or S or R)+ (L or 0.8W) note (1)

1.2D+1.6(Lr or S or R)+ (L or 0.8W)

VI 1.2D+1.6W+f1L+ 0.5(Lr or S or R) (16-4)

4. 1.2D+1.6W+1.0L+ 0.5(Lr or S or R) note (1)

1.2D+1.6W+1.0L+ 0.5 (Lr or S or R)

VII 4a. 1.2D+(1.6W+2.0Fa)+ 1.0L+ 0.5 (Lr or S or R ) note (1) and note (3)

1.2D+(1.6W+2.0Fa)+1.0L+ 0.5 (Lr or S or R )

VIII 1.2D+1.0E+f1L + f2S (16-5) 5. 1.2D+1.0E+1.0L + 0.2S note (1)

1.2D+1.0E+f1L + f2S

IX 6. 0.9D+1.6W+1.6H note (2)

0.9D+1.6W+1.6H

X 6a. 0.9D+(1.6W+2.0Fa)+1.6H note (2) and note (3)

0.9D+(1.6W+2.0Fa)+1.6H

XI 7. 0.9D+1.0E+1.6H note (2)

0.9D+1.0E+1.6H

XII 0.9D+(1.0E or 1.6W) (16-6) 0.9D + (1.0E or 1.6W)

Notes for Reinforced Concrete Design Load Table:

1. For the ASCE-7 Load Combination Numbers (3), (4), and (5), the load factor on L is permitted to equal 0.5 for all occupancies in which the live load is less than or equal to 100 psf, with the exception of garages or areas occupied as places of public assembly.

2. For the ASCE-7 Load Combination Numbers (6) and (7), the load factor on H shall be set equal to zero if the structural action due to H counteracts that due to W or E. Where lateral earth pressure provides resistance to structural actions from other forces, it shall not be included in H but shall be included in the design resistance.

3. Load Factor for Fa may be modified for specific projects with NYCT approval.

4. Load Factor for Groundwater Pressure may be modified for specific projects with NYCT

approval.

5. Surcharges due to roadway and sidewalk live loads, including horizontal effects, shall be considered as part of Live Load L.



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3.4 Structural Steel Design

Applicable Codes Applicable Loading

NYSBC ASCE 7 Load Combination

I D (16-7) D

II D + L (16-8) D+L

III 1. D+F D+F

IV 2. D+H+F+L+T D+H+F+L+T

V 3. D+H+F+(Lr or S or R) D+H+F+(Lr or S or R)

VI D+L+(Lr or S or R) (16-9) D + L + (Lr or S or R)

VII 4. D+H+F+0.75(L+T)+

0.75(Lr or S or R)

D+H+F+0.75(L+T)+

0.75(Lr or S or R)

VIII D+(W or 0.7E)+L+ (Lr or S or R) (16-10)

D+(W or 0.7E)+L+ (Lr or S or R)

IX 0.6D+W (16-11) 0.6D+W

X 5. D+H+F+ (W or 0.7E) D+H+F+ (W or 0.7E)

XI 5a. D+H+F+W+1.5Fa D+H+F+W+1.5Fa

XII 6. D+H+F+0.75(W or 0.7E) + 0.75L+0.75( Lr or S or R)

D+H+F+0.75(W or 0.7E) +0.75L + 0.75(Lr or S or R)

XIII 6a. D+H+F+0.75W +0.75L+ 0.75(Lr or S or R)+1.5Fa

D+H+F+0.75W +0.75L+ 0.75(Lr or S or R)+1.5Fa

XIV 7. 0.6D+W+H 0.6D+W+H

XV 7a. 0.6D+W+H+1.5Fa 0.6D+W+H +1.5Fa

XVI 0.6D+0.7E (16-12) 0.6D+0.7E

XVII 8. 0.6D+0.7E+H 0.6D+0.7E+H

Notes for Structural Steel Design Load Table:

1. Load Factor for Fa may be modified for specific projects with NYCT approval.

2. Surcharges due to roadway and sidewalk live loads, including horizontal effects, shall be considered as part of Live Load L.



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3.5 Seismic Load Combinations

Seismic Loading Combinations depend on the type of structure being designed. The Load Combinations for Cut-and-Cover, Cavern, and Tunnel Structures are covered in the relevant chapters.

3.6 Flow Chart for Seismic Analysis

Perform Static Analysis:

Derive Earth Pressure (static) and hydrostatic pressure Perform Preliminary analysis and member sizing Create 3-D model for computer analysis and perform static analysis Complete the evaluation of the members and connections for all loading except seismic

Perform PROSHAKE to get shear stress, strain and free field displacement/deformation of the soil

Determine the flexibility ratio of the structure

Determine displacement of the structure from the flexibility ratio

Ensure that the soil is stiffer than the structure

If the soil is found to be softer than the structure, perform soil structure interaction evaluation using a finite difference or finite element program and determine the structure’s displacement

Apply the calculated transverse and longitudinal displacements and the force in the vertical direction to the structure

Add the seismic loads with proper response modification factor to the pertinent load combinations

The earthquake elastic loads (EQ) calculated from the 3-dimensional analysis in the three perpendicular directions, shall be combined using the Square Root of the Sum of the Squares (SRSS) method.

In lieu of the SRSS method the earthquake elastic loads resulting from the three perpendicular directions may be combined using the following three loading cases:

For MDE and ODE level:

EQ1 = 1.0 Ql + 0.3 Qt +/- 0.3 Qv EQ2= 0.3 Ql + 1.0 Qt +/- 0.3 Qv EQ3 = 0.3 Ql + 0.3 Qt +/- 1.0 Qv

Where Ql, Qt and Qv = Loads due to seismic deformations in longitudinal transverse and vertical direction



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3.7 Construction Loading Combinations

Load combinations for structures during construction shall be as per ASCE 37

3.8 Criteria to Be Satisfied

3.8.1 Reinforced Concrete

3.8.1.1 Design Method

Reinforced Concrete Design shall be as per ACI 318 Strength Design Method.

3.8.1.2 Fatigue

Structures subject to dynamic loads shall be designed for over 2,000,000 load applications over the life of the structure. The design method for the Concrete Invert shall be as per AREMA Code.

3.8.1.3 Crack and Deflection Control

Concrete cracking shall be limited to as per ACI 318.

3.8.2 Structural Steel

3.8.2.1 Design Method

Design of structural steel shall be in accordance with Allowable Stress (Service Load) Design (ASD) method or Load And Resistance Factor Design (LRFD) method. The design methods for Structural Steel shall be as per AISC and AWS D.1.1.

3.8.2.2 Fatigue

Structures subject to dynamic loads shall be designed for over 2,000,000 load applications over the life of the structure as specified in AISC.

3.8.2.3 Deflection Control

Deflection of steel elements shall be limited per the requirements of the AISC 360.



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Geotechnical

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Chapter 4

Geotechnical

Table of Contents

Section Item Page

4.0 Scope 28


4.2 Subsurface Investigation Principles 28

4.3 Geotechnical Input 29

4.4 Geotechnical Design Criteria 29

4.5 Investigation Process 29

4.6 Testing and Borings 31

4.7 References 31



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CHAPTER 4

Geotechnical

4.0 Scope

The geotechnical investigation shall include the following areas:

All excavation work including cut-and-cover work Tunneling work Seismic Design





1. Essex, Randy. Geotechnical Baseline Reports for Underground Construction, Guidelines and Practice. New York: ASCE, 1997

2. International Society for Rock Mechanics (ISRM). Bedrock Classification System. Basic Geotechnical Description of Rock Masses, 1980.

3. International Society for Rock Mechanics (ISRM). Bedrock Classification System. Suggested Methods for the Quantitative Description of Discontinuities in Rock Masses, 1977.

4. United States. Department of the Army Corps of Engineers. Geophysical Exploration for Engineering and Environmental Investigations. USACE EM 1110-1-1802, Aug 1995.

5. United States. Department of the Army. Corps of Engineers. Geotechnical Investigations. EM-1110-1-1804.

6. United States. Department of the Army. Corps of Engineers. Laboratory Soils Testing Engineering Manual 1110-2-1906, May 1, 1980.

7. United States. Department of the Army. Corps of Engineers. Soil Sampling Engineering Manual 1110-1-1906.

8. United States. Federal Highway Administration. Geotechnical Earthquake Engineering. FHWA H1-99-012, Dec 1998.

9. United States. Federal Highway Administration. Geotechnical Instrumentation. Pub No. FHWA H1-98-034, Oct 1998.

10. United States. Federal Highway Administration. Subsurface Investigations. No. HI-97-021, Nov 1997.

4.2 Subsurface Investigation Principles

Subsurface explorations shall follow the general principles defined in FHWA publication Subsurface Investigations, No. HI-97-021, Nov 1997.



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4.3 Geotechnical Input

All geotechnical input used in the design shall be based on information derived from subsurface investigation programs and included in the Geotechnical Data Reports (GDR) and Geotechnical Baseline Report (GBR).

Site-specific design parameters shall include:

Groundwater Levels. Soil and Rock Unit Weights. Bearing Capacity. Angle of Internal Friction. Coefficient of Active, Passive, and At-Rest Pressures. Sub-grade Modulus. Consolidation. Unconfined Compressive Strength. Resistivity , Chemical Analysis, Sensitivity, etc.

4.4 Geotechnical Design Criteria

Geotechnical design criteria that are required for structural design shall be provided by the Geotechnical Engineer.

4.5 Investigation Process

The site should be thoroughly investigated by the help of historical and physiographic maps and fieldwork. Aerial photographs and remote sensing techniques should be applied to study these maps as well as satellite images. This study should establish the primary physiographic and geologic structures and groundwater condition by delineating the subsurface streams.

4.5.1 Subsurface Investigation

Underground structures and facilities shall be located from existing available drawings to avoid interference during subsurface exploration and subsequent construction. Supplementary ground investigations to determine the location and orientation of underground utilities shall be undertaken, by either excavating exploratory Test Pits or using Ground Penetrating Radar.

4.5.2 Groundwater Levels

The groundwater levels used in the design of the temporary and permanent works shall be based on review of all available information and the data collected from the subsurface investigation program, and shall be as recommended in the Geotechnical Baseline Report. Long-term variations in the groundwater level and the possibility of future significant changes in groundwater elevation shall be considered in establishing the design groundwater levels. The stages or condition of groundwater level that the design shall consider are as follows:

Construction Level Normal High Level Normal Low Level Flood Level



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4.5.2.1 Construction Level

The construction level shall consider all events during the time span over which construction takes place. It shall take into account all aspects of the proposed temporary works and the case of an excavation over or adjacent to the works during the entire construction duration of the project.

4.5.2.2 Normal High Level

The normal high level shall be based on the maximum groundwater level at the structure location, including perched groundwater levels, measured during the course of the subsurface investigation program.

4.5.2.3 Normal Low Level

The normal low level shall be based on the maximum groundwater level at the structure location, measured during the course of the subsurface investigation program.

4.5.2.4 Flood Level

The flood level shall be based on the published 500-year flood level obtained from Flood Insurance Rate Maps published by the Federal Emergency Management Agency (FEMA). According to these maps, the 500-year flood elevation is approximately one foot above the 100- year elevation.

4.5.3 Soil and Rock Investigation

Test borings shall be taken to explore the subsurface material viz., soils and rocks. The prime focus shall be given to soil and rock classification, discontinuities in the rock, and bearing capacity of both soil and rock.

4.5.4 Top of Rock

The level at which conventional soil drilling equipment meets refusal and use of rock drilling equipment is required to advance the borehole.

Bedrock may be considered to be at the same level as top of rock..

4.5.5 Decomposed Rocks

4.5.5.1 Lateral Pressure for temporary and permanent structures

Unless otherwise evaluated and provided by Geotechnical Engineer, the structures shall be designed with the following lateral pressure coefficients.

Ko = 0.5 and Ka = 0.3

4.5.6. Hydrostatic Load for Structure in Rock



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Full hydrostatic pressure load shall be considered to be acting on the structure. No reduction shall be considered unless the structural system is designed as drained and meets the requirements of U.S. Army Corps of Engineers manual EM 1110-2-2901, chapter 9.1h.

4.6 Testing and Borings

The following is a table showing representative testing work to be performed for cut-and-cover, tunneling and seismic work.

Table 4.1: Sample Boring and Testing Requirements

Borings In-situ Field Testing Laboratory Testing Field Geophysical Testing

SOIL: 1. Standard

Penetration test. 2. Cone Penetration

test. 3. Undisturbed soil

sampling

1. Vane test 2. Flat Dilatometer

test. 3. Pressuremeter test

1. Sieve Analysis 2. Liquid limit

plasticity test. 3. Direct shear test 4. Unconfined

compressive test (triaxial test)

Cross-hole wave propagation (Seismic tomography) test.

ROCK CORES: 1. Recovery. 2. Rock quality

percentage. 3. Record the

Discontinuities.

1. Megascopic (visual Petrography.)

2. Pressuremeter test.3. Plate Load test

(Deformation Modulus of subgrade reaction, Bearing Capacity).

1. Microscopic Petrography.

2. Compressive Strength test (Uniaxial-Triaxial).

3. Brazilian tension test.

4. Drillability test (Index Test for TBM Performance prediction)

Seismic Refraction test to delineate – Soil-Rock or discontinuities or void zones created by open joints and faults. (Cross hole Seismic tomography)

Groundwater table from strainer holes.

1. Groundwater sampling for contaminants.

2. Packer permeability test.

Groundwater chemistry.

-----------

Bore hole imaging 1) Orientations of discontinuities.

2) Stress measurements

1. Hydrofractures study.

2. Rock core scanning

Acoustic televiewer survey.

The Geotechnical Engineer shall review the design requirements and determine any additional testing needs.

4.7 References

1. Raines, Gregory L. Geotechnical Investigations for Mechanical Tunneling. American Society for Civil Engineering.



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Materials

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Chapter 5

Materials

Table of Contents

Section Item Page

5.0 Materials 33

5.1 Cast-In- Place Concrete 33

5.2 Pre-cast Concrete 33

5.3 Shotcrete 33

5.4 Fill Concrete 33

5.5 Grout 33

5.6 Reinforcing Steel 33

5.7 Structural Steel 32

5.8 Steel to Steel Fastening 34

5.9 Concrete to Steel 35



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CHAPTER 5

Materials

5.0 Materials

5.1 Cast-in-Place Concrete

The minimum 28 day compressive strength of cast-in-place concrete shall be 4,000 psi, unless otherwise noted.

5.2 Pre-Cast Concrete

The minimum 28 day compressive strength of precast concrete shall be 5,000 psi, unless otherwise noted.

5.3 Shotcrete

The minimum 28 day compressive strength of Shotcrete shall be 4,000 psi, unless otherwise noted.

5.4 Fill Concrete

The controlled low strength concrete used as Fill materials shall have minimum 28 day compressive strength of fill concrete shall be 2,000 psi, unless otherwise noted.

5.5 Grout ( Cementitious )

The minimum 7 day compressive strength of grout shall be 5,000 psi, unless otherwise noted.

5.6 Reinforcing Steel

Steel bars for concrete reinforcement shall comply with ASTM A 706, or ASTM A 615, Grade 60.

Welded splices shall not be used for ASTM A 615 reinforcing bars. Plain wire for welded wire fabric and spiral reinforcement shall comply with ASTM A 82. 5.7 Structural Steel

5.7.1 Applicable Material and Specification reference are provided in the Table 5.1 and Table 5.2



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Table 5.1 Structural Shape

No Type Material

Specifications

Material Strength (ksi)

Note Comment Fy Fu

1 W SHAPES ASTM A992 50 65

Material specification provided here are for preferred materials. Use of other comparable material shall be contingent on Approval of

Engineer Availability

verified.

2

M. SHAPES, S-

SHAPES AND HP-

SHAPES CHANNELS

ASTM A36 36 58

ASTM A572 50 65

3 ANGLES ASTM A36 36 58

4 STRUCTURAL TEE Split from W, M, S, shapes

As Above

5a

5b

RECTANGULAR (AND

SQUARE) HHS.

ROUND HHS

ASTM A500 Grade B

46 58

ASTM A500 Grade C

50 62

6 STEEL PIPE ASTM A53

Grade B 35 60

Table 5.2 STRUCTURAL PLATE

STRUCTURAL

PLATE STRUCTURAL

BAR

ASTM A 36 up to 8”

36 58



verified.

ASTM A572

50

65

RAISED

PATTERN STEEL PLATE

ASTM A786 Commercial

Grade

ASTM A36 36 58

ASTM A572 50 65

SHEET AND

STRIP ASTM A606

ASTM A607

Steel For

Galvanized Metal Deck

ASTM A 653 33



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5.8 Steel to Steel Fastening

5.8.1 Applicable Material and Specification references are provided in Table 5.3

Table 5.3 Steel to Steel Fastening

No.. Type Material

Specifications

Material Strength

(ksi) Note Comment

Fy Fu

1

Bolts Heavy Hex

ASTM A325 Type 1

105 Over 1 to 1.5 Dia Material specification provided here are for preferred materials. Use of other comparable material shall be contingent on Approval of


verified.

120 .5-1.0 Dia ASTM A325

TYPE 3 105

For corrosion resistance

ASTM 490 Grade 1

120

ASTM A490 Grade 3

150

2 Tension Control Bolts

ASTM F1852

150 1 1/8

120 0.5 to 1 inch

3 Nuts

(Heavy Hex) ASTM A563

4 Washer ASTM F436 Hardened Flat and Beveled

5

Threaded Rods

ASTM A36 36 58 Plain and upset ends

ASTM A572 50 65

6 Forged Steel Clevis And Turn Buckle

AISI C-1035

35 60

7 Steel Eye Bolt

And Nut AISI

C-1030

8 Sleeve Nut AISI

C-1018 Grade 2

9 Steel Stud ASTM A108

Type B 60

5.8.3 Welding Filler Material

Welding Filler material shall be in accordance with Structural Welding Code – Steel, American Welding Society, AWS D1.1.



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5.9. Concrete to Steel

5.9.1 Applicable material and specification reference are provided in Table 5.3

Table 5.3 Anchor

No Type Material

Specification

Material Strength (ksi) Note Comment

Fy Fu Anchor

Rod

ASTM F1554

Grade 36

36

58

Hooked, Headed

Threaded and Nutted



verified.



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Cut-and-Cover Structures

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Chapter 6


Table of Contents

Section Item Page

6.0 Scope 38


6.2 Loads and Pressure 39

6.3 Load Combinations 40

6.4 Additional Design Considerations 42

6.5 Roof and Mezzanine / Intermediate Floor 43

6.6 Lateral Support Systems – Walls 43

6.7 Invert / Base Slab 47

6.8 Shoring Wall Support 48

6.9 Joints 49

6.10 Control of Groundwater 49

6.11 Design Assumptions, Analysis, and Methods 51

6.12 Seismic Design 55

6.13 Groundwater Leakage 60

6.14 Project Conditions 61

6.15 Ground Modification / Improvement 61

6.16 Zone Of Influence For Deep Excavations 62

6.17 References 62

6.18 Figures 64



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CHAPTER 6


6.0 Scope

The design criteria presented in this chapter shall govern the design of all underground structures with the exception of deep foundations, which are covered in Chapter 7. The Cut-and-Cover Structures include:

Tunnel Structures Station Structures Underground Substation Structures Pump Plant Structures Ventilation Shafts and other Structures of a similar nature

The structures shall be designed to sustain the most severe combination of dead and live load, along with hydrostatic and earth pressure, to which they may be reasonably be expected to be subjected. Effects of erection and other temporary loads occurring during construction shall also be considered.





1. American Concrete Institute (ACI). ACI 201.2R-01 Guide to Durable Concrete, Reported by ACI Committee 201.

2. American Society of Civil Engineers (ASCE). Guideline of Engineering Practice For Braced and Tied-Back Excavations. ASCE Geotechnical Special Publication No. 74.

3. United States. Naval Facilities Engineering Command. Soil Mechanics: Design Manual 7.01. NAVFAC DM-7.01.

4. United States. Naval Facilities Engineering Command. Foundations and Earth Structures: Design Manual 7.02. NAVFAC DM-7.02.

5. United States. Department of the Army. Corps of Engineers. Waterstops and Other Preformed Joint Materials for Civil Works Structures, Publication #EM1110-2-2102, Hyattsville, MD: U.S. Army Corps of Engineers Publications Depot, 1995.

6. United States. Federal Highway Administration. Earth Retaining Structures Reference Manual. Publication No FHWA NHI-99-015, April 1999.

7. United States. Federal Highway Administration. Geotechnical Engineering Circular No.4 Ground Anchors and Anchored Systems. Publication No. FHWA IF-99-015, June 1999.



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6.2 Loads and Pressure

6.2.1 General

All components of underground structures shall be designed for the applicable loads described in Chapter 2 and 3 as modified herein and for those loads and forces specified in the chapters that follow.

6.2.2 Dead Load

The dead load shall be as defined in Chapter 2. The depth of earth shall be the actual depth or an assumed depth of cover of 8 feet, whichever is greater. The actual depth of cover shall be measured from the top of the structure’s roof to the highest of the following: ground surface, roadway crown, or the top of the officially proposed street grade.

6.2.3 Earth Loads

The lateral earth pressure imposed by vertical soil loads to be used for structural design shall be based on information obtained from the geotechnical investigations. Consideration shall be given to dry, moist, and submerged earth pressures. In addition, the effects of specified or anticipated construction methods and procedures such as bracing procedures, compaction of fill adjacent to structures, and similar factors shall be taken into account.

6.2.4 Existing Structures

Underground structures (temporary and permanent) shall be designed for additional loading from existing adjacent buildings when the horizontal distance from the building line to the nearest face of the underground structure is less than 1.0 times the depth of the underground structure below the building foundation. Additional loads shall not be considered where the existing adjacent structures are founded or permanently underpinned at a depth below the zone of influence of the underground structure.

Each existing structure shall be considered individually. In the absence of specific data for a given height of building and type of occupancy, foundation loads shall be computed according to the applicable building codes.

Vertical and lateral loads on underground structures resulting from existing structures above or adjacent to underground structures shall be distributed as shown in Figures 6.14a and 6.14b, or from other acceptable elastic solutions.

Where the load due to adjacent structures is unequal on the two sides of new subway structure, the most critical load combination shall be used both in the balanced and asymmetric load cases.

6.2.5 Hydrostatic Pressure

The effects of hydrostatic pressure shall be considered whenever the presence of groundwater is indicated. It shall be computed at 62.4 pounds per square foot per foot of depth below the design groundwater level for the case being analyzed. Where hydrostatic pressures pertain, lateral earth pressures shall be computed using the submerged weight of soil. Groundwater levels to be used in design shall be established by the Geotechnical Engineer. Long-term variations in the



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groundwater level and the possibility of future significant changes in groundwater elevation shall be considered in establishing the design groundwater levels.

6.2.6 Earthquake Forces

See Chapters 2 & 3 for the requirements for seismic design of underground structures. Seismic Load Combinations for cut-and-cover structures are provided in Section 6.12.5. Temporary structures shall be designed for earthquake loadings as per Design Loads on Structures During Construction, ASCE Standard SEI/ASCE 37., except in areas determined by the Engineer.

6.2.7 Load Factors

The load factors shall be in accordance with Chapter 3.

6.2.8 Self-Straining Load

Self-straining loads (T), due to differential settlements of foundations and from restrained dimensional changes due to temperature, moisture, shrinkage shall be considered.

6.2.9 Shrinkage and Creep

Temperature and shrinkage reinforcement shall be provided for 100% of the specific ACI 318 requirement at each face. This applies to roof slab, walls, and invert slab.

Creep effects shall be incorporated in the design as per the requirements of ACI 318.

6.2.10 Thermal Loads

Thermal loads shall be as indicated in Chapter 2.0.

6.2.11 Flood Load

500 Year Flood shall be considered.

6.2.12 Construction Loads

The loads on structures during construction shall be as per Design Loads on Structures During Construction, ASCE Standard SEI/ASCE 37.

6.3 Load Combinations

6.3.1 General

As a minimum, the four basic non-seismic loading cases described below shall be investigated. Loading and combinations shall be developed from the applicable load cases in Chapters 2 and 3. Additional, temporary, and construction loading cases shall be investigated as required by site-specific conditions.



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6.3.2 Symmetrical Loadings

Cases Ia & Ib: Maximum vertical load including dead loads, live loads, surcharge loads and hydrostatic pressure combined with maximum lateral pressures due to soil and rock (Figures 6.1a and 6.1b).

Cases IIa & IIb: Minimum vertical load (dead load only), surcharge load, and hydrostatic pressure combined with maximum lateral pressure due to soil and rock (Figures 6.2a and 6.2b).

6.3.3 Asymmetrical Loadings

Case IIIa & IIIb: Maximum vertical load including dead loads, live loads, surcharge loads and hydrostatic pressure combined with lateral pressures as follows: Maximum lateral pressures (pressure at rest) due to soil loads, applied to one side of the structure and active pressures from soil on the opposite side (Figures 6.3a and 6.3b).

Case IVa & IVb: Maximum vertical load (dead and live),surcharge load along with maximum lateral earth pressure (pressure at rest) applied on one side of the structure and active pressure on the opposite side. No hydrostatic pressure shall be considered for this case (Figures 6.4a and 6.4b).

Case Va and Vb : Existing Building Load Surcharge

Additionally, where construction bulkhead walls are incorporated into permanent structure, the design of connections between walls and roof or invert slabs is governed by the unbalanced lateral load condition.

6.3.4 Construction Conditions

Construction procedures may result in conditions that are more severe than the general loading conditions given above. Stresses in the partially completed structure and in individual members shall be analyzed for appropriate critical conditions existing at the various stages of construction.

6.3.5 Buoyancy

Buoyancy forces shall be computed at 62.4 pounds per square foot per foot of depth below groundwater table. Based on the probable maximum elevation of the groundwater table, adequate resistance to flotation shall be provided at all sections for full hydrostatic uplift pressure on the structure’s foundation. Such resistance shall be as detailed in the following sections.

6.3.5.1 Completed Structure

Resistance shall consist of the dead weight of the completed structure plus the weight of the backfill overlying the structure which is located within the vertical planes drawn through the outer edges of the structure roof and through all joints separating adjacent structural sections. Provision shall be made in the design, or a construction sequence shall be specified, to prevent buoyancy that might result from a rise in the water table before all backfill is placed.

When evaluating buoyancy loads, unless otherwise indicated in the Geotechnical Report, the compacted unit weight of the dry compacted soil above the roof slab shall be taken as indicated in Chapter 2. The weight of street pavement, live load, and sidewall friction effects shall be



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neglected for the purpose of computing the factor of safety against uplift. The required factor of safety against uplift under these conditions shall be 1.10, and for Flood Loading, the factor shall be 1.05.

6.3.5.2 Partially Completed Structure

A construction sequence, together with all temporary measures necessary to provide adequate safeguards against flotation during all stages of construction shall be indicated. Resistance will consist of the dead weight of the completed portion of the structure plus the additional resistance provided by those safeguards indicated in the construction sequence to be provided. Side wall soil friction shall be neglected. The required factor of safety against uplift for the partially completed structure shall be 1.05.

Rotational effects due to buoyancy shall be considered where the main structure is markedly asymmetrical. Local asymmetry shall not be considered unless the section is isolated by structural joints.

6.4 Additional Design Considerations

6.4.1 Fatigue

Fatigue for Steel Structures shall be designed as per AISC 360

Fatigue for Concrete Structures shall be designed as per AREMA.

6.4.2 Crack Control

Crack Control Criteria for Concrete Structures shall be as per ACI 318

6.4.3 Deflection control

6.4.4.1 Steel

Deflection Criteria for Steel shall be as per AISC 360.

Unless otherwise noted specifically in the contract documents, all structural steel members shall be designed to satisfy both the following limitations on deflections under the noted loads:

1) Live Loading: L/360

2) Total Loading: L/240

where L denotes the unsupported length of the member

The total loading above comprises of: dead loads + superimposed dead loads + live loads.

If in a given design, condition 1 is satisfied but the limit of condition 2 is exceeded, then the designer may specify cambering of the member using either of the following conditions:

a. camber = 65 percent of (dead + superimposed dead load) deflection

b. camber = 70 percent of dead load deflection



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The figure obtained for camber shall be rounded to the nearest 1/8 inch. In no case shall a specified camber be less than ¾ inch. The prescribed camber may then be subtracted from the deflection under total loading of the member and a new check of limiting condition 2 above shall be performed to its satisfaction.

If computed deflections are based on continuity of the member over several supports, the designer shall evaluate the effect of unbalanced loading condition(s) on all applicable spans in determining the maximum plausible deflection for use as the governing condition in service.

6.4.4.2 Concrete

Deflection Criteria for Concrete shall be as per ACI 318.

6.4.4.3 Composite Construction

The long-term Young’s modulus for concrete shall be taken as 50% of the short-term modulus.

6.4.4.4 Stray Current Corrosion Control

The design shall incorporate the provision of stray current corrosion control in metals.

6.5 Roof Slab and Mezzanine / Intermediate Floor

6.5.1 Roof Slab

The roof slab is one of the most vital structural components of the tunnel box because of its high loads from traffic and soil loads above. The tunnel roof shall be cambered to mitigate the effect of long term loads (i.e. slab plus backfill). In computing the long term deflection, the immediate deflection shall be multiplied by a factor of 2, unless a detailed creep analysis is made to establish otherwise.

Structural roof slabs shall be pitched to 1/4” per foot for drainage. Pitching shall not be provided by waterproofing. Roof slab pitch shall be in addition to the camber.

6.5.2 Mezzanine / Intermediate Floor

Mezzanine/Intermediate Floors carrying active track shall be designed for fatigue, crack control, and deflection control criteria. Floor slabs shall be pitched 1/8” per foot to floor drain.

6.6 Lateral Support Systems – Walls

Four main shoring systems are:

Soldier Pile and Lagging Steel Sheeting Concrete (SPTC) / Reinforced Concrete Slurry Wall Secant / Tangent Pile Wall

6.6.1 Lateral Earth Pressure

Lateral Earth Pressure for all shoring wall configurations shall be as given in Table 6.1.



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6.6.2 Soldier and Lagging System

Soldier and Lagging System shall be considered as a Flexible System.

6.6.2.1 Primary Use

Soldier pile walls shall be used for relatively shallow excavations, generally above the groundwater level.

6.6.3 Steel Sheet Piling System

Steel Sheet Piling System shall be considered as a Flexible System.

6.6.3.1 Primary use

Shall be used primarily as a temporary retaining structure However, this wall type may not be used near sensitive buildings where noise and vibration are an issue or in areas of loose fill that may settle during wall installation.

6.6.4 Slurry Wall System

Slurry Wall System shall be considered as a Rigid System.

6.6.4.1 Description

Wall types to be considered in design:

Soldier Pile Tremie Concrete (SPTC) Wall:

SPTC wall are commonly constructed of vertical wide flange sections set in a slurry stabilized trench with a reinforcing cage placed between the soldier piles to transfer earth and water loads laterally to the soldier piles. They provide a relatively watertight wall, significant strength in the vertical direction, greater flexibility for moment connections within the excavation and relatively easy connections for temporary cross lot bracing and wales.

Conventional Reinforced Concrete Wall:

A conventional reinforced concrete slurry wall uses reinforcement cages that are placed in the slurry trench before concrete tremie pour. The reinforcement bars are proportioned to resist bending principally in the vertical direction between bracing levels. Supplemental bars shall be provided to serve as internal walers or to distribute forces around inserts or openings. This method of reinforcement is currently used particularly for permanent walls and where tie back anchors are used. Panel end joints are formed by stop end pipes or other suitable forming devices.

Precast Concrete Panel Wall:

A variation of the above wall types is the Precast Concrete Panel Wall in which pre-cast concrete wall elements are placed in the excavation trench. This method will produce the best quality finished wall. This type of wall requires the use of cement bentonite slurry, which will eventually harden in the void between the wall and soil.

The use of a Precast Concrete Panel wall becomes less practical for deeper excavations and at locations where utility crossings or obstructions can be expected.



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Table 6. 1: Cut-and-Cover Structure Lateral Pressure Distribution (Soil)

Lateral Support System

Stiffness (Note 1)

Bracing Type

Lateral Earth Pressure Magnification

Factor (MF) -to be applied to Lateral

Earth Pressure

Other Evaluation

1 Temporary Flexible H < 25 ft

Internally Braced Wall

Figure 6.5 (Pressure Distribution for

Braced Loads) 1

1. Soldier Pile and Lagging 2. Steel Sheet Piling MF = 1.3

x

2 Temporary Flexible Wall H ≥ 25 ft



Braced Loads) 1

1. Soldier Pile and Lagging 2. Steel Sheet Piling MF = 1.3

Soil Structure Interaction (SSI) by: a) Finite Element or b) Finite Difference

Method.

3 Temporary Rigid Wall



Braced Loads) 1

Slurry wall 1. Secant Pile 2. Tangent Pile MF = 1.4

x

4 Permanent Rigid Wall


Figures 6.1a through 6.4b,

6.14a & 6.14b

. x Soil Structure

Interaction (SSI) by: a) Finite Element or b) Finite Difference

Method.

5 Temporary Flexible H < 25 ft

Tied –Back Walls

Figure 6.7 and Figure 6.8 (Pressure Distribution for tied-back walls ) 1

1. Soldier Pile and Lagging 2. Steel Sheet Piling MF= 1.3

x

6 Temporary Flexible Wall H ≥ 25 ft

Tied –Back Walls

Figure 6.7 and Figure 6.8 (Pressure Distribution for tied-back walls) 1

1. Soldier Pile and Lagging 2. Steel Sheet Piling MF= 1.3.

Soil Structure Interaction (SSI) by: a) Finite Element or b) Finite Difference

Method.

7 Temporary Rigid Wall

Tied –Back Walls

Figure 6.7 and Figure 6.8 (Pressure Distribution for Tied –Back walls1)

1 .Slurry wall 2 .Secant Pile 3. Tangent pile MF =1.4

x

8 Permanent Rigid Wall

Tied –Back Walls

Figures 6.1a through 6.4b, 6.14a & 6.14b

x Soil Structure Interaction (SSI) by: a) Finite Element or b) Finite Difference

Method. Note 1: Flexible Wall: 1. Soldier Pile and Lagging 2. Steel Sheet Pile Rigid Wall: 1. Slurry Wall 2. Secant Pile 3. Tangent Pile H = Depth of Excavation

1 NAVFAC Design Manual 7.02, Sept 1986



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6.6.4.2 Primary Use

Shall be used primarily as a Temporary Retaining Structures and, where approved by the Engineer, as a Permanent Retaining structure.

Typically slurry walls shall be used at sites where a relatively water tight excavation support wall is required. This situation will occur when:

Groundwater lowering outside the excavation limits may lead to potentially damaging settlement of nearby structures or other facilities

When it is not practical to dewater a site, i.e., adjacent to an open body of water.

Where seepage gradients initiated by dewatering operations may risk migration of existing groundwater contamination plumes. With penetration into an underlying stratum of low permeability or with sufficient penetration below the bottom of the excavation, a slurry wall will provide an effective seepage barrier that can preserve groundwater conditions outside the excavation.

It shall also be used at sites where it is necessary to restrict ground displacements adjacent to the excavations. This is of particular concern when the excavation is in close proximity to a building or other structure, which is founded above the bottom of excavation level. As a relatively rigid excavation support system, a slurry wall typically will result in smaller ground displacements than a soldier pile and lagging support system.

Advantages of Permanent Excavation Support Wall

Eliminates second wall Reduces width of excavation Reduces quantities of excavation and backfill Faster construction Lower cost

Disadvantages of Permanent Excavation Support Wall

Requires tighter construction Precludes installing exterior waterproofing systems Requires seepage mitigation Grouting Seepage collection Separate architectural facing often desired

6.6.5 Tangent / Secant Wall System

Tangent / Secant Wall System shall be considered as a Rigid System.

6.6.5.1 Description

A tangent or secant pile wall consists of a line of bored piles. If the bored piles are contiguous or tangent to each other, the wall is called “tangent pile”. In an alternate case referred to as a “secant pile”, the pile elements are overlapped so as to form an interlocking wall.



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Tangent pile walls and secant pile walls are stiff, continuous walls that are constructed by the top down method. Similar to slurry (diaphragm) walls, tangent pile and secant pile walls can be used when it is necessary to minimize groundwater lowering outside the excavation or to reduce ground displacements.

6.6.5.2 Primary Use

Shall be used primarily as a Temporary Retaining Structures and, where approved by the Engineer, as a Permanent Retaining Structure.

The advantages and disadvantages tangent and secant pile walls are similar to those of slurry walls. An additional advantage of tangent and secant pile walls is that they can be constructed using conventional bored pile (or drilled shaft) excavation equipment and procedures with which more contractors are familiar. Also, this type of wall may be more suitable than slurry walls at constricted work sites since less area is needed for slurry containment and treatment and for fabrication and handling of rebar cages.

Disadvantages in comparison to slurry walls:

Increased seepage through vertical joints. More difficult connections for bracing members, ground anchors and attached slabs Rough and irregular exposed face.

6.7 Invert / Base Slab

Invert slabs shall be designed as structural members on elastic foundations using the design parameters established by the Geotechnical Engineer.

Vertical pressures on invert or base slabs may be divided into hydrostatic and earth pressure components. The hydrostatic component shall be distributed across the width of the slab in proportion to the depth of each portion of the base slab below the design groundwater table. Distribution of the earth pressure component shall be based on the soil type and the specified construction procedures if they affect the distribution, and may include elastic foundation effects if significant changes in slab stresses are induced thereby. As one condition of distribution, assume the earth pressure to be uniform across the width of the slab.

6.7.1 Uplift Water Pressure At Base Slab

The base slab shall be designed to resist the uplift pressure acting at the bottom of the base slab.

The design water level shall be determined from the site investigation and from the mean high water level (MHWL) and 500-year flood plain.

6.7.2 Permanent Slurry Wall

Where the Slurry Wall is designed to be used as permanent structure, the base slab shall be anchored to the slurry wall to transfer all the forces from the wall to the base slab and vice versa.

Connection details shall be such that they provide a watertight connection.



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6.8 Shoring Wall support

6.8.1 Internal Bracing

The principal components of each internal bracing tier are longitudinal beams or “wales” and transverse compression members or “struts”.

The bracing tier shall be positioned so that they support the shoring wall and permit efficient construction of the permanent structure.

The vertical spacing of bracing tiers shall be a maximum of 15-20 ft.

The maximum depth of cut in any excavation step is usually 3 feet below the centerline of the next bracing.

The following requirements shall be observed in the design and detailing of temporary structures for the support of excavation.

All connections of struts, wales, and wall systems shall be designed and detailed to resist tensile and shearing loads equal to 10 percent of the design compression loads for static forces. (This requirement is a minimum criterion, and not additive to any static design tensile or shearing loads.)

The maximum slenderness ratio of struts shall be limited to 120, and the maximum unit stress for static loads limited to 15,000 psi for excavations adjacent to sensitive or historic structures.

The maximum slenderness ratio of secondary bracing members shall be limited to 200.

Each strut shall be pre-loaded at installation to 50 percent of its maximum design load.

Temporary bracing shall account for temperature effects. Temperature variations in cut-and-cover excavations can cause substantial load increases on the bracing systems and shall be considered in the design. The design change in temperature shall conform to NYCT Guidelines. The load increase due to thermal effects will vary depending on the end-restraint conditions (i.e. wall stiffness, soil stiffness, etc.). A detailed analysis is required for determining these loads.

Allow for 15 percent overstress of the struts when thermal effects are applied.

6.8.2 Tie backs

Tie backs shall be designed as per report no. FHWA-IF-015, Geotechnical Engineering Circular No.4.

6.8.3 Roadway Decking

The design shall be as per DG 453 Field Design standards with the modification that impact factors shall be considered in the design of Decking Structures.



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6.9 Joints

6.9.1 Expansion Joints

Provisions for expansion shall be made in all at grade structures. Where a structural element is partially underground and partially above ground, and where an above ground element is attached to an underground element, particular care shall be taken in detailing to accommodate differential thermal movements.

Reinforcing steel shall not be continuous through the joint. Shear forces shall be transferred across the joint, preferably by a key. Alternatively, smooth dowels may be embedded on one side of the joint and provisions made on the other side to break the dowel bond, and to provide space for dowel movement. All expansion joints in base and roof slabs and in walls against earth shall contain a nonmetallic waterstop with a minimum width of 9 inches. Thorough consideration shall be given to ensuring structural integrity and watertightness. Expansion joint locations shall be indicated in drawings.

6.9.2 Contraction Joints

Contraction joints shall be provided in at grade structures at intervals not greater than 32 feet. Contraction joints shall be unbonded joints and designed not to transmit the forces perpendicular to the joint that may occur under any design condition, and shall be designed according to the criteria described above for expansion joints.

6.9.3 Construction Joints

Construction joint locations and details shall be indicated on the drawings.

6.9.4 Joints in Steel Frames

Provisions shall be made in structural steel frameworks of at grade structures for the temporary accommodation of fabrication and erection tolerances without introducing significant distortions in the frame.

6.10 Control of Groundwater

6.10.1 Purpose

Cut-and-Cover construction requires control of groundwater when it adversely affects construction or performance of the support system.

The purposes are:

To permit excavation in the dry, and to reduce water pressure acting on the support system

To minimize disturbance, heave, or softening of the excavated bottom and to prevent piping or flow of materials through the wall elements.

To increase passive resistance of interior berms (or of the interior sub grade) to lateral inward movement.

To aid construction of components, such as tiebacks, reaction elements for raking braces, elevator pits, permanent under drainage systems and the like.



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6.10.2 Field Investigations

In addition to the determination of subsurface conditions referred to in Chapter 4, pre-construction exploration must take into account the data needed to plan a water control program. Included in the routine investigation, should be the measurement of groundwater levels within and around the intended excavation to a level at least 1.5 times the maximum depth of the excavation below the highest water surface observed in the borings. No test boring records should be accepted without a statement of the water levels observed at each borehole or an explanation for the absence of such information or its lack of reliability.

The exploration program generally will be in one of the following three classes:

1. A minimum investigation includes:

Determination of groundwater or piezometer levels in each boring at the time of investigation, noting the presence of perched, depressed or artesian water levels, and describing any occurrence of running soil or loss of wash water.

Grain size analyses of potential aquifer soils shall be performed. The D10 value so determined can be used through empirical correlations to estimate permeability. When using grain size data to estimate permeability, it should be recognized that this approach may discount the effects of in-situ structure. For example, thin discrete layers of sand can result in a relatively high horizontal permeability, even though a significant fraction of fines are indicated by the grain analysis.

2. Detailed investigations shall include, in addition:

In-situ permeability determinations by falling head or rising head tests in borings, installation of observation wells or simple piezometers to measure to measure water levels, continuing observations over a sufficient time period to establish the typical variation in levels, and research of local references and case histories to assess water table fluctuations.

3. Special investigations include, in addition:

Full scale deep well pumping tests or water pressure tests between packers in cased boreholes; study of the original and present conditions of nearby water carrying utilities; undisturbed sampling for laboratory permeability testing; and installation of sensitive piezometers for observation of water table fluctuations. In some cases, the groundwater is sampled for tests of chemical constituents, dissolved or suspended materials or potential corrosion characteristics.

6.10.3 Minimizing the Disturbance of the Excavated Bottom

The main cause of disturbance of fine-grained soils is the movement of personnel and equipment over a sub grade that has softened due to the removal of overlying weight and the action of seepage. In coarser soils, an upward seepage gradient causes a reduction of effective stress, thus a reduction of shear strength and an increase in compressibility.

In fine-grained soil, a mud mat of lean concrete acts as a pavement, distributing the weight of personnel and equipment. The mud mat shall be drained by bleeder holes connected to gravel pockets beneath the mat. Alternatively, a filter fabric can be placed on a silt or clay sub grade beneath a stone ballast.



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For coarse-grained soils the disturbance can be minimized by placing a crushed stone or gravel ballast layer on the sub grade and pumping water from the sumps or ditches. The ballast acts as a pavement and as a weighted filter, increasing the effective stresses acting on the sub soils. An alternative procedure, which alone may suffice to stabilize coarse-grained soils, is to maintain water levels several feet below the base of excavation by pumping.

6.10.4 Controlling Surface water

Measures must be taken to control the surface water entering the excavation, which can be troublesome and dangerous. Specifications shall inform bidders of known potential sources of difficulty and remind the contractor of the responsibility for taking measures to control runoff.

6.10.5 Preventing Bottom Blowout

Conditions of bottom blowout, boiling, or heave must be evaluated during design, and measures like monitoring of piezometric levels below excavation during excavation must be identified in the design and specifications.

6.10.6 Effects of dewatering on Adjacent Areas and Control Measures

Dewatering can result in distress in adjacent properties manifested in settlements caused by the following factors:

1. Piping of fines resulting in loss of ground. 2. Consolidation of compressible soils due to increase in effective stresses. 3. Deterioration of existing foundation elements.

The following measures must be considered and identified in contract documents as required to control detrimental effects of exterior draw down:

1. Creating a positive cut-off with a deep well to maintain pre-existing water levels. 2. Recharge systems to pump the water back into the soil or to raise the piezometric levels. 3. Careful monitoring of the construction, including vertical and horizontal movements of the

adjacent ground surface and any structures.

A qualified hydrologist shall be consulted in all phases of the groundwater control during design and during construction.

6.11 Design Assumptions, Analysis, And Methods

6.11.1 General

Unless mentioned otherwise, all structures and their components shall be designed to safely support the design loads specified in Chapter 2.

Load combinations for temporary and construction loads shall be as per Chapter 3.

6.11.1.1 Reinforced Concrete Load Combinations

The following Load combinations for all permanent structures are derived from load combinations in Chapter 3.



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For specific projects with NYCT approval, alternative load factors for groundwater pressure and floodwater loads may be taken as follows:

Ground Water Pressure = 1.4 & Flood Water Load Fa = 1.2

For load combinations using this alternative load factors the following notation applies:

Table 6.2: Additional Load Definition Table

Parameter Definitions

FNHW Hydrostatic loads due to the normal high ground water table

FNLW Hydrostatic loads due to the normal low ground water table

HNHW Horizontal loads from earth (soils and rock) and surcharge pressure based on the normal low groundwater level

HNLW Horizontal loads from earth (soil and rock) and surcharge pressure based on the normal low groundwater level

Ha Horizontal loads from earth (soil and rock) corresponding to the 500-year flood level and surcharges

Table 6.3 : Modified Load Combination ( Concrete )

Cut-and-Cover Structures and Tunnels in Soil

Applicable Combinations (as listed in chapter 3)

Combinations Using Alternative Load Factors

I 1.4D U = 1.4D

III 1.2(D+T)+1.6(L+H) U = 1.2(D+T)+1.4FNHW+1.6(HNHW + L)

U = 1.2(D+Fa +T) +1.6(Ha+L)

IX 0.9D+1.6H U = 0.9D+1.4FNHW +1.6HNHW

X 0.9D+2.0Fa+1.6H U = 0.9D+1.2Fa+1.6Ha

1.2D+1.6L+0.9H U = 1.2D+1.6L+0.9(FNLW+HNLW)

6.11.1.2 Application of Structural Steel Load Combinations

The following is a summary of load combinations that are applicable to a structural system designed to support underground structures.

For specific projects with NYCT approval, alternative load factors for groundwater pressure and floodwater loads may be taken as follows:

Ground Water Pressure = 1.0 & Flood Water Load Fa = 1.0



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Table 6.4 : Modified Load Combination ( Steel )

Applicable Combinations (as listed in Chapter 3)

Combinations Using Alternative Load Factors

I D D

II D+L D+L

IV D+H+L+T D+HNHW+FNHW+L+T

XI D+H+1.5Fa D +Ha+Fa

XIII D+H+0.75L+1.5Fa D+Ha+Fa + 0.75L

XIV 0.6D+H 0.6D+Ha+Fa

XV 0.6D+H +1.5Fa 0.6D+ HNHW+FNHW

6.11.2.1 Method of Analysis

Step I - Soil-structure interaction method (SSI) shall be used for the analysis of temporary structures and cut and cover structures with slurry walls or other earth support walls used as part of permanent structure. This analysis, which is based on staged excavation, will determine strut loads, as well as wall deformations, bending moments and shears during various stages of construction. It will also estimate the ground movements outside the excavation.

The following loading conditions shall be considered in the soil-structure interaction analysis:

Excavation/Construction Stages Final Condition Unbalanced Earth Pressure (Non-Seismic) Final Condition with Seismic Loads

Step II- Frame analysis shall be performed for all permanent structures.

The following loading conditions shall be considered in the frame analysis:

Balanced Earth Pressure (At-Rest Lateral Earth Pressure) Balanced Earth Pressure (At-Rest Lateral Earth Pressure) in combination with Seismic

Loadings Unbalanced Earth Pressure (Non-Seismic)

6.11.2.2 Permanent Structures – The design procedure for permanent structures shall be as follows:

Structures with cast-in-place concrete walls (where the slurry wall or other earth support wall is not used as the permanent structural wall - The design shall be based on frame analysis only. Soil-structure interaction analysis shall not be required.



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Structures with slurry wall or other earth support wall used as part of the permanent structure - The analyses shall be performed using both soil-structure interaction analyses and frame analyses. The structures shall be designed for the most critical loads of both analyses.

6.11.2.3 Asymmetric Loads – Unbalanced soil pressure conditions due to existing building surcharge and adjacent future excavations shall be evaluated using the following two-step process.

Step 1 – Apply unbalanced soil pressure based on K0 and Ka (at-rest and active soil pressures respectively), as per this guideline and existing building surcharge on the K0 side of the station; and calculate lateral deflection at the top of the box. If the deflection is less than 0.0015h, where h is the height of the structure above the rock level, calculate the resulting moments and shears and include them in the design of the structure.

Step 2- If the deflection at the top of the structure exceeds 0.0015h ( h = portion of the box above the top of rock), the unbalanced soil condition shall be modeled by increasing the active pressure by a factor α and decreasing the ‘at rest’ pressure by a factor 1/a, to limit the deflection at the top of the structure to 0.0015h. The value of α may vary between 1 and the ratio of K0/Ka.

If reaches K0/Ka and the deflection at the top of the structure still exceeds 0.0015h. the underground structure shall be redesigned with stiffer members or connections to limit the deflection at the top of the structure to below or equal to 0.0015h. Where the top of rock varies from one side of the box to the other, the more critical condition shall govern.

6.11.2.4. Structural Stability - The structures shall be designed to have the ability to resist unbalanced lateral loads and shall not depend on the surrounding soil for stability.

6.11.2.5 Joint Restraints - In order to minimize cracking and the potential for water leakage, the joints between concrete slabs and walls shall be designed as fully fixed unless approved by the Engineer.

6.11.2.6 Criteria of Analysis

In all loading cases, the structural framing shall be balanced or in equilibrium. Adjacent soil or rock shall not be considered to provide a reaction to the framing system. As such, all lateral loads, reversible or otherwise, shall be resisted by the frame alone.

The effect of lateral rock springs shall be considered in frame analysis. The soil springs shall be considered only below the invert level. Lateral resistance of soil above the invert level shall be neglected

Figure 6.13 shows locations of soil and rock springs for analysis.

Evaluation of the frame shall be performed with the same end conditions for all load cases including seismic.

6.11.2.7 Detailed Methodology

Framed structures shall be analyzed by rational elastic methods which consider the effects of relative stiffness of connected members, relative displacement, rotation of joints, and the effects of axial deformations. Consideration shall be given to the variations in elastic properties and



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stress distribution of complex frameworks resulting from different construction sequences. Any limitations on construction operations inherent in the design assumptions shall be noted on the project drawings and specified in the special provisions. Conversely, advantage may be taken of specified construction procedures or sequences to effect a more favorable distribution of loads or stresses.

In the analysis of the structural frame of the tunnel, loads and pressures representing each loading shall be applied. Shears, thrusts, and bending moments for each element of the frame (worst case) are then determined through rigid frame analysis, using commonly accepted methodology.

Where further rigorous analysis is required, a three dimensional Finite Element analysis shall be performed taking into account the soil-structure interaction.

For the frame analysis of reinforced concrete stations, the cracked moment of Inertia (Ic) instead of the gross moment of inertia (Ig) shall be used.

6.11.3 Design of Earth Support Walls

Except where specifically defined as unnecessary in other parts of this document, soil-structure interaction method (SSI) shall be used for the analysis of cut-and-cover structures with slurry walls or other earth support walls used as either temporary structures or as part of the permanent structure. This analysis, which is based on staged excavation, will determine strut loads, as well as wall deformations, bending moments and shears during various stages of construction. It will also estimate the ground movements outside the excavation.

Excavation and Construction Stages shall be considered for both temporary and permanent structures, and the following loading conditions shall be considered for the permanent case:

Final Condition Final Condition with Seismic Loads

In addition, a frame analysis shall be performed where the earth support wall is part of the permanent structures.

6.11.4 Foundations

The allowable bearing capacity of soil shall be as established as per Chapter 7 – Foundations, and by the Geotechnical Engineer.

6.12 Seismic Design

6.12.1 Underground Structures

The response of a tunnel to seismic shaking motions can be described in terms of three principal types of deformations:

1. Axial Deformation

2. Curvature Deformation

3. Racking



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6.12.2 Axial Deformation and Curvature Deformation

The first two types, axial and curvature deformations are induced by components of seismic waves that propagate along the tunnel axis. When the component waves produce particle motions parallel to the longitudinal axis of the tunnel, they cause alternating axial compression and tension strains. Curvature results from component waves that produce particle motions in the direction perpendicular to the tunnel axis.

Two levels of analytical approaches can be used for evaluating the axial and curvature deformations along a tunnel structure: (1) simplified plane wave method or close-form solutions, and (2) numerical analyses. In the simplified plane wave method, tunnels are considered to be flexible in response to axial and curvature deformations.

The induced strains and stresses in the tunnel liners are estimated by assuming that the tunnels conform to the imposed deformations from the surrounding ground in the free-field condition. If significant soil-structure interaction exists, this method may lead to an overly conservative design, and then the close-form solutions based on the beam-on-elastic foundation procedure should be used. The plane wave method and the close-form solutions shall be used initially.

Numerical analyses will be considered only when analyses using the simplified methods are inconclusive or could not produce a realistic design. If required, there are several methods of analysis that can be considered in the numerical analysis, including lumped mass methods, continuum finite element, finite difference methods, and discrete element methods.

6.12.3 Racking

The general procedure for seismic design of underground structures shall be based primarily on the ground deformation approach specified herein. During earthquakes, underground structures move together with the surrounding geologic media. The structures, therefore, shall be designed to accommodate the deformations imposed by the ground. The analysis of the structure’s response can be conducted first by ignoring the stiffness of the structure, leading to a conservative estimate of the ground deformations. This simplified procedure is generally applicable for structures embedded in rock or stiff/dense soil. In cases where the structure is stiff relative to the surrounding soil, the effects of soil structure interaction shall be taken into consideration.

6.12.3.1 Racking and Vertical Motions

Seismic design of the transverse cross section of a structure shall consider two loading components:

The racking deformations due to the vertically propagating shear waves. Inertia forces due to vertical seismic motions.

1. Loads due to Racking Deformations, Qh. Racking deformations are defined as the differential sideways movements between the top and bottom elevations of the box structures, shown as Δs in Figures 6.10 and 6.11. The internal forces, Qh, associated with the seismic racking deformation, Δs, shall be derived by imposing the differential deformation on the structure in an elastic frame analysis. The procedure for determining Δs, for both MDE and ODE level design and with the consideration of soil structure interaction effects, is as follows:



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a. Define structure’s geometry.

b. Perform preliminary static analysis and member sizing.

c. Estimate the free-field ground strains γmax (at the structure elevation) caused by the vertically propagating shear waves of the design earthquakes.

d. Determine Δfree-field, the differential free-field relative displacements corresponding to the top and the bottom elevations of the box structure by

Δfree-field = h • γmax

where: h = height of the box structure

e. Determine the racking stiffness, Ks of the proposed design of the box structure from a structural frame analysis. The racking stiffness shall be computed using the displacement of the roof subjected to a unit lateral force applied at the roof level, while the base of the structure is restrained against translation, but with the joints free to rotate. The ratio of the applied force to the resulting lateral displacement yields Ks. In performing the structural frame analysis, appropriate moment of inertia values, taking into account the potential development of cracked section, shall be used.

f. Determine the flexibility ratio, Frec of the proposed design of the structure using the following equation:

Frec = (Gm / Ks) • (w/h)

where: w = width of the box structure Gm = average strain compatible shear modulus of the soil/rock

layer between the top and bottom elevation of the structure. The strain compatible shear modulus shall be derived from the strain compatible, effective shear wave velocity, Cse,

g. Based on the flexibility ratio obtained form Step 3 above, determine the racking ratio, Rrec, for the proposed structure using Figure 6.12, or alternatively using the following formula:

Rrec = 4(1-νm) / {[(3 – 4νm) / Frec] + 1}

h. Determine the racking deformation of the structure, Δs, using the following relationship:

Δs = Rrec • Δfree-field

i. The seismic demand in terms of internal forces as well as material strains are calculated by imposing Δs upon the structure in a frame analysis.

2. Loads due to Vertical Seismic Motions, Qv. Loads due to vertical seismic motions on cut-and-cover structures are accounted for by applying a vertical static loading, equivalent to a fraction of the slab and the overburden materials (directed up or down, whichever results in a more critical load case):

Qv = 0.22 (D) for MDE level design Qv = 0.06 (D) for ODE level design

Where: D = Dead loads as defined in Chapter 2



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The coefficients for Qv for MDE and ODE level shall be verified by Geotechnical

Engineer.

Seismic loads due to racking deformations and vertical seismic motions shall be combined with non-seismic loads using the loading combinations in Section 3.5 – Seismic Loading.

For a running cut-and-cover (or a box type) structure that is 2-dimensional in nature, seismic design should consider the effect of ground motion in the transverse and vertical direction only. The effect of ground motion in the longitudinal direction need not be considered. The earthquake loads, EQ, shall consider the following two cases:

EQ1 = Qh ± 0.3Qv

EQ2 = 0.3Qh ± Qv

For a box type structure that will be affected by ground motions in all three directions, the earthquake elastic loads (EQ) shall be calculated as per Section 3.6 – Flow Chart for Seismic Analysis

In addition, the material strains of the main structural members shall be checked not to exceed the allowable values for both MDE and ODE level design. The allowable values are specified below.

6.12.4 Acceptance Criteria

6.12.4.1 Reinforced Concrete

MDE level – limiting strain ec = 0.004 for bending and ec=0.003 for compression and bending

ODE level – limiting strain ec = 0.003 for all cases.

(Reference ATC-32)

6.12.4.2 Structural Steel

MDE level – structure is allowed to go to yield level. ODE level – overstressing of the structure of 50% is permissible. Connections – allowable stresses are the same as above.

(Reference [5])

6.12.5 Seismic Loading Combinations

6.12.5.1 Loading Combinations (Reinforced Concrete Structures)

Seismic loads due to racking deformations and vertical seismic motions shall be combined with non-seismic loads using the following loading combinations

Group Load = 1.2(D + FNHW + HNHW) + f1L + 1.0EQMDE/RMDE for MDE level design And = 0.9D + FNHW + HNHW + 1.0EQMDE/RMDE for MDE level design



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Group Load = 1.2(D+ FNHW + HNHW) + f1L+ 1.0EQODE/RODE for ODE level design And = 0.9D + FNHW + HNHW + 1.0 EQODE/RODE for ODE level design

Uncertainty of HNHW shall be considered in design.

Uncertainty is the critical upper or lower bound load.

EQMDE and EQODE = Earthquake Loads for MDE and ODE level, see Section 6.12.3.

RMDE = Response Modification Factor = 2.0 RODE = Response Modification Factor = 1.0

f1 to be obtained from NYSBC

6.12.5.2 Loading Combinations (Steel Structures)

Seismic loads due to racking deformations and vertical seismic motions shall be combined with non-seismic loads using the following loading combinations

Group Load = D + FNHW+ HNHW + L + EQMDE/RMDE for MDE level design and = 0.6D + FNHW + HNHW + EQMDE/RMDE for MDE level design

Group Load = D + FNHW + HNHW + L + EQODE/RODE for ODE level design and = 0.6D + FNHW + HNHW + EQODE/RODE for ODE level design

Symbols are as defined in Sections 3.2 and 3.5.2

Uncertainty of HNHW shall be considered in design.

Uncertainty is the critical upper or lower bound load.

EQMDE and EQODE = Earthquake Loads for MDE and ODE level, see Section 6.12.3.

RMDE = Response Modification Factor = 2.0

RODE = Response Modification Factor = 1.0

6.12.5 Interface Joints

Interfaces between the cut-and-cover structures and the more massive structures, such as the station sections and ventilation/access structures, shall be designed as flexible joints to accommodate the differential movement .The design differential movements shall be established by the Geotechnical Engineer.

6.12.6 Ventilation /Access Shafts

The seismic considerations for the design of vertical shaft structures are dictated by curvature deformation. Consideration shall be given to the curvature strains and shear forces of the lining resulting from vertically propagating shear waves. Force and deformation demands may be critical in cases where shafts are embedded in deep, soft deposits. In addition, potential stress concentrations at the following critical locations along the shaft shall be properly accounted for:

1. Abrupt change of the stiffness between two adjoining geologic layers. 2. Shaft/tunnel or shaft/station interfaces.



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3. Shaft/surface building interfaces.

Flexible connections shall be used between any two structures with drastically different stiffness/mass in poor ground conditions.

6.12.7 Other Seismic Considerations

6.12.7.1 Liquefaction

Liquefaction and liquefaction related ground instability shall be evaluated at relevant locations along the project alignments. Empirical procedures based on CPT data or SPT blow counts may be used (MCEER, 1997). An initial screening study (MCEER 1998) shall be conducted followed by more refined analyses and evaluation of its impact to the proposed facility. Special attention shall be paid to loose fill and Holocene alluvium at the project site. The effects of liquefaction on the design of the foundations as well as structures shall be thoroughly investigated. These effects shall include, but not be limited to, the following:

1. Down drag and lateral/vertical resistance of deep foundation, 2. Loss of bearing capacity and settlements of shallow footings, 3. Post liquefaction (post-earthquake) stability and deformations of embankments, 4. Increased lateral pressures and buoyancy forces on walls and underground structures, 5. Lateral spreading along gentle slopes.

If the liquefaction impact analyses yield unacceptable performance of the structures, mitigation measures shall be incorporated into the design.

6.12.7.2 Seismic Slope Stability and Landslide

The potential for seismically induced landslides and slope instability shall be identified along the proposed alignment, particularly in areas where existing slopes have displayed signs of movement under static conditions. If pseudo-static seismic stability analyses indicate insufficient safety margin against the landslide movements, then an appropriate method of analysis, (e.g., the Newmark time history analysis) shall be used to estimate the movements. The impact of the potential slope movements on the affected structures shall be assessed. If the impact analyses yield unacceptable performance of the structures, mitigation measures shall be incorporated into the design.

If a reduction in the safety margin of the existing slope could result from the proposed construction of the facility, the design shall incorporate appropriate remedial measures to prevent such a reduction.

6.13 Groundwater Leakage

6.13.1 Drainage

Provisions shall be made to collect and drain water seeping through the walls or floor whether such structure components are waterproofed or not.

6.13.2 Waterproofing

Where a Slurry or Secant/Tangent Pile Wall System is used as a permanent structure, a waterproofing membrane shall be provided below the base slab and above the roof slab.



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Although the drainage channel along the face of the slurry wall can accommodate minor amounts of seepage, the connection between the base slab and the slurry wall shall be designed to provide a watertight connection

For a wall system built independently of the shoring wall, a waterproofing membrane shall completely encapsulate the entire station/tunnel box.

6.13.3 Waterstops

Waterstops shall be used in all construction joints in exterior walls, floors, and roofs, irrespective of water table.

For maximum effectiveness in preventing joint leakages, water stops must be continuous and carefully installed (including splices) per the manufacturer’s recommendations. The concrete shall be carefully placed and vibrated around waterstops.

6.14 Project Conditions

6.14.1 Maintenance of Operations

The underpinning activities shall be scheduled to avoid impacts to rail operations as much as possible. All impacts on rail operations shall be identified clearly during the initial development of the design.

6.14.2 Pre-construction Survey of Utilities and Maintenance

A complete picture of utilities entering the site of planned excavation shall be assembled by the Engineer during the design. Utility lines that will be intercepted, blocked, or relocated must be identified in the contract documents in greater detail. Specifications shall call attention to known or suspected locations of these utilities and procedures required for their treatment.

Where it is determined that a service disruption during construction is necessary, the utility owner shall be consulted and disruption constraints shall be defined.

6.14.3 Utility Relocations

During construction of cut-and-cover sections, existing utilities must be either supported below the temporary traffic deck over the excavation, or relocated. Also, in low headroom stations many existing utilities may be within the station mezzanine space and need to be relocated. One location for relocating these utilities is beneath sidewalks outside the slurry walls. The selection of the wall system must consider the available space between the slurry wall and the existing buildings.

6.15 Ground Modification / Improvement

Ground Modification / Improvement shall be considered for Cut-and-Cover Construction where the following conditions exist.

Protection of buildings adjacent to Cut-and-Cover Intersection of Soft Ground Tunnels with Cut-and-Cover Excavation The Permeability of the soil needs to be decreased



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The following methods shall be considered and the cost/benefits evaluated.

Cement Injection Grouting Chemical Injection Grouting Compaction Grouting Compensation Grouting Jet Grouting Ground Freezing

6.16 Zone of Influence for Deep Excavations

The design of Cut-and-Cover Structures shall take into account the impact on adjacent structures in the three zones identified below (refer to Figure 6.9a).

Zone A:

Foundations within this zone generally require underpinning unless particular precautions are adopted to limit ground movements, such as: stiff slurry wall and supports, top down construction, compensation grouting etc. Horizontal and vertical pressure on support wall/box structures of non-underpinned foundations within this zone must be considered in the design of the excavation support system. Ground movement assessments are generally required.

Zone B:

Foundations within this zone generally do not require underpinning. Horizontal and vertical pressure on support wall/box structures of non-underpinned foundations within this zone must be considered. Ground movement assessments are generally required.

Zone C:

Underpinning structures must receive their support within this zone. Horizontal and vertical pressures on support wall/box structures bearing in this zone need not be considered.

6.17 References

6.17.1 Non Seismic References

1. Bickel, Kuesel and King. Tunnel Engineering Handbook. Chapman & Hall, 1996.

2. Xanthakos, P. Slurry walls as Structural Systems. New York: McGraw-Hill Book Company, 1979.

6.17.2 Seismic References

1. Applied Technology Council (ATC). ATC-32, Improved Seismic Design Criteria for California Bridges: Provisional Recommendations. 1996.

2. Idriss, I. M. and Sun, J. I. A Computer Program for Conducting Equivalent Linear Seismic Response Analyses of Horizontally Layered Soil Deposits. Center for Geotechnical Modeling, Department of Civil and Environmental Engineering, University of California at Davis, 1992.

3. Youd, T. L., and Idriss, I. M. Proceedings of the NCEER Workshop on Evaluation of Liquefaction Resistance of Soils. NCEER-97-0022, NCEER, 1997.



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4. Wang, J., Seismic Design of Tunnels – A Simple, State-of-the-Art Design Approach, Monograph 7, 1991. William Barclay Parsons Fellowship, Parsons Brinckerhoff, 1993.

5. United States. Department of Transportation. Seismic Design Considerations for Mass Transit Facilities, Publication No. DOT-T-94-19, May 1994.



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6.18 Figures



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Figure 6.5 Ref: NAVFAC 7.02, 1986.

6.6



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Figure 6.6

Ref: NAVFAC 7.02, 1986.



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Figure 6.7 Pressure Distribution for Tied-Back Walls

Ref: NAVFAC 7.02, 1986.

6.5



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Figure 6.8 Pressure Distribution for Tied-Back Walls

Ref: NAVFAC 7.02, 1986.

6.5



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Figure 6.10

Figure 6.11



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Figure 6.12, [Ref. 4] [Ref. 3]



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Building or Construction Loads

Figure 6.15a

( See Notes in Table 6.5 )



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Building or Construction Loads ( Contd )

Figure 6.15 b

( See Notes in Table 6.5 )



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Notes for Figure 6.15a and 6.15b

Definition of Symbols:

B’ = Length of area load in direction parallel to side of excavation (ft) H’ = Distance between horizontal loading plane and bottom of excavation (ft) P’s = Calculated lateral pressure due to surcharge (psf). Q’ = Total load per ft of length parallel to retaining structure, or total footing load. xH’ = distance from retaining structure to footing load or parallel line load or to leading edge of area load or perpendicular line load.

a. Load Cases are as per the following table:

No. LOAD CASES y* z* P’s

1 Isolated (individual) footing considered as point load

0.6 0.4 (2.1-1.8x)Q’ /2 (H’)2

2 Continuous footings considered as line load parallel to retaining structure

0.4 0.25 (1.1-0.5x)Q’ / 2H’

3 Area Load 0.4 0.25 (0.8-0.5x)Q’ / 2H’

4 Continuous footing considered as line load perpendicular to retaining structure

0.6 0.4 (1.4-1.2x)Q’ /2 (H’)2

Table 6.5 Surcharge Lateral Pressure

*: See Figure 6.15a and Figure 6.15b for explanation of the terms y and z.

b If the building foundations are underpinned, the transfer of building load to a lower level

should be considered in evaluating resultant lateral pressure using acceptable procedures.



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Chapter 7

Foundations

Table of Contents

Section Item Page

7.0 Scope 87

7.1 Foundations 87

7.2 Loading and Load Combinations 87

7.3 Geotechnical Data 87



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Chapter 7

Foundations

7.0 Scope

This section covers the provisions regulating the design and construction of foundations of buildings and other structures and involves Geotechnical and Structural considerations in the selection and installation of adequate supports for the loads transferred from the structure above.

7.1 Foundations

Foundations shall be designed in accordance with the requirements of the Building Code of New York State (NYSBC) as follows:

a. Foundation and Soils Investigations Section 1802 b. Excavation, Grading and Fill Section 1803 c. Allowable Load bearing values of Soils Section 1804 d. Footings and Foundations Section 1805 e. Retaining Walls Section 1806 f. Pier and Pile Foundations Section 1808 g. Driven Pile foundations Section 1809 h. Cast In Place Concrete Pile Foundations Section 1810 i. Composite Piles Section 1811 j. Pier Foundations Section 1812

Where the design stipulations are not specified, the relevant Article Number of Subchapter 11 – Foundations of the Building Code of the City of New York (NYCBC), shall be followed.

Where the more stringent stipulation is provided in NYCBC, the design shall comply with the requirements of NYCBC.

7.2 Loading and Load Combinations

All loading and combinations shall be as per Section 1605 Building Code of New York State (NYSBC).

7.2.1 Seismic Loading

Seismic design criteria shall be in accordance with the requirements of Building Code of New York State (NYSBC) Chapter 17 and as specified in Chapter 2,3,6,and 9.

7.3 Geotechnical Data

All Geotechnical data to be used in the design shall be verified by Geotechnical Engineer or as provided in Geotechnical Baseline Report (GBR).



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Chapter 8


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8.0 Scope 89


8.2 Settlements 89

8.3 Classification of Damage 94

8.4 Protective Measures 95

8.5 References 95



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Chapter 8


8.0 Scope

This section addresses the factors affecting ground movements and subsequent settlement of adjacent buildings resulting from cut-and-cover construction, and the assessment of potential damages due to these settlements. The design guidelines and criteria presented in this section govern the protection of existing structures through the use of appropriate construction techniques, in-situ wall types, and protective measures.





As noted in the document

8.2 Settlements

Some of the factors affecting in-situ wall movements and thus, the associated ground settlements and settlement of adjacent structures are:

Soil and Groundwater Conditions Changes In Groundwater Level Depth and Shape of Excavation Type and Stiffness of the Wall and Its Supports Surcharge Loads Duration of Wall Exposure

The general pattern of wall movement and adjacent ground deformation due to braced and tied-back excavations is illustrated in Figure 8.1.



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8.2.1 Ground Settlements Resulting from In-Situ Wall Construction

Ground movements occurring as a result of the installation of in-situ walls can be estimated using empirical methods developed from experience on completed projects. These methods account for wall properties, construction methods, soil conditions, panel widths, etc. Settlements are additionally affected by the following factors related to the wall installation process:

Vibrations Due to Pile Driving Lag Time in Placing Supports Depth of Excavation Below Support Placement Preloading of the In-Situ Wall Groundwater Control Wall Settlement

8.2.2 Assessment of Ground Settlement Distribution

The following, dimensionless diagrams can be used to obtain an estimate of actual vertical surface settlement due to settlements caused during the excavation and bracing stages of construction. Movements associated with other activities, such as dewatering, deep foundation removal or construction, and wall installation, should be estimated separately.

Figure 8.1



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8.2.3 In-Situ Wall Movements

8.2.3.1 Limits on Wall Deformations

Typical values of wall deformation for acceptable earth support systems associated with good construction are:

Threshold Value 0.0015H Limiting Value 0.0025H

Where H is the excavation depth.

8.2.3.2 Control of Groundwater

Criteria for permissible groundwater drawdown shall be established based on analysis to estimate potential settlement of adjacent structures. The criteria shall also consider the impact of the drawdown on the structural integrity of the foundations [Man. 1].

Drawdown within the excavation limits shall be sufficient to provide a minimum factor of safety of 1.1 against an unstable bottom in granular soils and bottom heave in cohesive soils [Man. 1].

Figure 8.2 [Ref. 2]



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8.2.4 Assessment of Wall Movement and Risk of Damage to Buildings

Deformations resulting from construction can adversely affect adjacent structures causing minor to severe damage. In order to screen adjacent structures that are at risk for damage, the three-stage process summarized below shall be followed [Ref. 3].

As part of the existing building survey, buildings adjacent to the proposed alignment will be surveyed to assess and document their state prior to the start of construction.

Stage 1 - Preliminary Assessment

The preliminary assessment shall establish the area of influence of the proposed excavations. The types and methods of construction for each of the elements shall be assessed and the anticipated zones and extent of ground settlements resulting shall be approximated. See Figure 6.9a for a diagram of zones of influence.

Structures that fall completely outside the zone of influence need not be considered.

Figure 8.3 [Ref. 2]



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Stage 2 - Rigorous Assessment

Each structure within the zone of influence shall be reviewed to determine the extent of potential damage due to the construction.

The following table evaluates the severity of damage to structures using horizontal strain and angular distortion.

Strains due to ground settlements shall also be evaluated using the methodology outlined in Mair et al [Ref. 3]. The potential damage category can then be determined from Table 8.1 using the resulting strain value. In this approach, the building is assumed to have no stiffness and to conform to the ‘green field site’ settlement. Because the inherent stiffness of the building tends to reduce both the deflection ratio and the horizontal strain, the resulting, predicted category of damage will usually be greater than the actual damage.

Stage 3 - Detailed Evaluation

A detailed evaluation should be undertaken for buildings where a second stage assessment indicates slight to moderate damage. Computer models using finite difference analysis (e.g. FLAC) or finite element analyses (e.g. SIGMA/W or PLAXIS) shall be used to predict ground movements. This assessment should account for three-dimensional aspects of the excavation and building layout. In addition, details of the building should be taken into account to determine its structural continuity.

The following factors shall be considered in the detailed evaluation:

Wall type Time dependent movement of the wall Bracing properties Bracing levels

Figure 8.4 Range of Deformations Typical of Excavations in Various Soils Relative to Building Damage Potential [Ref. 2].



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Construction sequence Excavation method Ground movements as a result of wall installation Effects of groundwater Soil properties Soil-structure interaction effects Adjacent structure stiffness Foundation conditions

The results of the detailed evaluations can also help determine the required mitigation for the protection of the building from excessive damage. See also Section 8.4 – Protective Measures.



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8.3 Classification of Damage

Table 8.1: Classification of visible damage to walls with particular reference to ease of repair of plaster and brickwork or masonry [Ref. 3].

Category of damage

Normal Degree of Severity

Limiting Tensile Strain

(lim)

Description

0 Negligible 0.00 To 0.05% Hairline cracks less than about 0.01mm. 1 Very

Slight 0.05 to 0.075%

Fine visible cracks in external brickwork or isolated fractures. Easily repaired during normal decoration, door and windows may sticks slightly

Typical crack widths up to 1 mm. 2 Slight 0.075 to 0.15% Cracks are visible externally and inside the building can

be a series of several slight fractures. The cracks are easily filled and redecoration is probably required. Repainting may be required externally to ensure. Weather-tightness.

Typical crack widths up to 5 mm. 3 Moderate 0.15 to 0.3% Cracks will require some opening up and patching by a

mason. Suitable linings can mask recurrent cracks. Repointing of external brickwork and possibly a small 1 amount of brickwork to be replaced. Doors and windows are sticking. Service pipes may fracture and weather- tightness is often impaired. Also depends on the number of cracks.

Typical crack widths 5 to 15 mm or several greater than 3 mm.

4 Severe

> 0.3% Severe cracking requires extensive work involving 25.0mm braking out and replacing sections of walls, especially Over doors and windows, Windows and doorframes become distorted, And the floor begins to slope Noticeably. Walls leaning or bulging occur and some ~ loss of bearing beams is possible. Service pipes are disrupted. Also depends on the number of cracks.

Typical crack widths are 15 to 25 mm but also depend on the number of cracks.

5 Very Severe

Very severe cracking requires a major repair job Severe involving partial or complete rebuilding. Beams lose 5 bearing; walls lean badly and require shoring. Windows broken with distortion and there is danger of instability. Also depends on the number of cracks.

Typical crack widths are greater than 25 mm but also depend on the number of cracks.



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8.4 Protective Measures

Protective measures include mitigating and/or minimizing the impact of settlement effects on critical structures. Comparative costs of protective measures versus the predicted settlement effects due to construction should be evaluated.

8.4.1 Mitigation of Structural Damage

The following forms of preventive measures shall be considered during design:

Offset the building settlement by injecting grout in the ground below the building (ground improvement/modification.

Underpin the building too introduce an alternate foundation in order to prevent ground movement effects on the building.

Jacking to counteract settlement.

Strengthen the structure to increase the stiffness and counter the additional stresses imposed due to tunneling.

Top Down Construction: In this process, the objective is to build parts or all the underground portion of the building from the top down rather than from the bottom up: hence, it also provides progressive underpinning. The method is compatible with deep excavations because it eliminates strutting, anchoring, or bracing berms.

8.5 References

1. Goldberg, D.T., Jaworski, W.E., and Gordon, M.D. Lateral Support Systems and Underpinning. Report FHWA-RD-75-128 and 129, Vols. I and II, FHWA, Washington, D.C., Apr. 1976.

2. Clough, G.W., and O’Rourke, T.D. “Construction Induced Movements of In Situ Walls”, Proceedings: Design and Performance of Earth Retaining Structures. Ithaca, NY: Cornell University, June 1990.

3. Mair, R.J. Taylor, R.N. and Burland, J.B. “Prediction of ground movements and assessment of risk of building damage due to bored tunnels”, Proceedings: International Symposium on Geotechnical Aspects of Underground Construction in Soft Ground. London 1996 (eds Mair, R.J. and Taylor, R.N.), Balkema, 713-716.

4. DHA Document, Design Criteria Manual. May 2003.

5. DHA Document, Guideline Document – Evaluation of Ground Movements and Impacts on Adjacent Structures. Jan 2003.



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6. Metropolitan Transit Authority LIRR. East Side Access Design Criteria. New York, NY, May 2001.



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Chapter 9

Tunnel Structures

Table of Contents

Section Item Page

9.0 Scope 99


9.2 Structure Types 99

9.3 Summary of Tunneling Methods in Soft Ground

100

9.4 Summary of Tunneling Methods in Rock 100

9.5 Subsurface Investigations and Data 102

9.6 Mined Tunnel and Cavern 103

9.7 Bored TBM Tunnels in Rock Error! Bookma

rk not defined.

9.8 Ground Modification / Improvement 128

9.9 Seismic Design 128

9.10 References 132



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Chapter 9

Tunnel Structures

9.0 Scope

To provide geotechnical and structural guidelines and criteria for the planning, design and construction of tunnels and caverns in rock and mixed ground.



1. American Society for Testing and Materials (ASTM). ASTM A820 Standard Specification for Steel Fibers for Steel Fiber-Reinforced Concrete.

2. American Society for Testing and Materials (ASTM). ASTM C1116-91 Standard Specification for Fiber-Reinforced Concrete and Shotcrete.

In addition, refer to Chapter 1, Section 1.2.1.


1. American Society of Civil Engineers (ASCE). Technical Engineering and Design Guides No.18, Rock Foundations.

2. Metropolitan Transit Authority LIRR. East Side Access Design Criteria, Section No. 7. New York, NY, May 2001.

3. United States. Department of the Army, U.S. Army Corps of Engineers, Engineering and Design – Rock Reinforcement, Publication #EM1110-1-2907

4. United States. Department of the Army, U.S. Army Corps of Engineers, Engineering and Design – Systematic Drilling and Blasting for Surface Excavations, Publication #EM1110-2-3800

5. United States. Department of the Army, U.S. Army Corps of Engineers, Engineering and Design – Tunnels and Shafts in Rock, Publication #EM1110-2-2901

6. United States. Naval Facilities Engineering Command. Soil Mechanics: Design Manual 7.01. NAVFAC DM-7.01, 1998.

7. United States. Naval Facilities Engineering Command. Foundations and Earth Structures: Design Manual 7.02. NAVFAC DM-7.02.

9.2 Structure Types

Facilities to be excavated and supported by tunneling shall include but are not limited to:



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Mainline Running Tunnels: Tunnels that house the running subway trains between stations. Single Track Connection Tunnels: Single tunnels that house the running subway train at

turnouts. Tunnel Turnout Caverns: Enlarged sections of tunnel or caverns excavated to accommodate

subway tunnel turnouts and relay/storage tracks. Relay/Storage Track Caverns (Pocket Tracks): Single track lines where full-length trains can

be stored when not in use. This track section will require cavern excavation, which includes three track lines.

Crossover Caverns: A mainline running tunnel section where trains can cross from the south to the north tunnel and visa versa. These tunnel sections require cavern construction.

Cross Passages: Short sections of drill and blast tunnel, which interconnect the north and south running mainline running tunnels.

Access Shafts: Construction shafts from street level to subway level which allow entry to tunnels during construction. Workers, materials, and equipment use these shafts for entry to and egress from the underground works.

Splicing Chamber: Excavated opening adjacent to a subway tunnel where high- Voltage cables are spliced. Splicing chambers will be located in cross passages.

Sumps: Excavated openings for collecting and pumping water in tunnels and stations. All tunnel sumps will be located in cross passages.

Station Cavern: Station area created by sequential excavation of bored or mined running tunnel.



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9.3 Summary of Tunneling Methods in Soft Ground

The following table summarizes the construction methods and the lining methods generally applicable to each of the required structure types in soft ground. The choice of any construction method and lining method shall be thoroughly evaluated and presented to NYCT prior to the execution of work.

BORED TUNNELS IN SOFT GROUND

Structure Type

Subway Structure

Construction Methods

Lining Methods

Single Track Tunnels

Mainline Tracks

Connecting Tracks

Closed Face TBM Single Pass Segments, Bolted and Gasketed

Junk Segment and CIP Sequential Excavation (SEM)

Initial Lining + Concrete Final Lining

Cross Passages

Cross

Passages

Sequential Excavation (SEM )

Initial Lining + CIP Final Lining

Shafts

Access

Shafts

Sequential Excavation ( SEM )

Initial Retaining Support + CIP Final Lining

Conventional Junk Segments + CIP Final Lining Single Pass Segments, Bolted and

Gasketed

Table 9.1: Summary of Methods of Tunneling in Soft Ground



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9.4 Summary of Tunneling Methods in Rock

The following table summarizes the construction methods and the lining methods generally applicable to each of the required structure types in Rock. The choice of any construction method and lining method shall be thoroughly evaluated and presented to NYCT prior to the execution of work.

BORED TUNNELS IN ROCK

Structure Type

Subway Structure

Construction Methods

Lining Methods

Single Track Tunnels

Mainline Tracks

Connecting Tracks

Hard rock TBM Initial lining + CIP final lining Junk segments + CIP final lining Single Pass Segments, Bolted and

Gasketed Multi-Mode TBM Junk segments + CIP final lining

Single Pass Segments, Bolted and Gasketed

Drill-and-Blast Initial Lining + CIP Final Lining

Road Header

Caverns Crossovers Storage

Tracks

Drill-and-Blast (SEM)

Initial Lining + CIP Final Lining

Road Header (SEM)

Cross Passages

Cross Passages

Drill-and-blast

Road header

Initial lining + CIP final lining

Shafts Access Shafts

Conventional / Sequential Excavation Method (SEM)

Initial Lining + Concrete/ Shotcrete Final Lining

Junk Segments + Concrete Final Lining

Single Pass Segments, Bolted And Gasketed

Raise Drilling and

Reaming

Table 9.2: Methods of Excavation of Bored Tunnels in Rock

9.5 Subsurface Investigations and Data

After review of existing geotechnical data, ground conditions at proposed locations shall be determined by performing appropriate subsurface investigations. All geotechnical data, discussion of subsurface conditions, recommended geotechnical design parameters and discussion of construction considerations, shall be presented in appropriate geotechnical reports including:

Geotechnical Data Reports (GDR) and



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Geotechnical Baseline Reports (GBR).

The requirements of detailed geotechnical work shall be as addressed in Chapter 4 – Geotechnical.

9.6 Mined Tunnels and Caverns

9.6.1 Support Definition

The following definitions apply:

Initial ground support measures shall be determined by appropriate engineering analysis based upon the ground conditions encountered at the face during the construction phase, but are not included as final support in design calculations.

Final support elements are prescribed during the design phase, and shall be considered to support the total loading requirements for the design life of the structure.

9.6.2 Design Philosophy/Principles (Initial Support System)

A rock mass classification system shall be used to define the support elements of the initial lining in different rock classes. The rock formation shall be subdivided into classes based on available data and in accordance with the RMR and Q rock mass classification systems. Where tunnel excavation is in good rock, as defined by the rock mass classification system, and where tunnel excavation will not adversely influence other structures, initial support can be defined by rock mass classification system. However rock wedge analysis will be required to determine initial support lengths and orientations. In all other cases, initial lining shall be supported by stability and deformation analysis. Initial rock reinforcement shall not be considered as part of the final lining.

Based on the rock classification, geological information, surcharge loads, geometry of the opening, presence of adjacent structures, water pressure, et cetera, the tunnel alignment shall be divided in support classes. The type of support and excavation method shall be defined for each support class.

Initial support systems shall be designed as ground reinforcement or as direct support to establish a stable opening for continuing construction operations.

A wedge analysis shall be performed for all openings in rock as part of the initial lining design, to define a rock reinforcement pattern, length, and orientation.

When applicable, surcharge loads shall be considered in the analysis of excavation support systems.

Adjacent and/or overlying structures potentially affected by the proposed excavation shall be considered in the analysis. Numerical analysis modeling soil structure interaction will be required in such cases. Numerical analysis will also be required for complex excavation such as intersections between tunnels and caverns

9.6.3 Geotechnical Parameters

The following geotechnical parameters, as a minimum, shall be used to develop the ground models for numerical analysis of tunnels and caverns and in the design of the initial support and final lining.



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9.6.3.1 Geological Factors:

Hydrogeological Model Seismological Model Structural Geological Model

9.6.3.2 Soil Properties

Index Properties Angle of Internal Friction (Undrained and Effective) Cohesion (Undrained and Effective) Modulus of Elasticity (Undrained and Effective) Poisson’s ratio

9.6.3.3 Rock Properties

1.0 Intact Rock: UCS, Tensile Strength, Cohesion, Friction Angle, Unit Weight. Poisson’s ratio

2.0 Discontinuities: Compressive Strength, Roughness and Surface Shape, Number of Joint sets, Spacing and Persistency, Orientations (Dip/Dip Direction)

9.6.3.4 Rock Mass Classification

There are several rock mass classification systems such as RMR and Q.

a ) Rock Mass Rating (RMR):

RMR was initially developed by Bieniawski (1973) to develop engineering parameters for analysis tunnels and caverns at shallow depths. The following six parameters are determined for this rating:

Uniaxial compressive strength of intact rock materials, Rock quality designation (RQD), Joint or discontinuity spacing, Joint conditions (roughness and surface shape), Ground water condition, and Joint orientation



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Table 9.3 : Rock Rating System (After Bieniawski, 1989 )



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b ) Application of RMR:

Average Stand-up Time for Arched Roof (Shown in Table 9.3) Cohesion and Angle of Internal Friction (Shown in Table 9.3) Modulus of Deformation

For qc (UCS of Intact Rock) >100MPa Ed = 2 RMR – 100 GPa (applicable for RMR >50) (Bieniawski, 1978) Ed = 10 (RMR -10)/40 GPa (applicable for RMR < 50) (Serafim and Pereira 1983) Where Ed = Elastic Modulus of Rock Mass

c) Support Design:

Table 9.4 : Guideline for excavation and support of rock tunnels in accordance with the rock mass rating system (Bieniawski, 1989) (Note: Unreliable in very poor rock masses)



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d ) Rock Mass Quality (Q) – System:

The Q system, developed by Barton at the Norwegian Geotechnical Institute gives the most detailed description of the rock mass. The Q system assumes a jointed rock mass and summarizes the main aspects of a rock mass that govern excavation behavior. Rock quality designation (RQD) from drill core Number of joint Sets (Jn) from Joint survey Discontinuity roughness (Jr) from Joint survey Discontinuity wall alteration, weathering or in fill mineralogy (Ja) from Joint survey Water pressure or estimates of inflow (Jw) from Hydrological survey Geological setting and in situ stress state (relative to intact rock strength) (SRF) from

Geological survey

The relationship between these factors is shown below

SRF

Jw

Ja

Jr

Jn

RQDQ

e ) Application of Q:

Estimation of Support Pressure

)Q (20

Jr P

1/3r MPa (N. Barton 2002)

Estimation of Unsupported Span Max Span (unsupported) = ESR 2.0 (Q0.4) meters where, ESR = excavation support ratio

Design of Support



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Figure 9.1: Estimated support categories based on the tunneling quality index (Q) (After Grimstad and Barton 1993)

Modulus of Deformation of Rock Mass

E (mean) = 25log Q ( Gpa)



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Figure 9.2 : Estimation of rock mass deformation modulus from two classification methods of RMR and Q (Barton 1993)

9.6.3.5 Rock Failure Criteria

For intact rock and heavily jointed rock masses that may be considered homogeneous and isotropic, the shear strength of the rock mass shall be expressed either by the Hoek-Brown Failure Criterion as indicated below or by the Mohr-Coulomb Criteria.

σ’1 = σ’3 + σci + {mb (σ’3/ σci ) + s}a

where: σ’1 = major principle effective stress at peak strength

σ’3 = minor principle effective stress

σci = uniaxial compressive strength of intact rock

mb = material constants for Hoek-Brown criterion

s = material constant for Hoek-Brown criterion a = material constant for Hoek-Brown criterion = 0.5.

Equivalent effective shear strength parameters applicable to the Mohr-Coulomb failure criteria shall be estimated using the Hoek-Brown failure criteria constants in accordance with Hoek, Carranza-Torres, and Corkum, 2002.



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9.6.4 Loads

The structure types are selected to meet the alignment requirements and geotechnical conditions. The design approach is dependent on the technology used for the construction and the interaction between the ground and the structure.

9.6.4.1 Dead Load

The dead load is the weight of the structure with permanently installed appurtenances. See Chapter 2 - Loads

9.6.4.2 Live Load

See Chapter 2 for applicable live loads

9.6.4.3 Surcharge Load

Surcharge Loads are those loads applied at the ground surface. The influence of these loads on the underground structure depends upon the subsurface conditions and upon the depth of the overburden. The magnitude of the surcharge load shall be established by the Geotechnical Engineer.

9.6.4.4 Seismic Loads

No seismic consideration needs to be taken into account for design of initial support structures.

9.6.4.5 Ground Pressure

The underground structure is a compound structure consisting of the soil or rock formation surrounding the excavation, the initial ground support system, and the final structure. The ground pressures will vary at different stages of the construction as well as with the type of ground support system used. Initial and final linings shall be proportioned to support the varying ground loads, both vertical and horizontal as established by the Geotechnical Engineer.

9.6.4.6 Water Pressure

The influence of water pressure shall be analyzed both for the construction condition and for the service condition. Mined underground structures shall be designed for full hydrostatic pressure, except where an appropriate hydrostatic pressure relief system, approved by NYCT, is provided.

9.6.5 Design Loads for Lining

9.6.5.1 Initial Lining and Support

The initial support for the tunnels shall be designed to withstand, as a minimum, the following loads:

Self-weight of initial support elements Earth pressure, with appropriate ground-structure interaction Hydrostatic pressure and buoyancy if any. Rock Tunnels in excavation stage are drained,

therefore no hydrostatic pressure. Surcharge loading



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Loads due to adjacent building foundations Loads and effects of adjacent tunnels and excavations Construction Loads

9.6.5.2 Load Combinations

The most critical loading combinations for design shall be considered.

9.6.6 Material Properties

9.6.6.1 Mined Tunnel Lining

The initial support with fiber reinforced shotcrete shall be as follows:

Minimum Compressive Strength fc' = 6,000 psi Modulus of Elasticity Ec = 57,000 • fc' Modulus of Rupture = 10 • fc' Steel fiber reinforcement = Grade 60 ksi minimum.

9.6.6.2 Materials for initial supports for Caverns and Others

Allowable materials shall be as tabulated below:

Material Comment

Structural Steel Structural Steel Ribs shall be designed for a minimum yield stress as specified by AISC.

Rock Bolts Rock Bolts shall be designed for loads that are 60 percent of the Guaranteed Ultimate Strength (GUTS).

Cast-In- Place Concrete The minimum 28 day compressive strength, fc' ≥5,000 psi.

Fill and Mud Slab Concrete

The minimum 28 day compressive strength, fc' ≥1,500 psi.

Shotcrete The minimum 28 day compressive strength prior to addition to any fiber reinforcement fc' ≥6000 psi.

Table 9.6: Materials

9.6.7 Initial Support Analysis and Design

9.6.7.1 Methodology

The analysis methods proposed for mined and cavern structure design are listed below. Alternate methods may be proposed for approval of the Engineer

1. Empirical Methods (See 9.6.3.4)

Q System RMR System



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. Analytical Methods:

Beam Analysis Key-block Analysis Rock Arch Analysis

3. Numerical Methods

Continuum Discontinuum

The results of these three type of analysis methods shall be integrated to determine the final design of the initial and final linings.

An overview of the Initial Lining Design Methodology follows:

9.6.7.2 Empirical Design Methodologies

Several different type of empirical design methods may be used, the most common being the Norwegian Geotechnical Institute Rock Tunneling Quality Index (Q system) and the Rock Mass Rating (RMR system) These methods attempt to classify the rock to allow comparison with other excavations from around the world and therefore estimate the likely support requirements. These methods differ in the detail with which they classify the rock mass and the confidence that can be placed in the support predicted. See 9.6.3.4 Rock Mass Classification.

9.6.7.3 Analytical Methodology

Analytical methods include such techniques as closed form solution and structural analysis. It is important that analytical methods and failure criteria be selected that can model the anticipated or identified failure mechanism and mode of failure most appropriately.

The following are examples of analytical design approaches for different geotechnical conditions:

Beam Analysis for stratified hard rock masses or hard rock masses with pseudo-stratification.

Key-block Analysis for hard rock moderately to widely spacing jointed Rock Arch Analysis for weak rocks (highly jointed rock masses) or soft rocks

9.6.7.4 Numerical Modeling Techniques

Modeling shall consider the rock mass as continuum for highly to moderately jointed rock masses and discontinuum for moderately jointed to wide spacing jointed rock masses. These generally require the use of one of two types of modeling tool, Finite Difference (FD)/Finite Element (FE) or Discrete Element (DE).

9.6.7.5 Initial support design considerations:

a) Rock Cover above Mined Caverns

An analysis of the rock cover above the mined cavern shall be performed using conventional wedge analysis, numerical analysis, and/or empirical methods depending upon the complexity of the



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configuration. This analysis shall determine the amount of competent rock required above the mined cavern to prevent structurally controlled failure and stress induced failure.

b) Rock Stress Considerations

Numerical analyses of cavern construction sequence and of the final structure shall be based on in-situ rock stress conditions as discussed in the appropriate GDR or GBR. The analyses shall consider initial ground reinforcement if any, strength and stiffness of the in-situ rock between the excavations, and resultant rock stress redistribution. The analyses shall take into account probable excavation and support installation sequence. As a design guideline, the resultant rock stresses calculated by appropriate numerical analyses should not exceed 35 percent of the in-situ rock mass brittle failure strength as determined by Hoek-Brown parameters as updated by Hoek, Carranza-Torres and Corkum or equivalent Mohr-Coulomb criteria. If resultant stresses exceed 35 percent of the in-situ rock mass brittle failure strength, additional rock support beyond that indicated by routine Q and RMR system calculations or block analyses shall be evaluated and incorporated into the design.

The structural support of initial and final lining shall be verified by loading induced by the rock in-situ stresses.

c) Stress/Strain Analysis

Horizontal and vertical rock stresses vary with depth and local or regional conditions. Generally, for relatively shallow depths such as those for the proposed mined stations, the in-situ vertical stresses are controlled by the depth and unit weight of overburden above the excavation in the following equation:

v = Hrr +Hss

where: Hr = depth of rock r = Unit weight of rock Hs = depth of soil s = Unit weight of soil

Although the vertical design loading is likely to be dominated by the ground loading, other loads may be generated by surface loading from sources such as traffic.

In situ horizontal stresses are dependent on a number of factors that include:

Vertical Stress Locked-in regional stresses from geological events Local geological anomalies such as faults or igneous intrusions Reduction in stress due to nearby excavation or weathering Increase in stress due to bearing foundations

Generally horizontal stresses are expressed as a proportion of the vertical stress using the coefficient K0 where:

K0 = h /v

Horizontal stress may be higher or lower than the vertical stress depending on the influence of the factors listed above.



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This range should include expected variations in the in-situ horizontal stress except where the stress is influenced by one of the following;

Load transfer from the building to the rock mass, Stress relief due to excavation for the building foundation, Stress concentrations associated with the excavation for the building foundation, or Tectonic stresses.

d) Key-block Analysis for Structural Failure Modes and Periphery Control

A rock mass contains discrete joint systems that may cause the rock to deform along discontinuities rather than through stress-strain relationships. Design of the initial support systems against this failure mechanism requires an understanding of several parameters including the block size, the shear strength of the joints defining each block, and the in-situ horizontal stress ranges likely to be encountered.

e) Rock Bolt Design

The type and length of Rock Bolts required for rock support reinforcement shall be identified based on the following:

Rock mass properties as given in the GDR Excavation geometry and size Installation methods Underground or overhead obstructions Existing structures Right of way and easement limitations as given in the GBR

Rock bolt lengths used for analysis shall not be less than:

Rock Bolt lengths shall not be less than 6 feet for non-tensioned bolts and 10 feet for tensioned bolts

�The length required for support of rock blocks as identified in the force equilibrium method;

The length required to anchor outside of the failure zone around the excavation as determined by a stress strain analysis with a Hoek-Brown or Mohr-Coulomb failure criterion, and

The length required to stabilize wedges in the crown, as determined by stress-strain is continuous analysis.

Rock bolts shall be designed so that the stress in the bolts does not exceed 60% of the guaranteed ultimate tensile strength of the bolt (GUTS).

Performance of the rock bolt reinforcement shall be verified by a finite element/finite difference analysis or discrete element analysis

f) Sequential Excavation

To control ground deformation during excavation of tunnels and caverns in weak/poor rocks and large openings such as station caverns or intersections between tunnels in hard rock, sequential excavations shall be considered. Sequential excavation considerations are as follows:

In weak/poor rocks and soft ground, side drifts followed by center drift is recommended.



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Size of drifts and their excavation sequences shall not cause any unpredictable induced stress in the installed ground reinforcement (Rock bolts and shotcrete).

Stand up time for excavation sequences can be determined from empirical approached (RMR) in conceptual design, however to finalize the excavation performance 3D numerical modeling shall be prepared .

Ground reaction curves shall be prepared to predict support responds in soft ground or weak/poor rock excavation.

9.6.8 Final Lining Analysis and Design

9.6.8.1 The permanent tunnel lining shall be designed, as a minimum, but not limited to, for the following loads:

Self-weight of lining and other permanent elements Earth pressure, with appropriate ground-structure interaction. Hydrostatic pressure and buoyancy Live loads due to use and occupancy Equipment loads Impact and derailment loads Seismic effects Surcharge loading Loads due to adjacent building foundations Loads and effects of adjacent tunnels and excavations Construction loads Temperature loads

9.6.8.2 Load cases to be considered

The final lining shall be designed to account for all dead and live loads imposed upon it, plus ground and surcharge loads that will not be supported by the initial support elements over the design life of the structure.

The final lining shall also be designed to withstand the rock loading due to the weight of the potentially unstable rock wedges and/or key-blocks. This loading shall be applied as a distributed load over the exposed area of the wedge.

The final lining shall be cast-in-place reinforced concrete, shotcrete, or pre-cast concrete segments. An impermeable membrane shall be placed between the initial support elements and final lining to prevent groundwater seepage into the structure. If pre-cast segments are used, they shall be bolted and gasketed to insure watertightness.

The lining design shall consider the full range of probable ground variability.

9.6.8.3 Allocation of Initial Support Elements to the Final Lining

Initial support elements that are not confirmed to last the design life of mined tunnels and caverns shall be ignored for final lining design.

The support that complies with the design and construction requirements for the design life of the mined structure and that can be fully integrated into the final support shall be allowed to contribute



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100 percent of their capacity to the final lining. However some percent of these supports capacities may be considered as sacrificial capacity. Initial support elements that may be assumed to contribute to the final lining design include:

Double corrosion protected rock bolts Fully grouted (cementitious) stainless steel rock bolts Fully encapsulated (polyester) fiberglass rock dowels Structural steel members embedded in concrete Shotcrete

9.6.9 Analysis Model and design for Mined Tunnel and Cavern Design

9.6.9.1 Structural Design

Following is the methodology of structural design of typical Mined Tunnel and Cavern design

a. Finite Element Model Model the structure by using appropriate Finite Element Programs like STAAD or LARSA

or any other suitable program. Calculate member Forces : moment ( Mu) , axial thrust (Nu) and shear (Vu) under various

load combinations and boundary conditions Calculate displacements induced by various service load combinations, and verify

displacements against ACI permitted deflections. Design of flexural and compression reinforcement using Moment Vs Axial Load Interaction

Capacity Diagram Verify structural model performance from the calculated rock compression displacements

and lining pressures on rock. b. Strength Design Criteria Reinforced concrete design shall be as per ACI 318, For detailed methodology, see Appendix A

c. Material Properties Material properties shall be minimum as follows :. Minimum Compressive Strength fc' = 5,000 psi Modulus of Elasticity Ec = 57,000 • fc' Modulus of Rupture = 10 • fc' Steel reinforcement = Grade 60 ksi minimum.

d. Properties of Rock Springs Rock support shall be modeled by means of springs. Vertical springs are to be attached to the bottom of invert slab. Lateral springs are to be used for the side walls. Radial springs are to be used for the arch portion of the cavern . Effects of inclusion of tangential springs in arches into the model are to be considered for the critical load combinations .

Radial spring stiffness along cavern’s arch shall be calculated from Army Corps of Engineers EM 1110-2- 2901:

Kr = Er b θ /(1+ νr)



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Where

Kr = Radial Spring Stiffness

Er = Rock mass Modulus

νr = Poisson ratio of Rock Mass

θ = arc subtended by the beam element (radian )

b = length of tunnel element considered.

Vertical Spring stiffness below cavern footings can be evaluated from CURTIS 1976:

Kv = Em/Cd B (1- νr ˆ2))

Where

Em = Rock mass modulus

νr = Poisson ratio of Rock Mass

Cd = 3.7 , Factor for footing shape and size;

B = Footing width

Considering the following facts :

There will be thermoplastic waterproofing and drainage layer- fleece as a bond breaker between the final liner and initial liner, compressible of the composite materials and contact grouting will be provided between the final and initial liner, a compression gap may be assumed between the station cavern final liner and initial rock support.. Therefore in the model , a gap can be assumed on the spring curves for radial springs and lateral springs on the liner.

No tension capacity shall be allowed on these radial springs. Horizontal spring stiffness for cavern footing shall be so chosen such that the horizontal

spring reaction does not exceed the frictional strength of foundation materials.

e. Serviceability Criteria Serviceability criteria shall be as per ACI 318. Maximum deflection shall be as per Table 9.5b. Cracked section properties with moment of inertia value of 0.3Ig shall be used for

strength design method. For service load analysis, a value of 1.43 x 0.3Ig = 0.43 Ig ( ref Section 10.11.1 ) shall be

used.



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Additional long term deflection resulting from creep and shrinkage of flexural members shall be determined by multiplying the immediate deflection caused by the sustained load considered , by a factor

Λ =ζ/( 1+ 50 ρ’ ) where

ζ = time dependent factor (conservatively may be taken as 2 for 5 years or more ). and

ρ’ = reinforcement ratio for non prestressed compression reinforcement ( conservatively may be taken as zero. ).

Therefore, Λ = 2.0/(1+ 50 x 0) = 2.0

Section Property for service load evaluation , I = 0.35Ig x (1.43/2.0) = 0.25 Ig

f. Minimum reinforcement criteria

Minimum reinforcement ratio = 0.18% ( 0.09% in each face ) per ACI 318 shall be maintained.

g. Design Loads Dead loads

Self weight of the structure, superimposed dead load shall be considered.

Live Loads

Where appropriate, the train live load on the invert as given in Chapter 2

Rock Loads 1. Determine fracture sets and orientation

2. Determine wedge size and wedge loads Ground water loads

Full hydrostatic pressure load shall be considered to be acting on the structure. No reduction shall be considered unless the structural system is designed as drained and meets the requirements of U.S. Army Corps of Engineers manual EM 1110-2-2901, chapter 9.1h

Temperature Loads

Temperature load gradient shall be applied along the cavern perimeter to represent temperature difference between the outside and the inside concrete surface. The following two cases shall be considered.

i. When temperature on the interior face of the concrete liner is higher than the exterior face of the liner ii. When the temperature on the interior face of the concrete liner is lower than the exterior face of the liner.

Shortening due to temperature change may be modified by a factor of 1.5 considering the fact that the shortening is to take place over a period of time.( reference # xx )

h. Load Combinations Load combinations shall be as per Chapter 3- Loads.

i. Pressures induced by lining on Rock ( Rock Bearing Capacity )

The Pressures induced by deformed lining shall be checked against rock bearing capacity.



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The amount of rock displacements indicated the capacity of design to accommodate additional lining displacements due to fleece/ membrane compressibility, concrete shrinkage and drill and blast damage.

9.6.10 Watertightness and Waterproofing

9.6.10.1 Watertightness During Tunnel and Cavern Driving

An assessment of water inflow during excavation shall be made. This assessment shall include the potential for groundwater drawdown in the soils above the rock in which the tunnel or cavern is excavated.

For cases where significant drawdown may be expected, designs shall include facilities and procedures to minimize inflow.

Numerical methods shall be used to calculate inflows and flow patterns for cases where significant groundwater drawdown is expected.

9.6.10.2 Watertightness for Finished Tunnels and Caverns

Watertightness of the finished tunnel shall be established and shall be approved by NYCT.

There shall be no visible ingress of water or damp patches above springline.

Damp patches only below spring line. A damp patch is discoloration of part of the surface of the liner, moist to touch. There shall be no visible movement of a film of water across a surface.

9.6.10.3 Waterproofing

Caverns and tunnels shall be designed with full membrane waterproofing supplemented by drains and sumps installed to collect unintended seepage water.

Waterproofing shall be designed for maximum hydrostatic pressure. This pressure shall correspond to the groundwater elevation during a 500 -year flood.

Waterproofing shall consist of a thermoplastic waterproof membrane placed over a geotextile drainage fabric in a manner that ensures the drainage fabric makes contact with the wall of the primary lining while it is in direct contact with the waterproofing membrane

In addition, waterproofing elements shall consist of, gaskets, geotextile drainage mat, and water stops as required by the configuration of the ground supports and the layout of the tunnel and cavern lining.

The membrane shall seal the tunnel against water inflow from the surrounding ground into the tunnel. The membrane shall be continuous around the perimeter of the tunnel including the floor, walls, and roof. It shall also be continuous along the axis of the tunnel for the full length of the tunnel.

The waterproofing membrane can be attached to the crown and walls of the primary lining by fixing it to previously installed bolts or nails. At no location shall the membrane be penetrated.



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The final lining shall be placed inside of the impermeable membrane. The objective is to create a seal between the primary lining and the secondary lining, which extends around the full circumference of the opening. The circumferential cavern seal shall be fully connected with the cavern end seals, which in turn will be connected with tunnel seals. No gaps in the waterproofing seal shall be allowed.

9.6.11 Preliminary Lining Treatment – Surface Smoothing

Wall treatment shall be applied to the primary lining in order to create a smoothed surface over the walls, crown, and floor for placement of waterproofing membrane. All rock bolt heads, and other protruding objects must be covered and smoothed over so that no tears or punctures can occur in the membrane. Shotcrete may be used for this treatment. In the case of steel sets and lagging, concrete or shotcrete must be introduced into open areas between sets in order to provide for the smooth walls and crown surfaces.

9.6.12 Grouting the Final Lining

The crown area of the final lining shall be grouted to fill any open space between the primary lining, the waterproofing membrane, and the final lining.

9.6.13 Cavern Drainage

The loading from groundwater is the major element of the design and is the governing load case.

Fully encapsulated membranes have a history of unplanned leakage into caverns. Mitigation of the leaks will always be difficult and costly.

Design shall consider the cost benefits of pressure relieved linings and drained inverts.

9.7 Bored TBM Tunnels in Rock

9.7.1 Support Definitions

The following definitions apply:

Initial support elements are prescribed during the design phase, and shall be installed as designed to support the full expected loading encountered during construction.

Final support elements are prescribed during the design phase, and shall be considered to support the total loading requirements for the design life of the cavern.

9.7.2 Design Philosophy/Principles

The Design Philosophy/Principles outlined in Section 9.6.8 with regard to Mined Tunnels and Caverns apply equally to the design of Bored TBM Tunnels in Rock The design of the initial support elements and the final lining shall be developed to the extent necessary to show that the proposed bored tunnel can be constructed:

to provide the required space, to support all loading conditions to which they will be subjected, to meet the specified watertightness criteria, and to be in compliance with ground movement criteria given herein.



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9.7.2.1 Single-Pass Lining

For the single-pass lining system, segmental linings shall be formed from either steel fiber or conventionally reinforced precast concrete. Precast concrete linings shall be designed to provide adequate water tightness, avoiding the need for a secondary lining. Design for the linings shall incorporate a taper such that, to maintain line and level, packing of rings shall not be required.

9.7.2.2 Two-Pass Lining

For the two-pass lining system, a primary lining is installed as excavation proceeds. After the tunnel is fully driven, the permanent lining is placed. The following types of liners may be used for tunnels and shafts:

Sprayed concrete initial liner, with a cast-in-place secondary lining Segmental primary liner with a cast-in-place permanent liner

9.7.3 Initial Support Analysis and Design

As per Section 9.6.2, except for the following points.

9.7.4 Rock Cover above Bored TBM Tunnels

Where the amount of competent rock above the tunnel is less than one-half of the tunnel diameter, special design and construction measures shall be evaluated such that ground movements at the crown do not exceed 0.50 inches.

9.7.5 Rock Bolt Design

Rock Bolt design methodology shall be similar to Section 9.6.7.5 e)

9.7.6 Final Lining Analysis and Design

Two types of Lining shall be considered.

1. Segmental Lining 2. Cast- in- Place lining (CIP)

9.7.7 Segmental Lining – Analysis and Design

9.7.7.1 Segmental Lining Design

The segmental lining designs shall include following items:

1. Model the segmental lining ring by using appropriate Finite Element Programs like STAAD or LARSA or any other program , calculate member Forces under various load combinations and boundary conditions.

2. Calculate additional moments due to birdmouthing. 3. Check lining seismic deformation 4. Evaluate Design sections by using PCA Column Method 5. Check lining shear capacity 6. Check crack width at service loads 7. Check segments strength under jacking loads



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8. Check segment tensile splitting stress 9. Check stress of segments during demoulding, handling, stacking and erection. 10. Check stress of segmental lining induced during routing. 11. Design bolts 12. Determine Tunnel Lining Taper.

The segmental lining design shall be based on forces calculated in steps 1 thru 4 and additional moment due to birdsmouthing calculated in Section 9.7.7.1.11.

Moment Vrs Axial Load Interaction Capacity Diagram method shall be used to perform the reinforced concrete design ( See Appendix 9A for details).

9.7.7.1.1 Additional Moments Induced by Birdsmouthing

The single segments shall be checked for all stresses induced by initial and unequal gaps resulting from deficiencies in fabrication and in erection (Karoly Szechy (1973).

Assume uniform pressure at contact surface

e0 = d – (Nkb / 2bfc’)

Where

e0 : the initial eccentricity

d : the distance between the centerline and recess

kb : the homogeneity factor of concrete

b : width of the segments

N : normal force from calculation in Section 6.1

f’c: concrete compressive strength

Gap due to erection and fabrication deficiencies, e = 0.25 inch shall be added to the initial eccentricity. The total additional bending due to birds mouthing thus will be:

Mb = ± (e0+ e) N

9.7.7.2 Analysis Model

Two different types of models shall be considered to the joints of the segmental lining. One model (method one) shall assume pinned connection at the joint and use gross moment of inertia of the member. The other one (method two) shall assume continuity at the joints and uses effective moment of inertia to modify the stiffness of the lining (see section 9.7.7.4.1).

Because the segmental lining shall be fully grouted, rock-structure interactions shall be modeled by introducing both radial and tangential springs. A model without tangential spring shall be included in the calculation to ensure a conservative design when there is slip between lining and rock.



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9.7.7.3 Materials Shall be as follows Precast reinforced concrete segments (minimum 28-day compressive strength of 5,000 psi) Precast steel and/or polypropylene fiber reinforced concrete (minimum 28-day compressive

strength of 7,000 psi) Fabricated steel segments (minimum design strength of 50 ksi) Bolts : Gaskets:

9.7.7.4 Geometry

9.7.7.4.1 Effective Moment of Inertia (Method Two)

The existence of joints will affect the rigidity of the segmental lining. The effective moment of inertia Ie shall calculated following Muir Wood (1975):

Ie = Ij + (4/n) 2 I Ie ≤ I , n > 4

Where

Ij is the effective value of I at the joint

I is the moment of inertia of the lining

n is the number of segments

Since Ij << I, Ie = (4/n) 2 I

9.7.7.4. 2 Rock Springs

As mentioned in the earlier sections, since the segmental linings are grouted with the rock, both radial and tangential rock springs shall be introduced in the finite element analysis to model the effects.

The spring stiffness is determined from the following equations

Kr = Er,bθ/(1+νr)

Kr = 1,500,000x12x(S/R)x(1/(1+0.25))

Kt = 0.5Kr/ (1+ νr)

Where

Kr: radial spring stiffness

Kt: tangential spring stiffness

Er: rock mass modulus, 1,500,000 to 3,3000,000 psi

νr : Rock Poisson’s ratio, 0.25



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θ : lining ring arc subtended by the beam element (radians)

b : width of tunnel lining considered.

S: length of arc,

R: external radius of the tunnel = 10.75 feet

The rock springs are to be modeled as 1 foot long.. Tributary area for the springs is assumed to be 1’ X 1’. The stiffness of the springs is calculated as following:

K = A x Ec / L

Where

K: Modulus of subgrade

A: Equivalent area of concrete member

Ec: Yong’s modulus of concrete

The radial springs shall be assumed to be compression only springs. The equilibriums of forces are achieved through iteration.

9.7.7.5 Loading

The structural lining shall be designed to withstand all loading and environmental effects

1. Self Weight

2. Live Load

a. Superimposed surface loading based on traffic loading and effects b. Railway traffic loading

3. Temperature 4. Hydrostatic Pressure

1. Full hydrostatic pressure shall be used in the evaluation. 5. Rock load

1. Determine fracture sets and orientation

2. Determine wedge size and wedge loads

6. Seismic Load :

.

The response of segmental tunnel to seismic load can be described in three principal types of deformations (DG452A, Section 9.10):



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1. Axial deformation

2. Curvature deformation

3. Ovaling deformation

7. Miscellaneous Geotechnical Loading

a. Appropriate soil and variable hydrostatic loading b. Long and short term ground yield or squeeze c. Unequal grouting pressures d. Loads arising from adjacent tunneling, or excavation e. Openings in the linings f. Long and short term loads induced by the construction procedure g. All forces which may be applied by the use of a tunneling shield or boring machine

8. Jacking Loads: The tunnel linings shall be designed to withstand all jacking loads from the TBM jacking system. The lining design shall be compared with ram loads from the TBM proposed for use by the Contractor. If necessary, appropriate adjustments in either the lining design or the TBM shall be made.

9. Handling and Stacking Loads Handling using vacuum pad lifting devices and

the methods for stacking segments shall be specified in the contract specifications. Static calculations shall be carried out to determine bending moments introduced during segment stacking. Handling forces shall be checked using a dynamic factor of 3.

10. Load combination The load combinations shall be based on Section 3.3 of DG 452A

9.7.7.6 Miscellaneous Criteria Checks

9.7.7.6.1 Crack width

The underground elements under ground water pressure have to satisfy a crack width check to control water ingress.

Crack width under service load is limited to 1/125 inch according to general engineering practice in structures that require water tightness. The calculation shall show that the reinforcement for the segments satisfied the criteria.

The maximum crack width at the tension face shall be calculated as following (Gergely and Lutz, 1968):

W = 0.076 β f s (dc A)3/2

Where



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W: expected maximum crack width in 0.001 inch units

β: ratio of distances to the neutral axis from the extreme tension fiber and from the centroid of area of steel : use 1.35 for one way slab

f s: steel stress in ksi

dc: concrete cover measured from outmost fiber of concrete to the center of bars.

A : tension area per bar

9.7.7.6.2 Check Seismic Deformations

The tunnel should be checked for three principal types of deformations due to seismic motions. The axial and curvature deformations are induced by components of seismic waves that propagate along the tunnel axis. Seismic ovaling deformations are caused by the propagating shear wave.

9.7.7.6.3 Check Segment Linings Stress Due to Jacking Load

The maximum thrust from the TBM machines shall be checked against the bearing stress and tensile splitting stress.

Bearing Stress Check

Uniform distributed compression load due to jacking shall not exceed 0.65√fc:

Check bursting due to jack load

High axial force may cause splitting at the end of precast segments. The tensile splitting force is calculated based on ACI 318-02 18.13.5.

Mb = F/2( h/4- a/4) = Fh/8 (1-a/h)

And

T = Mb/l= 2 Mb/h : Therefore l = h/2

T = F/4 (l-a/h )

Provide rebars to resist the split tensile force:

9.7.7.6.4 Checking Bursting due to Radial Compression Force

High axial force may cause splitting at the end precast segments. Consider birdmouthigng at the radial joint . Provide rebars to resist the split tensile force.

9.7.7.6.5 Check precast segment stress during demoulding

The precast segment shall remain uncracked during demoulding. The check precast segment stress during demoulding shall be computed with dynamic load factor = 2.0.



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The maximum moment during demoulding shall be calculated with ft = 7.5 √fc’:

9.7.7.6.6 Check Stress of Lining Segments during Erection

The segments shall not crack during erection while they are lifted through erector socket

9.7.7.6.7 Check Segmental Lining Stress Induced During Grouting

The effect of grouting pressure shall be evaluated and added to other pertinent stresses to the liner.

9.7.7.6.8 Check precast segment stress during stacking

The stress induced during stacking shall not cause segments crack.

9.7.7.6.9 Design Radial and Circumferential Bolts

The segments are bolted together during construction by bolts .

These bolts help to keep the gaskets and hydrophilic seal in compression during ring installation.

The capacity of bolt considering the tributary area for one bolt at circumferential joint shall be computed and compared with the capacity of bolt ( ASTM A 325 )

9.7.7.6.10 Determine Tunnel Lining Taper

Lining shall be tapered to accommodate the minimum design radius of the tunnel.

9.7.8 Analysis Model and Design of Cast-in-Place ( CIP) Lining

9.7.8.1 Analysis Model shall be same as for Mined Tunnel ( Section 9.6.9 ) except as follows:

Rock support shall be modeled by means of springs.

All springs are to be attached to the structure.

9.7.8.2 Design of Cast-in-Place ( CIP) Lining

Design methodology of CIP liners shall be same as in section 9.6.9.

9.7.9 Watertightness and Waterproofing

9.7.9.1 Watertightness During Tunnel Driving

The criteria shall be similar as per Section 9.6.10.1 .

9.7.9.2 Water tightness for Finished Tunnel

Water tightness of the finished tunnel shall be established and shall be approved by NYCT.

There shall be no visible ingress of water or damp patches above spring line.



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Damp patches only below spring line. A damp patch is discoloration of part of the surface of the liner, moist to touch. There shall be no visible movement of a film of water across a surface.

9.7.9.3 Waterproofing

For segmental Lining ( single pass lining system ) , waterproofing shall be provided with Neoprene Gaskets in accordance with Specification Section .

For Cast- in- Place lining ( two pass lining system ) , waterproofing requirements shall be as specified in section 9.6.10.3

9.7.10 Preliminary Lining Treatment –Surface Smoothing

Where required , surface smoothing shall be as per Section 9.6.12.

9.7.11 Grouting the Final Lining

Where required , the grouting of the final liner shall be as per 9.6.11.

9.8 Ground Modification / Improvement

Ground Modification / Improvement shall be considered for tunneling construction where the following conditions exist.

Inadequate Rock Cover Mixed Face Conditions in Lined Tunnels Intersection of Soft Ground Tunnels with Cut-and Cover Excavation Soft Ground Tunneling under Buildings Permeability of the soil needs to be decreased

The following methods shall be considered and the cost/benefits evaluated:

Cement Injection Grouting Chemical Injection Grouting Compaction Grouting Compensation Grouting Jet Grouting Ground Freezing

9.9 Seismic Design

9.9.1 General

The response of a tunnel to seismic shaking motions can be described in terms of three principal types of deformations:

1. Axial Deformation

2. Curvature Deformation

3. Ovaling



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9.9.2 Axial Deformation and Curvature Deformation

The first two types, axial and curvature, deformations are induced by components of seismic waves that propagate along the tunnel axis. When the component waves produce particle motions parallel to the longitudinal axis of the tunnel, they cause alternating axial compression and tension strains. Curvature results from component waves that produce particle motions in the direction perpendicular to the tunnel axis.

Two levels of analytical approaches can be used for evaluating the axial and curvature deformations along a tunnel structure:

a. Simplified plane wave method or close-form solutions b. Numerical analyses

In the simplified plane wave method, tunnels shall be considered to be flexible in response to axial and curvature deformations.

The induced strains and stresses in the tunnel liners shall be estimated by assuming that the tunnels conform to the imposed deformations from the surrounding ground in the free-field condition. If significant soil-structure interaction exists, this method may lead to an overly conservative design and, then the close-form solutions based on the beam-on-elastic foundation procedure shall be used. The plane wave method and the close-form solutions are both considered as simplified methods. Numerical analyses shall be considered only when analyses using the simplified methods are inconclusive or could not produce a realistic design. Methods of analysis that can be considered in the numerical analysis include lumped mass methods, continuum finite element, finite difference methods, and discrete element methods.

9.9.3 Seismic Loads Due to Ovaling Deformations

Seismic Loads Due to Ovaling Deformations. Seismic ovaling loads for the lining of bored or mined circular tunnels/shafts can be defined in terms of change of tunnel diameter (DEQ) caused by the propagating shear waves of the MDE and ODE. DEQ can be considered as seismic ovaling deformation demand for the lining. The proposed procedure for determining DEQ is summarized as follows:

1. Estimate the expected free field ground strains caused by the vertically propagating shear waves of the design earthquakes, for both MDE and ODE. The free-field ground strains can be estimated using the following formula:

γmax = Vs /Cse

where: γmax = maximum free-field shear strain at the elevation of the tunnel Vs = design peak ground velocity Cse = effective shear wave velocity of the soil/rock media surrounding the tunnel

Alternatively, the maximum free field shear strain can be estimated by a more refined free field site response analysis (e.g., SHAKE91, 1992). The effective shear wave velocity of the vertically propagating shear wave, Cse, shall be compatible with the level of the shear strain that may develop in the ground at the elevation of the tunnel under the design earthquake shaking. For rock, the ratio of Cse /Cs can be assumed equal to 1.0, where Cs is the low-strain shear wave velocity. For stiff to very stiff soil, Cse /Cs may range from 0.6 to 0.85 for MDE and from 0.75



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to 0.9 for ODE. Alternatively, site-specific response analyses can be performed for estimating Cse. Site-specific response analyses shall be performed for estimating Cse for tunnels embedded in soft soils.

The values of the low strain shear wave velocity, Cs, and the effective shear wave velocity, Cse, for various soil/rock units shall be established by the Geotechnical Data Report (GDR) and Geotechnical Baseline Report (GBR).

2. By ignoring the stiffness of the tunnel, the diameter change of the tunnel is estimated as follows:

DEQ = 2γ max (1-νm) D

where: νm = Poisson’s ratio of the surrounding ground D = diameter of the tunnel

3. If the structure is stiff relative to the surrounding soil, the effects of soil-structure interaction shall be taken into consideration. The relative stiffness of the lining is measured by the flexibility ratio, F, defined as follows:

F = {Em (1-νc2) R 3}/ {6 Ec Ic(1+ν m )}

where: Em = strain compatible elastic modulus of the surrounding ground Ec = elastic modulus of the concrete lining R = nominal radius of the concrete lining Ic = moment of inertia of the concrete lining (per unit width) νc = Poisson’s ratio of the concrete lining νm = Poisson’s ratio of the surrounding ground

The strain compatible elastic modulus of the surrounding ground Em shall be derived using the strain compatible shear modulus Gm corresponding to the effective shear wave propagating velocity Cse.

The moment of inertia of the concrete lining, Ic, shall be determined based on the expected behavior of the selected lining under the combined seismic and static loads, accounting for cracking and joints between segments and between rings as appropriate.

4. The diameter change, DEQ, accounting for the soil structure interaction effects shall be estimated using the following equation:

DEQ = 1/3 (K1 F γmax D)

where: K1 = Seismic Ovaling Coefficient = 12(1-νm) / (2F + 5 - 6νm)

The seismic ovaling deformation shall be combined with deformations resulting from non-seismic loads defined in other Sections of this Chapter.

9.9.3.1 Acceptance Criteria

For the ODE level design, the lining shall be designed to respond essentially in an elastic manner with no ductility demand. The material strains of the lining shall be checked not to exceed 0.001 for concrete and 0.002 for steel.



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For the MDE level design, inelastic deformations are allowed, but shall be kept to the acceptable levels: the material strains of the lining shall be checked not to exceed 0.002 for concrete and 0.006 for steel.

For the MDE level design, the concrete strain may be allowed to exceed 0.002 but not to exceed 0.004 provided that the strain is predominantly in flexural mode.

9.9.3.2 Strength Requirement

The lining shall also be designed to satisfy the strength requirements for the ODE level design. The internal forces, EQ, associated with the seismic ovaling deformation, DEQ shall be derived by elastic analysis using the effective Ic value.

The loading combination shall be as follows:

Group Load = 1.0 [D + L+ B + E + EQ]

where: D = Dead loads L = Live loads B = Hydrostatic pressure and buoyancy E = Static Soil/Rock pressure on lining EQ = Elastic seismic force due to seismic ovaling deformation, DEQ

For mined station sections, E corresponds to loads due to weight of the loosened zone above roof and shall be determined by the geotechnical engineer, taking into consideration the proposed construction methods and sequences.

9.9.4 Seismic Loads Due to Axial and Curvature Deformations

The tunnel lining shall be designed to accommodate seismic strains caused by axial and curvature deformations of the ground. The strains due to combined axial and curvature deformations can be estimated by combining the longitudinal strains generated by axial and bending strains as follows:

εEQ = (Vs /Cs,H ) sin cos [rAs /(Cs,H )2] cos 3θ

where: Vs = design peak ground velocity As = design peak ground acceleration Cs,H = horizontally traveling shear wave velocity r = radius of the tunnel lining θ = angle of wave propagation with respect to the tunnel axis

The horizontally traveling shear wave velocity, Cs,H , corresponds to the seismic shear wave propagation through the deeper rocks rather than to that of the shallower soils where the tunnel may be located. In general, this velocity value varies from about 2 to 4 km/sec.

Cs,H shall be established by the Geotechnical Engineer.

The angle of wave propagation, θ, should be the value that maximizes the combined axial strains.



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9.9.4.1 Acceptance Criteria

For the ODE level design, the longitudinal strains, εEQ, due to the axial and curvature deformations shall be checked not to exceed 0.001 for concrete and 0.002 for steel.

For the MDE level design, the allowable material strains are 0.002 for concrete and 0.006 for steel.

9.9.5 Interface Joints

Interfaces between the tunnel structures and the more massive structures, such as the cut-and-cover structures, mined station sections, and ventilation/access structures, shall be designed as flexible joints to accommodate differential movements.

The design differential movements shall be established by the Geotechnical Engineer.

9.10 References

1. Bickel, Kuesel and King. Tunnel Engineering Handbook. Chapman & Hall, 1996

2. Wang, J. Seismic Design of Tunnels. June 1993.

3. Hoek, Kaiser, and Bawden. Support of Underground Excavations in Hard Rock. 2000

4. DHA Report on Method on Tunneling Study, June 2002

5. DHA Report on Options for Waterproof Tunnel Linings.

6. Parson Brinkerhoff Integrated Study – Method of Tunneling and Tunnel Structures Study, March 2003.

7. Hoek, Carranza-Torres, and Corkum. Hoek-Brown Failure Criterion – 2000 Edition. Proc. North American rock Mechanics Society. Toronto: July 2002.

8. Hoek, Evert. Practical Rock Engineering – An On-going Set of Notes, Rocscience Website.

Figure 9.3 [Ref. 2]



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9. Bieniawski, Z.T. 1976. Rock mass classification in rock engineering. In Exploration for rock engineering, proc. of the symp., (ed. Z.T. Bieniawski) 1, 97-106. Cape Town: Balkema.

10. Bieniawski Z.T. 1989. Engineering Rock Mass Classifications. Wiley, New York. 251 pages.

11. Grimstad, E. and Barton, N. 1993. Updating the Q-System for NMT. Proc. int. symp. On sprayed concrete - modern use of wet mix sprayed concrete for underground support, Fagernes, (eds Kompen, Opsahl and Berg). Oslo: Norwegian Concrete Assn.

12. Serafim, J. L. and Pereira J. P. 1983. “Considerations of Geomechanics Classification of Bieniawski, Int. Symp. Eng. Geol. Underground Constr., LNEC, Lisbon, Vol. 1, pp. II.33 – II.42.

13. Nicholson G. A. and Bieniawski Z. T. (1990). A Non-linear Deformation Modulus Based on Rock Mass Classification, Int. J. Min. & Geol. Engg., (8), pp. 181-202.

14. Hoek E. and Brown E. T. (1997). Practical Estimates of Rock Mass Strength, Int. Jr. Rock Mech. And Min. Sci. and Geomech. Abstr., Pergamon, Vol. 34, No. 8, pp. 1165-1186.

15. Unal, E. (1983). Rock Mass- Tunnel Support Interaction Analysis, Ph. D. Thesis, University of Roorkee, India.

16. Barton N., 2002. “Some New Q-value correlations to assist in site characterization and tunnel design”. Int. Jr. Rock Mech. And Min. Sci., 39 pp. 185-216.

17. Barton N., 1993. “Application of Q-System and Index Tests to Estimate Shear Strength and Deformability of Rock Masses”, Workshop on Norwegian Method of Tunneling, New Delhi, India, pp. 66-84.

18. Post-Tensioning Institute, Recommendations for Prestressed Rock and Soil Anchors, Fourth Edition.

19. FHWA-IF-015, Geotechnical Engineering Circular No.4.



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Chapter 10


Table of Contents

Section Item Page

10.0 Scope 135


10.2 Assessment of Tunneling-Induced Settlements 135

10.3 Classification of Damage 142

10.4 Protective Measures 143

10.5 References 143



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Chapter 10


10.0 Scope

This section addresses the factors affecting ground movements and subsequent settlement of adjacent buildings resulting from tunneling and mining activities, and the assessment of potential damages due to these settlements. The design guidelines and criteria presented in this section govern the protection of existing structures through the use of appropriate construction techniques and protective measures.





As noted in the text.

10.2 Assessment of Tunneling-Induced Settlements

Some of the factors affecting the associated ground settlements and settlements of structures are:

Rock, Soil, and Groundwater Conditions Changes In Groundwater Level Depth and Shape of Excavation Method of Tunneling Number and Placement of Adjacent Tunnels Type of Liner/Supports Time to Liner/Support Installation

Ground movements due to tunneling and mining can occur ahead of the area excavated, above the excavation, and over time. Figure 10.1 shows the settlement trough above an advancing tunnel and conventional methods outlined in Mair et al. [Ref. 5] can be used to estimate ground movements due to tunneling.



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.

Figure 10.1: Settlement Above Advancing Tunnel [Ref. 5]

Figure 10.2 Surface Settlement Trough [Ref. 10]



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10.2.1 Zone of Influence and Estimate of Ground Movement

10.2.1.1 Bored Tunnels in Rock

Where one diameter of rock cover exists above the tunnel, no measurable movement is expected at the ground surface. If insufficient cover exists above the tunnels, then the same techniques used to evaluate rock and ground movements outlined for mined caverns in rock can be used to estimate ground movements above the tunnels.

10.2.1.2 Bored Tunnels in Soft Ground

Ground movement due to shield tunneling is best viewed in 5 phases as described by Mair & Taylor [Ref. 5] and shown diagrammatically in Fig. 10.3.

The transverse settlement trough can be estimated using techniques outlined by O’Reilly and New [Ref. 6] and the longitudinal settlement trough can be estimated using methods outlined by Lake et al. [Ref. 7].

10.2.1.3 Mined Tunnels and Caverns in Hard Rock

Factors affecting ground movement resulting from mined tunnels and caverns include but are not limited to the depth of excavation, method of excavation, rock characteristics, failure modes, rock support systems and geometry of the excavation. Ground movements occur immediately, during construction, and over time.

Figure 10.3 (from [5])



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Depending on the rock mass properties, depth, cavern geometry, method of excavation, convergence of stresses in the rock around the excavated cavern can cause the roof of the cavern to move up or down. Movement of the cavern crown and side walls can result in ground movements.

In order to estimate the amount of ground movement due to convergence, the excavation of the mined tunnel and cavern can be modeled using programs such as UDEC, PHASE2 or FLAC3D. The parameters used as input are the in-situ stresses that exist in the rock, the configuration of the cavern, rock support and the sequence of excavation.

The results of the analysis will provide movement at the crown, ground surface, and points near adjacent foundations and utility lines.

10.2.2 Settlements – Utilities

Utilities and underground pipelines, and their displacements due to tunneling shall also be considered. Electric cables, steam lines, water utilities, sewer, gas, fuel lines, and fiber optic cables are a few of the items at risk. Surface displacements and the entire field of ground movements shall be calculated, in order to predict the effect of underground excavations on utilities.

10.2.3 Control of Groundwater

The effect of potential groundwater table drawdown due to tunneling activities, and the resultant consolidation settlement shall be evaluated. Improper control of groundwater can cause unacceptable ground movements. Care must be taken to minimize groundwater problems.

10.2.4 Limits on Actual Settlement and Angular Distortion

10.2.4.1 Structures

The criteria for total settlement and angular distortion (differential settlement between two defined points on a structure) is primarily a function of a structure’s framing. “Historic” or “sensitive” structures are generally masonry wall bearing structures where as “modern” structures generally are concrete or steel framed. The latter can experience significantly more distortion before exhibiting structural duress.

10.2.4.2 Utilities

During the design process and prior to the commencement of tunneling or other excavation work, the threshold and limiting values for vertical deformation of utilities within the zone of influence shall be established, in consultation with the respective utility company.

10.2.5 Assessment of Ground Movements and Risk of Damage

Deformations resulting from construction can adversely affect adjacent structures causing minor to severe damage. In order to screen adjacent structures that are at risk for damage, the three-stage process summarized below shall be followed [Ref. 5].



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10.2.5.1 Three Stage Process for Buildings

As part of the existing building survey, buildings adjacent to the proposed alignment will be surveyed to assess and document their state prior to the start of construction.


The preliminary assessment shall establish the zone of influence of the proposed excavations. Conventional methods shall be used for this stage. Surface and subsurface displacements shall be estimated.

Structures that fall completely outside the zone of influence need not be further considered.


Each structure within the zone of influence shall be reviewed to determine the extent of potential damage due to the construction.

The following figure evaluates the severity of damage to structures using horizontal strain and angular distortion.

Strains due to ground settlements shall also be evaluated using the methodology outlined in Mair et al [Ref. 5]. The potential damage category can then be determined from Table 10.1 using the resulting strain value. In this approach, the building is assumed to have no stiffness and to conform to the ‘green field site’ settlement. Because the inherent stiffness of the building tends to reduce both the deflection ratio and the horizontal strain, the resulting category of damage will usually be greater than the actual damage.


A detailed evaluation should be undertaken for buildings where a second stage assessment indicates slight to moderate damage. Computer models using finite difference analysis (e.g. FLAC) or finite element analyses (e.g. SIGMA/W or PLAXIS) shall be used to predict ground movements. This assessment should account for three-dimensional aspects of the excavation and building layout. In addition, details of the building should be taken into account to determine its structural continuity.

Figure 10.2 Range of Deformations Typical of Excavations in Various Soils Relative to Building Damage Potential [Ref. 2].



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The following factors shall be considered in the detailed evaluation:

Tunneling method Time dependent ground displacements Effects of groundwater Soil properties Soil-structure interaction effects Adjacent structure stiffness Foundation conditions

The results of the detailed evaluations can also help determine the required mitigation for the protection of the building from excessive damage. Design decisions shall be re-evaluated in light of potential damage to existing structures.

The following limitations shall be considered when using numerical methods for tunneling [Ref. 9]:

The tunneling process involves a three-dimensional deformation pattern around the front, which should be accounted for in the analysis.

The behavior of soils and soft rocks is complex and is difficult to accurately model, even with the most elaborate constitutive models; moreover, parameters such as the soil deformation modulus, which are essential to the output of numerical analyses, can hardly be estimated with sufficient accuracy with existing testing techniques.

The construction techniques involve complex soil-structure interaction phenomena; these should be well understood and their effect accounted for in an appropriate manner in the model.

10.2.5.1 Three Stage Process for Utilities

The history and existing condition of the utilities within the zone of influence shall be assessed and documented prior to the start of construction. The relative stiffness of the utility and soil, movement capacity of joints, location of joints relative to the shape of the displacement profile, and resistance to shear between the soil/backfill and the utility shall also be determined.


The preliminary assessment shall establish the zone of influence of the proposed excavations. Conventional methods shall be used for this stage. Surface and subsurface displacements shall be estimated.


When a utility has the potential to exceed the threshold limits determined as per Section 10.2.4.2, the following assessment shall be performed:

Locate and review utility company records and test pit information where available. Estimate pipe strains and joint rotations using the approach outlined by Bracegirdle et al.

[Ref. 4].




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A detailed evaluation shall be undertaken for utilities where a second stage assessment indicates that pipe and joint strains exceed limiting values. Pipe strains and joint rotations shall be further determined using information and empirical data from Attewell et al. [Ref. 8]. Ground movements shall be evaluated using Finite Element Method (FEM) or Finite Difference method (FFM) using soil, structure, and utility interaction.

Based on the results of the detailed evaluation, establish the need for protective work like ground improvement and/or replacement of the system concerned. In some cases the design may need to be revisited.



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10.3 Classification of Damage

Table 10.1: Classification of visible damage to walls with particular reference to ease of repair of plaster and brickwork or masonry [Ref. 5].

Category of damage

Damage Tensile Strain

Description

0 Negligible 0.00 To 0.05% Hairline cracks less than about 0.01mm. 1 Very

Slight 0.05 to 0.075%

Fine visible cracks in external brickwork or isolated fractures. Easily repaired during normal decoration, door and windows may sticks slightly

Typical crack widths up to 1 mm. 2 Slight 0.075 to 0.15% Cracks are visible externally and inside the building can

be a series of several slight fractures. The cracks are easily filled and redecoration is probably required. Repainting may be required externally to ensure. Weather-tightness.

Typical crack widths up to 5 mm. 3 Moderate 0.15 to 0.3% Cracks will require some opening up and patching by a

mason. Suitable linings can mask recurrent cracks. Repointing of external brickwork and possibly a small 1 amount of brickwork to be replaced. Doors and windows are sticking. Service pipes may fracture and weather- tightness is often impaired. Also depends on the number of cracks.

Typical crack widths 5 to 15 mm or several greater than 3 mm.

4 Severe

> 0.3% Severe cracking requires extensive work involving 25.0mm braking out and replacing sections of walls, especially Over doors and windows, Windows and doorframes become distorted, And the floor begins to slope Noticeably. Walls leaning or bulging occur and some ~ loss of bearing beams is possible. Service pipes are disrupted. Also depends on the number of cracks.

Typical crack widths are 15 to 25 mm but also depend on the number of cracks.

5 Very Severe

Very severe cracking requires a major repair job Severe involving partial or complete rebuilding. Beams lose 5 bearing; walls lean badly and require shoring. Windows broken with distortion and there is danger of instability. Also depends on the number of cracks.

Typical crack widths are greater than 25 mm but also depend on the number of cracks.



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10.4 Protective Measures

Protective measures include mitigating and/or minimizing the impact of settlement effects on critical structures. Comparative costs of protective measures versus the predicted settlement effects due to construction should be evaluated.

All existing structures that are supported by structural elements that will be removed or disturbed as part of the project activities shall be underpinned, or otherwise temporarily supported, while project construction is underway.

10.4.1 Mitigation of Structural Damage

The following forms of preventive measures shall be considered:

Shield the structure from the settlement trough by a barrier between the tunnel and the building foundation. The barrier is not connected directly to the foundation and therefore, does not transfer the load directly to the structure.

Offset the building settlement by injecting grout in the ground below the building.

Underpin the building to introduce an alternate foundation in order to nullify ground movement effects on the building.

Jacking to counteract settlement

Strengthen the structure to increase the stiffness and counter the additional stresses imposed due to tunneling.

In cases where slight to moderate damage to existing structures is indicated by the Detailed Evaluation preventive measures shall be considered. The effects of the considered mitigation should be determined and the cost-effectiveness compared to repairing damage caused during construction should be evaluated.

10.5 References

1. Goldberg, D.T., Jaworski, W.E., and Gordon, M.D. Lateral Support Systems and Underpinning. Report FHWA-RD-75-128, Vol. 1, FHWA, Washington, D.C., Apr. 1976.

2. Clough, G.W., and O’Rourke, T.D. “Construction Induced Movements of In Situ Walls”, Proceedings: Design and Performance of Earth Retaining Structures. Ithaca, NY: Cornell University, June 1990.

3. Metropolitan Transit Authority LIRR. East Side Access Design Criteria. New York, NY, May 2001.

4. Bracegirdle, A,. Mair, R.J., Nyren, R.J., and Taylor, R.N. “A methodology for evaluating potential damage to cast iron pipes induced by tunneling”, Proceedings: international Symposium on Geotechnical Aspects of Underground Construction in Soft Ground. London 1996 (eds Mair, R.J. and Taylor, R.N.), Balkema, 659-664.pp. 1510-1533.

5. Mair, R.J. Taylor, R.N. and Burland, J.B. “Prediction of ground movements and assessment of risk of building damage due to bored tunnels”, Proceedings: International Symposium on Geotechnical Aspects of Underground Construction in Soft Ground. London 1996 (eds Mair, R.J. and Taylor, R.N.), Balkema, 713-716.



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6. O’Reilly, M.P., and New, B.W., (1983) “Settlements above tunnels in the United Kingdom, their magnitude and prediction”, Proceedings: Tunneling 1982, Brighton 1982, pp. 173-181. Report of discussion. Trans. Inst. Mining Metallurgy, Vol. 92, Section A, pp. A35-A48.

7. Lake, L.M., Rankin, W.J., Hawley, J. (1992), “Prediction and effects of ground movements caused by tunneling in soft ground beneath urban areas”, Funders Report/CP/5, report prepared under contract to DIRIA by Mott, Hay and Anderson, now Mott MacDonald.

8. Attewell, P.B., Yeates, J., and Selby, A.R. Soil movements induced by tunnelling and their effects on pipelines and structures. Blackie, 1986.

9. Leca, E., Leblais, Y., and Kuhnhenn, K. Underground Works in Soils and Soft Rock Tunneling.

10. Peck, R.B. “Deep excavations and tunneling in soft ground”. Proceedings 7th International Conference Soil Mechanics and Foundation Engineering. Mexico, 1969. State-of-the-Art Volume, pp 225-290.

11. Design Summary Report, Central Artery (1-93)/Tunnel (1-90) Project Construction Contract C17A1 Congress Street to Broad Street, Boston, Massachusetts, Prepared by Fay, Spoffordand Thorndike, Inc./Howard Needles Tammen and Bergendoff A Joint Venture in association with GZA GeoEnvironmental, Inc., Seelye StevensodDeLeuw Cather, Haley & Aldrich, Inc., Frederic R. Harris, Inc., GEI Consultants, Inc., November 1996 (including Addenda through February 24,1997).

12. DHA Document, Design Criteria Manual. May 2003.

13. DHA Document, Guideline Document- Evaluation of Ground Movements and Impacts on Adjacent Structures. Jan 2003.



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Chapter 11

Underpinning

Table of Contents

Section Item Page

11.0 Scope 146

11.1 Underpinning 146

11.2 Basic Criteria of Underpinning 146

11.3 Underpinning Methods 147

11.4 Instrumentation and Monitoring 147

11.5 References 148



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Chapter 11

Underpinning

11.0 Scope

This section deals with the requirements of underpinning where excavation is undertaken using tunneling methods or rigid retaining walls such as slurry/diaphragm walls or secant/tangent piles. The underpinning requirements for other excavation methods are provided in the Chapter on Underpinning in NYCT Field Design Standard, DG 453.

11.1 Underpinning

Underpinning of a structure shall be considered only if the estimated movement of the structure exceeds allowable limits.

The protection of existing structures shall be accomplished by the use of protection walls around the excavation, underpinning the existing structure, or a combination of these two methods. When determining the appropriate method of protection, consideration shall be given to the sequence of construction and the effect of placement of the protection on other phases of construction. Consideration also shall be given to the right-of-way requirements of the different protection methods.

The influence of existing structures on excavation or tunneling activities and the influence of excavation or tunneling activities on the settlement, and/or rotation and stability of existing structures shall be analyzed and evaluated both from structural and geotechnical standpoints. Evaluations shall be made for all buildings or structures along the project alignment that encroach on or are immediately adjacent to the proposed project structures.

In addition to the structure’s proximity to the proposed project, the age, type, use and construction of the existing structure shall be considered. Based on these evaluations, design parameters shall be established for the allowable settlement, differential settlement and rotation of each building affected by excavation or tunneling activities.

11.2 Basic Criteria of Underpinning

General requirements for initial appraisal of the need for underpinning are shown in Figure 6.9.

As shown in the figure, the area of influence of the construction excavation is divided into three zones designated A, B, and C.

In general, structures within Zone A shall require underpinning and all underpinning must develop capacity with the required factor of safety within Zone C.

Where building foundations located immediately outside of Zone A carry a load heavy enough to expand the active zone, (Zone A), underpinning shall generally also be required.

Foundations of lighter structures that are located within Zone A adjacent to the excavation may not need to be underpinned if the protection wall is designed to carry the loads and movement can be limited to tolerable amounts.



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Foundations within Zone B generally do not need to be underpinned.

In all cases in which foundations falling within Zones A and B are not underpinned, the project structure shall be designed to resist vertical and horizontal pressures resulting from the presence of the foundations.

If underpinning is required, foundation loads will be transferred to Zone C through the use of walls or drilled piers, or by various types of driven, jacked or drilled piles. All underpinning members shall be completely independent of the rail structure and isolated in such a manner that transfer of train vibrations to the supported structures shall be minimal.

11.3 Underpinning Methods

Underpinning methods shall be as follows:

Pit Piers Jacked Piles Micro Piles Column Pick-Up Foundation Grouting

The Contractor shall be responsible for restoration, which shall be defined as the correction by repair or replacement, of structures damaged or altered as a result of construction operations. Restoration shall be required to a condition equivalent to that existing prior to the start of the work.

11.4 Instrumentation and Monitoring

A comprehensive monitoring program shall be specified to achieve the following:

Predict and avoid failure (reveal unknowns) Evaluate critical design assumptions (reduce risks) Minimize damage to adjacent structures Assess contractor’s means and methods Provide QA, especially for design-build Control construction process(avoid delays) Devise remedial methods to fix problems Document performance for assessing damages Inform stakeholder (answer questions and calm fears) Reduce litigation Improve processes Advance state-of-practice

The contract drawings and specifications shall provide detailed requirements addressing the above requirements.



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11.5 References

1. Goldberg, D.T., Jaworski, W.E., and Gordon, M.D. Lateral Support Systems and Underpinning. Report FHWA-RD-75-128 and 129, Vols. I and II, FHWA, Washington, D.C., Apr. 1976.



Chapter 12 Seismic Design Requirement for Architectural,

Electrical and Mechanical Component

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Chapter 12

Seismic Design Requirement for Architectural, Electrical, Mechanical, Signal and Communication Components

Table of Contents

Section Item Page

12.1 Scope 150

12.2 Methodology 150





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Chapter 12

Seismic Design Requirement for Architectural, Electrical, Mechanical, Signal and Communication Components

12.1 Scope

Seismic Design requirements for Architectural, Electrical, Mechanical, Signal and Communication components founded in Underground Structures are not explicitly specified in NYS Building Code.

The following methodology is recommended to be used to determine the forces in the supporting structure and attachments (components) for all Architectural, Electrical, Mechanical, Signal and Communication components.

12.2 Methodology

1. Determine Seismic Design Category of the structure. Components shall be considered to have the same category as that of the structure that they occupy or to which they are attached. ( Reference: NYS Building Code Section 1621.)

2. Determine the Seismic Design Category by using one of the following methods. This is required due to the fact that during the structural design process of the underground structures, seismic design category is not required to be determined explicitly

Method I:

Generate the following tables based on NYS Building Code Section 1613.5.6, Tables 1613.5.6 (1) and 1613.5.6 (2) for the determination of the Seismic Design Category

Table 12.1

Site Class Value of SDS (see note below ) Occupancy Category

I or II III IV

A 0.229g B B C

B 0.287g B B C

C 0.344g C C D

D 0.419g C C D

E 0.556g D D D





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Table 12.2

Site Class Value of SD1 (see note below) Occupancy Category

I or II III IV

A 0.051g A A A

B 0.063g A A A

C 0.108g B B C

D 0.152g C C D

E 0.222g D D D

Note :

Values are obtained from the USGS Data multiplied by 2/3 to obtain the design value. for zip code of 10001.Obtain the relevant values for other applicable zip codes.

Method II

a. Generate site specific response spectrum ( Under MDE and ODE cases ) for every floor or elevation of the structure.

b. Time history input shall be from the NYCDOT Time History as per Section 2.12, Chapter 2. Software like PROSHAKE or other current similar softwares shall be used to generate the data.

c. Obtain the short period acceleration SDS and long period acceleration SD1 from the Response Spectrum

d. Determine the most severe seismic design category from the tables 1613.5.6 (1) and 1613.5.6 (2) of NYS Building .

3. Design of the all Architectural, Electrical, Mechanical, Signal and Communication Components

shall be based on the most severe Seismic Design Category 4. Structural Design shall provide the following data to other disciplines for the design of the

components and attachments: Value of SDS/SD1 Seismic Design Category .

5. Component Importance Factor I p shall be determined by the respective Engineering Discipline.





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