NSCP Chapter 3 Version 5

3-1

National Structural Code of the Philippines, Volume 1

SECTION 301 - GENERAL

301.1 SCOPE

This chapter sets forth requirements for excavations, fills,

footings and foundations for any building or structure.

301.2 QUALITY AND DESIGN

The quality and design of materials used structurally in

excavations, fills, footings and foundations shall conform to

the requirements specified in Chapters 4, 5, 6 and 7.

301.3 ALLOWABLE BEARING PRESSURES

Allowable stresses and design formulas provided in this

chapter shall be used with the allowable stress design load

combinations specified in Section 203.4.

SECTION 302 - EXCAVATION AND

FILLS

302.1 GENERAL

Excavation or fills for buildings or structures shall be

constructed or protected that they do not endanger life or

property. Reference is made to Section 109 of this code for

requirements governing excavation, grading and earthwork

construction, including fills and embankments.

302.2 CUTS

302.2.1 General. Unless otherwise recommended in the

approved geotechnical engineering or engineering geology

report, cuts shall conform to the provisions of this section.

In the absence of an approved geotechnical engineering

report, these provisions may be waived for minor cuts not

intended to support structures.

302.2.2 Slope. The slope of cut surfaces shall be no

steeper than is safe for the intended use and shall be no

steeper than 1 unit vertical in 2 units horizontal (50% slope)

unless a geotechnical engineering or an engineering

geology report, or both, stating that the site has been

investigated, and giving an opinion that a cut at a steeper

slope will be stable and not create a hazard to public or

private property, is submitted and approved.

302.3 EXCAVATIONS

302.3.3 Existing footings or foundations which may be

affected by any excavation shall be underpinned adequately

or otherwise protected against settlement and shall be

protected against lateral movement.

302.2.4 Protection of adjoining property. The

requirement for protection of adjacent property and the

depth to which protection is required shall be defined by

prevailing law. Where not defined by law, the following

shall apply:

1. Before commencing the excavation, the person

making or causing the excavation to be made shall

notify in writing the owners of adjoining building not

less than 10 days before such excavation is to be

made and that the adjoining building will be

protected. The condition of the adjoining building

will be documented prior to excavation. Technical

documents pertaining to the proposed underpinning

and excavation plan shall be provided the owner of

the adjacent property.

2. Unless it can shown through a detailed

geotechnical investigation that underpinning is unnecessary,

GENERAL & EXCAVATION AND FILLS

FOUNDATIONS AND EXCAVATIONS 3-2


any person making or causing an excavation shall protect

the excavation so that the soil of adjoining property will not

cave in or settle,

In cases where the adjacent building will have more

basements than the proposed building, the foundation of the

proposed building should be designed so as not to impart

additional lateral earth pressures on the existing building

(see section 304.4).

302.3 FILLS

302.3.1 General. Unless otherwise recommended in the

approved geotechnical engineering report, fills shall

conform to the provisions of this section. In the absence of

an approved geotechnical engineering report, these

provisions may be waived for minor fills not intended to

support structures.

Fills to be used to support the foundations of any building

or structure shall be placed in accordance with accepted

engineering practice. A geotechnical investigation report

and a report of satisfactory placement of fill, both

acceptable to the building official, shall be submitted when

required by the building official.

No fill or other surcharge loads shall be placed adjacent to

any building or structure unless such building or structure is

capable of withstanding the additional vertical and

horizontal loads caused by the fill or surcharge.

Fill slopes shall not be constructed on natural slopes steeper

than 1 unit vertical in 2 units horizontal (50% slope)

302.3.2 Preparation of Ground. The ground surface

shall be prepared to receive fill by removing vegetation,

non-complying fill, topsoil and other unsuitable materials,

and by scarifying to provide a bond with the new fill.

Where the natural slopes are steeper than 1 unit vertical in 5

units horizontal (20% slope) and the height is greater than

1.5 meters, the ground surface shall be prepared by

benching into sound bedrock or other competent material as

determined by the geotechnical engineer. The bench under

the toe of a fill on a slope steeper than 1 unit vertical in 5

units horizontal (20% slope) shall be at least 3 meters wide.

The area beyond the toe of fill shall be sloped for sheet

overflow or a paved drain shall be provided. When fill is to

be placed over a cut, the bench under the toe of fill shall be

at least 3 meters wide but the cut shall be made before

placing the fill and acceptance by the geotechnical engineer

as a suitable foundation for fill.

302.3.3 Fill Material. Detrimental amounts of organic

material shall not be permitted in fills. Except as permitted

by the geotechnical engineer, no rock or similar irreducible

FIGURE 302-1 SETBACK DIMENSIONS FOR CUT AND FILL SLOPES

H/5 but

0.60 m

min. and

3 m max.

H/2 but 0.6m

min. and 6m

max.

Toe of

Slope

Natural or Finish

Grade

Cut or Fill

Slope

PA*

PA*

H

* Permit Area Boundary

Top of

Slope

Natural or Finish

Grade



material with a maximum dimension greater than 300 mm

shall be buried or placed in fills.

EXCEPTION:

The placement of larger rock may be permitted when the

geotechnical engineer properly devises a method of

placement, and continuously inspects its placement and

approves the fill stability. The following conditions shall

also apply:

1. Prior to issuance of the grading permit, potential

rock disposal areas shall be delineated on the

grading plan.

2. Rock sizes greater than 300 mm in maximum

dimension shall be 3 meters or more below grade,

measured vertically.

3. Rocks shall be placed so as to assure filling of all

voids with well-graded soil.

302.3.4 Compaction. All fills shall be compacted in lifts

not exceeding 20cm in thickness to a minimum of 90

percent of maximum density as determined by ASTM

Standard D-1557. In-place density shall be determined in

accordance with ASTM D-1556, D-2167, D-2922, D-3017

or equivalent. A minimum of three tests for every 500 m2

area should be performed for every lift to verify compliance

with compaction requirements.

302.3.5 Slope. The slope of fill surfaces shall be no

steeper than is safe for the intended use. Fill slopes shall be

no steeper than 1 unit vertical in 2 units horizontal (50%

slope) unless substantiating data justifying steeper slopes

are submitted and approved.

302.4 SETBACKS

302.4.1 General. Cut and fill slopes shall be set back

from site boundaries in accordance with this section subject

to verification with detailed slope stability study. Setback

dimensions shall be horizontal distances measured

perpendicular to the site boundary. Setback dimensions

shall be as shown in Figure 302-1.

302.4.2 Top of Cut Slope. The top of cut slopes shall not

be made nearer to a site boundary line than one fifth of the

vertical height of cut with a minimum of 0.6 meter and a

maximum of 3 meters. The setback may need to be

increased for any required interceptor drains.

302.4.3 Toe of Fill Slope. The toe of fill slope shall be

made not nearer to the site boundary line than one half the

height of the slope with a minimum of 0.6 meter and a

maximum of 6 meters. Where a fill slope is to be located

near the site boundary and the adjacent off-site property is

developed, special precautions shall be incorporated in the

work as the building official deems necessary to protect the

adjoining property from damage as a result of such grading.

These precautions may include but are not limited to:

1. Additional setbacks.

2. Provision for retaining or slough walls.

3. Mechanical or chemical treatment of the fill slope

surface to minimize erosion.

4. Provisions for the control of surface waters.

302.4.4 Modification of Slope Location. The building

official may approve alternate setbacks. The building

official may require an investigation and recommendation

by a qualified geotechnical engineer to demonstrate that the

intent of this section has been satisfied.

302.5 DRAINAGE AND TERRACING

301.7.1 General. Unless otherwise indicated on the

approved grading plan, drainage facilities and terracing

shall conform to the provisions of this section for cut or fill

slopes steeper than 1 unit vertical in 3 units horizontal

(33.3% slope).

302.5.2 Terrace. Terraces at least 2 meters in width shall

be established at not more than 10 meters vertical intervals

on all cut or fill slopes to control surface drainage and

debris except that where only one terrace is required, it

shall be at midheight. For cut or fill slopes greater than 20

meters and up to 40 meters in vertical height, one terrace at

approximately midheight shall be 4 meters in width.

Terrace widths and spacing for cut and fill slopes greater

than 40 meters in height shall be designed by the civil

engineer and approved by the building official. Suitable

access shall be provided to permit proper cleaning and

maintenance.

Swales or ditches on terraces shall have a minimum

gradient of 5 percent and must be paved with reinforced

concrete not less than 75 mm in thickness or an approved

equal paving. They shall have a minimum depth at the

deepest point of 0.3 meter and a minimum paved width of

1.5 meters.

A single run of swale or ditch shall not collect runoff from a

tributary area exceeding 1,000 m2 (projected area) without

discharging into a down drain.

302.5.3 Subsurface Drainage. Cut and fill slopes shall

be provided with subsurface drainage as necessary for

stability.

302.5.4 Disposal. All drainage facilities shall be

designed to carry waters to the nearest practicable drainage



way approved by the building official or other appropriate

jurisdiction as a safe place to deposit such waters. Erosion

of ground in the area of discharge shall be prevented by

installation of non-erosive down drains or other devices.

Building pads shall have a drainage gradient of 2 percent

toward approved drainage facilities, unless waived by the

building official.

EXCEPTION:

The gradient from the building pad may be 1 percent if all

of the following conditions exist throughout the permit

area:

1. No proposed fills are greater than 3 meters in

maximum depth.

2. No proposed finish cut or fill slope faces have a

vertical height in excess of 3 meters.

3. No existing slope faces steeper than 1 unit vertical in

10 units horizontal (10% slope) have a vertical

height in excess of 3 meters.

302.5.5 Interceptor Drains. Paved interceptor drains

shall be installed along the top of all cut slopes where the

tributary drainage area above slopes toward the cut and has

a drainage path greater than 12 meters measured

horizontally. Interceptor drains shall be paved with a

minimum of 75 mm of concrete or gunite and reinforced.

They shall have a minimum depth of 300 mm and a

minimum paved width of 750 mm measured horizontally

across the drain. The slope of drain shall be approved by

the building official.

302.6 EROSION CONTROL

302.6.1 Slopes. The faces of cut and fill slopes shall be

prepared and maintained to control against erosion. This

control may consist of effective planting. The protection for

the slopes shall be installed as soon as practicable and prior

to calling for final approval. Where cut slopes are not

subject to erosion due to the erosion-resistant character of

the materials, such protection may be omitted.

302.6.2 Other Devices. Where necessary, check dams,

cribbing, riprap or other devices or methods shall be

employed to control erosion and provide safety.

FOUNDATION INVESTIGATION 3-5


SECTION 303 - FOUNDATION

INVESTIGATION

303.1 GENERAL

Foundation investigation shall be conducted at each

building site when required by the building official.

For structures three storeys or higher, it is recommended

that an exhaustive geotechnical study be performed to

evaluate in-situ soil parameters for foundation design and

analysis. It is recommended that a minimum of one

borehole per two hundred (200) square meters of the

structure’s footprint be drilled to a depth of at least five

meters into hard strata or until a suitable bearing layer is

reached unless otherwise specified by the consulting

geotechnical engineer. The total number of boreholes per

structure should be no less than two (2) for structures whose

footprints are less than three hundred (300) sq.m and no

less than three (3) for those structures with larger footprints.

For buildings with basements, it is recommended that the

depth of boring should extend to twice the least dimension

of the structure’s footprint (2B).

The building official may require that the interpretation and

evaluation of the results of the foundation investigation be

made by a registered civil engineer experienced and

knowledgeable in the field of geotechnical engineering.

303.2 SOIL CLASSIFICATION

For the purposes of this chapter, the definition and

classification of soil materials for use in Table 304-1 shall

be according to ASTM D-2487.

Soil classification shall be based on observation and any

necessary tests of the materials disclosed by borings or

excavations made in appropriate locations. Additional

studies may be necessary to evaluate soil strength, the effect

of moisture variation on soil-bearing capacity,

compressibility, liquefaction and expansiveness.

303.3 LIQUEFACTION STUDY

The building official may require a geotechnical evaluation

in accordance with Section 303.6 when, during the course

of the foundation investigation, all of the following

conditions are discovered:

1. Shallow ground water, 2 meters or less.

2. Unconsolidated saturated sandy alluvium (N < 15)

3. Seismic Zone 4.

EXCEPTION:

The building official may waive this evaluation upon receipt

of written opinion of a qualified geotechnical engineer that

liquefaction is not probable.

303.4 EXPANSIVE SOIL

Soils meeting all four of the following provisions shall be

considered expansive, except that tests to show compliance

with Items 1, 2 and 3 shall not be required if the test

prescribed in Item 4 is conducted:

1. Plasticity index (PI) of 15 or greater, determined in

accordance with ASTM D 4318.

2. More than 10 percent of the soil particles pass a No.

200 sieve (75 _m), determined in accordance with

ASTM D 422.

3. More than 10 percent of the soil particles are less than

5 micrometers in size, determined in accordance with

ASTM D 422.

4. Expansion index greater than 20, determined in

accordance with ASTM D 4829.

303.4.1 Design for expansive soils. Footings or

foundations for buildings and structures founded on

expansive soils shall be designed in accordance with

Section 1805.8.1 or 1805.8.2.

Footing or foundation design need not comply with Section

303.4.3 or 303.4.4 where the soil is removed in accordance

with Section 303.4.4, nor where the building official

approves stabilization of the soil in accordance with

Section 303.4.5.

303.4.2 Foundations. Footings or foundations placed on or

within the active zone of expansive soils shall be designed

to resist differential volume changes and to prevent

structural damage to the supported structure. Deflection

and racking of the supported shall be limited to that which

will not interfere with the usability and serviceability of the

structure.

Foundations placed below where volume change occurs or

below expansive soil shall comply with the following

provisions:

1. Foundations extending into or penetrating expansive

soils shall be designed to prevent uplift of the

supported structure.

2. Foundations penetrating expansive soils shall be

designed to resist forces exerted on the foundation due

to soil volume changes or shall be isolated from the

expansive soil.



303.4.3 Slab-on-ground foundations. Moments, shears

and deflections for use in designing slab-on-ground, mat or

raft foundations on expansive soils shall be determined in

accordance with WRI/CRSI Design of Slab-on-Ground

Foundations or PTI Standard Requirements for Analysis of

Shallow Concrete Foundations on Expansive Soils. Using

the moments, shears and deflections determined above,

nonprestressed slabs-on-ground, mat or raft foundations on

expansive soils shall be designed in accordance with PTI

Standard Requirements for Design of Shallow Post-

Tensioned Concrete Foundations on Expansive Soils. It

shall be permitted to analyze and design such slabs by other

methods that account for soil-structure interaction, the

deformed shape of the soil support, the place or stiffened

plate action of the slab as well as both center lift and edge

lift conditions. Such alternative methods shall be rational

and the basis for all aspects and parameters of the method

shall be available for peer review.

303.4.4 Removal of expansive soil. Where expansive soil

is removed in lieu of designing footings or foundations in

accordance with Section 302.3.2, the soil shall be removed

to a depth sufficient to ensure a constant moisture content in

the remaining soil. Fill material shall not contain expansive

soils and shall comply with Section 302.3.3.

Exception: Expansive soil need not be removed to the

depth of constant moisture, provided the confining pressure

in the expansive soil created by the fill and supported

structure exceeds the swell pressure.

303.4.5 Stabilization. Where the active zone of expansive

soils is stabilized in lieu of designing footings or

foundations in accordance with Section 305.2, the soil shall

be stabilized by chemical, dewatering, presaturation or

equivalent techniques.

303.5 COMPRESSIBLE SOILS

If the boreholes show that the proposed structures are to be

built above compressible fine-grained soils (with N< 6 ), it

is recommended that consolidation tests be performed in

accordance with ASTM D 2435 to determine the settlement

parameters for the site.

If wide, massive loads within the structures to be built on

compressible fine-grained soils are to be expected for

prolonged periods of time built, the settlement effects on

adjacent structures should be evaluated as well.

303.6 REPORTS

The soil classification and design-bearing capacity shall be

shown on the plans, unless the foundation conforms to

Table 305-1. The building official may require submission

of a written report of the investigation, which shall include,

but need not be limited to, the following information:

1. A plot is showing the location of all test borings

and/or excavations.

2. Descriptions and classifications of the materials

encountered.

3. Elevation of the water table, if encountered.

4. Recommendations for foundation type and design

criteria, including bearing capacity, provisions to

mitigate the effects of expansive soils, provisions to

mitigate the effects of liquefaction and soil strength,

and the effects of adjacent loads.

5. Expected total and differential settlement.

6. Laboratory test results of soil samples.

7. Field borehole log containing the following

information

a). Project location

b). Depth of borehole

c). Ground elevation

d). Ground water table elevation

e). Date started and finished

When expansive soils are present, the building official may

require that special provisions be made in the foundation

design and construction to safeguard against damage due to

this expansiveness. The building official may require a

special investigation and report to provide these design and

construction criteria.

303.7 SOIL TESTS

Tables 303-2 and 303-3 summarize the commonly used

field and laboratory tests needed in determining the in-situ

soil parameters for use in foundation design and analysis.



Table 303-2 Laboratory and Field Tests

Laboratory /

Field Test

ASTM

Designation

Output Data /

Parameter Obtained

Classification of Soils

Moisture content D2216-05 Moisture/ water

content

Grain size

analysis

D422-63 Soil gradation

Atterberg Limits D4318-05 Liquid limit, plastic

limit

USCS D2487-00 Classification of

soils

Specific Gravity D854-05 Specific gravity

Shrinkage Limit D427-04 Shrinkage limit

Organic Matter D2974-00 Moisture content,

ash content and

percent organic

matter in soil

Swedish Weigh

Sounding Test

D422-63

UCT Test (Soils) D2166-00 Strength parameters

Tri-axial (UU

Test)

D2850-03a Strength parameters

Tri-axial (CU

Test)

D4767-04 Strength parameters

Oedometer (1-D

Consolidation)

D2435-04 Consolidation

parameters

Laboratory Vane

Shear


Direct Shear

Test


UCT for Intact

Rock


Standard

Penetration Test

D1586-99 N-value

Modified Proctor

Test

D1557-02 Maximum dry

density

Standard Proctor

Test

D698-00a Maximum dry

density

Field Density

Test

D1556-00 Maximum dry

density

CBR Lab Test D1883-05 CBR

Cone Penetration

Test

D3441-05 Soil strength

parameters

Table 303-3 Geophysical Tests

Field Test ASTM

Designation

Output Data /

Parameter Obtained

Geophysical Tests

Seismic refraction

Seismic

reflection

D5777-00 Maps subsurface

geologic conditions,

lithologic units and

fractures.

Ground

Penetrating

Radar

D7128 Maps lateral

continuity of

lithologic units and

detects changes in

the acoustic

properties of

subsurface

geomaterials.

Crosshole

seismic survey

D6432-99 Subsurface geologic

mapping, detection

of buried structures

and utilities

Geo-resistivity

Survey

D4428 Determine

horizontal traveling

compression and

shear seismic waves

at test sites.

303.8 LIQUEFACTION POTENTIAL AND

SOIL STRENGTH LOSS

When required by Section 303.3, the potential for soil

liquefaction and soil strength loss during earthquakes shall

be evaluated during the geotechnical investigation. The

geotechnical evaluation shall assess potential consequences

of any liquefaction and soil strength loss, including

estimation of differential settlement, lateral movement or

reduction in foundation soil-bearing capacity, and discuss

mitigating measures. Such measures shall be given

consideration in the design of the building and may include,

but are not limited to, ground stabilization, selection of

appropriate foundation type and depths, selection of

appropriate structural systems to accommodate anticipated

displacements, or any combination of these measures.

The potential for liquefaction and soil strength loss shall be

evaluated for a site peak ground acceleration that, as a

minimum, conforms to the probability of exceedance

specified in Section 208.6.2. Peak ground acceleration may

be determined based on a site-specific study taking into

account soil amplification effects.

In the absence of such a study, peak ground acceleration

may be assumed equal to the seismic zone factor in Table

208-3.



303.9 ADJACENT LOADS

Where footings are placed at varying elevations, the effect

of adjacent loads shall be included in the foundation design.

303.10 DRAINAGE

Provisions shall be made for the control and drainage of

surface water around buildings. (See also Section 305.5.5.)

ALLOWABLE FOUNDATION AND LATERAL 3-9


SECTION 304 - ALLOWABLE

FOUNDATION AND LATERAL

PRESSURES

304.1 FROM GEOTECHNICAL SITE

INVESTIGATION AND ASSESSMENT.

The recommended allowable foundation and lateral

pressures shall be estimated from a reasonably exhaustive

geotechnical site investigation and assessment, which shall

include at least the following:

a) Description of regional geologic characteristics;

b) Characterization of in-situ geotechnical conditions;

c) Factual report on the in-situ and laboratory tests

performed to characterize the site (See Section

303.7 for a list of in-situ and laboratory tests

commonly carried out for geotechnical site

characterization);

d) Disclosure of the assumptions and the applicable

analytical or empirical models used in estimating

the allowable foundation and lateral pressures;

e) Calculations carried out and Factor of Safety (FS)

assumed in arriving at the recommended allowable

foundation and lateral pressures; and

f) Evaluation of existing potential geologic hazards

and those that may be induced or triggered by the

construction/installation of the structure.

The geotechnical site investigation and assessment shall be

performed by a registered civil engineer experienced and

knowledgeable in the field of geotechnical engineering.

A geotechnical investigation and assessment shall be

presented in a report. The report, together with a brief

resume and a sworn statement of accountability of the

geotechnical engineering consultant who prepared it, shall

be included in the submittals to be reviewed and examined

by the building official or government authority in charge

of issuing the relevant permits such as environmental

compliance certificate and/or building permit.

304.2 PRESUMPTIVE LOAD-BEARING AND

LATERAL RESISTING VALUES.

When no exhaustive geotechnical site assessment and

investigation is performed, especially when no in-situ or

very limited tests are carried out, the presumptive load-

bearing and lateral resisting values provided in Table 304-1

shall be used. Use of these values requires that the

foundation design engineer has, at the least, carried out an

inspection of the site and has become familiar with the

predominant soil or rock characteristics of the site.

Presumptive load-bearing values shall apply to materials

with similar physical characteristics and dispositions. Mud,

organic silt, organic clays, peat or unprepared fill shall not

be assumed to have a presumptive load-bearing capacity

unless data from a geotechnical site assessment and

investigation to substantiate the use of such a value are

submitted.

For clay, sandy clay, silty clay and clayey silt, in no case

shall the lateral sliding resistance exceed one-half the dead

load.

304.3 MINIMUM ALLOWABLE PRESSURES.

The recommended allowable foundation and lateral values

shall be with the allowable stress design load combinations

specified in Section 203.4.

304.4 FOUNDATIONS ADJACENT TO EXISTING

RETAINING/BASEMENT WALLS

In cases where the adjacent building will have more

basements than the proposed building, the foundation of the

proposed building should be designed so as not to impart

additional lateral earth pressures on the existing building

(see section).

ALLOWABLE FOUNDATION AND LATERAL 3-10


Table 304-1 Allowable Foundation and Lateral Pressure

Class of Materials1

Allowable Foundation Pressure

2

(kPa)

Lateral Bearing

Below Natural

Grade3

(kPa/m of

depth)

Lateral Sliding4

Coefficient5 Resistance

6

(kPa)

1. Massive Crystalline Bedrock 200 200 0.70 -

2. Sedimentary and Foliated Rock 100 60 0.35 -

3. Sandy Gravel and /or Gravel(GW & GP) 100 30 0.35 -

4. Well-graded Sand, Poorly-graded Sand, Silty Sand,

Clayey Sand, Silty Gravel and Clayey Gravel (SW,

SP, SM, SC, GM and GC)

75 25 0.25 -

5. Clay, Sandy Clay, Silty Clay and Clayey Silt (CL, ML,

MH, and CH) 50

a 15 - 7

1 A geotechnical site investigation is recommended for soil

classification (Refer to Section 303).

2 All values of allowable foundation pressure are for

footings having a minimum width of 300mm and a

minimum depth of 300mm into the natural grade. Except as

noted in Footnote ‘a’, an increase of 20% is allowed for

each additional 300mm of width and/or depth to a

maximum value of three times the designated value. An

increase of one-third is permitted when using the alternate

load combinations in Section 203.4 that include wind or

earthquake loads.

3 The resistance values derived from the table are permitted

to be increased by the tabular value for each additional foot

(305mm) of depth to a maximum of 15 times the tabular

value. Isolated poles for uses such as flagpoles or signs and

poles used to support buildings that are not adversely

affected by a 0.5inch (12.7mm) motion at the ground

surface due to short-term lateral loads are permitted to be

designed using lateral-bearing values equal to two times the

tabular values.

4 Lateral bearing and sliding resistance may be combined.

5 Coefficient to be multiplied by the dead load.

6 Lateral sliding resistance value to be multiplied by the

contact area. In no case shall the lateral sliding resistance

exceed one-half the dead load.

a No increase for an increase of width shall be allowed.

PILES - GENERAL REQUIREMENTS 3-11


SECTION 305 - FOOTINGS

305.1 GENERAL

Footings and foundations shall be constructed of masonry,

concrete or treated wood in conformance with Chapters 4, 6

and 7. Footings of concrete and masonry shall be of solid

material. Foundations supporting wood shall extend at least

150 mm above the adjacent finish grade. Footings shall

have a minimum depth as indicated in Table 305-1, unless

another depth is warranted, as established by a foundation

investigation.

The provisions of this section do not apply to building and

foundation systems in those areas subject to scour and

water pressure by wind and wave action. Buildings and

foundations subject to such loads shall be designed in

accordance with approved national standards.

TABLE 305-1 Minimum Requirements for Foundations

1,2,3

Number of

Floors

Supported

by the

Foundations

Thickness of

Foundation Wall

(mm)

Width

of

Footing (mm)

Thickness

of

Footing (mm)

Depth

Below Undisturbed

Ground

Surface

(mm) Concrete Unit

Masonry

1 150 150 300 150 300

2 200 200 375 175 450

3 250 250 450 200 600

1 Where unusual conditions are found, footings and foundations shall be as required in Section 305.1.

2 The ground under the floor may be excavated to the elevation of the top of the footing.

3 Foundation may support a roof in addition to the stipulated number of floors. Foundations supporting roofs only shall be as required for supporting one floor.

305.2 FOOTING DESIGN

Except for special provisions of Section 307 covering the

design of piles, all portions of footings shall be designed in

accordance with the structural provisions of this code and

shall be designed to minimize differential settlement when

necessary and the effects of expansive soils when present.

Slab-on-grade and mat-type footings for buildings located

on expansive soils may be designed in accordance with the

geotechnical recommendation as permitted by the building

official.

305.3 BEARING WALLS

Bearing walls shall be supported on masonry or concrete

foundations or piles or other permitted foundation system

that shall be of sufficient size to support all loads.

Where a design is not provided, the minimum foundation

requirements for stud bearing walls shall be as set forth in

Table 305-1, unless expansive soils of a severity to cause

differential movement are known to exist.

EXCEPTIONS:

1. A one-story wood or metal-frame building not used

for human occupancy and not over 40 m2 in floor

area may be constructed with walls supported on a

wood foundation plate when permitted by the

building official.

2. The support of buildings by posts embedded in earth

shall be designed as specified in Section 305.7.

Wood posts or poles embedded in earth shall be

pressure treated with an approved preservative. Steel

posts or poles shall be protected as specified in

Section 306.10.

305.4 STEPPED FOUNDATIONS

Foundations for all buildings where the surface of the

ground slopes more than 1 unit vertical in 10 units

horizontal (10% slope) shall be level or shall be stepped so

that both top and bottom of such foundation are level.

305.5 FOOTINGS ON OR ADJACENT TO

SLOPES

305.5.1 Scope. The placement of buildings and structures

on or adjacent to slopes steeper than 1 unit vertical in 3

units horizontal (33.3% slope) shall be in accordance with

this section.

305.5.2 Building clearance from ascending slopes. In

general, buildings below slopes shall be set a sufficient

distance from the slope to provide protection from slope

drainage, erosion and shallow failures. Except as provided

for in Section 305.5.6 and Figure 305-1, the following

criteria will be assumed to provide this protection. Where

the existing slope is steeper than 1 unit vertical in 1 unit

horizontal (100% slope), the toe of the slope shall be

assumed to be at the intersection of a horizontal plane

drawn from the top of the foundation and a plane drawn

tangent to the slope at an angle of 45 degrees to the

horizontal. Where a retaining wall is constructed at the toe



of the slope, the height of the slope shall be measured from

the top of the wall to the top of the slope.

305.5.3 Footing setback from descending slope surface. Footings on or adjacent to slope surfaces shall be founded

in firm material with an embedment and setback from the

slope surface sufficient to provide vertical and lateral

support for the footing without detrimental settlement.

Except as provided for in Section 305.5.6 and Figure 305-1,

the following setback is deemed adequate to meet the

criteria. Where the slope is steeper than 1 unit vertical in 1

unit horizontal (100% slope), the required setback shall be

measured from an imaginary plane 45 degrees to the

horizontal, projected upward from the toe of the slope.

305.5.4 Pools. The setback between pools regulated by

this code and slopes shall be equal to one half the building

footing setback distance required by this section. That

portion of the pool wall within a horizontal distance of 2

meters from the top of the slope shall be capable of

supporting the water in the pool without soil support.

305.5.5 Foundation elevation. On graded sites, the top

of any exterior foundation shall extend above the elevation

of the street gutter at point of discharge or the inlet of an

approved drainage device a minimum of 300 mm plus 2

percent. The building official may permit alternate

elevations, provided it can be demonstrated that required

drainage to the point of discharge and away from the

structure is provided at all locations on the site.

305.5.6 Alternate setback and clearance. The building

official may approve alternate setbacks and clearances. The

building official may require an investigation and

recommendation of a qualified engineer to demonstrate that

the intent of this section has been satisfied. Such an

investigation shall include consideration of material, height

of slope, slope gradient, load intensity and erosion

characteristics of slope material.

305.6 FOUNDATION PLATES OR SILLS

Wood plates or sills shall be bolted to the foundation or

foundation wall. Steel bolts with a minimum nominal

diameter of 12 mm shall be used in Seismic Zone 2. Steel

bolts with a minimum nominal diameter of 16 mm shall be

used in Seismic Zone 4. Bolts shall be embedded at least

180 mm into the concrete or masonry and shall be spaced

not more than 2 meters apart. There shall be a minimum of

two bolts per piece with one bolt located not more than 300

mm or less than seven bolt diameters from each end of the

piece. A properly sized nut and washer shall be tightened

on each bolt to the plate. Foundation plates and sills shall be

the kind of wood specified in Chapter 6.

305.7 DESIGNS EMPLOYING LATERAL

BEARING

305.7.1 General. Construction employing posts or poles

as columns embedded in earth or embedded in concrete

footings in the earth may be used to resist both axial and

lateral loads. The depth to resist lateral loads shall be

determined by means of the design criteria established

herein or other methods approved by the building official.

305.7.2 Design Criteria

305.7.2.1 Nonconstrained. The following formula

may be used in determining the depth of embedment

required to resist lateral loads where no constraint is

provided at the ground surface, such as rigid floor or rigid

ground surface pavement.

FIGURE 305-1 SETBACK DIMENSIONS FOR BUILDING CLEARANCE FROM SLOPES

H/2 but

need not

exceed

4.5m max. H/3 but need not

exceed 12 m max.

H

Toe of Slope

Top of Slope

Face of Structure

Face of Footing



A

hAd

3.411

2 (305-1)

Where:

bS

PA

1

2.3

b = diameter of round post or footing or diagonal

dimension of square post or footing, meters.

d = depth of embedment in earth in meters but not

over 3.5 meters for purpose of computing

lateral pressure.

h = distance in meters from ground surface to point

of application of “P.”

P = applied lateral force in kilonewtons .

S1 = allowable lateral soil-bearing pressure as set

forth in Table 304-1 based on a depth of one

third the depth of embedment (kPa).

S3 = allowable lateral soil-bearing pressure as set

forth in Table 304-1 based on a depth equal to

the depth of embedment (kPa).

305.7.2.2 Constrained. The following formula may

be used to determine the depth of embedment required to

resist lateral loads where constraint is provided at the

ground surface, such as a rigid floor or pavement.

bS

Ph254d

3

2. (305-2)

305.7.2.3 Vertical load. The resistance to vertical

loads is determined by the allowable soil-bearing pressure

set forth in Table 304-1.

305.7.3 Backfill. The backfill in the annular space

around column not embedded in poured footings shall be by

one of the following methods:

1. Backfill shall be of concrete with an ultimate

strength of 15 MPa at 28 days. The hole shall not be

less than 100 mm larger than the diameter of the

column at its bottom or 100 mm larger than the

diagonal dimension of a square or rectangular

column.

2. Backfill shall be of clean sand. The sand shall be

thoroughly compacted by tamping in layers not more

than 200 mm in thickness.

305.7.4 Limitations. The design procedure outlined in

this section shall be subject to the following limitations:

305.7.4.1 The frictional resistance for retaining walls

and slabs on silts and clays shall be limited to one half of

the normal force imposed on the soil by the weight of the

footing or slab.

305.7.4.1 Posts embedded in earth shall not be used to

provide lateral support for structural or nonstructural

materials such as plaster, masonry or concrete unless

bracing is provided.

305.8 GRILLAGE FOOTINGS

When grillage footings of structural steel shapes are used

on soils, they shall be completely embedded in concrete.

Concrete cover shall be at least 150 mm on the bottom and

at least 100 mm at all other points.

305.9 BLEACHER FOOTINGS

Footings for open-air seating facilities shall comply with

Chapter 3.

EXCEPTIONS:

Temporary open-air portable bleachers may be supported

upon wood sills or steel plates placed directly upon the

ground surface, provided soil pressure does not exceed 50

kPa.



SECTION 306 - PILES - GENERAL

REQUIREMENTS

306.1 GENERAL

Pile foundations shall be designed and installed on the basis

of a foundation investigation as defined in Section 303

where required by the building official.

The investigation and report provisions of Section 303 shall

be expanded to include, but not be limited to, the following:

1. Recommended pile types and installed capacities.

2. Driving criteria.

3. Installation procedures.

4. Field inspection and reporting procedures (to include

procedures for verification of the installed bearing

capacity where required).

5. Pile load test requirements.

The use of piles not specifically mentioned in this chapter

shall be permitted, subject to the approval of the building

official upon submission of acceptable test data,

calculations or other information relating to the properties

and load-carrying capacities of such piles.

306.2 INTERCONNECTION

Individual pile caps and caissons of every structure

subjected to seismic forces shall be interconnected by ties.

Such ties shall be capable of resisting, in tension or

compression, a minimum horizontal force equal to 10

percent of the largest column vertical load.

EXCEPTION:

Other approved methods may be used where it can be

demonstrated that equivalent restraint can be provided.

306.3 DETERMINATION OF ALLOWABLE

LOADS

The allowable axial and lateral loads on piles shall be

determined by an approved formula, by a foundation

investigation or by load tests. Static axial compressive pile

load test shall be in accordance with ASTM Standard D-

1143, and lateral load testing of piles shall conform with

ASTM Standard D-3966. Dynamic pile tests shall be in

accordance with ASTM Standard D-4945. Static axial

tensile load testing to determine the uplift capacity of pile-

soil systems shall be in accordance with ASTM Standard

D-3689.

306.4 STATIC LOAD TEST

Static axial compressive pile load test shall be in

accordance with ASTM Standard D-1143. The building

official may require that the test be conducted under the

supervision of a registered civil engineer experienced and

knowledgeable in the practice of static pile load testing

When the allowable axial compressive load of a single pile

is determined by a static load test, one of the following

methods shall be used:

Method 1. It shall not exceed 50 percent of the yield point

under test load. The yield point shall be defined as that

point at which an increase in load produces a

disproportionate increase in settlement.

Method 2. It shall not exceed one half of the load, which

causes a net settlement, after deducting rebound, of

0.03mm/kN of test load, which has been applied for a

period of at least 24 hours.

Method 3. It shall not exceed one half of that load under

which, during a 40-hour period of continuous load

application, no additional settlement takes place.

306.5 DYNAMIC LOAD TEST

High-strain dynamic load test may be used to determine the

bearing capacity of piles, in accordance with ASTM

Standard D-4945. The building official may require that

the test be conducted by a registered civil engineer

experienced and knowledgeable in the practice of dynamic

load testing.

306.6 COLUMN ACTION

All piles standing unbraced in air, water or material not

capable of lateral support shall conform with the applicable

column formula as specified in this code. Such piles driven

into firm ground may be considered fixed and laterally

supported at 1.5 meters below the ground surface and in

soft material at 3 meters the ground surface unless

otherwise prescribed by the building official after a

foundation investigation by an approved agency.

306.7 GROUP ACTION

Consideration shall be given to the reduction of allowable

pile load when piles are placed in groups.

Where soil conditions make such load reductions advisable

or necessary, the allowable axial and lateral loads

determined for a single pile shall be reduced by any rational

method or formula submitted to the building official.



306.8 PILES IN SUBSIDING AREAS

Where piles are driven through subsiding fills or other

subsiding strata and derive support from underlying firmer

materials, consideration shall be given to the downward

frictional forces, which may be imposed on the piles by the

subsiding upper strata.

Where the influence of subsiding fills is considered as

imposing loads on the pile, the allowable stresses specified

in this chapter may be increased if satisfactory

substantiating data are submitted.

306.9 JETTING

Jetting shall not be used except where and as specifically

permitted by the building official. When used, jetting shall

be carried out in such a manner that the carrying capacity of

existing piles and structures shall not be impaired. After

withdrawal of the jet, piles shall be driven down until the

required resistance is obtained.

306.10 PROTECTION OF PILE MATERIALS

Where the boring records of site conditions indicate

possible deleterious action on pile materials because of soil

constituents, changing water levels or other factors, such

materials shall be adequately protected by methods or

processes approved by the geotechnical engineer.

The effectiveness of such methods or processes for the

particular purpose shall have been thoroughly established

by satisfactory service records or other evidence, which

demonstrates the effectiveness of such protective measures.

306.11 ALLOWABLE LOADS

The allowable loads based on soil conditions shall be

established in accordance with Section 306.

EXCEPTION:

Any uncased cast-in-place pile may be assumed to develop

a frictional resistance equal to one sixth of the bearing

value of the soil material at minimum depth as set forth in

Table 305-1 but not to exceed 25 kPa unless a greater value

is allowed by the building official after a foundation

investigation as specified in Section 303 is submitted.

Frictional resistance and bearing resistance shall not be

assumed to act simultaneously unless recommended after a

foundation investigation as specified in Section 303.

306.12 USE OF HIGHER ALLOWABLE PILE

STRESSES

Allowable compressive stresses greater than those specified

in Section 307 shall be permitted when substantiating data

justifying such higher stresses are submitted to and

approved by the building official. Such substantiating data

shall be included in the foundation investigation report in

accordance with Section 306.1.

PILES - SPECIFIC REQUIREMENTS 3-16


SECTION 307 - PILES - SPECIFIC

REQUIREMENTS

307.1 ROUND WOOD PILES

307.1.1 Material. Except where untreated piles are

permitted, wood piles shall be pressure treated. Untreated

piles may be used only when it has been established that the

cutoff will be below lowest groundwater level assumed to

exist during the life of the structure.

307.1.2 Allowable stresses. The allowable unit stresses

for round woodpiles shall not exceed those set forth in

Chapter 6.

The allowable values listed in, for compression parallel to

the grain at extreme fiber in bending are based on load

sharing as occurs in a pile cluster. For piles which support

their own specific load, a safety factor of 1.25 shall be

applied to compression parallel to the grain values and 1.30

to extreme fiber in bending values.

307.2 UNCASED CAST-IN-PLACE

CONCRETE PILES

307.2.1 Material. Concrete piles cast in place against

earth in drilled or bored holes shall be made in such a

manner as to ensure the exclusion of any foreign matter and

to secure a full-sized shaft.

The length of such pile shall be limited to not more than 30

times the average diameter. Concrete shall have a specified

compressive strength f’c of not less than 17.5 MPa.

EXCEPTION:

The length of pile may exceed 30 times the diameter

provided the design and installation of the pile foundation

is in accordance with an approved foundation investigation

report.

307.2.2 Allowable stresses. The allowable compressive

stress in the concrete shall not exceed 0.33f’c. The

allowable compressive stress of reinforcement shall not

exceed 34 percent of the yield strength of the steel or 175

MPa.

307.3 METAL-CASED CONCRETE PILES

307.3.1 Material. Concrete used in metal-cased concrete

piles shall have a specified compressive strength f’c of not

less than 17.5 MPa.

307.3.2 Installation. Every metal casing for a concrete

pile shall have a sealed tip with a diameter of not less than

200 mm.

Concrete piles cast in place in metal shells shall have shells

driven for their full length in contact with the surrounding

soil and left permanently in place. The shells shall be

sufficiently strong to resist collapse and sufficiently

watertight to exclude water and foreign material during the

placing of concrete.

Piles shall be driven in such order and with such spacing as

to ensure against distortion of or injury to piles already in

place. No pile shall be driven within four and one-half

average pile diameters of a pile filled with concrete less

than 24 hours old unless approved by the geotechnical

engineer.

307.3.3 Allowable stresses. Allowable stresses shall not

exceed the values specified in Section 307.2.2, except that

the allowable concrete stress may be increased to a

maximum value of 0.40f’c for that portion of the pile

meeting the following conditions:

1. The thickness of the metal casing is not less than 1.7

mm (No. 14 carbon sheet steel gage).

2. The casing is seamless or is provided with seams of

equal strength and is of a configuration that will

provide confinement to the cast-in-place concrete.

3. The specified compressive strength f’c shall not

exceed 35 MPa and the ratio of steel minimum

specified yield strength Fy to concrete specified

compressive strength f’c shall not be less than 6.

4 The pile diameter is not greater than 400 mm.

307.4 PRECAST CONCRETE PILES

307.4.1 Materials. Precast concrete piles shall have a

specified compressive strength f’c of not less than 20 MPa,

and shall develop a compressive strength of not less than 20

MPa before driving.

307.4.2 Reinforcement ties. The longitudinal

reinforcement in driven precast concrete piles shall be

laterally tied with steel ties or wire spirals. Ties and spirals

shall not be spaced more than 75 mm apart, center to center,

for a distance of 600 mm from the ends and not more than

200 mm elsewhere. The gage of ties and spirals shall be as

follows:

1. For piles having a diameter of 400 mm or less, wire

shall not be smaller than 5.5 mm (No. 5 B.W.gage).



2. For piles, having a diameter of more than 400 mm

and less than 500 mm, wire shall not be smaller than

6 mm (No.4 B.W.gage).

3. For piles having a diameter of 500 mm and larger,

wire shall not be smaller than 6.5 mm

(No.3 B.W. gage).

307.4.3 Allowable stresses. Precast concrete piling shall

be designed to resist stresses induced by handling and

driving as well as by loads. The allowable stresses shall not

exceed the values specified in Section 307.2.2.

307.5 PRECAST PRESTRESSED CONCRETE

PILES (PRETENSIONED)

307.5.1 Materials. Precast prestressed concrete piles

shall have a specified compressive strength f’c of not less

than 35 MPa and shall develop a compressive strength of

not less than 27 MPa before driving.

307.5.2 Reinforcement

307.5.2.1 Longitudinal reinforcement. The

longitudinal reinforcement shall be high-tensile seven-wire

strand conforming to ASTM Standards. Longitudinal

reinforcement shall be laterally tied with steel ties or wire

spirals.

307.5.2.2 Transverse reinforcement. Ties or spiral

reinforcement shall not be spaced more than 75 mm apart,

center to center, for a distance of 600 mm from the ends

and not more than 200 mm elsewhere.

At each end of the pile, the first five ties or spirals shall be

spaced 25 mm center to center.

For piles having a diameter of 600 mm or less, wire shall

not be smaller than 5.5 mm (No. 5 B.W.gage).

For piles having a diameter greater than 600 mm but less

than 900 mm, wire shall not be smaller than 6 mm

(No. 4 B.W.gage).

For piles having a diameter greater than 900 mm, wire shall

not be smaller than 6 mm (No.3 B.W.gauge).

307.5.3 Allowable stresses. Precast prestressed piling

shall be designed to resist stresses induced by handling and

driving as well as by loads. The effective prestress in the

pile shall not be less than 2.5 MPa for piles up to 10 meters

in length, 4 MPa for piles up to 15 meters in length, and 5

MPa for piles greater than 15 meters in length.

The compressive stress in the concrete due to externally

applied load shall not exceed:

fc = 0.33f’c - 0.27 fpc (307-1)

Where:

fpc = effective prestress stress on the gross section.

Effective prestress shall be based on an assumed loss of 200

MPa in the prestressing steel. The allowable stress in the

prestressing steel shall not exceed the values specified in

Section 418.5.

307.6 STRUCTURAL STEEL PILES

307.6.1 Material. Structural steel piles, steel pipe piles

and fully welded steel piles fabricated from plates shall

conform to one of the material specifications listed in

Section 501.3.

307.6.2 Allowable stresses. The allowable axial stresses

shall not exceed 0.35 of the minimum specified yield

strength Fy or 85 MPa, whichever is less.

EXCEPTION:

When justified in accordance with Section 306.12, the

allowable axial stress may be increased above 85 MPa and

0.35Fy, but shall not exceed 0.5Fy.

307.6.3 Minimum dimensions. Sections of driven H-

piles shall comply with the following:

1. The flange projection shall not exceed 14 times the

minimum thickness of metal in either the flange or

the web, and the flange widths shall not be less than

80 percent of the depth of the section.

2. The nominal depth in the direction of the web shall

not be less than 200 mm.

3. Flanges and webs shall have a minimum nominal

thickness of 10 mm.

Sections of driven pipe piles shall have an outside diameter

of not less than 250 mm and a minimum thickness of not

less than 6 mm.

307.7 CONCRETE-FILLED STEEL PIPE

PILES

307.7.1 Material. The steel pipe of concrete-filled steel

pipe piles shall conform to one of the material

specifications listed in Section 501.3. The concrete in



concrete-filled steel pipe piles shall have a specified

compressive strength f’c of not less than 17.5 MPa.

307.7.2 Allowable stresses. The allowable axial stresses

shall not exceed 0.35 of the minimum specified yield

strength Fy of the steel plus 0.33 of the specified

compressive strength f’c of concrete, provided Fy shall not

be assumed greater than 250 MPa for computational

purposes.

EXCEPTION:

When justified in accordance with Section 306.12, the

allowable stresses may be increased to 0.50 Fy.

307.7.3 Minimum dimensions. Driven piles of uniform

section shall have a nominal outside diameter of not less

than 200 mm.

FOUNDATION CONSTRUCTION - SEISMIC ZONE 4 3-19


SECTION 308 - FOUNDATION

CONSTRUCTION-SEISMIC ZONE 4

308.1 GENERAL

In Seismic Zones 4, the further requirements of this section

shall apply to the design and construction of foundations,

foundation components and the connection of

superstructure elements thereto. See Section 421.9 for

additional requirements for structural concrete foundations

resisting seismic forces.

308.2 FOUNDATION AND GEOTECHNICAL

INVESTIGATIONS

Where a structure is determined to be in Seismic Zone 4 in

accordance with Section 208.4, an investigation shall be

conducted and shall include an evaluation of the following

potential hazards resulting from earthquake motions: slope

instability, liquefaction and surface rupture due to faulting

or lateral spreading.

In addition, the following investigations shall also be met:

1. A determination of lateral pressures on basement and

retaining walls due to earthquake motions.

2. An assessment of potential consequences of any

liquefaction and soil strength loss, including estimation

of differential settlement, lateral movement or

reduction in foundation soil-bearing capacity, and shall

address mitigation measures. Such measures shall be

given consideration in the design of the structure and

can include but are not limited to ground stabilization,

selection of appropriate foundation type and depths,

selection of appropriate structural systems to

accommodate anticipated displacements or any

combination of these measures. The potential for

liquefaction and soil strength loss shall be evaluated for

site peak ground acceleration magnitudes and source

characteristics consistent with the design earthquake

ground motions. Peak ground acceleration shall be

determined from a site-specific study taking into

account soil amplification effects, as specified in

Section 208.4.

308.3 FOOTINGS AND FOUNDATIONS

Where a structure is assigned to Seismic Zone 4 in

accordance with Section 208.4, individual spread footings

founded on soil defined in Section 208.4.3 as Soil profile

Type SE or SF shall be interconnected by ties. Ties shall be

capable of carrying, in tension or compression, unless it is

demonstrated that equivalent restraint is provided by

reinforced concrete beams within slabs on grade or

reinforced concrete slabs on grade.

308.4 PIER AND PILE FOUNDATIONS

Where a structure is assigned to Seismic Zone 4 in

accordance with Section 208.4, the following shall apply.

Individual pile caps, piers or piles shall be interconnected

by ties. Ties shall be capable of carrying, in tension and

compression, unless it can be demonstrated that equivalent

restraint is provided by reinforced concrete beams within

slabs on grade, reinforced concrete slabs on grade,

confinement by competent rock, hard cohesive soils or very

dense granular soils. Concrete shall have a specified

compressivestrength of not less than 3,000 psi (20.68 MPa)

at 28 days.

Exception: Piers supporting foundation walls, isolated

interior posts detailed so the pier is not subject to lateral

loads, lightly loaded exterior decks and patios and

occupancy category IV and V specified in Section 103 not

exceeding two stories of light-frame construction, are not

subject to interconnection if it can be shown the soils are of

adequate stiffness, subject to the approval of the building

official.

308.4.1 Connection to pile cap. For piles required to resist

uplift forces or provide rotational restraint, design of

anchorage of piles into the pile cap shall be provided

considering the combined effect of axial forces due to uplift

and bending moments due to fixity to the pile cap.

Anchorage shall develop a minimum of 25 percent of the

strength of the pile in tension. Anchorage into the pile cap

shall be capable of developing the following: In the case of

uplift, the lesser of the nominal tensile strength of the

longitudinal reinforcement in a concrete pile, or the

nominal tensile strength of a steel pile, or the pile uplift soil

nominal strength factored by 1.3 or the axial tension force

resulting from the load combinations of Section 203. In the

case of rotational restraint, the lesser of the axial and shear

forces, and moments resulting from the load combinations

of Section 203 or development of the full axial, bending

and shear nominal strength of the pile.

308.4.2 Design details for piers, piles and grade beams.

Piers or piles shall be designed and constructed to withstand

maximum imposed curvatures from earthquake ground

motions and structure response. Curvatures shall include

free-field soil strains modified for soil-pile-structure

interaction coupled with pier or pile deformations induced

by lateral pier or pile resistance to structure seismic forces.

Concrete piers or piles on soil type SE or SF sites, as

determined in Section 208.4.3, shall be designed and

detailed in accordance with Sections 410 within seven pile

diameters of the pile cap and the interfaces of soft to



medium stiff clay or liquefiable strata. Grade beams shall

be designed as beams in accordance Section 4. When grade

beams have the capacity to resist the forces from the load

combinations in Section 203.

308.4.3 Flexural strength. Where the vertical lateral-

force-resisting elements are columns, the grade beam or

pile cap flexural strengths shall exceed the column flexural

strength. The connection between batter piles and grade

beams or pile caps shall be designed to resist the nominal

strength of the pile acting as a short column. Batter piles

and their connection shall be capable of resisting forces and

moments from the load combinations of Section 203.

308.5 DRIVEN PILE FOUNDATIONS

308.5.1 Precast Concrete Piles. Where a structure is

assigned to Seismic Zone 4 the longitudinal reinforcement

with a minimum steel ratio of 0.01 shall be provided

throughout the length of precast concrete piles. Within three

pile diameters of the bottom of the pile cap, the longitudinal

reinforcement shall be confined with closed ties or spirals

of a minimum 3/8 inch (9.5 mm) diameter. Ties or spirals

shall be provided at a maximum spacing of eight times the

diameter of the smallest longitudinal bar, not to exceed 6

inches (152 mm). Throughout the remainder of the pile, the

closed ties or spirals shall have a maximum spacing of 16

times the smallest longitudinal bar diameter not to exceed 8

inches (203 mm).

308.5.2 Precast Prestressed piles. Where a structure is

assigned to Seismic Zone 4, the following shall apply. The

minimum volumetric ratio of spiral reinforcement shall not

be less than 0.007 or the amount required by the following

formula for the upper 20 feet (6096 mm) of the pile.

0.12s c yhf f (308.5.1)

Where:

fc = Specified compressive strength of concrete, psi

(MPa).

fyh = Yield strength of spiral reinforcement,

psi (586 MPa).

s = Spiral reinforcement index (vol. spiral/vol.

core).

At least one-half the volumetric ratio required by Equation

4-1 shall be provided below the upper 20 feet (6096 mm) of

the pile. The pile cap connection by means of dowels. Pile

cap connection by means of developing pile reinforcing

strand is permitted provided that the pile reinforcing strand

results in a ductile connection.

Where the total pile length in the soil is 35 feet (10 668

mm) or less, the lateral transverse reinforcement in the

ductile region shall occur through the length of the pile.

Where the pile length exceeds 35 feet (10 668 mm), the

ductile pile region shall be taken as the greater of 35 feet

(10 668 mm) or the distance from the underside of the pile

cap to the point of zero curvature plus three times the least

pile dimension.

In the ductile region, the center-to-center spacing of the

spirals or hoop reinforcement shall not exceed one-fifth of

the least pile dimension, six times the diameter of the

longtitudinal strand, or 8 inches (203 mm), whichever is

smaller.

Circular spiral reinforcement shall be spliced by lapping

one full turn and bending the end of the spiral to a 90-

degree hook or by use of a mechanical or welded splice.

Where the transverse reinforcement consists of circular

spirals, the volumetric ratio of spiral transverse

reinforcement in the ductile region shall comply with the

following:

1 1.40.12 1

2

gcs

yh ch c g

Af P

f A f A

(308.5.2)

but not less than:

1 1.40.12

2

cs

yh c g

f P

f f A

(308.5.3)

and need not exceed:

0.021s (308.5.4)

Where:

Ag = Pile cross-sectional area, square inches

(mm2).

Ach = Core area defined by spiral outside diameter,

square inches (mm2).

f c = Specified compressive strength of concrete,

psi (MPa).

fyh = Yield strength of spiral reinforcement

P = Axial load on pile, pounds (kN).

s = Volumetric ratio (vol. spiral/ vol. core).

This required amount of spiral reinforcement is permitted to

be obtained by providing an inner and outer spiral. When

transverse reinforcement consists of rectangular hoops and

cross ties, the total cross-sectional area of lateral transverse

reinforcement in the ductile region with spacings, and

perpendicular to dimension, hc, shall conform to:

10.3 1 1.4

2

gcsh c

yh ch c g

Af PA s h

f A f A

(308.5.5)

but not less than:



1 1.40.12

2

csh c

yh c g

f PA s h

f f A

(308.5.6)

where:

fyh = 70,000 psi (483 MPa).

hc = Cross-sectional dimension of pile core

measured center to center of hoop

reinforcement, inch (mm).

s = Spacing of transverse reinforcement measured

along length of pile, inch (mm).

Ash = Cross-sectional area of tranverse

reinforcement, square inches (mm2).

f c = Specified compressive strength of concrete,

psi (MPa).

The hoops and cross ties shall be equivalent to deformed

bars not less than 10mm in size. Rectangular hoop ends

shall terminate at a corner with seismic hooks. Outside of

the length of the pile requiring transverse confinement

reinforcing, the spiral or hoop reinforcing with a volumetric

ratio not less than one-half of that required for transverse

confinement reinforcing shall be provided.

308.6 CAST-IN-PLACE CONCRETE

FOUNDATIONS

Where a structure is assigned to Seismic Zone 4 a minimum

longitudinal reinforcement ratio of 0.005 shall be provided

for uncased cast-in-place drilled or augered concrete piles,

piers or caissons in the top one-half of the pile length a

minimum length of 10 feet (3048 mm) below ground or

throughout the flexural length of the pile, whichever length

is greatest. The flexural length shall be taken as the length

of the pile to a point where the concrete section cracking

moment strength multiplied by 0.4 exceeds the required

moment strength at that point. There shall be a minimum of

four longitudinal bars with transverse confinement

reinforcement provided in the pile within three times the

least pile dimension of the bottom of the pile cap. A

transverse spiral reinforcement ratio of not less than one-

half of that required in Section 410 for other than Soil

Profile Type SE, SF or as determined in Section 208.4.3 or

liquefiable sites is permitted. Tie spacing throughout the

remainder of the concrete section shall neither exceed 12-

longitudinal-bar diameters, one-half the least dimension of

the section, nor 12 inches (305 mm). Ties shall be a

minimum of 10mm bars for piles with a least dimension up

to 20 inches (508 mm), and 12mm bars for larger piles.

Date post:	08-Feb-2016
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NSCP Chapter 3 Version 5

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