Rock Classification for Tunnelling Projects

Ian McFeat SmithDirector IMS Tunnel Consultancy Ltd

Rock Classification for Tunnelling Projects

Special Design Issues for Tunnel Complexes and Rock Caverns

Rock Classification for the Selection of Tunnel Support Systems

Predicting Tunnel Boring Machine (TBM) Performance

Management and Prediction of Water Inflows

Tunnelling Costs and Programming

Risk Assessment

New Code of Practice for Tunnelling

Role of Rock Classification for Payment Purposes in Risk SharingContracts

Early Form of Rock Classification ?

The problem is mathematics is black and white but the real world is grey Albert Einstein

Site Investigation

Special Design Issues for Tunnel Complexes and Caverns

Rock Cavern for Tai Koo MTR Station

Impact of major joints / weathered seams on primary support system

Modification of lining design philosophy

Impact of incorrect on site rock classification on design and construction liability

Rock Classification for Selection of Tunnel Support Systems

NORWEIGN GEOTECHNICAL INSTITUTES (NGI) Q - SYSTEM

Q = RQD x Jr x JwJn Ja SRF

where RQD is the rock quality designationJn is the joint set numberJr represents the joint roughnessJa represents the joint alterationJw is a joint water reduction factorSRF is a stress reduction factor

Further RQD represents rock block sizeJn

Jr represents joint shear strengthJa

And Jw represents active stressSRF

Selection of Temporary Supports using Q system

Construction of twin 16 18m span tunnels for Eagles Nest Tunnels (Current)

Key Issues for Classification of Rock Masses in Tunnelling

1) Variability of geology /temp supports 2) 3D - RQD assessment? 3) Proportion of blast fractures?

CSIR GEOMECHANICS CLASSIFICATION OF JOINTED ROCK MASSES

System involves measurement, selection of a rating and addition of these for each of the following rock mass parameters:

INTACT STRENGTH OF ROCK RQD % SPACING OF JOINTS m CONDITION OF JOINTS GROUND WATER

RATING ADJUSTMENT FOR ADVERSE JOINT ORIENTATIONS

From the overall rating the following is provided:

AVERAGE STAND UP TIME COHESION OF ROCK MASS ANGLE OF FRICTION

Description of IMS Rock Classes

IMS DescriptionRock Class

1 Massive competent rock mass2 Favourable rock mass3 Moderately fractured / weathered rock4 Highly fractured or weathered 5A Fault zones 5B Fault gouge / soils

Application of IMS rock classes for preliminary design of Sha Tin Heights tunnel

Rock Classification for Estimating Tunnel Boring Machine (TBM) Performance

Hong Kongs first TBM project - Open type hard rock Tunnel Boring Machine (TBM)

Hong Kongs first TBM projects cable tunnel and double shielded TBM for Tolo Tunnel

Hard rock earth pressure balance TBM for tunnelling in mixed face conditions

TBM excavated tunnel no effective overbreak and no support required

Comparison of support requirements for drill and blast and TBM excavated cable tunnels

Use of IMS rock classification for estimating overbreak for different methods of tunnelling

Management and Prediction of Water Inflows in Rock Tunnelling

Water Inflow Issues for Tai Po to Butterfly Valley Aqueducts

Cumulative water inflows experienced in aqueduct

Tai Po to Butterfly Valley Large Disseminated Inflows in TBM Drives

Large inflows through individual open joints and shear zones

Tai Po to Butterfly Aqueduct water inflow at full hydrostatic head (700m)

SSDS subaqueous tunnels. Large inflows at full hydrostatic head below urban areas

Site measurement of Water Reduction Factor R with time.

PREDICTION OF WATER INFLOWS INTO ROCK TUNNELS IN HONG KONG

METHOD OF PREDICTING INFLOW REDUCTION

FACTOR (R)

Water Source Head Factor (Hf) Horizontal Separation (df)

Size Factor (Sf) Head m/100 (m) Separation df dmm= 1 400

Source Sea

Sf 1.0

Head m

Hf 0 1.0

Major Valley/ Reservoir

0.85 >100 1.0 50 0.65

Large Valley/ Reservoir

0.7 100 1.0 100 0.5

Small River/ Reservoir

0.5 80 0.8 200 0.29

Stream 0.3 50 0.5 300 0.13 Ridge 0.1 20 0.2 400 0

For d = 0 to 400m only Notes : R = Sf x Hf x df with R being dimensionless.

PREDICTION OF WATER INFLOWS INTO ROCK TUNNELS IN HONG KONG

Prediction of Initial (Ii) and Final Inflows (Fi)

Ii = R.IF & Fi = R2IF

IF VALUES FOR IMS ROCK CLASSES (l/min/m)

IMS Rock Class 1 2 3 4 5 IF values

High 0.6 1.4 12.2 37 3.8

l/min/m

Average

0.45 1.05 6.55 24 3.1

Low 0.3 0.7 0.9 11 2.4

GUIDE TO GROUND TREATMENT FOR PRE-GROUTING OF ROCK TUNNELS

Rock mass classification

IMS Rock Class

Grouting required Grout material

1. JOINTED ROCK 1.1 Massive, no joints 1 No grouting N/A 1.2 Very few joints;

< 0.1 joints/m 1 Spot or targeted grouting MFC, if

joints >0.5mm; OPC

1.3 Few joints; < 1 joints/m, 2 joint sets

2 Limited to continuous MFC

1.4 Jointed rock; 2 joint sets

3 Continuous MFC

1.5 Very jointed rock; 10 joints/m

4-5A Continuous, closer spacing, in stages

MFC, UFC

2. FAULT ZONES 2.1 Zones with clay 5A-5B Displace, wash out/replace,

compact OPC, MFC

2.2 Silty zones 5A-5B Penetrate, very close spacing, in stages

UFC, Chemical

2.2 Sandy zones 5A-5B Penetrate, close spacing, in stages

MFC, UFC

2.3 Gravel zones or sugar cube rock

5A-5B Penetrate, quick set, in stages OPC, MFC

2.5 Mixed material 5A-5B Penetrate, displace, compact, replace, in stages, close spacing

OPC, MFC, UFC, Chemical

3. REGIONAL STRUCTURAL ZONE

Depends of size of zone and composition. Often a combination of 1.5 and 2.5 above.

Tunnelling Costs and Programming

Risks for Tunnelling

Risks - rockhead Issues Key risks 1. Defining rockhead? - 5m CDG below 12mof

competent rock; 2. tunnelling close below rockhead in urban areas

Collapse of HK MTR Island Line Tunnels in Hennessy Road,1983

Island Line TunnelsKey Risks Rock tunnelling (blasting) in urban areas with low

rockhead cover ; blast vibrations restrictions ; damage to third parties

Athens Metro: Collapses of TBM Tunnels to Street Level

Key Risk - lack of geological risk management plan

Hong Kong MTR large boulders in soft ground

Singapore and Hong Kong Key Risk: Failure of Earth Pressure Balance System for tunnelling

in extreme mixed face conditions; risk to third party property

PUBLIC LIABILITY ISSUES

EPB EPB

EPB EPB

EPB EPB

EPB

EPB

EPB

EPB

MEDIUM PRESSURE

EPBMEDIUM

PRESSURE EPB

MEDIUM PRESSURE

EPB

MEDIUM PRESSURE

EPB

LOW PRESSURE

EPB

LOW PRESSURE

EPB

LOW PRESS EPB

OPEN OPEN

OPENOPEN

LOW PRESSURE

EPB

20 40 60 80 100 SPT

CLAY

SILT

SAND

GRAVEL

Slurry or Special Measures

Slurry or Special Measures

SLURRY

SLURRY

SLURRYSLURRY

SLURRY

Special Measures

SOIL DENSITY

FILLALLUVIUM

MARINE SAND COMPLETELY WEATHERED GRANITES

SOFT / LOOSEVERY FIRM VERY STIFF

IMS Method of Selecting Face Controlfor Soft Ground TBMs

New Joint Code of Practice for Tunnels British Tunnelling Society The Association of British Insurers

New Code of Practice for Tunnels

Client responsible for sufficiency of site investigations

Geotechnical data forms part of contract

Geotechnical baseline conditions i.e. rock classification, to bedrawn up by Client or Tenderer

Geotechnical baseline conditions and used for assessing unexpected geological conditions

Risk assessment and management at all stages of development of project

Continuous tracking and mitigation of risks through risk register

Insurance cover may be suspended or cancelled in event of a breach of code requirements

Risk Levels and Action Plans

Mitigation to be undertaken as resources permit.

R4

Mitigation should be completed before works begin.

R3

Work shall not begin until mitigation implementation has been completed and verified.Mitigation should reduce risk to R3 Level

R2

Work shall not begin until mitigation implementation has been completed and verified. Mitigation of risk of high priority and risk must be reduced significantly or alternative methods adopted.

R1

Action and TimescaleRisk Level

The IMS Risk Evaluation System

Key Risk Categories

quality, level of detail and contributionPROGRAMME A delay risk as a percentage of overall programmePROGRAMME B

commercial risk as a percentage of cost of worksCOMMERCIAL B cost of project relative to available funds and previous worksCOMMERCIAL A quality of contract documents, partnering and risk sharingCONTRACT management systems and site cultureMANAGEMENT for type and scale of works and by contractorPRECEDENCE/ EXPERIENCE ground control requirements, support, and excavation difficultyTUNNELLING METHODS

including layout, number of working faces, interfaces, ease of access, and spoil disposal

COMPLEXITY OF WORKS

robustness of design, quality of specifications and implementation

DESIGN & SPECIFICATION

predictability, achievability of watertightness specification and likely impact

WATER ISSUES classification and variability of conditionsGROUND CONDITIONS adequacy and qualitySITE INVESTIGATION

proximity to tunnels of adjacent man-made structures and other constraints

CONSTRAINTS type of terrain and coverTERRAIN

Score Forms IV Ground Conditions

1Highly consistent4Consistent generally easy to predict9Intermediate moderate risk

16Highly variable high risk

25Major variations / impossible to predict accurately6 Variability

1No risk e.g. competent rock tunnel

4Low risk e.g. consistent soft ground or moderate rock

9Intermediate e.g. soft ground or variable rock moderate risk

16Poor e.g. soft ground with boulders / low rockhead cover

25Very poor e.g. IMS Rock Class 5B, extreme mixed ground; rockhead at tunnel crown; regions of high seismicity; very high in situ stresses

5 Ground Mass Characterisation

(rock and soft ground tunnels to be classified using IMS rock or soil classes)

ScoreRisk EvaluationRisk Type

Score Forms V Water Issues

1No Impact Expected4Low Risk9Intermediate Moderate Risk16High Impact Anticipated25Extreme Risk Major Impact9 Likely Impact of

Inflows in terms of Ground Movements, Disposal, Tunnel Instability

1Very Easy to Achieve4Low Risk 9Intermediate Moderate Risk16Difficult to Achieve25Very Unlikely to be Achieved8 Watertightness

Specifications

1Consistent or low flows Likely4Small risk 9Intermediate Moderate risk16Difficult variable inflows25No local precedence much uncertainty creating very high risk7 Predictability of

Inflows

ScoreRisk EvaluationRisk Type

Score Forms XI Contract

1Client assumes all risks4Risks are allocated to party most able to manage them9Equal client specified distribution of risks

16Risk sharing occurs but biased in favour of the Client25All risks are transferred to the Contractor27 Risk Sharing1Client participates in partnering and encourages broad involvement4Client actively involved in partnering but lacking experience.9Client passively involved in partnering but lacking experience.

16Parties accept partnering in principle but reluctant strict focus on contract rather than problem solving

25Partnering is not allowed strict pursuit of contract conditions. 26 Partnering

(general attitude towards mutual co-operation)

1Excellent Quality, Well structured, Clear and Easy to Implement4Good standard 9Just Sufficient Moderate Risk

16Poor Quality Many Ambiguities25Very Poor, Inappropriate for Job, Allocation of Risks Unclear25 Quality of

Contract Documents

ScoreRisk EvaluationRisk Type

Re-measurement Risk Sharing Forms of Contract

Tunnel for Tolo Effluent Export Scheme HK Governments first TBM project - 7.5 km long tunnel

completed within budget and 6 months ahead of programme; using double shielded TBM

Re-measurement Risk Sharing Contract for Tolo Tunnel:

Only major risk sharing contract used for tunnelling in HK to date. Payment for geological conditions made on re-measurement of IMS rock classes

Re-measurement Risk Sharing Contract for Tolo Tunnel:

Actual Limit to Governments Risk

The Present System

Rock Classification for Tunnelling Projects

Special Design Issues for Tunnel Complexes and Rock Caverns

Rock Classification for the Selection of Tunnel Support Systems

Prediction of Tunnel Boring Machine (TBM) Performance

Prediction and Management of Water Inflows

Tunnelling Costs and Programming

Risk Assessment

New Code of Practice for Tunnelling

Role of Rock Classification for Payment Purposes in Risk SharingContracts