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Singapore, Wen, LTA experience in underground construction

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    IEAust Singapore 12 Jan 2012 1

    Underground Construction

    Pitfalls to Avoid

    D Wen, BSc, PhDPE, PE(Geo), AC(Geo), CEng, MICE, MIEAust, CPEng

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    Soil Investigation & Interpretation

    Maintenance

    Interfaces Base Stability

    Gaps in Retaining Walls

    Buildings on Mixed Foundations

    Underground Construction - Pitfalls to Avoid

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    Soil Investigation & Interpretation

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    Soil Investigation & Interpretation

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    5/695IEAust Singapore 12 Jan 2012

    Interpreted Profile of Surface Wave Velocity

    Interpreted Rock Profile

    Soil Investigation & Interpretation

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    Soil Investigation & Interpretation

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    Maintenance

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    Maintenance

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    Maintenance

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    Maintenance

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    TBM Launching

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    TBM Launching

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    Braddell Road Proposed Depressed Road

    TBM Launching

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    F1

    30m3 F1 sandsflowing into the

    TBM launching

    chamber through

    the gap between

    the TBM shield andthe shotcrete

    support of the

    launching

    chamber.

    Road closed foremergency repair.

    CPT carried out to

    confirm no cavities

    under road.

    TBM Launching

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    TBM Launching

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    TBM Launching or Docking

    Ground treatment for TBM launching /

    docking: TBM Length + One Ring Length

    Quality control of ground treatment

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    Interface between Stable & Weak Soils

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    600mm of

    settlement

    on CTE

    due to

    DTSS

    tunnelling

    Interface between Stable & Weak Soils

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    Weak ground / strong, stable ground

    Face pressure governed by overlying

    weak ground

    Interface between Stable & Weak Soils

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    IDEALISED PROFILE IN GRANITE

    Interface between Rock & Soil

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    Interface between Rock & Soil

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    Flushing of the annular gap

    Water ingress

    Limit of EPB Technology

    Coarse granular

    material / rocks

    Insufficient fines to form

    plastic plug

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    Good EPB Spoil

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    Difficult to Turn a Mixture of Cut Rock and Granular Spoil into EPB Spoil

    May Be Unable to Maintain Target Pressure

    Cut Rock & Granular Spoil

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    Interface between Rock & Soil

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    Interface between Rock & Soil

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    Mixed face of strong or very strong rock

    with flowing or squeezing soils

    Predominantly granular spoil

    Need to have high face pressure, but spoil

    does not readily form a plug in EPB

    machines

    Interface between Rock & Soil

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    Cutterhead Intervention

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    Over-excavation by Slurry TBM

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    Feeding Pipe

    Discharge Pipe

    Flow meterDensity meter

    Excavation Management System

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    Normal Excavation Condition Over Excavation Condition

    Excavated

    Qty(Cum)

    Jack Stroke (m)

    Theoretical

    Value

    Theoretical

    Value

    Jack Stroke (m)

    Excavate

    dQty(Cum)

    Excavation Management System

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    Base Stability of Excavation

    Hydraulic uplift

    D D

    Uk1

    k2

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    Base Stability of Excavation

    Example of hydraulic uplift failure reported by Davies (1984)

    Hydraulic uplift

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    Base Stability of Excavation

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    Shaft Excavation

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    Base Stability of Excavation

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    Base Stability of Excavation

    B St bilit f E ti

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    Base Stability of Excavation

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    Gaps in Retaining Walls

    Soil stability in the gaps

    marine clay squeezing through the gaps into

    excavation, causing localized soil collapse

    Large ground settlements at areas with

    gaps in diaphragm walls

    Water leaking through the gaps into the

    excavation

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    Gaps in Retaining Walls

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    Gaps in Retaining Walls

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