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Challenges in Design and Construction of Deep Excavation With Case Studies - KVMRT in KL Limestone

Gue See SewG&P Professionals Sdn Bhd

www.gnpgroup.com.my

20 July 2016

CONTENTS

� INTRODUCTION� SOIL PARAMETERS� NUMERICAL ANALYSES� CASE HISTORIES

� 3 Underground Stations for KVMRT� Circular Shaft for Launching of TBM� Hydraulic Failure @ Penang

� CONCLUSIONS

INTRODUCTION

� Deep basement construction� Urban areas for parking space� Infrastructures, e.g. KVMRT

� Risk associated with deep basement construction high!

Human Size

Excavated depth24.5m - 28.5m (6-level basement)

Retaining wall1.2m thick diaphragm walls

FAILURES of DEEP EXCAVATION

Stress path of real soil

Stress path using Mohr-Coulomb

model

Overestimation of shear strength!!!

SOIL PARAMETERS

SOIL PARAMETERS

� Some important soil parameters related to retaining wall and support system design:�Shear strength parameters (su, φ’ & c’)�Soil permeability�Soil stiffness

SOIL PARAMETERS

� Soil stiffness� Important parameters for retaining wall design

BUT difficult to obtain reliably� In Malaysia, sometimes based on empirical

correlations�Laboratory tests unreliable and values

obtained significantly smaller than appropriate values for retaining wall design

�Designer should be aware of small-strainnature of retaining wall design

SOIL PARAMETERS

� Soil stiffness�Seismic tests or seismic piezocone appears

promising�Basis of empirical correlations should be

understood – e.g. local soil conditions, constitutive model used, etc.

�Example, correlations in Kenny Hill formation using hardening soil model of PLAXIS software

Field and laboratory methods to evaluate shear wave velocity

Soil Type Maximum small-strain shear modulus, G0 (kPa)

Soft clays 2,750 to 13,750

Firm clays 6,900 to 34,500

Silty sands 27,600 to 138,000

Dense sands and gravels 69,000 to 345,000

Typical values of maximum small-strain shear modulu s

NUMERICAL ANALYSES

GROUND MOVEMENT INDUCED BY DEEP EXCAVATION

FINITE ELEMENT ANALYSIS

� Some important considerations in FEM:�Locations of the boundaries of the problem�Details of mesh�Modelling of stages of construction�Modelling of interfaces�Use of suitable constitutive soil model�Use of appropriate soil parameters, especially

empirical parameters

CONSTITUTIVE SOIL MODELS

� Various constitutive soil models, e.g. Mohr-Coulomb, Cam Clay, Hardening Soil, Soft Soil, etc.�Proper understanding and limitations of

each model important!� Incorrect use of soil models in Nicoll Highway!

Berjaya Times Square

� Hardening Soil Model of PLAXIS able to model the problem sufficiently accurate

� From FEM back-analysis, the correlations between soil stiffness (E’) and SPT ‘N’ as follows:�E’ = 2000*SPT‘N’(kN/m 2)�E’ur = 3*E’ = 6000*SPT’N’(kN/m 2)

MONITORING TRIGGER LEVELS

To be developed based on specific project/site requ irements depending on factors such as risk to public safety, nature of

the works, site control measures, etc.

MONITORING TRIGGER LEVELS� Example for inclinometer:

� Alert : 0.8*Maximum predicted lateral movement using moderately conservative parameters

� Action : 0.9*Maximum predicted lateral movement using moderately conservative parameters

� Alarm : 1.0*Maximum predicted lateral movement using moderately conservative parameters


� Excavated depth24.5m - 28.5m (6-level basement)

� Retaining wall1.2m thick diaphragm walls

� Support systemPrestressed Ground Anchors

TYPICAL SUBSOIL PROFILE

FINITE ELEMENT MODELLING

-10 0 10 20 30 40Wall Relative Lateral Displacement (mm)

-50

-40

-30

-20

-10

0

Dep

th (m

)

Measured ProfileFEM Back Analysed

Excavate to R.L.35.0m

Stage 1


-50

-40

-30

-20

-10

0

Dep

th (m

)


Stage 2


-50

-40

-30

-20

-10

0

Dep

th (m

)

Stage 3



-50

-40

-30

-20

-10

0

Dep

th (m

)

Stage 4



-50

-40

-30

-20

-10

0

Dep

th (m

)

Stage 4



-50

-40

-30

-20

-10

0

Dep

th (m

)

Stage 6


WALL A


� Hardening Soil Model of PLAXIS able to model the problem sufficiently accurate

� From FEM back-analysis, the correlations between soil stiffness (E’) and SPT ‘N’ as follows:�E’ = 2000*SPT‘N’(kN/m 2)�E’ur = 3*E’ = 6000*SPT’N’(kN/m 2)

CASE HISTORIES

Case History 1 :Deep Excavation for Three (3) Underground Stations for KVMRT

– Sungai Buloh to Kajang Line (Line 1)

Locations of the MRT Underground Stations

Geology of Kuala Lumpur

All three underground stations in KL Limestone Formation (with Karstic Features)

Karstic Features of Kuala Lumpur Limestone Formation

Valley in the bedrock

Cavity in the Bedrock Highly fractured bedrock

Limestone Pinnacle

Typical Karstic Feature :

CAVERN/CAVITY EXPOSED AFTER EXCAVATION

Typical Karstic Feature :

Typical Excavation Section for Underground Station

(Note: Rock slope strengthening indicated is provisional only. Actual locations and extent of rock slope strengthening are determined after geological mapping works and kinematic analysis).

Subsoil Bedrock

Material type Silty Sand Limestone

Averagedepth

5m 5m below

Unit weight 18 kN/m3 24 kN/m3

SPT N 2 - 4 -RQD - 0 – 100%AverageUCS

- 50 MPa

Effectiveshearstrength

c’= 1 kPaɸ’= 29º

c’= 400 kPaɸ’= 32º

ElasticModulus,E' (kPa)

4000 -12000

1.0E6 –1.0E7

Hydraulicconductivity,k

1.0E-5 m/s

0 – 31 Lugeon

Conchrane Underground Station

Conchrane Station Bedrock Contour

Secant Pile Wall

Typical Secant Pile Wall Elevation View

Description PropertiesWorking loads (kN) 212; 424; 636; 848No. of strand 2; 4; 6; 8Strand diameter 15.24mmBreaking load 260.7 kNFactor of safety 1.6Strand U-turn radius 47.5mmReduction factor 0.65Drill hole diameter 175mmAllowable bond stress

400 kPa (limestone)

Free length Varies (until bedrock)

Bond length (m) 3; 3; 4.5; 6

Temporary Ground Anchor Support System

Grouted Layer

Curtain & Base Grouting to seal the Limestone Karstic Features

Typical Curtain & Base Grouting Holes Layout

Construction Sequence

1 2

3 4

Constrution Sequence (con’t)

5 6

7 8

Exposed Vertical Rock Face of the Excavation

Rock Bolting and Shotcrete.

Maluri Portal (excavation in progress)

Steel Decking for the Traffic diversion above @ Maluri

Maximum 25m deep

TRX Station (Excavation in Progres)

Maximum 45m deep

Conchrane Station (Excavation Stage)

Conchrane Station (Launching of 2 nd TBM)

Maximum 35m deep

Case History 2 :Circular Shaft for Launching of TBM

Circular TBM Launching Shaft

Circular Shaft during Excavation

Design Based on Hoop Force

<

Case History 3 :Hydraulic Failure @ Penang

100 Years Ago

The Site

Subsoil Profile

Original Design

Original Retaining Wall (Insufficient Depth)


Thickness of Clay insufficient to resist Water Uplift Pressure

Water Uplift Pressure


Water flowed through cracks in the Silty Clay

layer



Water Ponding in the Pit


Lowering of ground water level � Causing settlement to surrounding ground

The Site after FailurePonding of water

gushed in.

Cracks of Houses

Settlement of Ground

Groundwater Changes

0 5 10 15 20 25

Distance from Excavation / Depth of Excavation

-6

-4

-2

0

2

4

Red

uce

d L

eve

l (m

CD

)

Ground water level from Piezometer(Days from the date of investigation)

(28 days)

(49 days)

(84 days)

Ground Level

0 50 100 150 200 250 300

Distance from Excavation (m)

PZ 4PZ 5

PZ 1PZ 2

PZ 3

PZ 8

PZ 7

Estimated Original Groundwater Table

Ground level

Additional SettlementExcavation

Side Retained Side

Earlier settlement before investigation not available.

0 2 4 6 8 10 12

Distance from Excavation / Depth of Excavation

-30

-25

-20

-15

-10

-5

0

Additi

onal S

ettle

ment (m

m)

Settlement ProfileLine no. (Days from the date of investigation)

Line 3 (27 days)

Line 3 (62 days)

Line 4 (27 days)

Line 4 (62 days)

Line 5 (27 days)

Line 5 (62 days)

0 20 40 60 80 100 120 140

Distance from Excavation (m)

Remedial Works

HYDRAULIC FAILURE

� Base instability caused by piping�Seepage due to high groundwater level

� Available methods�Terzaghi’s method�Critical hydraulic gradient method

HYDRAULIC FAILURE CHECKS

HYDRAULIC FAILURE

� Terzaghi’s method recommended�Based on latest research by Tanaka &

Verruijt (1999)�Factor of safety required – 1.2 to 1.5

HEAVING DUE TO ARTESIAN PRESSURE

HYDRAULIC FAILURE

� Heaving due to artesian pressure

�Factor of safety – 1.0 to 1.2�Smaller FOS sufficient as it did not

consider shear strength or adhesion strength of the ground and retaining wall

Video of Hydraulic Failure

CONCLUSIONS

CONCLUSIONS

� Parameters & calibrations� Constitutive models� Impact of lowering water table & Mitigation

measures

Successful deep excavation depends on:

ACKNOWLEDGEMENTThe input from the following team members for KVMRT and in this presentation are very much appreciated:-

- Ir. TAN Yean Chin- Ir. CHOW Chee Meng- Ir. KOO Kuan Seng- TIONG Chiong Ngu- Ir. Dr. GUE Chang Shin

G&P Professionals Sdn Bhd

THANK YOU

G&P Professionals Sdn Bhdwww.gnpgroup.com.my

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