Oasys User Group ForumNumerical Modelling of

Soil-structure Interaction Problems

Hoe Yeow

SoftwareIn-house Oasys SAFE for 2D problems

Propped excavation Berm excavation Tunnel & tunnelling

-20.00 20.00 60.00 100.0

X [m]Scale x 1:500 y 1:500

-5.000

.0

5.000

10.00

15.00

20.00

25.00

Y [m

]

Façade model Embankment and slope

SoftwareBP00.1

In-house Oasys LS-Dyna for 3D problems (PC based)

Car crash Air bag

Gravity foundation Tunnelling Piled raft

BRICK soil modelState of the art non-linear, small strain fine grain soil model(Simpson 92)

London ClaySingapore Marine ClayFlorence claysBangkok clays Hong Kong CDG (back analyses only)

Why Numerical Modelling? HP000.1

• Design requirements

• Economic design

• Justifying critical design

• Complex problems, evaluating risks

• Investigate failures

• Ground movement damage assessments

• Client’s requirements

Design Requirements (Potts and Zdravkovic, 1999)

Economic DesignBP00.1

2m

HomogeneousIsotropicclay

1m

= 20kN/m3

d

1m c5kPa25 = 0.67sw = 0

8m

1

3

5

7

9 8.7m

7.3m

6.0m

LE PseudoFE FE/FD

Wa

ll E

mb

ed

me

nt

d (

m)

500

1000

1152

837734

LE PseudoFE FE/FD

Cal

cula

ted

Max

imum

ULS

Wal

l BM

(kN

m/m

)

• minimum saving of £860,000• reduction of excavation programme

from 15 months to 6 months

page 145 …..

… combined numerical modelling and observation methodValue for money - Batheaston Bypass BP00.1

(1998)

Value for money – Canary Wharf Piled Raft BP00.1

• Base grouted bored pile (capacity m)• Raft action to increase mean effective stress• Savings of 30% in piling cost• Complex soil-structure interaction

Justifying critical design and approval BP00.1

Metsovitikos Bridge (original design)

Tunnelling operation

- complex ground conditions- highly 3D- slope stability- ubiquitous joint model

- complex SCL sequence(previously known as NATM)

- large excavation next to existing tunnels

Gravity anchor foundation

Ashford Box Design (1.8km cut and cover, 15m deep)BP00.1

• Non-symmetrical• Interaction btw. walls• Permanent under slab

drainage system• Permeability, kh > kv• Observation method

Complex problem, evaluate construction risks and approval

RC bored pile, 1.8m diameter

Steel tunnel 3.68m diameter, 0.508m segment width, 124mm flange thickness

Each elementis 0.508m wide,to represent a segment

Horizontal displacement

Deformed shape

200x magnified

Investigate failure BP00.1

Hull tunnel

Heathrow Express Tunnel Collapse

Ground Movement & Damage Assessments BP00.1

Excavation

Computedtunnel’sdistortion

Effects on existing tunnels

Britannic House

Client’s requirements (Florence TAV Station, Italy)

Tension piles

Pseudo-FEFREW

Railway loading

• Non linear, small strain soil model

• Coupled consolidation• Compare with pseudo-FE

computation

Non-linear soil model

Wall

28m

SAFE

Prop 1

Prop 2