Seismic Isolation of Earth Retaining Walls

Using EPS Compressible Inclusions -

Results from Centrifuge Testing

Athanasopoulos-Zekkos, K. Lamote

and G. Athanasopoulos

Tuesday, 7 June 2011

4th International Conference on Geofoam Blocks in

Construction Applications, 6-8 June 2011, Lillestrom,

Norway

•Northridge earthquake (Ms= 6.8) Los Angeles, USA, 1994

•Kobe earthquake (Ms= 7.0) Japan, 1995

•Chi – Chi earthquake (Ms= 7.3) Taiwan, 1999

Cantilever type retaining wall

Gravity type retaining walls

SEISMIC FAILURES OF RETAINING WALLS

•Niigata earthquake (Ms= 6.8), Japan, 2004

•Kashmir earthquake (Ms= 7.6) Pakistan, 2005

Bridge abutment

Bridge abutment wing wall

Cantilever type retaining wall

SEISMIC FAILURES OF RETAINING WALLS

SEISMIC CODE PROVISIONS

Eurocode 8: Design of structures for earthquake resistance -

Part 5: Foundations, retaining structures and geotechnical aspects

SEISMIC CODE PROVISIONS

Eurocode 8: Design of structures for earthquake resistance -

Part 5: Foundations, retaining structures and geotechnical aspects

An extension of the known method of static earthquake reduction

Isolation against earthquake lateral thrust using EPS Compressible Inclusion

Can be applied to existing walls

Cost reduction ??

SCOPE

Gravity wallBridge

abutmentBasement

wall

Cantilever

wall

• Very small unit weight

(closed cells filled with air)

and strength

ratio

• High values of stiffness

• Small values of Poisson’s• Very large void ratio

RESEARCH

DIRECTIONS

Mechanical behavior of EPS under

static and dynamic loading

(experimental investigation )

Behavior of seismically

isolated retaining walls

(analytical/numerical investigation)

Physical model testing:

shaking table, centrifuge

(experimental investigation )

CENTRIFUGE TESTING

Weight of natural material is

artificially increased (utilizing the

centrifuge forces), thus making the

behavior of the small scale model

to duplicate the behavior of the

prototype structure.

• use of small-scale models to accurately

simulate prototypes with realistic soil stress

states and depths,

• repeatability of results for like models,

• direct observation of modes of failures and

deformations,

• ability to apply earthquake motions with a

wide range of magnitudes and frequency

contents,

• evaluation of empirical methods and

validation of numerical modeling techniques

Advantages of Centrifuge Testing:

CENTRIFUGE TESTING

Centrifuge Characteristics:

• nominal radius of 2.7 m

•a maximum payload of 1.5 tons

• an available bucket area of 1 m2

•capacity in terms of the maximum

acceleration multiplied by the

maximum payload is 150 g-tonne

• 1-D shaking table with maximum

payload mass of 250 kg and a

maximum centrifugal acceleration of

100 g

Center for Earthquake Engineering

Simulation (CEES) at Rensselaer

Polytechnic Institute (RPI) in Troy, NY,

part of the

NSF NETWORK FOR EARTHQUAKE

ENGINEERING SIMULATION (NEES)

TEST SETUP & INSTRUMENTATION

2 production tests: 1 test without EPS inclusion and 1 with EPS inclusion

TEST SETUP & INSTRUMENTATION

TEST SETUP & INSTRUMENTATION

16 Strain Gages

(8 per wall)

0.1

8m

(4.0

0m

)

TEST SETUP & INSTRUMENTATION

2 Tactile Pressure Sensors

24/07/2011

TEST SETUP & INSTRUMENTATION

24 Accelerometers

4 Lasers

TEST SETUP & INSTRUMENTATION

4 Settlement sensors (LVDTs)

Data Acquisition System

24/07/2011

MODEL CONSTRUCTION

Pluviator

Rigid Box

Tactile Pressure Pad

MODEL CONSTRUCTION

EPS compressible inclusion

Foundation and Backfill soil

was Nevada Sand

ρEPS=20kg/m3

18

0m

m

18mm

PRODUCTION TESTS

Frequency (Hz) Amplitude (g)

20.05

3

20.1

3

20.2

3

20.3

3

20.35

3

Dynamic excitation was a sinusoidal

1-D motion of varying amplitude and

frequency:

TEST RESULTS

Static Lateral Earth Pressures

No EPS Inclusion With tr=10% EPS Inclusion

TEST RESULTS

Total (Static+Dynamic) Lateral Earth Pressures through half a cycle of loading

for 0.2g at 2Hz.

No EPS Inclusion With tr=10% EPS Inclusion

?

CONCLUSIONS

1. Data from the two centrifuge tests performed is first dataset to be

produced for true scale physical tests of retaining walls seismically

isolated using EPS.

2. Preliminary processing of data indicate that the EPS inclusions

acted as a buffer and reduced the seismic earth pressures on the

wall.

3. The seismic isolation efficiency of the tr=10% EPS layer for the case

of 0.2g at 2Hz was found to vary between 10% and 50% along the

height of the wall, with the highest efficiency being at the mid height

of the wall.

4. The presence of the EPS inclusion also helped reduce the variation

of earth pressures during the dynamic excitation which could be an

additional benefit.

Thank you !