eps 2011 - 05. seismic isolation of earth retaining walls using eps compressible inclusions
TRANSCRIPT
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 !