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Quake Summit 2010 October 9, 2010
Centrifuge Testing and Parallel Numerical Simulations of Lateral Pressures Measured
Against a Rigid Caisson
PI: Scott M. Olsonco-PIs: Youssef Hashash
Carmine PolitoRAs: Camilo Phillips
Mark MuszynskiAdvisory: Al Sehn Board Gonzalo Castro
Tom CoolingLelio Mejia
Knowledge Gap
To handle increasing infrastructure demand modern structures often require large dimension, rigid foundations
Engineers lack the design tools to predict the forces on large foundations resulting from seismic ground failure
Often resort to conservative designs that increase cost & time, environmental disturbance, and may increase permitting issues
Project Overview
Measure lateral spreading-induced pressures against a rigid foundation element
Explore novel approaches to mitigate effects of increase in lateral pressure
Use physical modeling (centrifuge testing) and parallel numerical simulations to approach a solution
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Laterally spreadingliquefied sand
Clay
1995 Kobe EarthquakeRokko Liner Bridge©EQE International
Large dimension foundation
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Zone ofimprovedsoil Caisson
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~Layer susceptible toground failure
Non-yielding layer
Overlying layer (?)
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Zone ofimprovedsoil Caisson
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Zone ofimprovedsoil Caisson
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~Layer susceptible toground failure
Non-yielding layer
Overlying layer (?)
Project Approach
We are using the physical experiments and numerical simulations with a “learned” soil model in an integrated fashion to optimize the design of future experiments and simulations (EDS-SDE)
Testing Schedule
Model ID
Date conducted
Caisson used
Clay cap
Deflection wall
Deflectionwall shape
Liq. stratum Dr (%)
Pore fluid
I-A Aug 2008 40-50 water
I-O June 2009 40-50 water
I-A2 July 2009 40-50 water
I-A3 Jan 2010 40-50 water
I-B Jan 2010 40-50 water
II-A Mar 2010 1 40-50 water
II-B April 2010 1 40-50 water
II-B2 May 2010 3 40-50 water
II-B3 Aug 2010 40-50 water
I-O2 Sept 2010 40-50 water
I-A4 TBD 65-75 water
II-A2 TBD TBD 40-50 water
I-O3 TBD 40-50 water
Instrumentation Layout
10
C aisson
13
6
9
25
4
2 Deg.
Input m otion
C aisson
N evada sandD r=40% -45%
L ightly cem enteddense sand
Tactile Pressure Pads
Test I-A3 Sand Displacement Tracking
D.6.25mbgs
B.1.25mbgs
A.Surface
C.3.75mbgs
Numerical Modeling
Numerical models (2D and 3D) have been developed for each centrifuge test configuration using OpenSees (McKenna and Fenves 2001) and the soil models developed at the UC-San Diego (Yang et al. 2003).
The model results (in terms of displacements and soil behavior close to the caisson) are very sensitive to the numerical procedure used to define the soil-caisson interface. We focused on two types of soil-caisson interfaces:
- EOF: equal degree of freedom (translation) between the nodes of the soil and the caisson elements
- GAP: use a connection element with limit force capacity between the soil and the caisson nodes which is able to transfer compression forces but cannot transfer tension forces to the soil elements
Laminar Ring (Free Field) Displacement
PWP and acceleration comparison : Location 1
C aisson
13
6
9
25
4
2 D eg.
Input m otion
C aisson
N evada sandD r=40% -45%
L igh tly cem enteddense sand
PWP and acceleration comparison : Location 3
C aisson
13
6
9
25
4
2 D eg.
Input m otion
C aisson
N evada sandD r=40% -45%
L igh tly cem enteddense sand
PWP and acceleration comparison : Location 6
C aisson
13
6
9
25
4
2 D eg.
Input m otion
C aisson
N evada sandD r=40% -45%
L igh tly cem enteddense sand
Pressure distribution against the caisson
Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs
Pressure distribution against the caisson
Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs
Pressure distribution against the caisson
Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs
Pressure distribution against the caisson
Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs
Pressure distribution against the caisson
Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs
Pressure distribution against the caisson
Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs
Pressure distribution against the caisson
Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs
Pressure distribution against the caisson
Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs
Pressure distribution against the caisson
Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs
Pressure distribution against the caisson
Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs
Pressure distribution against the caisson
Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs
Pressure distribution against the caisson
Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs
Pressure distribution against the caisson
Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs
Pressure distribution against the caisson
Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs
Pressure distribution against the caisson
Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs
Pressure distribution against the caisson
Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs
Pressure distribution against the caisson
Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs
Pressure distribution against the caisson
Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs
Pressure distribution against the caisson
Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs
Pressure distribution against the caisson
Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs
Pressure distribution against the caisson
Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs
Pressure distribution against the caisson
Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs
Net Pressure Comparison
Conclusions
After significant effort, the tactile pressure pads successfully captured lateral pressure distributions on the front and rear of the rigid caisson to allow net pressure evaluation
During shaking, the median pressure distribution on the upslope side of the caisson approached the undrained passive envelope developed using a liquefied strength ratio, su(liq)/'vo = 0.11
During shaking, the median pressure distribution on the downslope side of the caisson remain near Kactive. This is attributed to the general inertial effects at that location, along with possible drainage during the shaking
Conclusions (cont.)
The net pressure on the caisson is greater than that predicted using JRA and is similar to the pressure distribution observed by He et al. (2009) in the upper 3 m of the profile but begins to deviate at greater depth
One of the key elements to correctly simulating the model behavior using OpenSees is defining the soil-pile interface. There are different procedures to simulate the behavior at the soil-pile interface. The use of GAP element with limited force capacity is able to reproduce the boundary displacements, pore water pressure and acceleration time histories at different depths recorded in Test I-A3. We continue working to improve the procedure to properly model the soil – ground improvement interaction