*Quake Summit 2010 October 9, 2010

Centrifuge Testing and Parallel Numerical Simulations of Lateral Pressures MeasuredAgainst a Rigid CaissonPI: Scott M. Olsonco-PIs:Youssef HashashCarmine PolitoRAs: Camilo PhillipsMark MuszynskiAdvisory:Al Sehn Board Gonzalo CastroTom CoolingLelio Mejia

Knowledge GapTo 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 OverviewMeasure lateral spreading-induced pressures against a rigid foundation elementExplore novel approaches to mitigate effects of increase in lateral pressureUse physical modeling (centrifuge testing) and parallel numerical simulations to approach a solution

Project ApproachWe 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 shapeLiq. stratum Dr (%)

Pore fluidI-AAug 200840-50waterI-OJune 200940-50waterI-A2July 200940-50waterI-A3Jan 201040-50waterI-BJan 201040-50waterII-AMar 20101 40-50waterII-BApril 20101 40-50waterII-B2May 20103 40-50waterII-B3Aug 2010 40-50waterI-O2Sept 201040-50waterI-A4TBD65-75waterII-A2TBDTBD40-50waterI-O3TBD40-50water

Instrumentation Layout10

Tactile Pressure Pads

Test I-A3 Sand Displacement TrackingD.6.25mbgsB.1.25mbgsA.SurfaceC.3.75mbgs

Numerical ModelingNumerical 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 elementsGAP: 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

PWP and acceleration comparison : Location 3

PWP and acceleration comparison : Location 6

Pressure distribution against the caissonReference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

Pressure distribution against the caissonReference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

Pressure distribution against the caissonReference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

Pressure distribution against the caissonReference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

Pressure distribution against the caissonReference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

Pressure distribution against the caissonReference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

Pressure distribution against the caissonReference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

Pressure distribution against the caissonReference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

Pressure distribution against the caissonReference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

Pressure distribution against the caissonReference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

Pressure distribution against the caissonReference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

Pressure distribution against the caissonReference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

Pressure distribution against the caissonReference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

Pressure distribution against the caissonReference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

Pressure distribution against the caissonReference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

Pressure distribution against the caissonReference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

Pressure distribution against the caissonReference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

Pressure distribution against the caissonReference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

Pressure distribution against the caissonReference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

Pressure distribution against the caissonReference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

Pressure distribution against the caissonReference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

Pressure distribution against the caissonReference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

Net Pressure Comparison

ConclusionsAfter significant effort, the tactile pressure pads successfully captured lateral pressure distributions on the front and rear of the rigid caisson to allow net pressure evaluationDuring 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)/s'vo = 0.11During 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 depthOne 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

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