1 Quake Summit 2010 October 9, 2010 Centrifuge Testing and Parallel Numerical Simulations of Lateral Pressures Measured Against a Rigid Caisson PI: Scott

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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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~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


L igh tly cem enteddense sand


C aisson

13

6

9

25

4

2 D eg.

Input m otion

C aisson




C aisson

13

6

9

25

4

2 D eg.

Input m otion

C aisson



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

Documents

1 Quake Summit 2010 October 9, 2010 Centrifuge Testing and Parallel Numerical Simulations of Lateral Pressures Measured Against a Rigid Caisson PI: Scott