Quake Summit 2010 October 9, 2010

1. Centrifuge Testing and Parallel Numerical Simulations of Lateral Pressures Measured Against a Rigid Caisson Quake Summit 2010 October 9, 2010 PI: Scott M. Olson co-PIs: Youssef Hashash Carmine Polito RAs: Camilo Phillips Mark Muszynski Advisory: Al Sehn Board Gonzalo Castro Tom Cooling Lelio Mejia

2. 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

3. 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

4. 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)

5. Testing Schedule

6. Instrumentation Layout 10

7. Tactile Pressure Pads

8. Test I-A3 Sand Displacement Tracking B. 1.25m bgs A. Surface D. 6.25m bgs C. 3.75m bgs

9. 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

10. Laminar Ring (Free Field) Displacement

11. PWP and acceleration comparison : Location 1

12. PWP and acceleration comparison : Location 3

13. PWP and acceleration comparison : Location 6

14. Pressure distribution against the caisson Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

15. Pressure distribution against the caisson Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

16. Pressure distribution against the caisson Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

17. Pressure distribution against the caisson Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

18. Pressure distribution against the caisson Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

19. Pressure distribution against the caisson Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

20. Pressure distribution against the caisson Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

21. Pressure distribution against the caisson Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

22. Pressure distribution against the caisson Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

23. Pressure distribution against the caisson Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

24. Pressure distribution against the caisson Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

25. Pressure distribution against the caisson Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

26. Pressure distribution against the caisson Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

27. Pressure distribution against the caisson Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

28. Pressure distribution against the caisson Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

29. Pressure distribution against the caisson Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

30. Pressure distribution against the caisson Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

31. Pressure distribution against the caisson Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

32. Pressure distribution against the caisson Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

33. Pressure distribution against the caisson Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

34. Pressure distribution against the caisson Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

35. Pressure distribution against the caisson Reference PWP and tactile pressure pad measurements at 2.5 m, 5.0 m and 7.5 m bgs

36. Net Pressure Comparison

37. 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)/s'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

38. 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