Modeling Strain-rate Dependent Multidirectional Cyclic Behavior of Soft Clay
Advisor:
Juan M. Pestana
Research Student:
Tawat Anantanavanich
(e-mail: )
In recent years, the continuing development of natural resources beneath the continental shelf and slope, the pressure on coastal development, and the protection of the submarine environment have contributed to the emerged effort in better understanding the phenomena of seismic triggering submarine mass movements and their potential consequences such as tsunamis.
This work examines the response of normally consolidated to lightly overconsolidated soft clay in submerged slopes subjected to multidirectional seismic excitation under simple shear stress condition. Evidences from laboratory tests on cohesionless soil have indicated that the multidirectional effects are very important on the response of sand associated with larger deformation and higher amount of pore pressure. For the first time, the experimental studies from element level tests of the multidirectional effects on both monotonic and cyclic behavior of soft clay were performed. A simple effective stress constitutive relation to describe the response of soft clay under anisotropic multidirectional simple shear conditions was developed. The model is able to describe changes in undrained shear strength due to different initial conditions and directions of loading. In particular, the model has capabilities in predicting the rate-dependent behavior of soft clay by simple adjustments of some material parameters.
The proposed constitutive laws were implemented in a finite element program to evaluate the performance of submerge slope under multidirectional seismic excitation and assess their post-earthquake slope instability.
About Tawat
Education:
2006: Doctoral Candidate in Geotechnical Engineering, Department of Civil & Environmental Engineering, University of California at Berkeley.
2001: M.Sc., Geotechnical Engineering, Department of Civil & Environmental Engineering, University of California at Berkeley.
1999: B.E., Civil Engineering, Chulalongkorn University, Thailand
Selection and Modification of Ground Motion Time Histories
Advisor:
Norman Abrahamson
Research Student:
Jennie Watson-Lamprey
(e-mail: )
To obtain design time series, it is common practice to select empirical recordings of ground motion and modify them by scaling or by making them spectrum compatible. The computed nonlinear response of a system can vary greatly depending on the records selected even after making the time series spectrum compatible. A method of time series selection based on properties of the structure and ground motion, not simply magnitude and distance, is presented. The procedure is for use in nonlinear analyses that are intended to result in a median global nonlinear response given a design event.
In developing the time series selection procedure the structure specific properties are considered using a proxy of the non-linear system. Using a suite of recorded and scaled ground motions as inputs, a regression analysis is performed to develop a model for the proxy response based on the properties of the record and the proxy. Candidate scaled time series are evaluated to find those that have key record properties near their expected value and yield a response of the proxy that is near the expected response for an event. Those scaled time series with responses near the expected value are selected as the optimum time series for defining average response even if the scale factors are larger than commonly accepted.
Results for applications to structural response and slope stability are presented. The resulting time series selection methods allow for wider magnitude and distance bins for candidate time series, and reduce variability in the response of the system.
About Jennie
Education:
2005–present: Doctoral Candidate in Geoengineering, Department of Civil & Environmental Engineering, University of California at Berkeley. Advisor: Professor N. Abrahamson
2004: M.Sc., Geoengineering Program, Department of Civil & Environmental Engineering, University of California at Berkeley.
2002: B.A. in Geophysics, Columbia University, New York
Berkeley Geoengineering Alumni Association Newsletter Issue #1