University of California, Berkeley
Grant: $297,798 - National Science Foundation - Jul. 22, 2009
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Award Description: Recent earthquakes have provided numerous examples of the devastating effects of earthquake surface fault rupture on structures. Several major cities are built in areas containing active faults that can break the ground surface (e.g., Los Angeles, Salt Lake City, San Diego, San Francisco, and Seattle). Along with the often spectacular observations of damage, examples of satisfactory performance of structures were also observed. These examples of satisfactory performance indicate that similar to other forms of ground failure, such as mining subsidence, effective design strategies can be developed to address the hazards associated with surface fault rupture. Through this research project the effects of surface fault rupture on building foundations will be investigated with the goals of developing sound analytical procedures for evaluating the hazard, providing guidance regarding effective design concepts for buildings that are built near active faults, and advancing promising ground improvement techniques for mitigating this hazard. Recently, several researchers have begun investigating this problem. However, they have not satisfactorily addressed all key issues. A rational analytical, design, and mitigation framework for addressing surface fault rupture should be developed. With the renewed interest in addressing this hazard, the proposed research project is both timely and critical to making advances in earthquake hazard mitigation. This research will focus on analyzing the response of different building foundations at sandy soil sites with different relative densities and thicknesses that are subjected to reverse or normal fault movements. The surface fault rupture problem will be studied as a soil-structure-interaction phenomenon as opposed to what is normally done, which is bedrock fault rupture propagation through soil in the absence of buildings. The explicit finite difference method will be employed using the nonlinear effective stress UBC-SAND model in FLAC, because valid insights can be garnered from this approach that can build upon findings from previous studies. The research plan starts with reevaluating existing field and experimental studies. Three well-documented field case histories and two comprehensive centrifuge studies will be used to gain insight and to establish benchmarks for the proposed analytical method. After calibrating the proposed finite difference method with its nonlinear soil model, a comprehensive numerical investigation of the effects of earthquake surface fault rupture on building foundations is performed. Three promising mitigation techniques in addition to the use of a thickened mat foundation will be explored. The analytical results will be interpreted and presented with fundamental insights and practice oriented recommendations. Several government agencies and professional committees are now reexamining existing policies or developing new policies to address the surface fault rupture hazard. Advancements in surface fault rupture hazard mitigation lag behind those for other forms of ground failures such as lateral spreading. This is primarily due to the overreliance on avoidance. However, not all faults can be avoided, and not all faults require strict avoidance if mitigation techniques can be shown to be effective in handling the ground deformation associated with minor fault movements. Effective mitigation and design procedures are required, and their use requires robust analytical procedures. Government officials and engineers/geologists have requested that effective mitigation strategies be developed to allow facilities to be built atop faults when necessary. The results of the proposed research project will meet a critical need in society and help urban planners address this hazard.
Project Description: This project was awarded with an August 1, 2009 start date. As of October 1, 2009, which is two months into the project, the initial work on Phase I of the study (i.e., Re-Evaluation of Field and Experimental Studies of Surface Fault Rupture) has commenced. During this two month period, an extra license to the computer program FLAC has been purchased to enable efficient computations. The earthquake surface fault rupture problem is being investigated as a soil-structure-interaction phenomenon using the explicit finite difference method in FLAC with the nonlinear effective stress UBC-SAND soil model. The UBC-SAND soil model is being exercised to better describe its capabilities and limitations. Recent field studies and applicable experimental studies of earthquake surface fault rupture are being collected so that they can be used to validate and calibrate the proposed analytical model. The project is soliciting the assistance of a dedicated graduate student researcher from the newly arrived graduate students in the Geo-Engineering program at UC Berkeley. An incoming graduate student who will stay for the PhD and work as the graduate student researcher on this project has not been identified yet.
Jobs Summary: 00 (Total jobs reported: 0)
Project Status: Less Than 50% Completed
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