Effects of Void Redistribution on Liquefaction Flow of Layered Soils

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0070111Kutter, Bruce L.The assessment the post-liquefaction shear resistance behavior of soil is widely recognized as a controlling factor in many large remediation projects throughout the country and world. Decisions on whether to proceed with costly ground improvement projects to mitigate liquefaction hazards often hinge on highly uncertain estimations of post-liquefaction shear resistance of the soil. The objective of these research projects is to better understand the sources of uncertainty.One likely source of uncertainty is the lack of procedures to evaluate the effects of void redistribution on the post-liquefaction shear strength. Void redistribution may be associated with accumulation of earthquake induced pore pressures near interfaces between permeable and impermeable soil and by particle intermixing. A program of dynamic centrifuge modeling tests and laboratory triaxial tests are proposed, in collaboration with a proposed program of l-g shaking table tests conducted by Professor Kokusho at Chuo University, Japan, to study this problem. The centrifuge tests, to be conducted on the 9 m centrifuge at UC Davis will include models with multiple layers of contracting permeability.Professor Kokusho of Chuo University, Japan has observed flow failures and the formation of water interlayers beneath impermeable layers even in steeply sloping ground. Water interlayers, an extreme form of void redistribution raise serious questions regarding validity of typical stability calculations. Collaboration with Professor Kokusho will greatly enhance the benefits of this research by allowing comparisons between shaking table and centrifuge tests over a range of testing conditions.The proposed work includes funding to support, train, and provide valuable experience to graduate and undergraduate students. The MESA, MORE and WIE programs at UC Davis have agreed to help recruit a diverse pool of applicants for the undergraduate positions. The opportunities for students to design, conduct and analyze the large-scale experiments and to meet renowned experts from the US and Japan will be an extremely valuable.This project is supported under the 3rd-year competition under NSF 98-36. "US Japan Cooperative Research in Urban Earthquake Disaster Mitigation."