13 th World Conference on Earthquake Engineering Vancouver, B.C., Canada August 1-6, 2004 Paper No. 2081 SHEAR STRAIN DEVELOPMENT IN LIQUEFIABLE SOIL UNDER BI-DIRECTIONAL LOADING CONDITIONS Annie KAMMERER 1 , Jiaer WU 2 , Michael RIEMER 3 , Juan PESTANA 3 , and Raymond SEED 3 SUMMARY A comprehensive testing database composed of modeling-quality multi-directional cyclic simple shear testing on medium to high relative density, fully-saturated samples of Monterey 0/30 sand has recently been developed. This testing program incorporated a variety of multi-directional stress paths, including a large number of stress paths never before examined. Results from these tests have proven useful for enhancing current understanding of liquefaction behavior by allowing for a more complete theory to emerge. This new 3-dimensional theory greatly expands current understanding of liquefaction behavior and elucidates some areas in which current theory—which has been based principally on uni-directional laboratory testing—can be misleading or unconservative. Of particular interest are the topics of pore pressure generation and softening, the relationship between pore pressure and strain capacity, and the dilational lock-up in medium density sands that acts to limit large free-flow type deformations. Insight has also been gained on the complex effects caused by an initial static shear stress such as would be imposed by sloping ground conditions or the presence of a structure. INTRODUCTION In recent years, significant research effort has been focused on developing state-of-the-art constitutive soil models capable of accurately and reliably predicting the cyclic and permanent deformations of liquefiable materials over the small to moderate strain range (<1m). Unfortunately, the use of advanced constitutive soil models for liquefiable soils is being hampered by a lack of the high-quality laboratory testing for use in the validation of existing models and development of new ones. In particular, very little modeling- quality testing has been performed on: a) liquefiable materials experiencing multi-directional stress (or strain) paths, b) medium dense to dense sand that exhibits dilative behavior with limited strain potential and c) materials under initial “driving” shear conditions as would be found in sloping ground or under a structure. To address this need for modeling-quality data a program of simple shear testing was performed on medium to high relative density, fully saturated samples of Monterey 0/30 sand. The newly developed database that resulted is composed of two complementary series. The first consists of a comprehensive 1 Senior Geotechnical Engineer, Arup, San Francisco, California, USA. annie.kammerer@arup.com 2 Project Engineer, URS Corporation, Oakland, California, USA. jerry_wu@urscorp.com 3 Professor, University of California, Berkeley, California, USA. cegeot@ce.berkeley.edu