A comprehensive testing database composed of modeling-quality, bi-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 incorporated a variety of never before examined bi-directional stress paths on both level and sloping ground.
Results from these tests have proved useful for enhancing current understanding of liquefaction behavior by allowing a more complete theory to emerge. This new multi-directional theory greatly expands current understanding of liquefaction behavior and elucidates some areas in which current theory - which has been based principally on uni-directional testing - can be misleading or unconservative. Of particular interest are the topics of (a) pore pressure generation as a function of loading magnitude and direction (b) the effects of sloping ground conditions, and (c) the post-liquefaction pore pressure behavior within each cycle.
This paper also describes the impact of bi-directional loading on maximum achievable pore pressures and reexamines the classic pore-pressure based definition of liquefaction as ru=1.0 in light of recent results.