Abstract
Initial shear stress induced by nearby slopes, embankments and structures causes shear deformation in the ground, leading to sliding, tilting and uneven settlement of the structures due to liquefaction. In this study, a hollow torsional shear apparatus is used to study the effect of initial shear stress acting either on horizontal plane (θ0=0) or on inclined plane (θ0=45) on liquefaction behavior of medium to loose sand of relative density Dr≒30, 50% and fines content Fc=0 - 30%. A series of test results have revealed that the liquefaction failure is categorized into four types; Cyclic Failure for α=0, Cyclic Biased Failre for small α (θ0=0), Biased Gradual Failure and Biased Sudden Failure both for larger α. Among the 4 failure types, it is important to pay special attention to BSF type, which may develop abrupt strain increase due to initial stress in the process of pore-pressure build-up by cyclic loading. In comparing with undrained monotonic loading tests, the mechanism how the abrupt BSF type failure differs from the gradual BGF type failure has been clarified, in view of the difference in volume contractility of loose sand containing NP fines under initial shear stress.
