Effect of initial static shear stress on the undrained cyclic behavior of saturated sand by torsional shear loading

With the aim of gaining a better understanding of the role which the static shear plays on the large-deformation behavior of saturated sand, a series of undrained cyclic torsional shear tests on saturated Toyoura sand specimens up to single amplitude shear strain of about 50 % were performed. Several hollow cylinder specimens at relative density of 44 - 48 % were tested while varying the initial static shear and the subsequent cyclic shear stress levels. Depending on the degree of stress reversal, the loading pattern could be classified into three groups: stress reversal, intermediate and non-reversal. The observed failure behavior of specimens could be distinguished into liquefaction and residual deformation failures depending on the magnitude of combined static and cyclic shear stress. It was found that the presence of static shear does not always lead to an increase in the resistances to liquefaction and strain accumulation: they could either increase or decrease with increasing the static shear depending on the magnitude of combined shear stress, the type of loading and the failure behavior. As well, the mode of development of large residual deformation changed in accordance with the failure behavior which the specimen exhibited