Effects of initial static shear on liquefaction and large deformation properties of loose saturated Toyoura sand in undrained cyclic torsional shear tests

This study focused on the role which static shear plays on the large deformation behavior of loose saturated sand during undrained cyclic loading. A series of undrained cyclic torsional shear tests was performed on saturated Toyoura sand specimens up to single amplitude shear strain exceeding 50%. Three types of cyclic loading patterns, i.e., stress reversal, intermediate and non-reversal, were employed by varying the initial static shear level and the cyclic shear stress amplitude. The observed types of failure could be distinguished into liquefaction (cyclic and rapid flow) and residual deformation by comparing both monotonic and cyclic undrained behavior. It was found that the presence of initial static shear does not always lead to an increase in the resistance to liquefaction or strain accumulation; they could either increase or decrease with an increasing initial static shear level depending on the type of loading pattern and failure behavior. In addition, according to the failure behavior which the specimens exhibited, three modes of development of large residual deformation were observed.