Abstract: Because initial static shear stress exists in a sloped ground, soil is more possible to be liquefied and largely deformed than the level ground when subjected to a strong earthquake. So it is necessary to study the effects of initial static shear stress on the liquefaction and large deformation of liquefied soil. A series of cyclic torsional shear tests examine the saturated silts. The single amplitude shear strain exceeds 50% in the tests. The testing results show that the pore pressure of the specimens can reach the effective confining pressure under the combined effect of initial and cyclic shear stresses, namely the effective stress equals zero. Moreover, it is found that the cumulative strain increases gently during initial stage, and grows greatly later. Two types of large deformation of saturated silt can be distinguished: the cyclic liquefaction and the cumulative strain. At the same time, it is shown that, the cyclic shear strength decreases with the increasing of initial static shear stress ratio until initial static shear stress ratio reaches cyclic shear stress ratio, and starts to increase thereafter.

Key words: saturated silt liquefaction, large deformation, initial static shear stress ratio, cyclic shear stress ratio, cyclic shear strength