由于斜坡场地存在初始剪应力的作用，在强地震动作用下比水平场地更易发生液化大变形破坏，研究初始剪应力对土体液化大变形特性的影响是必要的。以饱和粉土为研究材料，开展了一系列单幅剪应变达到50%的循环扭剪试验。试验结果表明：在初始剪应力和循环剪应力的共同作用下，饱和粉土试样均发生孔压达到有效围压的零有效应力状态现象，累计变形呈平缓—急剧的发展模式，土体大变形的产生机制可区分为2种：循环液化和应变累计。随着初始剪应力比的增加，饱和粉土的循环强度呈现先减小后增大的特征，且在初始剪应力比接近循环应力比CSR时其循环强度最低。

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.