Effect of initial static shear stress on liquefaction behavior of saturated silt

In order to investigate the role which the initial static shear stress plays in the liquefaction of saturated silt, a series of cyclic torsional shear tests are conducted. Three types of cyclic loading patterns, stress reversal, intermediate and stress no-reversal, are employed by varying the initial static shear level τ_s and the cyclic shear stress amplitude τ_cy. The observed failure state types of the samples can be distinguished into the cyclic liquefaction and the excessive accumulated permanent deformation according to whether the pore pressure of the samples reaches the effective confining one. The test results show that under the low initial static shear level, an increase in the ratio SSR of the initial static shear stress τ_s to the initial effective mean confining stress leads to a decrease in the cyclic shear strength. However, under the higher initial static shear level, an increase in SSR increases the cyclic shear strength. It is found that the growth mode of the pore pressure ratio depends on the combination of the initial and cyclic shear stresses. When SSR≤0.1, with the increase of τ_cy, the growth mode of the pore pressure ratio changes from a state of "fast-steady-sharp" to a state of "fast-steady". On the other hand, the growth mode of the pore pressure ratio is in a state of "fast-steady" when SSR>0.1.