初始剪应力对饱和粉土液化特性影响试验研究

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

为探寻饱和粉土的液化特性,利用GDS空心圆柱仪进行了一系列循环扭剪试验。在初始剪应力τs和循环剪应力τcy共同作用下,试样的最小剪应力τmin=τs-τcy存在3种类型：τmin〈0,τmin=0和τmin〉0。试验结果表明：当τmin≤0时,试样的孔压可以达到有效围压,其破坏模式为循环液化;当τmin〉0时,试样的孔压始终达不到有效围压,其破坏模式为过大的累计应变。饱和粉土的循环强度随着初始剪应力τs与初始有效平均主应力0p′之比值SSR（初始剪应力比）的增加呈现出先减小后增大变化趋势,且SSR=0.1~0.15时的循环强度最低。当SSR≤0.1时,孔压比的发展模式随着循环剪应力比的增加由＂快—平稳—急剧＂的增长模式向＂快—平稳＂的增长模式转变;当SSR〉0.1时,孔压比的发展呈现＂快—平稳＂的增长模式。

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 τs and the cyclic shear stress amplitude τcy. 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 τs to the initial effective mean confining stress 0p′ 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 τcy, 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.