饱和南京砂液化后循环加载的动力表观黏度分析

Apparent kinetic viscosity of saturated Nanjing sand due to liquefaction-induced large deformation in torsional shear tests

饱和砂土在地震作用下会发生液化变形,从而引起建立在其上的建(构)筑物发生破坏。为了对饱和砂土液化后大变形的流体特性进行研究,采用英国GDS公司的空心圆柱扭剪仪进行了饱和砂土液化后循环加载的流动性特性试验研究,在试验中循环加载直至双幅剪应变达到100%。通过对试验结果的分析,主要研究了初始静剪应力及有效围压对饱和南京砂液化后发生大变形时的流体特性的影响规律。研究结果表明:根据超孔压比确定的"零有效应力"状态末端试样其实已经进入剪胀阶段,即超孔压的反应与液化时"零有效应力"状态相比具有明显的滞后效应;初始静剪应力主要对饱和南京砂初始液化后的"零有效应力"阶段的表观黏度与剪应变率关系曲线的影响较大,反而对反向卸载段的关系曲线影响较小。同时,试验结果表明砂土液化后循环加载条件下砂土的流动性明显比单调加载条件下的流动性大的多。

The post-liquefaction dynamic flow deformation of saturated sand may cause severe damages on the ground and underground structures. To investigate the dynamic flow characteristics of the post-liquefied saturated sand, a series of undrained cyclic torsional shear tests on saturated Nanjing sand are conducted using the hollow column torsional shear apparatus by applying and measuring double amplitude shear strain up to about 100%. Based on the test results, how the effective confining pressure and the initial shear stress affect its dynamic flow characteristics in the liquefaction state is analyzed. The results show that the sample is actually in the dilation state at the end of "zero effective stress" determined by the excess pore pressure ratio. In other word, compared with the post-liquefaction "zero effective stress" state, the response of the excess pore pressure is hysteretic. The initial static shear stress has great effect on the apparent viscosity-strain rate relationship curves of saturated Nanjing sand in the "zero effective stress" state and the dilation state, while it has little effect on the apparent viscosity-strain rate relationship curves of saturated Nanjing sand in the reversal unloading state. Meanwhile, the easy flow property of saturated Nanjing sand under cyclic loading is obvious stronger than that under monotonic loading.