双向耦合剪切条件下饱和松砂的液化特性试验研究

Liquefaction of sand under bi-directional cyclic loading

为了模拟海床及海洋建筑物遭受波浪荷载时所引起的循环应力,进行了一系列均等固结条件下的应力控制式轴向–扭转双向耦合循环剪切试验。加载路径在σd/2-τ应力空间内为椭圆。试验在保证椭圆面积不变的情况下,分别变化竖向和扭转向的荷载分量幅值,以此来探讨双向耦合剪切试验中各个分量的变化对饱和松砂的循环强度特性的影响。试验结果表明砂土在双向耦合荷载作用下,其液化强度与加载椭圆路径的面积和两个荷载分量比值密切相关。当轴向应力与剪应力幅值的比值保持不变时,砂土液化强度随着椭圆面积的增大而降低。而在椭圆面积保持不变时,当竖向与扭转向荷载分量的比值小于某一临界值0.6～0.75时,砂土液化强度随着比值的增加而增大,当竖向与扭转向荷载分量的比值大于某一临界值0.6～0.75时,砂土的液化强度随着比值的增加而减小,在临界值0.6～0.75之间表现出最高的强度。另外,在一个周期内孔隙水压力的循环变化与轴向应力相位一致,与循环剪应力相位相差90。

A set of stress controlled bi-directional cyclic loading tests under isotropic consolidated condition was conducted for simulating the cyclic stress induced by wave loading. The stress path followed during the test in terms of σd/2 and τ- was controlled in shape of ellipse. The area bounded by the elliptical stress path was kept unchanged while the amplitude of the axial and torsional shear stresses were varied to study the effect of two components on the strength and deformation behavior of saturated loose sand. It was shown that the resistance to liquefaction of saturated sand was considerably related with both the area of elliptical stress path and the ratio of the two stress components. For the same ratio of two stress components, the resistance to liquefaction of saturated sand decreased with the increasing area of the elliptical stress path. However, for the same area of elliptical stress path, the sand might exhibit the highest resistance to liquefaction at a critical ratio of axial and torsional shear stresses, 0.6-0.75. The resistance to liquefaction increased with the increasing ratio of σd/2 and τ when the ratio was less than the critical value, and decreased with the increasing ratio of σd/2 and τ when the ratio was larger than the critical value. Moreover, the pore water pressure developed gradually to the initial effective confining pressure with transient fluctuation and phase matching axial load.