斜椭圆应力路径下饱和松砂动力特性试验研究

利用空心圆柱扭剪仪模拟斜入射地震波作用形成的斜椭圆应力路径，对比研究了等向固结条件下饱和福建标准松砂在循环斜椭圆、圆形、扭剪、三轴路径下的动力特性。试验研究表明：土体循环孔压发展存在陡升型和陡降型两种模式；圆形路径下累积孔压增长速率最快，循环扭剪最小；归一化孔压与斜椭圆的倾角无关，但受斜椭圆长短轴比及动应力比影响。砂土的不排水动强度与动应力路径密切相关，循环扭剪和循环三轴最大，循环斜椭圆次之，圆形路径最小。地震波从特定角度入射时，形成近似圆形路径，若只将地震波视为垂直入射的S波，将高估地基土体抗液化强度。

Experimental research on behaviors of saturated loose sand subjected to oblique ellipse stress path

A set of tests with the hollow cylinder apparatus are conducted to simulate the oblique incident seismic waves. Tests are performed with two cyclic stress components involving the horizontal shear stress (torsional shear stress) and the vertical shear stress (stress difference between vertical normal stress and horizontal normal stress) to show an elliptical shape in the orthogonal coordinates of stress difference and shear stress. Then the dynamic characteristics of saturated Fujian standard loose sand, consolidated under isotropic undrained condition and applied with cyclic oblique elliptic stress path, cyclic circular shear, cyclic torsional shear and cyclic triaxial path, are studied. The experiment results show that the development of elastic pore pressure can be classified as “sharp dropping type” and “sharp rising type”. The cumulative rates of excess pore water pressure under cyclic circular shear and under cyclic torsional shear are the fastest and the slowest respectively. The normalizing pore pressure is independent of inclination angle of the obliquity of elliptic path, but depends on the ellipticity of cyclic stress path and stress amplitude CSR. Experimental results also indicate that undrained dynamic strength of Fujian sand is closely related to cyclic stress path. The cyclic torsional shearing path and cyclic triaxial path have the highest dynamic strength. The strengths under standard inclined elliptical loading path and under cyclic circular path are lower and the lowest respectively. Approximate circular path can be generated with seismic wave in a particular incident angle. If seismic wave is regarded as vertical incident S wave, the soil liquefaction strength would be overestimated.