饱和砂土排水与不排水剪切特性的比较研究

针对相对密度为30%的福建标准砂,利用土工静力-动力液压-三轴扭转多功能剪切仪,进行了复杂初始固结条件下应力路径变化的应力控制式单调排水与不排水剪切试验。试验过程中,控制平均主应力保持不变,分别探讨在排水与不排水条件下中主应力系数和主应力方向角对饱和砂土剪切特性和强度的影响。通过对比表明:在排水与不排水试验中,与排水条件无关,中主应力系数对归一化的应力—应变关系具有影响,但对体变或孔压的影响并不明显;当其余初始条件相同时,偏应力比随中主应力系数的增大而降低。主应力方向角的影响同样显著,排水试验的主应力方向角不同时,应力—应变关系所表现出的变化规律取决于水平面与竖直面上受到的剪应力作用,相变及峰值偏应力比和内摩擦角与主应力方向角之间存在抛物线型关系。不排水试验的峰值有效偏应力比随着主应力方向角的增大而减小。同时,对于不同的主应力方向,排水条件改变会影响试验得到的抗剪强度指标。

A Comparative Study on Drained and Undrained Shear Behavior of Saturated Sands

Various stress-controlled drained and undrained monotonic shear tests on the Chinese Fujian standard sand of relative density 30% under complex initial consolidation conditions with different stress paths are conducted by using the soil static and dynamic universal triaxial and torsional shear apparatus. The mean principal stress is controlled unchanged in the process of tests. The coefficient of intermediate principal stress and orientation of principal stress are varied so that their influences on shear behavior and strength of saturated sand under drained and undrained conditions are respectively explored. It is shown through comparison that the coefficient of intermediate principal stress influences the stress-strain normalization relationship,but does not make obvious effect on volumetric deformation as well as pore-water pressure. Under the same initial condition,the deviator stress ratio reduces with the increase of coefficient of intermediate principal stress. The above-mentioned phenomena do not relate to the drainage condition. Orientation of principal stress also influences remarkably on monotonic shear features of sand. In drained tests,variation pattern of stress-strain relationship which is associated with the orientation of principal stress depends on shear stresses on horizontal plane and vertical plane. Furthermore,the deviator stress ratios (or the frictional angles) at phase transformation state and at peak state are all of parabolic relation with the orientation of principal stress. In undrained tests,the effective deviator stress ratio attained at peak state reduces gradually with the increase of orientation angle of the principal stress. Meanwhile,for different orientations of principal stress,the shear strength indices obtained in the tests are affected by the variation of drainage conditions.