复杂应力条件下饱和砂土排水剪切强度的试验研究

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，在不同初始固结条件下控制试验过程的平均主应力保持不变，改变中主应力系数和主应力方向，进行了应力控制式单调排水剪切试验，着重探讨中主应力系数和主应力方向对砂土剪切强度的耦合影响。试验结果表明：在相同的试验条件下，中主应力系数对饱和标准砂的应力-应变关系具有影响，但对体变特性的影响并不明显。上述现象同初始固结应力比的大小无关。平均主应力一定，广义剪应力随中主应力系数增大而降低的趋势同时依赖于主应力方向的作用。中主应力系数对内摩擦角的放大效应同样受到主应力方向的影响。基于广义双剪应力准则，引入考虑主应力方向影响程度的权重系数，结合试验结果给出了考虑中主应力系数和主应力方向耦合影响的强度指标表达式。

Experimental research on behaviors of saturated sand subject to drained shear strength under complex stress conditions

The experimental tests of Fujian standard sand with relative density of 30 % are performed by using soil static and dynamic universal triaxial and torsional shear apparatus. A series of stress-controlled drained monotonic shear tests are conducted under complex stress conditions with constant mean principal stress. The coefficient of intermediate principal stress and orientation of principal stress are varied so that their coupled influences on shear behaviors of saturated sand are explored. Based on the comparative experimental results, under the same initial condition, coefficient of intermediate principal stress influences the stress-strain relationship of saturated sand, but does not make obvious effect on volumetric strain features. It is shown that the drained shear behaviors of sand are not dependant on consolidation stress ratio and considerably depend on coefficient of intermediate principal stress as well as orientation of principal stress. Furthermore, both coefficients of intermediate principal stress and orientation of principal stress affect friction angles at phase-transformation state(PTS) and at peak state. Finally, introducing a factor for weighing the influence of orientation of principal stress, and combining with the test results, an expression for strength indices taking coupled effect of coefficient of intermediate principal stress and orientation of principal stress into account is obtained by using generalized twinshear stress criterion.