主应力方向循环变化对饱和松砂不排水动力特性的影响

Effect of variation of principal stress orientation during cyclic loading on undrained dynamic behavior of saturated loose sands

利用新研制的土工静力-动力液压三轴-扭转多功能剪切仪进行了主应力轴循环变化的多种模式竖向和扭转双向耦合循环剪切及普通循环扭剪试验。针对福建标准砂, 在均等固结条件下着重研究了振动过程中主应力方向的不同变化模式对饱和松砂不排水循环特性的影响。试验研究结果表明: 振动过程中主应力方向的变化方式对饱和砂土不排水动强度具有显著的影响, 在所采用的五种类型循环剪切应力路径中, 主应力方向连续旋转条件下的动强度最低。进一步的研究发现: 对于初始均等固结条件,分别采用初始平均有效固结压力和循环破坏次数归一化的循环孔隙水压力比与循环次数比之间的关系与振动过程中主应力方向变化方式无关, 这种归一化循环孔隙水压力比随广义剪应变的变化规律及累积广义剪应变与循环次数比之间关系均与振动过程中主应力方向变化方式无关。

The static and dynamic universal triaxial and torsional shear apparatus of soil recently equipped in Dalian University of Technology is used to perform five types of tests for loose sands subjected to triaxial and torsional coupling cyclic shear and simple torsional shear. The effect of variation of principle stress orientation under cyclic loading on undrained cyclic shear behavior of Fujian Standard loose sand under isotropic consolidation condition is investigated. It has been shown through comparative tests that the change of orientation of principal stress during cyclic loading has a considerable influence on undrained dynamic strength of saturated loose sands. The dynamic strength under the cyclic rotation of principal stress axes is lowest among those obtained with five given types of stress paths of cyclic loading. The relationship between excess pore water pressure induced during vibration normalized with the initial effective confining pressure and the ratio of number of cycles with the cyclic number required at failure is independent of the variation mode of direction of principal stress during cyclic loading. Furthermore, both the change of the normalized excess pore water pressure with generalized shear strain and the change of the generalized shear strain with ratio of number of cycles are irrelevant to the change of orientation of principal stresses.