松砂不稳定行为的数值模拟研究

针对松散砂土的不稳定行为和静态液化现象，开展了一系列的双轴剪切试验离散元数值模拟，从宏细观的角度研究了松砂不稳定行为的各种影响因素及其发生机理。通过数值模拟发现，砂土的不稳定行为不仅与初始孔隙比有关，而且与土体结构的各向异性和围压有关。当加载方向与由颗粒接触法向所表征的结构各向异性主方向不共轴时，不稳定行为的发生会同时伴随着各向异性主方向的旋转。两个方向的角度差愈大，不稳定行为愈容易发生，颗粒的细观运动和细观结构重组现象也愈剧烈。不稳定状态点处的剪切荷载主要由颗粒间法向接触力承担，切向接触力仅起次要作用。

Numerical study on instability behavior of sand

The instability behavior and static liquefaction of loose sand are investigated by conducting a series of discrete element method (DEM) simulations in biaxial shear tests. The essential factors affecting the initiation of instability behavior are examined from both macroscopic and microscopic perspectives. The numerical simulation results reveal that the instability behavior of loose sand relies on the initial void ratio and fabric anisotropy as well as confining pressure. It is found that the initiation of instability is generally accompanied by the rotation of principal direction of fabric anisotropy if the loading direction does not coincide with the principal direction of fabric anisotropy which is characterized by normal contact unit. The larger the deviation between these two directions is, the easier the initiation of instability behavior becomes and the more intense particle rearrangements and microstructure reorganizations are expected to be as well. At the instability state, most deviatoric shear loads are carried by normal forces at contacts, and tangential forces merely play a secondary role.