不同沉积方向各向异性结构性砂土离散元力学特性分析

为探究沉积方向对各向异性结构性砂土力学特性的影响,首先采用椭圆颗粒生成两种不同沉积方向(水平与竖直)的各向异性净砂样,其次,引入一个考虑胶结厚度影响的微观胶接触模型从而生成各向异性结构性砂土。最后,对两种各向异性结构性砂土试样进行双轴压缩试验,并将水平沉积试样试验结果与室内试验结果对比验证该模型的可行性。同时,将两种不同方向试样的试验结果进行对比以探究沉积方向的影响。结果表明:两种试样应力–应变关系均呈软化及剪胀现象,水平沉积试样峰值偏应力较竖直沉积试样大,而二者残余阶段偏应力无明显差别;水平沉积试样临界孔隙比较竖直沉积试样大;胶结破坏速率及胶结破坏率变化与宏观力学特性变化相对应,且变化规律基本相同;水平方向沉积试样的胶结接触主方向始终保持竖直而竖直沉积试样的胶结接触主方向始终保持水平;在水平沉积试样中始终为水平分布颗粒长轴分布主方向,而竖直沉积试样中颗粒长轴逐渐向各向同性分布靠近。

DEM simulations of anisotropic structured sand with different deposit directions

In order to study the effects of deposit directions on the mechanical response of anisotropic structured sand, two anisotropic pure sand samples deposited in horizontal and vertical directions are prepared by using elliptical particles in NS2D first, and then a bond contact model considering the bond thickness is implemented into the pure anisotropic sand samples to prepare anisotropic structured sand samples. Biaxial compression tests are conducted on both samples, and the results of samples with horizontal deposit direction are compared with the laboratory test results to validate this model, then the results of two samples with different deposit directions are compared to study the effect of depositing direction. Test results show that strain softening and shear dilation occur in both samples. The peak deviator stress of the horizontal deposited sample is larger than that of the vertical deposited sample, while the residual shear forces are nearly the same. Besides, the critical void ratio of the horizontal deposited sample is larger than that of the vertical deposited sample. The changes of bond breakage percentage and bond breakage ratio of these two samples are of the same and are consistent with the stress-strain and volumetric mechanical responses. The number of bond contacts decreases in the two samples, and the bond contacts distribute in a vertical principal direction in the horizontal deposited sample and a horizontal principal direction in the vertical deposited sample during the tests. The principal direction of particle orientation is horizontal for the horizontal deposited sample throughout the tests, while the principal direction of particle orientation in the vertical deposited sample is firstly vertical and then develops towards an isotropy state.