各向异性结构性砂土离散元分析

天然沉积砂土力学特性受各向异性及结构性影响明显，实际工程中不能忽视。为探究二者的影响，首先在二维离散元程序NS2D中采用椭圆颗粒模拟了重力场中颗粒长轴主方向为水平的各向异性净砂样，随后基于结构性砂土胶结厚度分布规律及室内试验提出了一个新的微观胶结接触模型并将其引入各向异性净砂样以模拟天然各向异性结构性砂土，最后对该离散元试样进行了双轴试验模拟，将模拟结果与室内试验结果对比以验证该模型的适用性，并对其微观力学特性变化进行研 究。分析结果表明，随着剪切进行，各向异性结构性砂土呈明显应变软化及剪胀现象；胶结接触逐渐减少，且主方向始终为竖向方向；胶结破坏速率及胶结破坏率变化情况与宏观力学响应较一致，且胶结物多为拉剪破坏；土颗粒排列主方向始终为水平向，且水平向排列颗粒所占比例略微增大。

Discrete element analysis of anisotropic structured sand

Anisotropy and inter-particle bonding have large effects on the mechanical response of natural sand, which should be considered in engineering practice. In order to study the combined effects of these two factors, an anisotropic pure sand sample with elliptical particles and with a horizontal principal orientation is prepared in a discrete element method (DEM) code NS2D to simulate natural gravitational deposited sand. After the sample being deposited in a gravity field, a new bond contact model calibrated from statics of bond thickness in experiments is installed at the contacts. Finally, biaxial tests are conducted on the anisotropic structured sand sample. The simulation results are compared with laboratory test results to validate the DEM modeling. Besides, the micro-mechanical responses are also studied. Test results show that strain softening and dilation occurred with shearing. The number of bond contacts decreases and the principal direction of bond contacts are vertical during the tests. The variations of bond breakage percent and bond breakage ratio are consistent with the macro stress-strain and volumetric responses. The bonds are primarily damaged in tensile-shear failure mode rather than compression-shear; the principal orientation of particle arrangement is horizontal and the particle percent in horizontal direction increases slightly throughout the tests.