粗粒土应力诱发各向异性真三轴试验颗粒流模拟研究

基于颗粒流基本理论和物理试验结果,通过改进PFC3D程序中的内置代码,生成包含clump颗粒的混合试样以克服纯球体颗粒模拟粗粒土抗剪强度不足的缺陷,模拟粗粒土在真三轴状态下各主应力方向上的单向加荷试验,并从宏观和细观角度分析了复杂应力状态下粗粒土的应力诱发各向异性特征。试验结果显示:复杂应力状态对各向异性的诱发作用显著,各向宏、细观参数及应力–应变曲线显示出了显著的各向异性;单向加荷试验中加荷向始终为压缩变形,侧向变形复杂,且受初始中主应力系数B影响显著,且B值对非加载向泊松比的各向异性及加载向应力–应变曲线的影响亦较明显;模拟试验中配位数、孔隙率等细观参数的变化趋势能够反映试样体积变形的类型,两个细观参数的取值大小影响抗剪强度的强弱,并且各主应力方向单向加荷时,对应相同的应力增量配位数、孔隙率等细观参数表现出显著的各向异性;从细观角度看,应力诱发各向异性产生的原因归结于侧向围压差异所引起的细观结构变化。

Stress-induced anisotropy of coarse-grained soil by true triaxial tests based on PFC

Based on the results of laboratory tests on coarse-grained soil and the theory of three-dimensional particle flow code, a numerical model for true triaxial tests is obtained with mixed particles containing Clump particle. The Clump particle is generated with the tool of PFC and improvement of program code, to solve the insufficient shear strength problem on simulation of coarse grained soil by balls. A series of unilateral loading tests based on the PFC are performed, and the characteristics of complex stress-induced anisotropy of coarse-grained soil are studied from the macro-micro angle. The results indicate that the significant anisotropy showed by the macro parameters, meso parameters and stress-strain curves in the direction of three principal stresses is mainly induced by complex stress state. The deformation in the loading direction is compressive one in all cases, while the deformations in the other two lateral directions are complicated and greatly influenced by the value of B. Moreover, both the anisotropy of Poisson’s ratio and the stress-strain curve in the direction of a certain principal stress are easily affected by the value of B. In a mesoscopic view, the micro parameters in the direction of each principal stress like coordination number or porosity are very different, and their change trend can reflect the type of deformation and their values have a strong influence on the peak strength. It is also shown that the anisotropy of coarse-grained soil is due to the microstructure change caused by confining pressure difference.