基于围压柔性加载的土石混合体大型三轴试验离散元模拟研究

综合运用计算机三维扫描与随机模拟技术,建立了不同块石含量和空间分布的土石混合体三维随机细观结构模型和离散元模型,考虑围压柔性加载,基于柔性黏结颗粒膜方法,采用颗粒流程序对不同土石混合体试样进行了不同围压下的大型离散元三轴试验模拟,研究了块石含量和空间分布对土石混合体力学特性和变形破坏规律的影响。数值模拟结果表明:土石混合体的强度和抵抗变形的能力随含量和围压的增大而增强,且在相同含石量下,受内部块石空间分布的影响,试样的内摩擦角和黏聚力虽会表现出一定的离散性,但总体上,内摩擦角随着含石量增加基本呈线性增加,而黏聚力却随着含石量增加逐渐减小;在围压柔性加载下,土石混合体试样表现为鼓胀变形破坏,破坏后形成的剪切带为一个曲折条带,形态上呈非对称的X形分布,厚度约为试样高度的1/3~1/2倍,且试样的破坏形态及内部剪切带大小和分布形态不仅受块石含量和空间分布影响,而且也取决于围压大小;土石混合体试样在破坏过程中内部剪切带的形成是伴随局部颗粒的转动开始的,在应变到达峰值应变时,局部发生转动的颗粒相互连接贯通,此时剪切带已基本形成,此后随着应变继续增加,受峰后鼓胀变形的影响,试样内部颗粒的转动仍会发生一定的变化,同时伴随着剪切带大小和分布形态也发生相应的变化。

Discrete element simulation of large-scale triaxial tests on soil-rock mixtures based on flexible loading of confining pressure

Based on the computer three-dimensional scanning and stochastic simulation technologies, the three-dimensional random meso-structure models and discrete element models for soil-rock mixture (S-RM) samples with different stone contents and spatial distributions are established. Considering the flexible loading of confining pressure, the large-scale numerical triaxial tests on the S-RM samples under different confining pressures based on the flexibly-bonded particles method are conducted by particle flow code, and the effects of the stone content and spatial distribution on their mechanical properties and deformation and failure characteristics are studied. The numerical simulation results show that the strengths and deformation resistibility capacities of the S-RM samples increase with the increase of stone content and confining pressure, and their internal friction angles and cohesions vary to a certain extent under the same content but different spatial distributions of stones. However on the whole, the internal friction angle increases linearly with the increase of stone content, while the cohesion decreases. Under the flexible loading of confining pressure, the S-RM samples show bulging deformation and failure mode, and the shear band formed after failure is a meandering strip with an asymmetric X-shaped distribution, whose thickness is about 1/3~1/2 times the height of the S- RM samples. Moreover, the failure mode and the thickness and shape of shear band are affected by the stone content and spatial distribution and the confining pressure. The shear band formation is accompanied by the rotations of the local particles in the S-RM sample. When the strain reaches the peak strain, the locally rotating particles are connected to each other, indicating that the shear band has basically formed at this time. Since then, as the axial strain increases continually, the rotations of the internal particles still change because of the effect of the bulging deformation after the peak, and the thickness and shape of the shear band also change accordingly.