土体颗粒破裂过程离散元模拟的新方法

土体颗粒的破碎对土体的宏观变形和强度性质有重要影响。数值模拟方法是研究土体颗粒破碎机理的重要手段。采用离散元数值软件PFC模拟土体颗粒的破碎。首先利用PFC内置Fish语言编写颗粒破坏准则,使得单个颗粒在满足破坏函数时破裂成为多个粒径更小的颗粒,从而实现PFC中颗粒的可破碎性,降低了传统方法"团聚颗粒"模拟颗粒破碎时建模和参数选取的复杂性。随后运用Fish编写的程序模拟土体在单轴压缩条件下颗粒破碎的过程;并对土体颗粒破碎特征进行分析。分析可知:颗粒破碎随着加载进行逐步从土体上部向下发展;土体中颗粒的破碎现象在空间上并不均匀发生,主要集中在试样的上部;加载过程中试样孔隙率的变化可以分为两个阶段,第一个阶段与颗粒的位置调整相关;而第二个阶段则与颗粒破碎相关,且第二阶段变化更为明显。颗粒破碎最终导致土体颗粒的粒径分布更为不均匀,最终形成级配较好的土体;但试样初始阶段的颗粒仍然为土体的主要成分。模拟结果与室内试验的部分成果比较,模拟结果与试验观察到的破裂现象基本一致,表明运用新方法模拟颗粒破碎过程合理、可行。

New Method for DEM Simulation of Particle Crushing Evolution in Soil

Granular materials forming part of natural slopes, embankments, subgrades of foundations, and pavement structures are subjected to both static and dynamic loads during their engineering lives. As a result of these loads, particle crushing may occur. The present study demonstrates that the discrete-element method PFC can be used to visualize the evolution of this breakage process. In particular, the evolution of crushing in a simulated granular material subjected to uniaxial compression is presented. Even though DEM does not normally consider particle breakage, it is possible to simulate crushing by replacing one particle that has failed in tension with a combination of many particles of different sizes. The results from the simulation indicate that crushing does not develop uniformly throughout the sample, but rather concentrates in certain regions. These observations agree with experimental results of uniaxial tests conducted on sand. Other results from the simulation satisfactorily agree with experimental results previously reported by other researchers. In this way, by using a simplified failure criterion, DEM can be used to visualize and understand the evolution of granular crushing. This is something that is very difficult to do with laboratory tests alone.