不同边界对花岗岩三轴试验影响的三维离散元数值研究

Discrete element numerical study on the influence of different 3D boundaries on the triaxial simulation test of granite

摘要:

为了研究边界对花岗岩常规三轴离散元模拟试验的影响，使用颗粒流模拟软件（PFC3D），基于三维等效晶质模型（Grain?-Based-Model）方法生成花岗岩模型，同时利用有限元-离散元（FDM-DEM）耦合建模技术，分别建立刚性、柔性膜以及有限元单元（“Shell”）3种边界下的离散元三轴试验，结果表明：相较于“Shell”边界，刚性边界会提高岩样发生应力集中现象的概率，影响岩样的破坏形态；柔性膜边界会导致岩样在三轴加载过程中所受的实际围压大于目标围压，并显著提高岩样的残余强度；而“Shell”边界下的岩样所受围压稳定，发生应力集中的概率最小。综合分析可得：在花岗岩离散元三轴模拟中“Shell”边界是合适的选择。

关键词:花岗岩;三轴试验;有限元-离散元耦合;柔性膜边界;刚性边界;“Shell”边界;应力应变特性

Abstract:

This paper studies the influence of different boundaries on the conventional triaxial simulation test of granite. The particle flow code（PFC3D） was used to generate the granite model based on the method of grain?-based model. At the same time， the discrete element triaxial test models were established respectively for the three boundaries of the rigid membrane， flexible membrane and finite element （“Shell”） by using the FDM?-DEM coupling modeling technology. Test results shows that compared with the “Shell” boundary， the rigid boundary will increase the probability of stress concentration in the sample and affect the failure form of rock samples， the flexible membrane boundary will cause the actual confining pressure of the rock sample to be larger than the target confining pressure during the triaxial loading process， and significantly increase the residual strength of the rock sample. However， the confining pressure of the rock sample under the shell boundary is stable， and the probability of stress concentration is the smallest. Therefore， the shell boundary should be used in the triaxial test of discrete element simulation.

Key words:granite;triaxial test;FDM‍-DEM coupling;flexible membrane boundary;rigid boundary;“Shell” boundary;stress-strain characteristics