Investigation of Multiscale Failure Mechanism of Red Bed Soft Rock using Grain-Based Finite-Discrete Element Method Combined with X-Ray Micro-computerized Tomography

The mechanical properties and failure mechanisms of geomaterials are greatly affected by their heterogeneity. As a special complex rock medium, the mechanical response of red bed soft rock is of considerable importance in stability analyses and the protection of slopes. In this study, X-ray micro-computerized tomography (micro-CT) was used to obtain the spatial distribution of minerals in red bed soft rock. An image processing procedure was proposed to incorporate the extracted mesoscopic mineral and crack distribution into the model of the grain-based finite-discrete element method (GB-FDEM). Subsequently, a uniaxial compression test and Brazilian disc splitting test were performed to obtain the mechanical response and failure modes of mudstone. The microscopic fracture morphology and traces of intragranular and intergranular cracks under tensile and shear stress were analyzed in detail. The numerical results show that the GB-FDEM model successfully characterized the mechanical response, which was similar to that of the laboratory tests and the traditional homogeneous models. The presence of minerals and pre-existing cracks disturbed the stress distribution in the heterogeneous model, which resulted in a difference in local stress that reasonably explained the phenomenon of local fragmentation. The simulated macroscopic failure mode of the heterogeneous models was most consistent with the results of the laboratory tests. The systematic framework proposed in this study provides a powerful tool for further understanding the multiscale (micro, meso, and macro) failure mechanism of red bed soft rock and predicting a realistic fracture process while reducing the tedious and redundant laboratory tests.