Effect of Mineral Heterogeneity on the Triaxial Compressive Behavior of Granular Rock: A PFC3D‐GBM Numerical Study

Abstract

The mechanical properties of granular rocks are intrinsically linked to the heterogeneity of mineral grains. In this study, a 3D grain‐based model (PFC3D‐GBM) incorporating a hybrid contact model was established. Triaxial compression numerical simulations were conducted to investigate how confining pressure and mineral heterogeneity—characterized by spatial distribution, volume fraction, geometric size, and boundary strength of mineral grains—affect the fracture behavior and mechanical properties of coarse‐grained limestone. The results show that force chains serve as load‐bearing paths that distribute the external load. The orientation of these chains remains uniform, irrespective of the load magnitude. The ratio of high‐strength force chains to weak‐strength force chains (RHF/WF) and the ratio of high‐strength force chains to microcracks (RHF/c) serve as quantitative indicators of bearing capacity and fracture resistance. At lower confining pressure (σ3 ≤ 10 MPa), the specimens exhibit reduced peak strength and increased brittleness, with failure typically occurring along a single macroscopic fracture plane. As σ3 increases, the formation of “X”‐shaped failure becomes more pronounced. At the grain scale, a higher dolomite volume facilitates the formation of additional high‐strength force chains within the specimen, along with an increase in Tran‐D‐cs at peak stress. As Tran‐D‐cs require a higher concentration of stress, σp increases by 13%. Moreover, stronger grain boundary strength enhances the stress concentration needed for fracture by modifying the proportion of Trans‐c, leading to a 70 MPa increase in σp. Larger grain sizes, in turn, accommodate more force chains, necessitating a higher σp for fracture.