The Behavior of Compression‐Hardening at Crack Closure Stage Explored by Stiffness Rising Model (SRCM) Under Triaxial Compression: A DEM Study

ABSTRACT Native microcracks significantly influence the strength and deformation characteristics during the crack closure stage under triaxial compression. This study proposes a stiffness rising contact model (SRCM) with clear physical significance to describe the stiffness evolution at this stage, implemented within a 2D DEM framework. A series of biaxial rock numerical simulations is successfully conducted using sample dimensions consistent with the ISRM standard. Additionally, a three‐step application framework is presented in detail. First, based on triaxial experimental data, the relationship between the secant shear modulus () and deviatoric stress () during the crack closure phase is accurately described by a power function, with the crack closure threshold serving as the termination point for stiffness variation. and q are further characterized through the parameter in the SRCM and the average normal force () in particle agglomerates. The numerical simulation results for both stiffness rising and constant stiffness behaviors are compared with experimental data from red sandstone. The simulations demonstrate that by defining the crack closure stress (), the crack closure behavior of red sandstone can be effectively captured. The stress‐strain response predicted by the SRCM closely aligns with the experimental data, with significantly smaller errors compared to the constant stiffness model, thereby validating the proposed method.