Mechanical Properties and Hoek-Brown Parameter Prediction of Cleat-Developed Coal Rock Using Discrete Element Simulation

Coal masses with well-developed cleats exhibit pronounced heterogeneity and anisotropy, and obtaining intact cores for mechanical testing remains a persistent challenge in engineering practice. Conventional assessments using the Hoek-Brown (HB) criterion rely heavily on empirical geological indices and cannot establish a quantitative correlation between cleat characteristics and rock mass parameters, thereby leading to low accuracy and efficiency in strength evaluation. In this study, numerical coal models are established using the discrete element method (DEM) combined with laboratory mechanical tests, and a series of uniaxial and triaxial compression simulations are conducted. Results reveal that cleat intensity is negatively correlated with uniaxial compressive strength and peak strain, while matrix stiffness and intermediate principal stress positively affect the elastic modulus and strength of coal; the intrinsic mechanical parameters of cleats exert a limited influence on the macroscopic mechanical behavior. A linear correlation between 2D cleat areal density P21 and 3D intensity P32 is verified, and a prediction model for HB parameters m and s based on cleat features is developed. The proposed method only requires profile cleat statistics and a limited number of uniaxial tests to achieve efficient and reliable strength evaluation. It possesses considerable theoretical innovation and practical engineering value.