A coupled macro- and meso-mechanical model for heterogeneous coal

A thorough understanding of the deformation behavior, damage accumulation, and progressive failure of heterogeneous coal is a prerequisite for effective control of the surrounding rock and efficient exploitation of resources in underground coal mines. Such understanding can be obtained by analyzing both the macro- and meso-responses of coal to loading. Accordingly, a coupled macro- and meso-mechanical model for heterogeneous coal is developed and implemented in FLAC3D in the present study. The model is based on elasto-plastic mechanics and the energy dissipation and release principle, and heterogeneity is incorporated by the combination of a statistical approach and the discrete fracture network method. The model is calibrated by experimental data and is used to simulate stress-strain responses, the evolution of acoustic emission (AE) events, and energy conversion in compressed coal. The results reveal that: (1) the model can efficiently capture the dependency of the deformability, compressive strength and AE characteristics on the confining pressure; (2) the anisotropic behavior of heterogeneous coal is realistically realized, and the initiation, propagation and coalescence of micro-cracks can be located and tracked; and (3) stress paths, the degree of heterogeneity, and the unloading rate of confining pressure significantly influence the axial stress-strain response and AE event evolution in the stressed coal. The proposed model produces reasonable values for the roof weighting interval and expansion of the excavation-damaged zone around the gate when compared to the field data measured at the Dongzhouyao mine of China.