Experimental Study on Seepage Characteristics and Acoustic Emission Parameters of Coal Considering Hydro–Mechanical Coupling

To explore the peak strength, failure characteristics, seepage characteristics, and acoustic emission (AE) parameters of coal under various confining pressures, a ZST-1500 micro-computer controlled electro-hydraulic servo coal adaptive coupling experimental system was used to conduct hydro-mechanical coupling experimental of coal under various confining pressures. The results show that the stress-strain curve of coal under external load is divided into four stages: pore fracture compaction stage, linear elastic deformation stage, yield stage, and failure stage. The permeability presents three stages: slow decrease, rapid decrease, and rapid increase, and it presents a "V"-shaped trend. The peak strength of coal is positively correlated with adequate confining pressure. Confining pressure influences the macroscopic failure characteristics of coal, and the failure form gradually changes from multi-tensile crack shear failure to single-inclined plane shear failure. Confining pressure has little effect on permeability in pore and fracture compaction and linear elastic deformation stages of coal but significantly affects yield and failure. Different confining pressures would affect the relative value of permeability at each stage but would not affect the overall development trend of permeability curves. Increased confining pressure leads to decreased coal-based permeability strain-based loss rate (PSL) and weakened internal macroscopic deformation. The AE ringing count in the whole process of coal failure is strongly correlated with the stress-strain and permeability curves. According to the rise time/amplitude (RA)-average frequency (AF) distribution value, the fracture characteristics are mainly shear cracks under various confining pressures. Meanwhile, the proportion of shear cracks in coal gradually increases with the increase in confining pressure.