Numerical Simulation of Coal Strength and Failure Characteristics Under the Effect of Confining Pressure

In order to investigate the effect of confining pressure on coal strength and failure characteristics, the confining pressure effect was analyzed theoretically and simulated by FLAC^2D. It shows that ultimate strength of coal enlarges with increasing confining pressure, and ultimate strength and confining pressure has a nonlinear relationship；axial stress enlarges with increasing confining pressure. The stress area presents taper distribution and reverse taper distribution, cone angle of which is about 60°. Shear stress and shear zone all enlarge with increasing confining pressure. Shear zone develops from single shear to multiple-shear；the rupture form of coal changes with the changing confining pressure. The angle enlarges with the changing confining pressure；the surface of coal more easily achieves the plastic yield state if no confining pressure loaded. Plastic hardening has a remarkable effect on the post-yield coal with increasing confining pressure. It accords with power strengthen model. Yield limit of coal also gradually enlarges with increasing confining pressure.