Experimental research and numerical simulation: strength and rupture patterns of coal under Brazilian tensile test

Coal seam contains well-developed weak planes known as cleats. The strength and rupture patterns of coal with different cleat directions are significantly different in Brazilian tensile test (BTT). In this paper, a series of Brazilian tensile tests of coal specimens under different inclination angles of face cleat were carried out. Based on the experimental data, the influence of cleat direction on the failure strength (FS) and rupture patterns of coal specimens was analysed. Then the analytical model to calculate the anisotropic failure strength of coal under Brazilian test conditions was derived. The model cannot only predict the rupture patterns of coal specimens with different cleat directions and calculate the corresponding failure strength, but also can reflect the effect of cleat density on the strength. In the simulation, the rupture patterns of numerical model also fall into four types, which are consistent with the experimental results. The cleat density has no influence on the rupture patterns, but will decrease the failure strength. The connectivity of butt cleats is the key to determine whether the coal shear along the face cleats or butt cleats.