Failure behavior of a rock-coal-rock combined body with a weak coal interlayer

Using an MTS 815 testing machine, the deformation and failure behavior of a rock-coal-rock combined body containing a weak coal interlayer has been investigated and described in this paper. Uniaxial loading leads to the appearance of mixed cracks in the coal body which induce instability and lead to bursts in coal. If the mixed crack propagates at a sufficiently high speed to carry enough energy to damage the roof rock, then coal and rock bursts may occur – this is the main mechanism whereby coal bumps or coal and rock bursts occur after excavation unloading. With increasing confining pressure, the failure strength of a rock-coal-rock combined body gradually increases, and the failure mechanism of the coal interlayer also changes, from mixed crack damage under low confining pressures, to parallel crack damage under medium confining pressures, and finally to single shear crack damage or integral mixed section damage under high confining pressures. In general, it is shown that a weak coal interlayer changes the form of overall coal damage in a rock-coal-rock combined body and reduces the overall stability of a coal body. Therefore, the whole failure behavior of a rock-coal-rock combined body in large cutting height working faces is controlled by these mechanisms.