Effect of rock strength on failure mode and mechanical behavior of composite samples

Many dynamic events in coal mine are caused by the instability of coal-rock body. In order to study the influence of rock strength on this type of instability, uniaxial compression experiments of rock-coal-rock composite samples with different rock strengths are carried out, and the effect and mechanism of rock strength on the mechanical behavior and fracture mode of the composite samples are analyzed. The results show that major failure modes of the composite samples are conjugate X-shaped shearing fracture and splitting fracture. The angle between the shear fracture surface and the end face increases with rock strength. The splitting fracture in the coal body expands to the rock when the rock strength is low. The strength properties of the composite samples mainly depend on the coal strength instead of the rock strength. With the rock strength increasing, the peak strain of the composite samples decrease, and the differences from the coal strain and strain rate to rock strain and strain rate become greater. These failure modes and characteristics of deformation are shown to be determined by the difference between the elastic modulus of rock and coal constituting the composite samples.