Investigation on the mutation effect induced by the coupled destabilization of fault and overburden rock strata during coal mining

Abstract

The frequent occurrence of coal burst in coal mines is closely related to the destabilization of complex geological formations, and the fault as a typical geological structure is an important factor in inducing dynamic coal burst disaster. In this study, the distribution function solutions of displacement and energy fields characterizing fault sliding were derived. Under the engineering background of geological structure of the Yima mine area in Henan Province and the mining face 21221 of the Qianqiu coal mine, a physical model to simulate the mining process and fault sliding of the mining face was built. The multi-parameter evolution law of displacement, energy, and temperature of the overburden rock strata and fault area were monitored, and the mutation effect of fault and overburden rock strata instability was investigated. In addition, the mechanical mechanism of the association and coupling of overburden rock strata movement and fault slip instability caused by mining disturbance was discussed. The results show that the frequency of extreme value points of stress, displacement, and energy parameters on the fault surface under the mining disturbance presents a dense to sparse distribution from top to bottom along the vertical direction of the fault. In the meantime, the upper part of the fault surface in a non-stable state is more susceptible to the influence of mining than the lower part, which is the main power source of fault sliding. Fault sliding is a top-to-bottom, local-to-whole, low-energy followed by high-energy, gradually accelerated and discontinuous dynamic destabilization process, which is accompanied by three strain energy states of low-energy stability, gradual accumulation, and high-energy activation. The maximum strain energy increment appears in the upper part of the fault surface, and the massive release of strain energy will accelerate the top-to-bottom destabilization of the fault slip. During the sliding process of the fault surface, the temperature also shows the characteristics of stepwise increase, which is manifested as the constant temperature stage during the small disturbance, the local rising stage caused by the stress accumulation, and the global temperature surge stage caused by the sliding instability. The nonlinear and discontinuous dynamic instability of the fault is closely related to the movement and collapse of the overlying rock layer on the working face. The mutation effect of the coupled instability of the fault and overburden rock strata was studied based on the correlated coupling response between the movement of overburden rock strata and the fault sliding during the mining disturbance. It is manifested by the sudden increase of the overburden rock strata pressure near the fault, the drastic change of the stress on the fault surface, the accelerated change of the fault displacement and its development to the lower part, the large and frequent fluctuation of the strain energy, and the order increment of the temperature field. The studies indicate that the overburden rock strata collapse imposes impact loads on the unsteady slip of the fault, and the fault serious slip instability caused by the strain energy sudden release will also bring a secondary violent impact to the deformed and damaged overburden rock strata and cause a large area collapse. The resulting unloading effect provides additional space for the fault to move into the region, which further accelerates the slip instability of fault and the collapse of overburden rock strata, and easily induces coal burst disaster.

Keywords

• coal burst
• fault
• slip instability
• mutation effect
• monitoring and warning