Study on the Damage Evolution and Failure Mechanism of Floor Strata under Coupled Static-Dynamic Loading Disturbance

Abstract

In the field test, we found that the failure depth of the goaf floor strata tends to be further because the periodic breaking and caving of the immediate roof, upper roof, and roof key stratum has dynamic stress disturbance effects on the floor. To further analyze its formation mechanism, this paper studies the damage evolution and fracture mechanism of goaf floor rock under the coupled static-dynamic loading disturbance caused by roof caving, based on the stress distribution state, the damage evolution equation of coal measure rock, the damage constitutive model, and the fracture criterion of floor rock. The main conclusions are listed as follows: 1. Based on the mining floor stress distribution, the floor beam model establishes the response mechanism of floor rock stress distribution. Also, the equation of stress distribution at any position in floor strata under mining dynamic load is given. 2. Combining the advantages of Bingham and the Generalized-Boydin model, the B-G damage constitutive model is established, which can describe the constitutive characteristics of coal measure rock under the coupled static-dynamic loading disturbance well. Furthermore, the variation law of parameters changing with strain rate is analyzed. 3. According to the twin-shear unified strength yield theory and the B-G damage constitutive model, coal measure rock’s twin-shear unified strength damage fracture criterion is established. Finally, the stress distribution expression of floor strata under concentrated and uniform dynamic loads is introduced, and the fracture criterion of goaf floor strata under a coupled static-dynamic loading disturbance is proposed.