Research and application of fracture mechanics model of stope roof under the coupling of direct roof and basic roof

Periodic weighting is a typical characteristic of mine pressure. Accurate prediction of stope periodic weighting step is an important way to effectively reduce the occurrence of stope accidents. Aiming at the influence of the coupling between the basic roof defects and the direct roof on the periodic weighting step, the stope roof was regarded as a finite plate model with cracks. According to the coordinate deformation mechanism of the overburden rock, the fracture mechanics model of the stope roof was established based on the fracture mechanics theory. On this basis, the periodic weighting step function under the coupling between the direct roof and basic roof was derived. In addition, the influence of the parameters such as the fracture toughness of the basic roof rock, crack depth, direct roof thickness and elastic modulus on the periodic weighting step was analyzed based on 2 working faces of a mine area in northern Shaanxi. The research shows that: (1) The fracture toughness of the basic roof is in approximately linear relation with the periodic weighting step. (2) The crack depth ratio (crack depth/roof thickness) has a great influence on the periodic weighting step. In particular, the basic roof is unstable and destroyed when the crack depth ratio reaches 0.8. (3) The direct roof with the thickness less than 3 m has little effect on the periodic weighting step, but that with the thickness greater than 3 m has a significant effect on the periodic weighting step. Generally, the research results have important theoretical significance and engineering value for the prediction of periodic weighting step of stope roof and the selection of support.