Experimental study on mining-induced fracture form responseand permeability evolution of overlying strata

The pressure relief and permeability enhancement effect caused by the movement of the overburden strata and the development of cracks in the stope is the guarantee for efficient gas drainage. In order to explore the distribution of mining cracks in the stope and the evolution of the permeability of the overburden, based on similar simulation technology, the morphological response process of fractures was analyzed, and the permeability of the overlying rock was tested using the transient flow method with air as the medium. The results show that the fractures are distributed in frequency, and the near-open cut area is higher than the inside of the stope. On morphology, the angles are mostly concentrated in the horizontal angles of 0~10°, 90~110° and 170~180°. The angle of cracks in the near-open cut area is consistent with the pressure relief angle of the rock formation, but in the inner place the angle is orthogonal. During the mining process, the air flow data at the measurement point is related to the impact of mining. The flow at each measurement point in the horizontal direction has experienced three stages of fluctuation-surge-stability, and the stage of vertical flow surge is less obvious. The final stable flow is negatively correlated with the interval between the measuring point and the recovery horizon. Based on the data fitting, the relationship between overlying rock permeability and interlayer spacing can be described by the three-parameter logarithmic formula:kf =A-Bln(H-C). The physical meaning of the three parameters are stated. The research results could provide some guidance for the arrangement of engineering parameters of gas drainage.