Study on evolution characteristics of fracture field in hard thick overlying strata based on geological generalization

Accurately grasping the evolution characteristics of the water-conducting fracture zone in the mining overburden is an important basis for preventing the occurrence of water inrush disasters in the working face, especially for the high strength mining conditions in the western mines. Taking the 201 west wing area of Yushuwan Coal Mine as the background, taking the uniaxial compressive strength of each sandstone layer, RQD, and thickness of sandstone layer as the system cluster analysis indexes, this paper proposes a geological generalization method for thick bedrock, systematically studies the influence of different bedrock layer thickness on the development height, fracture angle, frequency, and joint strain energy evolution law of the water-conducting fracture zone, and determines the quantitative relationship between the height of the water-conducting fracture zone and the total joint strain energy. The research results show that: the development height of the hydraulic fracture zone simulated based on the geological generalization method presents a log-positive correlation increasing trend with the increase of the bedrock thickness, and the increasing rate gradually decreases. This law is verified by comparing with the measured results of the adjacent mines; with the increase of the thickness of bedrock, the development frequency of vertical cracks in the water-conducting fracture zone increases significantly, while the horizontal cracks in the water-conducting fracture zone increase, which indicates that the increase of the thickness of bedrock has a certain inhibition effect on the initiation and expansion of horizontal cracks in the water-conducting fracture zone; the development height of the water-conducting fracture zone is closely related to the energy release degree of the overlying rock. It increases exponentially with the increase of the maximum strain energy and the total strain energy of the joint, and the increasing rate gradually increases.