Migration evolution laws of overburden structure with deep-lying thick surface soil and disaster mechanism induced by high stress mutation

The evolution of overburden movement is the basic reason for the occurrence of underground dynamic disasters. It is important to know the law of overburden movement under specific stratum conditions and the mechanism of its evolution and disasters for the prevention and control of dynamic disasters. Based on 3301 panel as engineering background, this paper studies the overall failure morphology and combined migration evolution law of bedrock, surface soil layer and subsidence basin under different thickness combinations of topsoil-bedrock, and reveals the migration evolution law of overburden structure under two typical topsoil-bedrock combinations, as well as the mechanism and mechanism of mining stress transfer. The quantitative expression of bearing pressure under the condition of thick topsoil and thin bedrock is deduced, and the macro criterion for disasters caused by high stress mutation is presented. The rationality of the model is verified by engineering. The main conclusions are as follows: ① After coal mining, the weak bedrock shows asymmetric “trapezoid-like” failure pattern, the huge thick and loose surface soil presents “inclined funnel” failure pattern, and the surface soil migration evolution has the characteristics of fast response, wide migration range and large subsidence factor; ② The movement and evolution rules of the surface-bedrock double-layer media under different thickness combinations are quite different. Under the condition of thick surface layer and thin bedrock (type I), the bedrock plastic fracture occurs from bottom to top, the fragmentation of rock mass is small, and it is difficult to form a stable structure; under the condition of thick topsoil thick bedrock (type II), the bedrock is gradually transformed from plastic fracture to block fracture, the breaking step is gradually increasing, the key layer effect is gradually highlighted, the bearing capacity of the structure formed after breaking is increased, which can prevent the movement and subsidence of the overlying topsoil layer, and the subsidence of the surface is reduced to a certain extent; ③ Under the condition of deep and thick topsoil and thin bedrock, a large range of topsoil layer in front of the panel moves to the mined-out area, and the load concentrates on the bedrock above the panel and the coal body ahead. Due to the characteristics of weak bedrock, small size of broken rock blocks and the inability to form large-scale suspended roof, the load is restricted to be transferred farther ahead of the coal wall, resulting in the characteristics of large peak stress, small influence range and large fluctuation; ④ An estimation model of support pressure considering large-scale movement of deep topsoil and plastic fracture of bedrock is established. The calculation method of support pressure is obtained. Taking 3301 panel body parameter as an example, the influence range of support pressure is estimated to be 72 m, the peak value is 44.2 MPa, and the peak stress is 23 m from the coal wall, which has certain impact risk. The ground subsidence characteristics and mining stress monitoring results verify the scientific results of theoretical analysis and similar simulation.