Study On The Influence Of The Position Of Main Key Layer On The Evolution And Pemeability Of Cracks In Mining Overlying Strata

The key stratum plays a controlling role on the movement of overlying strata and affects the development height of mining fractures.In this paper,the research method of theoretical analysis,similar material simulation and numerical simulation is used to study the influence of the key layer position on the fracture evolution and permeability of the mining overlying rock.The main research achievements are as follows:(1)Based on the elastic thin plate theory,the deformation and failure mechanics model of overlying rock in different mining period is constructed,and the fracture and instability form of the rock strata of the mining overlying roof is revealed from the angle of the rock strata movement.(2)The simulation test model of three different main layers is established respectively.When the main key layer is located above the fracture zone,the height of the development height is about 10 times.When the main key layer is located on the "upper boundary of the crack zone",the development height of the water guide fracture zone is about 7 times.When the main key stratum is located in the "original caving zone",the height of the water fractured zone increases significantly,and even develops to the surface.(3)Based on PFC2D numerical simulation software,the excavation of three key layer schemes is simulated,and the law is basically consistent with similar material simulation test.By extracting porosity data,the permeability zoning of goaf can provide theoretical basis for prevention and control of roof water inrush.