Theoretical Study On The Influence Of Key Strata On Abutment Pressure Distribution

Coal mining will inevitably lead to overburden movement and load transfer,which will cause redistribution of stress and form abutment pressure in the surrounding rock of the stope.It is the root cause of deformation and caving,underground pressure and dynamic mine disaster of the surrounding rock.Previous studies for abutment pressure distribution do not consider the influence of the overburden key strata,and there is no calculation method of abutment pressure considering the influence of overburden key strata.In this paper,theoretical analysis method,numerical simulation,physical similarity simulation and field measurement are used to study the influence of key strata on the abutment pressure distribution,and a calculation method of abutment pressure based on overburden key strata is established.Through comparative analysis of the distribution law of abutment pressure under different overburden key strata conditions in Tingnan,Haizi,Gaojiapu and Guqiao coal mines,and using UDEC numerical simulation software and physical similarity simulation experiment,the distribution law of abutment pressure under different overburden key strata conditions are studied.It is found that the overburden key strata have significant influence on the distribution of abutment pressure.Based on the key stratum theory and Winkler's elastic foundation beam theory,it is found that the overburden load can transfer to coal-rock masses on both sides of the stope through fractured blocks in different layers of the key strata in the fissure zone and key strata in different layers of the curve subsidence zone,thus forming abutment pressure in the surrounding rock of the stope.The mechanism of the influence of the key strata on the abutment pressure distribution is revealed.Using Winkler's elastic foundation beam theory,we consider the fissure zone key strata on the coal mass side and the curve subsidence zone key strata as many elastic foundation beams interact with each other.For any two adjacent key strata,the load of the upper key stratum in the adjacent key stratum is transmitted to the lower key stratum by a nonuniform load through the elastic foundation consisting of the lower key stratum and its load rock.The calculation mechanics model of abutment pressure based on key strata is established,the calculation equations of abutment pressure with arbitrary section under different mining degree is deduced,and the calculation method of abutment pressure based on overburden key strata is obtained.The calculation of the abutment pressure distribution in stope is realized according to the parameters of borehole columnar and working faces.We also determined the calculating parameters of the method,especially the elastic foundation coefficients of the goaf under various mining dimensions.The calculation method was verified by field measurements and simulation results.The influences of thickness,stiffness,horizon and number of key stratum on the abutment pressure distribution under different mining dimensions are studied.It is found that there are obvious differences in the distribution of abutment pressure under different overburden key strata conditions.It is found that the smaller the thickness or stiffness of the key stratum or the farther away from the coal seam,the smaller the influence of the key stratum on the abutment pressure distribution.A method for determining the critical location of key stratum affecting the abutment pressure distribution is proposed.Based on the research results,the evolution law of abutment pressure is mastered under the ultrathick and hard key stratum in Tingnan coal mine.It is proposed that the working face 207 must stop 286 m from the main roadway and leave a,no less than 286 m wide,protection coal pillar.The critical locations of the key strata affecting the abutment pressure distribution are determined in Tingnan and Guqiao coal mines.It is concluded that the influence of the main key stratum on the abutment pressure distribution should be considered in Tingnan coal mine,while the influence of the main key stratum can be ignored in Guqiao coal mine.The superimposed stress distribution of the coal pillar is obtained between the first panel and the second panel in Gaojiapu coal mine.It is proposed that pressure-relieving blasting and strengthening support can be carried out in the high stress concentration area of the main roadway in the coal pillar to ensure the safe production of the mine.The dissertation has 92 figures,17 tables and 233 references.