Study On Stability Of Top Coal Of Large Section Open Cut Under Goaf In This Coal Seam

Northern Shaanxi is rich in coal reserves.Due to the limitation of technical level,the overall utilization rate is not high,resulting in the waste of coal resources.In order to fully recover the remaining coal resources,Daliuta coal mine has decided to mine the lower layer of 1-2 coal seam in Huojitu well in recent years.Now the open cut of 1-2 lower 203 working face is arranged below the goaf,which may face roof caving and other problems.Under the condition of ensuring the stability of the surrounding rock of the open cut,it is necessary to improve the driving and mining rate as much as possible.In this paper,by analyzing the failure form of top coal in open cut,the statically indeterminate coal beam model is established,the mechanical equation of coal beam is deduced,the thickness of unstable rock layer is calculated by using natural equilibrium arch,and the minimum thickness of top coal without breaking is determined by combining the tensile stress and shear stress of coal beam;Based on the elastic-plastic theory,the failure depth of the floor and the plastic influence range during excavation are analyzed.Combined with optical fiber,FBG sensor and DIC technology,the physical similarity simulation test is carried out to monitor the stress and deformation of surrounding rock of three kinds of open cut layout schemes with different top coal thickness.At the same time,the numerical simulation is used to compare the roof subsidence value,plastic zone range and vertical stress distribution law of the three schemes with and without support,Verify the influence of top coal thickness and support scheme.In 1-2 lower 203 working face,the displacement,stress and top coal structure of surrounding rock are monitored by various means to study the stability of surrounding rock and judge the rationality of top coal thickness and support scheme.The test results show that the main failure modes of top coal are tensile failure and shear failure.The minimum thickness of top coal is 3.5m,and the top coal will not break;The maximum plastic zone of top coal is 3.46m;"Bolt+anchor cable+steel beam+monomer" is used for combined support.Under the condition of no support,the maximum roof subsidence of 3 m,3.5 m and 4 m top coal thickness is 1.13 mm,0.71 mm and 0.24 mm respectively;In the numerical simulation,the maximum caving height of top coal is 4.088m,3.383m and 3.195m respectively;The range of plastic zone is 2.63m,2.52m and 2.23m respectively,and the maximum tensile stress above the open cut is 0.1MPa,0.57 MPa and 0.82 MPa respectively.In the numerical simulation,the roof subsidence is 23mm,20mm and 17mm,the plastic zone is 1.95m,1.62m and 1.31m,and the maximum stress is 0.31 MPa,0.94 MPa and 1.33 MPa.The thickness of top coal is 3.4?4.8m during open cut driving.The deformation of surrounding rock after support is small,the top coal is relatively complete and the stability of surrounding rock is good.The research results can provide a scientific and reasonable basis for the top coal thickness and support scheme of the North Wing lower slicing face of huojitujing 1-2 coal seam,and provide a theoretical basis for the mining of extra thick coal seam in Northern Shaanxi.