Study On The Mechanism Of The Pressure Relief By Roof Cutting In Gob-side Entry Retaining

Cut the top relief means in solving the difficult problem of hard roof under the left lane has become an independent school in this paper,Eastern of Pan Yi coal mine 1252(1)working face as the research background,using theory analysis,similar simulation,numerical simulation and industrial measurement methods,in-depth study of the cut top relief left lane in hard roof under the action mechanism.By means of similarity simulation,the image is reconstructed in the condition of cutting top or not,including five periods,namely,the excavation stability of the roadway,the first excavation,the first excavation stability and the two excavation,roadway surrounding rock and stress variation,analysing comparatively the difference between the stress and the change of the rock strata during the four periods of cutting roof or not,it is concluded that the effect of cutting top is obvious in the latter three periods,it can effectively alleviate the pressure problem of roadside support resistance,at the same time,it has changed the way of hard rock strata to break down,and prevented the large area subsidence and produced huge load.The numerical simulation method is used to analyze and compare the stress field and displacement field of the top or not,it is further proved that the deformation of surrounding rockstress,concentration of wall can be relieved after cutting,at the same time,the simulation analysis is carried out under the conditions of different cutting height,cutting angle and different mining height,variation of stress field and displacement field of surrounding rock of roadway,according to the 1252(1)working face,the optimal cutting angle is set at 35 degrees,and the optimal cutting height is 20m,which is consistent with practice.On the basis of the analysis of similar simulation and numerical simulation,the theoretical method is used to calculate the critical value of 30MPa,it is a basis to determine whether it can fall on its own and fill the goaf,whether there is a critical layer in the fracture zone is another basis,according to these two bases,the roof is divided into 4 types of strata,based on the actual geological conditions of the 1252(1)working face,it belongs to the second class.Based on the second type of rock stratum,the structural mechanics model is established,analysis of roof caving height and caving height,the length and thickness of the critical block B are deduced.Establishing the mechanical model of the second class rock stratum,the formula of critical support resistance is deduced,the results show that the support resistance is in direct proportion to the X2 of the hanging top distance,besides,adopting sensitivity analysis method,the block B feature length L and suspended from the top of the roadside support resistance influence,the paper puts forward the maintenance measures of roadway under the cover of the second kind of overlying rock structure.Through the measurement of the displacement stress and the maintenance of the tunnel,effectively demonstrate,the method of roof cutting and pressure relief can weaken the pressure concentration of hard roof,reduce the amount of roadway surrounding rock,effectively protect the integrity of the roadway,to promote the success of hard roof roadway.