Efect Of Overburden Strata Structure On Reasonable Width Of Inter Recovery Room Pillar In Mining Close Distance Seam

In the western region of China,the pre-driven recovery rooms technology is mainly used for equipment retracting.However,due to the influence of the special overburden structure formed near the stop-mining line,when the recovery rooms of the lower coal seam at different positions,the overburden rock structure of the coal pillar is different,leading to the great difference in the load.At present,the width of coal pillar mainly depends on the selection of experience.When the width is not reasonable,problems such as roof caving or waste of coal resources will occur.How to determine the reasonable width of coal pillar is an urgent problem to be solved.This article takes Lijiahao Coal Mine as the engineering background,through physical simulation and numerical simulation and theoretical analysis method,studies the overburden structure characteristics,pillar on the load calculation based on the analysis of structure mechanics model,the different location pillar stress,plastic zone and recovery rooms roof subsidence is analyzed,the reasonable width of coal pillar is obtained.The main conclusions are as follows:Firstly,the physical simulation experiment was used to study the structural characteristics of the overlying strata of coal seams under short distances.The results show that when the recovery room is arranged below the unmined coal seam in the upper coal seam,the structure of the overlying strata of the coal pillar in the roadway is similar to that of the final mining end formed by single coal seam mining.The coal mining rock damage to the interlayer,the basic structure is formed under the top seam "blique step voussior beam" process of mining coal seams and collapse in the next gob of load transmission is not formed pillar.When the recovery room is arranged below the goaf of the upper coal seam,the overlying strata structure of the coal pillar in the roadway is mainly the overlying rock structure formed by the mining of the upper coal seam and the short voussoir beam structure.The main reasons for the difference in load bearing between coal pillar are the structural differences formed in the upper coal seam above the coal pillar and the load bearing between key strata.Secondly,based on the structural characteristics of overlying strata,the load transfer mechanism of overlying coal pillar was analyzed,and themechanical model for calculating the load of coal pillar in the retracting passage of the shallow coal seam in the near lower coal seam was established.The calculation formula of coal pillar bearing load is derived,and it is concluded that coal pillar bearing overburden load is mainly composed of three parts:(a)the dead weight of interlayer rock in the caving angle range of coal pillar and lower coal seam above the recovery room;(b)the dead weight of rock in the caving zone of the upper coal seam and the load transferred by the short voussoir beam structure formed;(c)the short voussoir beam structure formed between the key strata and the upper key strata at the final mining end transmits load.Thirdly,the deformation and failure of surrounding rock and the vertical stress of recovery room pillar are studied by numerical simulation.The analysis shows that with the decrease of the width of the remaining coal pillar in the working face,the stress carried by the coal pillar is obviously transferred to the coal pillar between the roadway.When the retracting passage arranged in different positions is connected at the end of mining,the vertical stress transition from the mined-out area to the solid coal area has a trend of decomposition,expansion and transition,and tends to be stable.The roof subsidence and stress of the retracting passage have the same change trend.Coal seam under "pressure relief area" and the Angle of the influence of concentrated stress of coal pillar,the influence from the Angle of boundary in the direction of mined-out area layout retracement channel,its minimum between pillar under load.When the recovery room is located in the stress zone of the original rock,the coal pillars in the roadway bear the largest load compared to the other four positions.Finally,a numerical simulation model was established to optimize the reasonable width of the coal pillar under the corresponding working conditions.Based on the calculation equation of the width of the coal pillar between the lanes,the reasonable width of the coal pillar between the lanes on the 31109 working face of Lijiahao coal mine was determined to be 18 m.The results show that the research results in this paper have a guiding effect on the selection of the width of coal pillar in the recovery room under similar working conditions.