Ground Pressure Behavior Law Of Short Wall Face For Pillar Recovery In Main Roadway Of Shallow Coal Seam

After the coal seam mining is completed,the coal resources of the main roadway pillar are left in the stratum,resulting in a waste of resources.However,when the working face is arranged in the main roadway pillar,due to the small width of the main roadway pillar,the arranged working face is a short wall working face,which leads to high stress concentration in the local range of the three main roadways in the mining process.It is of great significance to master the law of ground pressure behavior in the mining process,According to the occurrence characteristics of main roadway coal pillar in Zhaojialiang Sany coal mine,based on the mechanical properties of surrounding rock in laboratory experiment,and through the research methods of theoretical calculation,physical similarity simulation,numerical calculation and field ground pressure monitoring,this paper studies the ground pressure behavior law in the mining process of main roadway coal pillar recovery face.The main conclusions are as follows:Based on the mechanical properties of surrounding rock in the laboratory,the position of the key layer of overburden is identified by using the key layer theory.Using the bending theory,it is preliminarily calculated that the initial breaking step distance of the basic roof of the stope is 83.28 metre and the periodic breaking step distance is 42.8 metre;Similar simulation experiments show that after the completion of mining in 3101 working face,the peak stress of the protective coal pillar near the goaf side between the return air roadway and 3101 working face is 5.12MPa,the stress concentration factor is 1.86,and the peak value is 7 metre away from the goaf;After the mining of 3102 working face is completed,the peak stress of the protective coal pillar near the goaf side between the main roadway and 3102 working face is 5.2MPa,the stress concentration factor is 1.89,and the peak value is 8.5 metre away from the goaf.After the mining of the coal pillar recovery working face of the main roadway is completed,the stress distribution above the protective coal pillar is saddle shaped.According to the coal pillar load mechanics model,the minimum width of the protective coal pillar is 13.8 metre,while the actual width of the protective coal pillar is 50 metre,The results show that the gob on both sides has little influence on the mining of coal pillar recovery face in main roadway;The numerical simulation shows that the maximum stress peak of the advance support of the stope is about 8.45MPa,the stress concentration factor is 3.07,the stress peak is 8m away from the coal wall,and the stress influence range is about 30 metre,which can provide a theoretical basis for the advance support of the roadway;The distribution of dip stress along the working face is characterized by small on both sides and large in the middle,and the occurrence degree of ground pressure in the middle of the working face is more intense in the process of mining;The field monitoring shows that the average initial pressure step distance of roadway pillar recovery face is 80.32 metre,and the average periodic pressure step distance is 38.54 metre;Along the working face,the working resistance of the hydraulic support tends to be small at both ends and large in the middle.During the initial pressure,the average working resistance of the support is 5165kN,and the pressure intensity is relatively strong.During the cycle,the average working resistance of the support is 4870kN.There is still a certain surplus in the support resistance of the working face.The ZZ7600/17.5/35 support shield hydraulic support can meet the requirements of safe production of the working face;After the inclined length of the working face is shortened,the initial pressure step is about 2.8 times of the normal working face,and the periodic pressure step is about 4.1 times of the normal working face.The initial pressure intensity changes greatly,while the periodic pressure intensity changes less.The reason is that the rock fragmentation and expansion coefficient in the goaf is large,and the overburden can form a balanced structure and reduce the stope pressure under its support.The on-site monitoring results are close to the simulation experimental results.The ground pressure behavior law of the main roadway pillar recovery face in Zhaojialiang Sany coal mine can not only provide theoretical guidance for the subsequent mining of the working face,but also provide reference for the main roadway pillar recovery face with similar geological conditions.