Study On Dynamic Instability Mechanism And Prevention Of Overlying Coal Pillars In Shallow Buried And Close Distance

Some resources in the shallow coal seams in western my country used room mining methods to control the movement of the overlying strata in the early days,leaving a large number of room mining pillars.When the resources are integrated,the lower coal seam mining will inevitably affect the stability of the overlying coal pillars.Once the coal pillars instability,it will cause the appearance of strong mine pressure in working face,threatening the life and property safety of underground personnel.This paper takes the mining under the coal pillars at close distances in the Yuanbaowan Coal Mine of Shuozhou,Shanxi Province as the background,and aims at the strong underground pressure when the 6107 working face of the No.6 coal seam advances to the overlying No.4 and No.3 coal seams under the coal pillars.Using methods such as field measurement,theoretical analysis,similar material simulation,3DEC numerical simulation,etc.,to study the influence of the instability of the overlying coal pillar on the mine pressure in working face,the movement of the overlying strata and the surface subsidence,reveal the instability mechanism of the room mining pillar and the disaster mechanism caused by strong mine pressure,And give the prevention and control countermeasures of strong mine pressure at the working face.The main research results are as follows:(1)The "Trinity" in-situ measurement was carried out on the working face,and the results showed that when strong mine pressure occurred on the working face,the local roof pressure was strong,resulting in local support crushed of the working face;the data of various measurement points of the internal rock movement in ground borehole has a sharp increase.The borehole dislocation position of the ground drilling TV peeping all has a step jump,the movement range of the overlying rock increases instantaneously,and the overall movement of the rock formation occurs.The surface sinks sharply within a certain range along the strike and inclination of the working face,forming a "collapse basin".The working face pressure support,the stepped rise of the borehole dislocation position and the sinking position of the surface step are basically consistent.It is determined that the instability of the 4 coal pillar is the main cause of the strong mine pressure at the working face.(2)Analyze the overlying coal pillar stability and evolution law of load-bearing stress before and after the mining of the lower coal seam working face.The influence range of the advanced abutment pressure of the working face is determined.The peak value of the advanced abutment pressure increases with the increase of the mining scale of the working face,and the interval between layers is an important factor affecting the influence range of the advanced abutment pressure.Theoretical analysis of the influence of the size of the remaining coal pillars on its stability shows that the overlying 4 coal pillars and 3 coal pillars can remain stable before mining in the lower coal seam,and the coal pillars of the overlying 4 coals will be destabilized after mining,but pillars of coal 3 remain stable.(3)Similar simulation studies show that the dynamic instability process of coal pillars is more complicated.The coal pillars on both sides of the goaf are first destroyed and destabilized,and adjacent coal pillars are then successively destroyed,which eventually leads to large-area instability of the coal pillars,resulting in a large overall appearance of the overburden.The overall cutting motion is large,and the huge impact load acts on the working face,causing the working face support crushed.The disaster mechanism caused by strong mine pressure at the working face was revealed,and the result was verified by numerical simulation.(4)The factors affecting the stability of coal pillars in room mining are analyzed,and it is found that both the buried depth of the coal seam and the mining height have a greater impact on the stability of the coal pillars.Weakening the overlying coal pillars and the hard rock layers in the overlying rock can effectively prevent strong mine pressure at the working face.Each weakening plan reduces the coal seam's leading Peak stress of advanced abutment pressure and overlying rock movement range to a certain extent.In contrast,weakening the 4th coal roof is the best prevention plan.The research results have certain guiding significance for safe mining under coal pillars in similar mines.The paper consists of 91 figures,13 tables,and 175 references.