Study On The Movement And Stress Evolution Laws Of Overburden In Near Shallow Coal Seam Mining With Different Mining Height

Shendong mining area is one of the most important coal energy base of China,this area is located in the Maowusu Desert and the Loess Plateau hinterland combination zone,the most surface covered with sand or loess layer,the shallow coal resources as the most typical shallow or shallow seam.Take near shallow seam mining of Shendong mining area as the background,through investigation of 15 working faces,mine pressure observation of 2 working face,the rock mechanics experiment and numerical simulation,study the movement and stress evolution laws of overburden,support load in different mining height(2~9m)of near shallow seam overburden migration,and draw the following conclusion:Research shows that the near shallow coal seam,with the mining height increasing,gob free space increases,to block more activity makes the rotation space of the overburden failure more intense;The lower key layer which play a main role in controlling overburden is destroyed when mining height reaches 6~7m,and caving zone increases;With the increasing height of caving,the upper key layer began to play a principal role.Besides the first step of the initial pressure and the cycle pressure step of the main roof is obviously reduced,the ground pressure is more frequent.And under the same advance conditions,the higher the mining height,the greater the surface subsidence.Through the analysis of the vertical stress of the upper and lower key strata,the higher the mining height is,the greater the vertical stress of the lower key stratum is,the higher the vertical stress of the upper key layer increases with the increase of the mining height.In the whole process,the horizontal stress of the upper and lower key layers increases with the increase of the mining height,especially the horizontal stress of the upper critical layer is higher than that of the lower key layer.With the increase of mining height,the lower key stratum becomes more and more severe,and the bearing capacity is weakened,and the upper key stratum plays a greater role,and the vertical stress,especially the horizontal stress is greater.The support simulation results show that the resistance increased with the mining height increases,when taken up to 7m or more,a sharp rise in resistance;When mining height reaches 9m,support maximum resistance up to 35000 k N,the supporting strength of 2~3MPa,may have been over current support manufacturing level;Support has the partial load,stress on the side near the coal wall is great than the side of gob;The simulation results are close to the measured load.