Stress field analysis and study on dynamic pressure mechanism under goaf of shallow depth and closed distance room and pillar mining

According to the complicated condition of the coal pillars left in the room and pillar mining goaf, such as the stress transmission of the coal pillar floor was overlapped, the periodic weighting was abnormal as well as the strong mine rock pressure and dynamic pressure phenomenon when No. 3-1 seam in Huoluowan Mine was passed thought the overburden room and pillar mining goaf in No. 2-2 seam, a theoretical analysis, numerical calculation, similar material simulation and other methods were applied to establish a model of the floor stress transmission law for the complex coal pillar in the room and pillar mining goaf of No. 2-2 seam. The paper had a discussion on the roof overburden structure when the coal pillar was passed and the combined action dynamic pressure mechanism of the "high stress - coal pillar - overburden rock movement" in No. 3-1 coal mining face under the influence condition of the coal pillars was reveal. The study results showed that under the large coal pillars in the room and pillar mining goaf in No.2-2 seam, the horizontal and vertical stresses were high and could research 9.7～15.3 MPa. The influence depth of the vertical stress was 42～58 m, the influence depth of the horizontal stress was 10 ～ 23 m and the shear stress affected scope was 25～50 m. When No.3-1 coal mining face was mining under the coal pillars with a wide of 20 m or 50 m, the advance support stress would be high and the stress concentration coefficient would be 4.44～5.00.When the coal mining face in No. 3-1 seam passed through the above large coal pillars, the dynamic pressure phenomenon would be the stress superposition from the upper seam to the lower seam. The inverted trapezoid rock pillar instability above the coal pillar and the roof collapsed movement combined effect results could guide the safety mining of No. 3-1 seam in Huoluowan Mine.