Ground Stress Distribution and Dynamic Pressure Development of Shallow Buried Coal Seam Underlying Adjacent Room Gobs

The condition of the coal pillars remained in the room-and-pillar gobs is complicated. The stresses loaded on the pillar floor may be transmitted and overlapped. It changes the stress environment of the lower coal seam roof, leading abnormal periodic weighting. In the procedure of coal seam 3-1 mining in the Huoluowan Coal Mine, the ground stress is high while the working face passing through the room pillars of overlying coal seam 2-2, leading to hydraulic shield being broken. In this paper, theoretical analysis, numerical calculation, and similar material simulation were used to analyse the stress environment of lower seam and the effect of coal pillars remained in close-distanced upper seam. The stress transfer model was established for the room pillars of coal seam 2-2, and the stress distribution of underlying strata was obtained based on theoretical analysis. The joint action of dynamic pressure of high stress-coal pillar with movement of overlying rock strata in the working face 3-1 under the coal pillar was revealed. The results showed that the horizontal stress and vertical stress under the large coal pillar of the room gob in coal seam 2-2 were high, being from 9.7 to 15.3 MPa. The influencing depth of vertical stress ranged from 42 m to 58 m. The influencing depth of horizontal stress ranged from 10 to 23 m. The influencing range of the shear stress was from 25 to 50 m. When the working face 3-1 was mined below the coal pillar of 20 m or 50 m, abutment pressure was relatively high. The stress concentration coefficient reached 4.44-5.00. The dynamic pressure of the working face was induced by the stress overlying of the upper and lower coal seams, instability of the inverted trapezoid rock pillar above the coal pillar, and collapsing movement of the roof. The studying results were beneficial for guiding the safety mining of the coal seam 3-1 in the Huoluowan Coal Mine