Asymmetric seformation mechanism of roadway at steeply inclined thick coal seam

In view of the asymmetrical deformation failure in the mining roadway at a steeply inclined special thick coal seam,some field observations,mechanical modeling calculations and numerical simulation analysis were used to reveal the asymmetrical deformation failure mechanism after the excavation of the roadway in steeply inclined coal seams. The stress field after the excavation of the roadway and the distribution characteristics of the plastic zone were analyzed. A new support and reinforcement scheme for the retractable U-shaped steel and asymmetric prestressed anchor ( cable) support was proposed. The study shows that:① the asymmetrical failure of the roadway is characterized by the subsid-ence,slippage,and internal expansion along the bedding of the hard rock strata along the side of the coal body;the subsidence of the top of the side of the hard rock is greater than that of the coal side and the central axis of the road-way inclines to the coal side. ② The asymmetric deformation mechanism of the roadway is that,under the effect of non-uniform load,the angle and size of the counterforce of the shoulder angle support on both sides of the roadway are changed. The reaction force of the hard rock lateral support is greater than that of the coal side. Also the inclination an-gle of the coal side is larger than the side of the hard rock. The side rock of the hard rock layer slides,sinks,and ex-pands along the bedding under the action of small angle and large stress,and the side of the coal body is pushed out of the drum under the action of nearly vertical angle force. ③ The bending moment of the roadway from the side of the hard rock to the side of the coal body is increasing all the time. The shear force appears to increase first,then decrease and then increase,and the direction changes in the second increase. The position of the direction change is the offset position of the roadway axis inclining to the side of the coal body. The axial force appears as a parabola,decreasing first and then increasing. The optimum and reasonable section of the roadway under non-uniform load acts is the “asymmetric three-hinged arches”. ④ The retractable U-shaped steel and asymmetric prestressed anchor (rope) sup-port are proposed,focusing on reinforcing the lateral support of the roadway coal body and the top support on the side of the hard rock.