Deformation mechanism and control technology of surrounding rock in soft and broken roof roadway

In view of the difficulty of supporting the roadway with weak and broken roof, it is found, through field investigation and borehole exploration, that the surrounding rock of weak broken roof roadway has a self-stabilizing and balanced arch structure, but it is extremely unstable. On-site sampling and testing showed that the low strength of the roof rock block, fracture development of the coal block of the ribs and the weak mudstone of the floor were the main reasons for the instability of the full-section deformation of the roadway. The unreasonable shape of the original support scaffold, poor roof connection, lack of integrity of the support, and inability to coordinate and deform the support system were the direct causes of roadway instability.Further tests show that the weak fractured rock sample of the roadway has higher bearing capacity after compaction under lateral restraint conditions, and it is difficult to self-stabilize without lateral restraint conditions. The weakly cemented rock mass formed by cementing with a certain cement has a significant improvement in its stability and load-carrying capacity.Based on the Pushl's natural equilibrium arch theory and the "analogous hyperbola" model, a "parabolic-semi-hyperbolic" fracture boundary expansion model for the surrounding rock of weak broken roof roadway was constructed. It is found that the load of the weak broken roof increases exponentially. When the coal is unstable, the roof is unstable. The load increased exponentially. The load on the top plate increases sharply during stabilization, and the floor heave is an important factor that causes the instability of the upper part.Therefore, it is proposed to strongly control the weak broken roof, strengthen the restraining of coal seamin the ribs, strengthen the control principle of preventing floorheave of the roadway and the supporting principle of "stabilizing solid ribs first for controlling the top, preventing the bottom first for stablizingsolid ribs". According to the actual situation of the No.5305 working face of Zhoujing coal mine, the combined control technology of "double-layer metal mesh + shotcrete + pre-supported truss scaffold + shrinkable longitudinal connector" was proposed. Through preliminary field engineering practice, good supporting effect has been achieved.