Failure mechanism of surrounding rock and control of floor heave in heterogeneous composite rock roadway

Under the complex stress environment of deep high ground stress and interlayer weak interlayer (structural surface), the deformation of the surrounding rock of composite coal (rock) roadway is severe, and the floor heave is particularly prominent. In view of the technical difficulties in the large deformation of the floor heave in the complex region of -830 roadway in a mine, the deformation and failure characteristics of the roadway are investigated, and the failure mechanics mechanism of the surrounding rock is analyzed. Based on the theory of slip-line field, a mechanical model for the floor heave is established and is used to derive an explicit analytical formula for the failure radius of the floor (R₀). With the help of ZDY borehole peeper, the development degree of damage cracks in the surrounding rock is quantified. The UDEC numerical calculation model is established to inverse the stress of the surrounding rock, fracture development characteristics and displacement distribution laws of composite rock roadway under the original support, and the deformation mechanism of floor heave of composite rock roadway is comprehensively analyzed. The results show that the high ground stress, large difference in the ultimate strength of adjacent rock, poor lithology of floor, no support or weak support of floor are the fundamental causes of deformation of the floor heave in composite rock roadway. Considering the results of field investigation and numerical simulation analysis, based on the control idea of "solid bottom-strong side" overall support and "strong-weak-strong" combined bearing ring to strengthen the floor plate step by step, a combined support technology of "full-section anchor cable + precast block inverted-arch" is proposed and applied to the repair practice of the floor heave of composite rock roadway. The field monitoring results show that the floor heave deforms slowly until it becomes stable within 60 days of roadway repair, and the maximum floor heave is about 67.9 mm, which is 95% lower than that under the original support conditions, greatly reducing the possibility of repeated repair of roadway and ensuring the safe and efficient mining of coal resources in the mine.