Determination of grouting layer and stability analysis of slurry-resisting overburden in separation grouting

The technology of bed separation grouting subsidence reduction is one of the important means of protecting surface buildings and infrastructures in mining areas, the selection of the grouting layer and the integrity of the slurry-resisting overburden below are the key factors affecting the effectiveness of subsidence reduction. By means of theoretical analysis, on-site test and field monitoring, the determination of grouting layer in separation grouting and the stability of the Slurry-resisting overburden are studied. The theoretical analysis method was used to study the deformation characteristics of the slurry-resisting overburden in the separation grouting technique. A deflection curve equation for the slurry-resisting overburden based on the elastic foundation beam theory was established, and the elastic foundation coefficient of the rock mass below the slurry-resisting overburden was calculated according to the degree of rock damage zoning. The maximum bending subsidence value of the grout slurry-resisting overburden under grouting pressure was obtained; based on the failure condition of strata, the stability analysis method of the slurry-resisting overburden is given, the height of the free space below the slurry-resisting overburden before and after grouting was calculated, and based on the relationship between the maximum bending subsidence value of slurry-resisting overburden and the free space below, the integrity of the slurry-resisting overburden in the state of fixed-support beams and elastic foundation beams was judged; on this basis, a new discrimination method of the grouting layer is proposed by considering the grouting stratigraphic conditions and the stability of the slurry-resisting overburden. This discrimination determines the potential grouting layers by calculating the height of the water conducting fracture zone and each key strata, and then distinguishes the feasibility of each potential grouting layer according to the integrity analysis of the slurry-resisting overburden, the safety factor is introduced to evaluate its stability. Taking the 11090 working face as an engineering application example, the reasonable grouting layer was determined through the discrimination method, and the overburden bed separation grouting is successfully implemented at 139.1 m from the coal seam. Combined with the measured data from the surface observation station and the estimated surface subsidence, the maximum surface subsidence value after grouting was 230 mm, the subsidence coefficient was 0.12, and the subsidence reduction rate reached 77.6%. The maximum inclination value of nearby residential houses is about 0.8 mm/m, and the horizontal deformation value is 0.7 mm/m, effectively protecting the surface buildings and infrastructures, while ensuring the normal progress of underground mining, verifying the rationality of the grouting layer discrimination method, and providing reference for the design of separation grouting layer and the control of surface subsidence in the mining area.