Construction of key bearing structures of the topsoil layer and dynamic control of surface structures

Aiming at the problems of high cost and large filling volume in goaf subsidence control through filling methods, this paper proposes a protective mining method for small-scale surface structures based on "artificial key bearing structure plus dynamic grouting". With theoretical analysis, physical and numerical simulation, this study investigates the mechanical characteristics of the key bearing structure, the stability of the key bearing structure under dynamic grouting, the characteristics of surface movement and deformation, and the influence of the key bearing structure parameters on the grouting filling. The results show that the filling volume is approximately piecewise linearly related to the depth of the key bearing structure. The closer the key bearing structure is to the surface, the smaller the grouting filling volume is. The key bearing structure is constructed in the surface soil layer by splitting grouting method. The stability of this structure and the upper surface soil layer can then be maintained by filling with dynamic grouting in the underlying separation layer and coordinating this process with the mining speed. The relationship model between key bearing structure parameters and grouting filling step is established, and the expression of dynamic grouting filling step is derived. It is found that the maximum filling step increases with the increase of tensile strength and thickness of the key bearing structure, and decreases with the increase of the ratio of topsoil load to building load. After dynamic grouting filling, the peak value of surface horizontal deformation above the key bearing structure is 1.59 mm/m, the peak value of inclination is 2.71 mm/m, and the peak value of curvature is 0.033×10⁻³ m⁻¹, which are reduced by 87.8%, 89.8%, and 80.8%, respectively. The surface deformation meets the requirements of the first-level damage grade of the structure and basically no maintenance is required.