Research on backfill technology of drilling shaft sinking method in porous water-bearing rock stratum

To solve the problem of the backfill layer of the drilling method in porous water-bearing rock stratum in western China, the mechanism of filling layer and material preparation were studied. Firstly, taking the central air return shaft of Kekegai Coal Mine as the engineering background, the fluid-structure interaction of surrounding rock, filling layer, and drilling shaft lining was analyzed by using Comsol Multiphysics numerical calculation software. The calculated results show that the effective stress and pore water pressure curves show obvious “pressure drop funnel” type characteristics (that is, the decrease rate is faster the closer to the shaft center), and the steep drop section of the curve is located in the backfill layer zone. It can be seen that the backfill layer not only plays the role of cementing and sealing water; but also has the function of load reduction in porous water-bearing rock stratum in western China. Then, based on the effective stress principle and Darcy seepage theory, it is proposed that the backfill material should have low permeability, high strength, large specific gravity, small expansion, unshrinking, and good fluidity of the mixture to meet the requirements of pumping mechanized construction. Therefore, it is proposed that high performance cement mortar should be used as the backfill material of the drilling shaft in the porous water-bearing rock stratum in western region. Finally, the main physical and mechanical properties of backfill material were measured by orthogonal test, and the influence of the mass content of fly ash and expansion agent on the factors of backfill materials was studied by the range analysis method. At the same time, the specific gravity, triaxial compressive strength, and permeability coefficient are taken as the final evaluation indexes of its performance. Moreover, through the orthogonal experiment and the filling material of the main physical and mechanical performance test, and based on the comprehensive balance method to obtain the backfill material of optimal mixing proportion of cement∶fly ash∶expansion agent∶water∶sand∶pumping agent=1∶0.286∶0.143∶2.144∶0.443∶0.014 3. The research results provide a theoretical and practical basis for the backfilling of the porous water-bearing rock stratum in western China.