Abstract: To solve the problems of preventing and controlling water for vertical shaft in ultra thick dissolved porous dolomite aquifer in southwest China, a grout-water two-phase radial diffusion model is proposed to study the diffusion laws of the grout in the porous stratum based on Darcy’s law. The fractional-flow equation of grout is derived and the advancing distance of the grout saturation along the radial direction is obtained. According to the distribution of the grout saturation along the radial distance, the diffusion area could be divided into grout area, grout-water mixing area and water area. The shock saturation front is the interface between the grout-water mixing area and the water area. The grout saturation face moves forward with the grout injection, and the effective diffusion distance of the grout to meet the requirement of water prevention is significantly smaller than the diffusion distance of the shock front. Moreover, the technical parameters of surface pre-grouting for sealing the dissolved porous dolomite aquifer in ventilation shaft of the Laohudong phosphate mine are studied by field test combining with numerical simulation. The optimal borehole spacing and effective diffusion distance are obtained. Consequently, the engineering design of surface pre-grouting for the ventilation shaft is proposed based on these technical parameters. Finally, after the completion of grouting, the sealing efficiency of the grouting for the ventilation shaft could reach up to 98.04% obtained from the water pressure test. The research results of the present paper could provide technical reference for water sealing by grouting for similar porous aquifer.

Key words: dissolved porous stratum, dolomite aquifer, grouting for water prevention, grout-water two-phase flow, radial diffusion model