Numerical Study on Diffusion Distance and Plugging Effect of Grouting in a Vertical Fracture Under High Water Pressure

Coal mining is threatened by the aquifers below coal seams, and grouting is used to reconstruct the aquifers before mining. However, water gushing-out sometimes still occurs from the grouted aquifers. In this paper, two aspects of grouting in a vertical fracture are studied by numerical methods, including the slurry diffusion distance and the influence of grouting stone body on water inflow and water pressure. First, a grouting model consisting of a fracture and a borehole is proposed based on the hydrogeological conditions and grouting processes. Two hydrodynamic models controlled by the grouting stone body are established to study the variation of the water inflow and the water pressure in the filled section of the fracture. Then, the numerical calculation is carried out in detail. The numerical results show that the diffusion distance following the flow direction is significantly greater than the distance against the flow direction. The dynamic viscosity is successfully used to simulate the plugging effect of the grouting stone body. For a same fracture section, when the ratio of the maximum filled area to the fracture section area before grouting is less than 90%, the flow velocity presents an upward trend with the flow section decreasing due to the Venturi effect caused by the grouting stone. When the ratio of these two areas is more than 90%, the change of the flow velocity can be explained by the equal percentage characteristic of the valve. The data monitored by typical boreholes during grouting show that the water inflow and the water pressure both reduce after grouting or water inflow decrease and the water pressure keep unchanged after grouting, which is approximately in line with the fracture flow pattern controlled by the valve open degree. This study is conducive to the theoretical research of grouting engineering.