Experimental Study on the Influence of Borehole Angles on Fracture Grouting in Limestone Aquifers

Grouting is an effective method to ensure mining safety by reconstructing confined aquifers. However, the effect of grouting on deep-buried aquifers is difficult to evaluate. Therefore, the experimental means in this paper are used to study the fracture grouting effect under the influence of borehole angles. A special device composed of boreholes and fractures is designed to study the whole process of grouting in limestone fractures. Four factors are tested in the experiment, including penetration distance, water separation, slurry stone body, and sealing effect. The results show that the slurry deposition can be divided into two stages, including the initial diffusion and the second gravity deposition. The water separation of mixed slurry is an important factor affecting the grouting effect. The slurry stone body formed through deposition is the key area for blocking water, and the borehole angles are the key to ensure the second gravity deposition. For a horizontal borehole, it is difficult to completely fill the space of fractures only by deposition and a certain angle is essential to achieve the second deposition. When the filling area of the fracture section is more than 90%, the flow characteristic of the fractures after grouting is closer to the equal percentage. When the filling area is less than 90%, the flow characteristics are approximately linear. At last, the data monitored in field grouting engineering are analyzed based on the grouting mechanism obtained from the experiment and the final consolidating form of slurry in a single fracture is described. The research is helpful for the optimization of grouting technology in the fractured aquifers under coal seams before mining.