Grouting Spread and Sealing Mechanisms in Rough-Walled Fractures under Flowing Water: A Visual Experimental Investigation

Gaining a profound understanding of grout spread in natural fractures is essential for designing grouting solutions to prevent the water inrush hazard in underground engineering. Although an experimental apparatus exists to observe grout propagation, most studies simplify fractures into parallel smooth plates. Real fractures have rough surfaces that influence grout propagation. It is critical to evaluate the grout behavior in rough-walled fractures to establish efficient grouting designs. We designed a novel model test device to observe the grouting process under flowing water. This device consists of a seepage system with a rough-walled fracture, a monitoring system, and a grouting system. Using transparent materials and 3D printing technology, we generated fracture models with controlled roughness levels. The monitoring system automatically records the spread pattern, the fluid pressure, and the water flow rate. This device provides the possibility of observing the real-time grout spread via a rough-walled fracture. On this basis, we investigated the impact of fracture roughness, water flow rate, grouting rate, and water-cement ratio on the grout propagation. Then, the sealing mechanism of cement-based grout in rough-walled fractures was discussed. It is found that the rough-walled fractures restrict grout propagation, imposing progressively greater constraints with increasing roughness. Relative to smooth-walled fractures, rough-walled fractures reduce grout spread area by 4.6–19.5 %, yet increase grouting pressure by 20.9–101.3 % and seepage pressure by 12.7–87.8 %. An evaluation index of the deposition effect based on flow rate at the fracture outlet was proposed, which is more suitable for evaluating the sealing efficiency of the grouting test with cement-based grout.