Experimental Study on the Diffusion Radius of Modified Slurry Used in Longwall Overburden Isolated Grouting

Abstract

The slurry diffusion radius is an important parameter in grouting engineering. In some cases, injection into partial overburden is needed in grouting engineering, and it is thus critical to control the slurry diffusion so as to reduce unnecessary grout take. In an effort to solve such issues in longwall overburden grouting, we proposed the addition of cement as a means of modifying fly ash slurry in order to reduce grout diffusion and grout take. The characteristics of the modified slurry were determined under different water-ash ratios and cement-blending ratios. The cement-blending ratio was found to have a small effect on the density of the slurry but a significant effect on the slurry’s precipitation rate and viscosity. The slurry diffusion experimental system was established to study the diffusion radius and consolidation. Results for both the fly ash slurry and the modified slurry revealed a circular diffusion pattern centered around the grouting borehole. The diffusion radius of the modified slurry made with 10% cement was 19.4% lower than that of the fly ash slurry, but its solidification thickness appeared to increase. The modified slurry diffusion had a two-stage effect: a “stability control stage” and a “consolidation control stage.” In the consolidation control stage, the diffusion radius of the modified slurry was smaller than that of the fly ash slurry, and this stage was the key to control the diffusion radius of the slurry. Field trials were conducted based on the results of the study, and grout take was reduced effectively. This research provides a theoretical basis for slurry diffusion radius control in longwall grouting.