Experimental study on concentration distribution of fracture grouting and discussion on its mechanism

Cement-based material is the most commonly used grouting material for anti-seepage and reinforcement in coal mines,which is a kind of suspension. For the fracture grouting in coal mines,the characteristics of the suspension affect the diffusion process of slurry and lead to a certain difference in the concentration distribution of slurry along the diffusion path. It severely affects the effect of grouting treatment. In order to investigate the concentration distribution of slurry in fracture grouting,a series of grouting laboratory test was carried out based on the self-developed grouting test platform. The ratio of the solid volume to the total volume of slurry after complete settlement was used as the characterization of the slurry concentration in fracture,and the concentration distribution characteristics along the diffusion path of slurry under different fracture apertures and the water-cement ratio were obtained. Based on the theory of non-Newtonian fluid mechanics,the formation mechanism of concentration distribution along the diffusion path of slurry was discussed. The results show that the concentration of each water-cement ratio slurry after grouting decreases with the increase of the diffusion distance,and shows a trend of flow thinning. The higher the slurry concentration near the grouting hole,the lower the slurry concentration at the slurry flow front. Under the condition of same fracture aperture,the concentration of slurry with low water-cement ratio along the diffusion path is greater than that of slurry with high water-cement ratio. The larger the fracture aperture is,the higher the slurry concentration is after grouting. The sedimentation and filtration characteristics of slurry during penetration result in the difference of concentration distribution of slurry after grouting. Combined with the above results,for the fracture grouting engineering,the slurry with relatively higher water cement ratio could be injected first to ensure that the slurry diffusion distance reaches the design value.Then the slurry with relatively lower water cement ratio is injected to increase the concentration of the entire slurry diffusion zone,thereby ensuring grouting effect.