Study On Grout Diffusion In Fracture-Pore Medium

Water gushing disaster controlling problem of underground engineering has been one of the main problems of underground engineering safety and rapid construction, and underground engineering rock mass has diversified structure, strong anisotropy, difference of hydrogeological conditions and characteristics, which puts forward a severe challenge to the grouting treatment. Among them, the underground engineering is widely existed in the rock mass (such as high porosity sandstone formation with high permeability), which is more serious and the surrounding rock mass is very strong, surrounding rock is not only as the main water storage medium, but also as the water guide channel and the fracture to form the groundwater flow channel. This kind of rock mass can be abstracted as pore-fracture medium in the study of grouting theory. The pore-fracture medium has the following characteristics: ①Fracture network is cutting across rock mass, and the fracture conductivity is strong;②The porous medium has high porosity and permeability, and compared with the fracture, the permeability performance is at the same order of magnitude. ￤hen the fluid flows in the medium, there is a strong mass exchange between the fracture flow and the pore flow in the fracture boundary. In this paper, based on the analysis method of fracture flow and pore flow, the diffusion of Newton fluid in the fracture pore dual medium is studied, the influence of different parameters on the diffusion of slurry in the double medium of fracture and pore was analyzed systematically, and achieved a series of achievements. Then based on the research results, the paper puts forward suggestions for improvement of the actual grouting design from two angles of grouting and reinforcement.(1) According to the hydraulic characteristics of fractured rock mass with severe fracture cutting and strong permeability of surrounding rock, the fracture pore dual medium model is established. The diffusion process of slurry is simplified as the horizontal radiation circle, which single fracture and porous medium is selected as the research object, with the seepage process of slurry in the side wall of the fissure channel in the process of diffusion of fracture, the motion control equations of the fracture grouting diffusion process and the permeability grouting diffusion process are established respectively. The two-way coupling of two diffusion processes is realized by using the permeability of slurry in the pore medium of the bedrock, and the corresponding mathematical model is established.(2) The paper presents an analysis thought of dual medium grouting diffusion which depended on the method of trial and error, an iterative calculation method is established for the diffusion of the pore-fracture medium, the effective description of the grouting diffusion process in the pore-fracture medium is realized, which can be used to solve the permeability of the grout in the pore of the bedrock at any moment of grouting, and provides a new idea for the analysis of the process of the pore-fracture medium. Through the calculation and finite element calculation software COMSOL to benchmark the dual medium grouting diffusion process results, verify the rationality of the proposed calculation method.(3) By using the proposed theoretical model and calculation method, the simulation of grouting process in different conditions is carried out, and the reasonable boundary conditions and initial conditions are selected. According to the actual working conditions, the grouting parameters are selected, and the pressure distribution law and diffusion pattern of the slurry in pore-fracture medium and single flat fracture are obtained.(4) Respectively for the impact of factors, and through the comparative analysis, a series of slurry diffusion laws were obtained. From two angles of grouting water plugging range and reinforcement range, the difference between the pore-fracture medium model and the traditional fracture grouting model is analyzed. And through the comparison of the parameters, the influence of the pore-fracture medium model on the grouting work is explained.(5) Based on the orthogonal experiment, the orthogonal experiment of 5 factors and 4 levels was selected, the influence factors of the infiltration and diffusion of the slurry in the bedrock pore medium are obtained:Fracture opening> permeability> porosity> grouting time> grouting rate. Hope to guide the work of grouting design.(6) Through the pore-fracture medium grouting diffusion experiment and analyzing the experiment phenomena, then combining with the results of the scanning electron microscope, we can draw the following conclusions:in the process of the pore-fracture medium grouting, the diffusion and migration of slurry is more complex than traditional fracture grouting or infiltration grouting, fracture channel has high permeability, and the permeability of the bedrock pore medium is several orders of magnitude lower than the fracture channel. Slurry from the fissure channel into the bedrock pore medium to generate cross flow, this process results in the diffusion of the slurry in the bedrock pore medium, rather than just the diffusion of the grout in the fracture system.