Backfill grouting diffusion law of shield tunnel considering porous media with nonuniform porosity

Current studies usually do not consider the effect of spatially inhomogeneous distribution of formation parameters on grout diffusion caused by shield tail voids. To solve the above problem, this study proposes a nonuniform pore model for porous media formation and establishes a one-dimensional penetration grouting diffusion model considering the spatial nonuniformity of formation pores under the condition of constant grouting pressure. This model was used to analyze the penetration diffusion behavior of grout in the strata and the influence of parameters such as grouting pressure, water-cement ratio, and formation displacement. The numerical solution was provided by the finite element software COMSOL. According to the degree of cement particle blockage, it is pointed out that there is an injectability control zone in the grouting process. A one-dimensional visualized penetration grouting diffusion simulation system considering the shield tail gap was designed, and a grouting diffusion test was carried out with cement slurry. The results show that grouting pressure, water-cement ratio, and soil displacement have a significant influence on the grout deposition process. The higher the grouting pressure, the lower the water-cement ratio, the faster the formation turns into the non-injectable state. The grouting pressure has little influence on the injectable control zone, while the larger the water-cement ratio, the greater the displacement of the formation, and the farther the injectability control zone is from the grouting hole. By comparing the nonuniform pore model with grouting test, the rationality of the nonuniform pore model is verified, which provides guidance and a basis for backfill grouting.