Synchronous grouting diffusion and parameter optimization of shield tunnels based on discrete element method

In order to evaluate the quality of the synchronous grouting of shield construction and to propose the regulation means of grouting parameters, taking the coastal sandy soil stratum as the target, the model tests on shield synchronous grouting are designed and carried out to obtain the slurry diffusion laws at various locations at the outside of a tunnel. On the basis of calibrating the contact parameters between particles in the discrete element model with the help of the test results, a continuous-discrete element coupling model for the shield synchronous grouting is established to simulate the process of filling and penetration of the slurry, and to analyze the main reasons leading to the difference in the thickness of the slurry layer in comparison with the test results, and then to optimize the filling effects of the slurry by adjusting the grouting parameters. The results show that the particle migration characteristics of the discrete element simulation model can effectively display the filling and permeation phenomena of the slurry in the excavation gap and the surrounding soil layer. Affected by the mobility, the slurry is easy to gather in the grouting hole, and if the grouting pressure is insufficient, it will lead to poor homogeneity of the slurry layer at the upper and lower sides of the tunnel which are far away from the grouting hole. The filling effects can be effectively improved by adjusting the pressure difference between the grouting holes of the shield machine. Affected by the pressure of the soil layer, the thickness of the slurry layer at the upper side of the tunnel is relatively thinner compared to that at the lower side, and the slurry at the lateral side of the tunnel will deposit under the action of its own gravity, and shows a distribution of "thin on the upper part and thick on the lower part".