Simulation Analysis on the Mud Film Stability for Urban Slurry Shield Tunnel

Objective As the sand layer located at the launching end of the slurry shield section is connected with seawater during the tunnel construction of Xiamen Metro Line 3, accidents like water and mud gushing, ground collapse may occur when the shield starts. Therefore, it is necessary to study the mud film stability of urban slurry shield tunnel to ensure the construction safety. Method A numerical model is developed to simulate the mud film formation and infiltration process under different permeability conditions by using the DEM-CFD (Discrete Element Method-Computational Fluid Dynamics) coupling method. The impermeability stability of the mud film is evaluated by analyzing the spatial distribution of slurry particles, the mud film hydraulic pressure changes, and the force chain network. Result & Conclusion The increase in sand particle size and slurry cohesion inhibits and enhances mud film formation, its long-term impermeability and mechanical stability under dynamic hydraulic loads respectively. The increase in cohesion enhances both the mud film forming density and the impermeability stability. However, the enhancement of impermeability stability is limited for the mud film on smaller grain size stratum. In sandy stratum with large pores and low cohesion, the mud film is prone to collapse, but increasing the cohesive force can effectively enhance its stability. Therefore, by selecting the appropriate particle size ratio and slurry cohesion, mud film impermeability stability can be improved to meet the engineering requirements.