Numerical Simulation and Critical Threshold Analysis of the Failure Process for Shield Tail Sealing System under High Water Pressure

The waterproof sealing performance of the shield tail sealing system is an important factor to ensure the safe construction of shield tunnels. This paper focuses on analyzing the shield project of the Wuhan metro, specifically examining the spatial arrangement of the shield tail sealing cavity and tail brush. By incorporating the linear permeability of the tail brush into our model, we aim to conduct numerical simulations using computational fluid dynamics (CFD) to investigate the performance of the shield tail sealing system under high water pressure. This study delves into the flow patterns of water and grease in the event of a failure in the shield tail sealing system. We aim to investigate how various parameters, including the structure of the shield tail brush, properties of the grease used, and other conditions, impact the waterproof sealing performance. The results show that under high-pressure water intrusion into the shield tail sealing system, water tends to permeate primarily through the bottom of the shield tail brush, which exhibits the highest permeability. This creates a dominant flow channel within the grease cavity. The failure process of the shield tail sealing is divided into five stages. Between pressure differences of ΔP = 0 to 1 MPa, the sealing ability of the shield tail shows minimal variation. Increasing the viscosity of grease and reducing the permeability of the tail brush can effectively prolong the breakdown time and enhance the safety capability of the shield tail. Beyond a pressure difference of ΔP = 1 MPa, these measures generally prove ineffective. Utilizing this model and the designated time limit for shield tail failure, we propose optimal grease and tail brush parameters to guide the safe construction of shield tunnels.