Experiment-based study on three dimensional seepage at tunnel junction of parts constructed by different methods

Composite construction methods may be adopted in some underwater tunnels due to complex geological conditions. However, the seepage field at the junction between parts constructed by different methods has been rarely reported. This study used the Pearl River Estuary Tunnel as a case study to conduct model experiments on the connection part and its adjacent mining and shield parts, which have different drainage systems. Through model experiments, the study explored the variation laws of water inflow and external water pressure on the tunnel lining. The experimental results were validated against numerical simulations. The results indicate that, longitudinally, the junction experiences pressure fluctuations due to variations in construction methods and tunnel cross-sectional dimensions. A logistic fit of the experimental data shows that fluctuations range from 12 to 21 m in the mining part and from 27 to 42 m in the shield part. The longitudinal distributions indicate that water pressure remains stable in the shield part, while in both the connection and mining parts it is influenced by the drainage pipes. Transversely, water pressure increases from the arch crown to the arch bottom, forming an approximately circular distribution. Both water pressure and inflow increase linearly with rising water levels. A comparison between experimental and simulation results shows a relative error of less than 9 %, confirming the accuracy of the experimental model. The study’s findings provide deeper insight into the seepage field at the junction of underwater tunnel parts, with implications for the design and construction of similar projects.