Influence of confined water on the limit support pressure of tunnel face in weakly water-rich strata

In the process of shield tunneling through soft soil layers, the presence of confined water ahead poses a significant threat to the stability of the tunnel face. Therefore, it is crucial to consider the impact of confined water on the limit support pressure of the tunnel face. This study employed the finite element method (FEM) to analyze the limit support pressure of shield tunnel face instability within a pressurized water-containing layer. Subsequently, a multiple linear regression approach was applied to derive a concise solution formula for the limit support pressure, incorporating various influencing factors. The analysis yields the following conclusions: 1) The influence of confined water on the instability mode of the tunnel face in soft soil layers makes the displacement response of the strata not significant when the face is unstable; 2) The limit support pressure increases approximately linearly with the pressure head, shield tunnel diameter, and tunnel burial depth. And inversely proportional to the thickness of the impermeable layer, soil cohesion and internal friction angle; 3) Through an engineering case study analysis, the results align well with those obtained from traditional theoretical methods, thereby validating the rationality of the equations proposed in this paper. Furthermore, the proposed equations overcome the limitation of traditional theoretical approaches considering the influence of changes in impermeable layer thickness. It can accurately depict the dynamic variation in the required limit support pressure to maintain the stability of the tunnel face during shield tunneling, thus better reflecting engineering reality.