Effect of seepage flow on face stability for a tunnel in water-rich silty clay overlying sandy cobble strata

The stability of the excavation face plays a pivotal role in ensuring the safety control of shield tunneling. However, there is a dearth of existing literature on the investigation of excavation face stability in inclined composite strata under the influence of seepage. This paper conducts model tests to investigate the instability of excavation faces in inclined strata under varying seepage conditions (three cases). It examines the variations in effective support pressure, surface settlement, and earth pressure throughout the process of instability. The experimental results were validated through numerical simulation. The instability zone and deformation modes are subjected to a comprehensive analysis. The results indicate that the presence of seepage enhances the limit support pressure, consequently reducing the required backward displacement to attain such pressure. The presence of seepage (k = 1.0 and k = 0.5) exerts a more pronounced influence on surface settlement, leading to amplified surface collapse when compared to the no-seepage case (k = 0). The influence extent in front of the excavation face gradually increases as the value of k increases. The soil arching effect is significantly weakened due to the influence of seepage, leading to substantial surface collapse. The findings of this study offer valuable insights into the operational strategies for shielding in water-rich silty clay layers overlying sandy cobble strata.