Investigation of Tunnel Face Stability under Partial and Complete Water Submergence

Drilling tunnels in geologically complex terrain where groundwater is located is associated with serious challenges to achieve stability, which often leads to excessive deformation, redistribution of stress, and collapse. The pressure of groundwater is decisive in affecting the stress state in the tunnel face, and decreases the effective stress and changes the hydro-mechanical behavior of the surrounding ground. This paper provides a detailed numerical study of the stability of the tunnel face under different geological and ground water conditions using the Finite Element Method (FEM) The analysis will first analyze the tunnel behavior in dry (non-submerged) condition by introducing the major geotechnical parameters, including cohesion and friction angle, elastic modulus and in-situ stress conditions The subsequent analysis will assess the influence of groundwaters on the tunnel face and periphery, referring to three different situations, such as non-submerged, partially-submerged, and fully-submerged conditions with the The findings indicate that high groundwater levels contribute greatly to face deformation and concentration of stress, especially when using weak and fractured ground conditions Fully submerged conditions reveal a significant decrease in the effective stress, that results in an increase in the instability potential relative to dry and partially submerged conditions Fully submerged conditions Fully submerged conditions represent the strongest decrease in effective stress, which contributes to a higher instability potential as compared to dry and partially submerged situations.