Face stability analysis of a submerged shield tunnel driven in inclined layered soils

Abstract

The excavation of submerged shield tunnels in saturated inclined layered soils is commonly encountered in engineering practice. However, previous studies have primarily focused on the tunnel face stability in saturated horizontal layered soils. Additionally, the existing approaches for calculating the seepage flow field have limitations in terms of accuracy or efficiency. To address these issues, a modified approach is proposed to evaluate the face stability of a circular shield tunnel driven in saturated inclined layered soils, enabling the assessment of face stability at various excavation locations. The distribution of pore water pressure is derived from a customized FEM solver and incorporated with the discretization-based rotational failure mechanism. Additionally, the validation of the rotational failure mechanism in saturated inclined layered soils is performed through numerical results, along with comparisons of the critical collapse pressure against previous theoretical results. The effects of soil interface position and attitude on tunnel face stability are further investigated. It is revealed that: (1) the proposed approach is highly effective in accurately estimating the critical collapse pressure at various tunneling positions for a submerged shield tunnel driven in saturated inclined layered soils; (2) the customized FEM solver significantly enhances computational efficiency and accuracy compared to previous theoretical approaches. Additionally, it requires significantly lower computational costs than the commercial FEM solver; (3) the critical collapse pressure decreases nonlinearly and then increases slowly with a gradually extended critical failure mechanism when a tunnel traverses an inclined soil interface for the upper cohesive and lower sandy soil layers.