Study of Asymmetric Face Failure and Limit Support Pressure During Curved Tunnels Excavation in Sandy Soils

Abstract

With the continuous urban development, tunnels are increasingly designed with curved alignments to avoid existing structures and to make better use of the underground space. However, these tunnels are usually subjected to complex forces, and current research on the curved tunnels face stability remains incomplete. This paper presents a detailed face stability analysis of curved tunnels, both analytically and numerically. Initially, a series of 3-D numerical simulations are performed to investigate the spatially asymmetric failure pattern of the soil ahead of the curved tunnel face and the stress transfer mechanism of the soil arching effect during the excavation process is explored. Subsequently, based on traditional limit equilibrium methods and the results from numerical simulations, an improved wedge-prism model and corresponding theoretical calculation formulas for the limit support pressure are proposed. The validity of the improved model is confirmed through illustrative analyses, while sensitivity analyses are conducted on the impacts of soil internal friction angle, structural depth ratio, and tunnel curvature radius on the limit support pressure. This study can aid in the calculation of the stability of the tunnel face and the limit support pressure in curved tunnel excavation.