Stability analysis of a 3D shallow tunnel face considering the inclined excavation and inclined ground surface

Abstract

In tunnel engineering, the phenomena of inclined excavation and inclined ground surface for mountain tunnels, urban tunnels and cross-river (sea) tunnels are common due to the constraints of landform, design and construction. Inclined excavation and inclined ground surface have significant influences on the stability of shallow tunnel faces. However, their comprehensive influences on the active and passive failure modes of a shallow tunnel face need to be further studied. An improved three-dimensional failure model of a shallow tunnel face with multi-blocks is constructed in this study while considering their comprehensive influences, and the reliability of active and passive failure models is verified through comparative analysis. In addition, a series of detailed parametric analyses and key failure modes are carried out. The tunnel inclined angle (δ1) and inclined angle (δ2) of the ground surface have significant influences on the shallow tunnel face stability for active and passive failure modes. The percentages of change in the ground surface failure region are 47.81% for active failure and 5.82% for passive failure when δ1 varies from −10° to 10°, and 24.44% and 18.57%, respectively, when δ2 varies from −10° to 10°. In practical engineering, δ1 and δ2 must be controlled to within a certain range because a large δ1 can easily induce active failure, and a large δ2 can easily induce passive failure of a 3D shallow tunnel face.