Replicating the sequential excavation method in tunnel model tests

Abstract

To investigate soil deformation and stress distribution during tunnel excavation, a series of model tests were conducted at varying buried depths. These tests replicated the three-bench excavation method employed in the Luochuan Tunnel, utilizing prefabricated initial support segments connected by 3D-printed sliding connectors to achieve rapid sequential excavations and support installations. The results indicated that: (1) Increased buried depth enhances soil stability before excavation and reduces both the duration and magnitude of tunneling-induced disturbances. (2) A longitudinal soil arch forms in advance of the excavation face and weakens as the excavation face approaches the monitored cross-section. During excavation, the soil above the tunnel’s maximum width line exhibits a strong stress unloading effect, while the lower soil experiences significant loading. Consequently, the soil pressure in different directions takes on a bottle shape before excavation and transitions to a butterfly shape during and after excavation. (3) As buried depth increases, the triangular core soil arch transforms into an M-shape, accompanied by an increase in both the height of the core soil arch and the extent of the loosened zone. (4) For a given tunnel width, the distance of surface cracks from the centerline increases with buried depth, suggesting the presence of inclined failure planes rather than vertical failure planes above the tunnel, as proposed by Terzaghi.