Effects of the ring-cut method as a settlement deterrent in a soft ground tunnel

This paper presents the results of centrifugal model tests and three-dimensional elasto-plastic finite element analyses carried out to clarify the effects of the ring-cut method on the restraint of the ground settlements ahead of a tunnel face. A model tunnel is excavated in a soft ground by a robot under a centrifugal loading state, and the ground settlements are measured during the progress of the face by a picture analysis system with high accuracy. The settlements generated by the full-face excavation method are compared with those generated by the ring-cut method for two kinds of grounds with different mechanical properties. The maximum settlement caused by the ring-cut method becomes about 36% of that caused by the full-face excavation method for the ground with low strength and about 58% for the ground with high strength. Considerations regarding these phenomena are given by conducting three-dimensional elasto-plastic finite element analyses.

► Settlements ahead of a face in a soft ground tunnel are measured in model tests.
► A tunnel is excavated by a robot under a centrifugal loading state.
► Two kinds of grounds with different mechanical properties are used.
► Settlement deterrent effect of a core left by ring-cut method is made clear.
► The effect changes with the mechanical conditions of the grounds.