ABSTRACT
Understanding the ground response to tunnelling is important for evaluating its effects on existing structures and buried infrastructure. The simulation of tunnel ground loss in soil using a geotechnical centrifuge is a convenient and widely accepted approach to analysing ground movements induced by tunnelling. Tunnel volume loss in the centrifuge is commonly simulated as a plane strain condition in which the internal tunnel pressure is released by extracting fluid from inside a flexible membrane (i.e. pressure control). There are relatively few cases in which mechanical models have been developed to simulate the tunnelling problem, where the tunnel volume loss is induced by an inwards radial movement of the model tunnel lining (i.e. displacement control). Existing mechanical model tunnels impose concentric movements of the tunnel lining towards the tunnel centre. This paper presents the development of an eccentric rigid boundary mechanical (RBM) model tunnel that has the ability to produce non-uniform radial displacements around the tunnel lining, causing maximum soil displacements at the tunnel crown and no displacements at the tunnel invert. The paper provides the detailed mechanical design of the model tunnel and results from three centrifuge tests in sand with tunnel cover to depth ratios of 1.3, 2.0 and 2.4. Greenfield tunnelling settlement trough data obtained using the newly developed RBM model tunnel are compared against previously published data obtained using a flexible membrane model tunnel.
