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The influence of a time delay between sequential tunnel constructions
In congested urban areas twin-tunnelling projects have an associated requirement for accurate predictions of any ground movements that may arise in order to minimize possible damage to existing structures. Much previous research has been carried out concerning the ground movements around single tunnels in greenfield conditions and this, along with field observations, forms the basis of most ground movement predictions. For twin-tunnel projects the prediction of overall ground movements is often based upon superposition of two equal settlement troughs. Previous research by the current authors has shown that this assumption may be invalid for most cases. The research presented in this paper considers the influence on observed ground movements of a construction process that involves a delay between the construction of each tunnel, compared with tunnels constructed simultaneously. A series of four centrifuge tests is described and the results are presented in terms of the ground movements measured at the surface