Centrifuge modelling of long-term tunnelling ground movements

The increasing demand for public transport provision in cities has resulted in a requirement for enlarged public transport infrastructure. Where underground railways represent an important component of these systems, tunnel construction will inevitably lead to some degree of ground movement that can cause damage to surface structures and buried structures and services. It is important, therefore, that in the design of tunnels in urban environments these ground movements are predicted reliably. Predicting short-term ground movements resulting from tunnelling is standard when assessing the potential for damage to adjacent infrastructure. However, long-term tunnelling-induced ground movements and how these develop are understood less well and a research programme, based on geotechnical centrifuge modelling, is being conducted to improve our fundamental scientific understanding of this. The first stage of the programme has been to develop an apparatus that simulates the construction of a tunnel with a lining of known stiffness and permeability and allows construction ground loss to be replicated correctly. This paper describes the initial development of the apparatus along with results and analysis that demonstrates the suitability of the technique for the proposed study. The results obtained were observed to represent the short-term settlements that might be expected above a tunnel excavated in clay. The results also prove the modelling technique suitable for application in a full parametric study in which the geometry and boundary conditions of the model will be varied together with the permeability of the tunnel liner.