Subsidence owing to tunnelling. II. Evaluation of a prediction technique

A numerical and a simplified empirical design procedure (based on the concept of the gap parameter) for predicting settlement above tunnels constructed in soft ground are evaluated with reference to 14 case histories. These records encompass very stiff to soft clays. A comparison of observed and calculated behaviour indicates that the proposed numerical and empirical approaches are capable of providing a reasonable estimate of the gap and the surface settlement provided that the soil parameters are reliably determined. It is suggested that the simplified procedure may be used for preliminary design. The gap parameter can also be used in conjunction with more sophisticated numerical methods to predict the variation in settlement with position and depth at critical sections of the tunnelling project. Key words : tunnelling, settlement, subsidence, clays, soft-ground analysis, design, case history, finite element.