A theoretical analysis of core extrusion and squeezing behaviour in tunnelling

摘要

The present paper investigates whether it is possible to predict squeezing intensity in tunnelling on the basis of the axial displacement of the core ahead of the face. Such a prediction would enable timely adaptations to be made to the temporary support and to the excavation diameter. The behaviour of the core ahead of the face is analysed by means of numerical computations which address the different effects of support measures and ground properties (strength, rheology and heterogeneity).The numerical results indicate that the prediction of convergence is theoretically possible only if the ground does not exhibit a pronouncedly time-dependent behaviour. Failing this, convergence predictions become very difficult, because core extrusion is governed by the short-term characteristics of the ground, which may be different from the long-term properties that govern final convergence. A large core extrusion represents a sufficient but not a necessary condition for large convergences to occur after excavation.