THE INFLUENCE OF TUNNEL EXCAVATION ON THE HYDRAULIC-HEAD

In this paper an alternative method is proposed for computing the effect of tunnelling on the piezometric head field during construction. The seepage flow equations, usually formulated in a fixed co-ordinate system are here reformulated within a frame of reference that advances together with the tunnel heading. The governing equations contain the advance rate as an additional parameter, and are solved by the finite element method. The quasi-steady state (i.e. the steady state in the moving frame of reference) can then be computed in a single step. Selection of a marching scheme in the time domain is, therefore, rendered unnecessary. Thanks to the economy of the proposed method, it has been possible to carry out comprehensive parametric studies, the results of which are presented in a dimensionless form. The applicability of the computational method to poroelastic problems is also addressed.