Tunnelling in soils: movements and structures

Abstract

The present dissertation describes some of the ground movement problems associated with tunnelling in soft ground. A possible response of pipelines to such ground movements is also studied in the context of a case history of pipes lying parallel to a tunnel centre line. Analyses of tunnel excavation with and without lining installation, and of the pipe behaviour, have been performed by means of the finite element method. Four examples of analysis and their results are presented, with the main characteristics related the each being highlighted. Field observations of ground movements caused by tunnelling in soil have been gathered together and added to those presented by Peck (1969) and Attewell (1977) in order to attempt to define empirical relations that could describe a geometric form of settlement profile and to predict its magnitude. A three-dimensional finite element program has been written in order to carry out the style of analysis that two-dimensional models cannot accommodate. The isoparametric hexahedral rectangular element has been used in view of its facility in programming and discretising the medium of interest. The computer program has been developed to allow for different loading conditions and calculations to be carried out using linear material behaviour only. Features which have been considered in the tunnel-ground-pipes analyses include simulation of incremental construction. Because it was clearly impractical to model the entire system of interest by means of a single finite element mesh, an alternative analytical-numerical hybrid technique is described.