Response of continuous pipelines to tunnel induced ground deformations

Abstract

This thesis develops analytical solutions for estimating the bending moments and axial loads in a buried pipeline due to ground movements caused by tunnel construction in soft ground. The solutions combine closed-form, analytical solutions for tunnel-induced, free-field ground deformations in a plane orthogonal to the heading (Pinto and Whittle; 2001) with Winkler models for pipe-soil interactions. The free-field ground deformations are described in terms of two parameters describing the modes of cavity deformation and the elastic Poisson's ratio of the ground. The solutions have been evaluated by others through comparisons with well-instrumented case studies for a variety of different tunneling construction methods and ground conditions. Analytical approximations for the vertical and horizontal spring stiffness coefficients in the Winkler models are interpreted from numerical finite element analyses. The proposed analyses are compared with prior solutions proposed by Vorster (2005) and Klar et al. (2005) that rely on empirical procedures to estimate the ground deformations and focus only on bending response of the pipeline. The current research provides independent validation of the vertical spring coefficient proposed by Klar et al., and derives a novel interpretation of the horizontal spring coefficient. Results of the proposed analyses are presented graphically in design charts that show the deformations of the pipeline as functions of the pipe and tunnel geometry, tunnel cavity parameters, elastic properties of the ground and relative pipe-soil rigidity parameters. The solutions are used to re-analyze the deformations of a water main associated with a pipe-jacking procedure at an instrumented site in Chingford, London reported by Vorster (2005). The thesis also presents a hypothetical example that considers the impacts of the construction of a largediameter sewer tunnel in soft clay using EPB construction methods (using free-field performance data from the N-2 project in San Francisco) on existing utilities. In this case, potential damage to cast-iron water pipes is clearly linked to the pipe section properties and the EPB tunnel face pressure. Data from well-documented case studies must now be obtained to validate the proposed analyses.