Jointed pipeline response to tunneling-induced ground deformation

Abstract

This paper focuses on the effect of tunneling-induced ground deformation on the response of jointed cast iron and ductile iron pipelines that (i) cross the settlement profile perpendicular to the tunnel centerline and (ii) connect through 90° tees with a pipeline parallel to the tunnel centerline. The modeling involves two-dimensional finite element analyses that account for coupled forces both parallel and perpendicular to the pipeline, and incorporates the results of large-scale laboratory tests to characterize the joints. Pipeline response is quantified with respect to joint rotation and pullout at various leakage levels as well as the allowable tensile strain. The paper describes soil displacements induced by a 6.1 m (20 ft.) diameter tunnel in clay and sand. Joint rotations and maximum tensile strains for pipelines in sand exceed those in clay by up to three for the same geometric conditions. Cast iron pipelines crossing the tunnel centerline are most vulnerable to leakage from joint rotation; ductile iron pipelines have sufficient capacity against joint leakage in all cases studied. Cast iron pipelines that connect with 90° tees are highly vulnerable to leakage from pullout due to lateral soil movement. Guidance is provided for risk assessment, design, and utility operations.