Axial pullout behaviour of fusible PVC pipes and fusion weld joints assessed using distributed fibre optic sensors

Abstract

Pipes are subjected to axial pulling forces that lead to shear stresses at the soil–pipe interface and axial strain distributions from various circumstances, including pulled-in-place pipe installation and permanent ground deformations. This study investigates the axial pullout response of fusible polyvinyl chloride pipes in dense sand. Three tests were conducted using a large-scale soil chamber to assess the development of axial resistance and the impact of non-continuous pulling and fusion weld joints. The measured maximum load response was significantly underpredicted by guidelines typically used in practice. Additionally, non-continuous pulling and changes to the pull rate had negligible impacts on the load–displacement response. Pipes were instrumented with distributed fibre optic sensors (DFOS) to capture the nonlinear development of strains along these flexible pipes and the mobilization of soil friction along the soil–pipe interface. Measurements have provided insight into the propagation of axial strains along the pipe, the additional longitudinal restraint provided by fusion weld joints, and their impact on the axial force distribution along pipes. The “locked-in” strains due to residual soil–pipe friction remaining after the axial pulling force is removed have also been measured using DFOS.