Distributed fibre optic sensing of strains on buried full-scale PVC pipelines crossing a normal fault

Seismic faulting is extremely detrimental to buried pipelines owing to bending moments and axial forces generated by the soil–pipe interaction. Pipe responses to ground rupture are usually evaluated by beam-on-spring analysis. However, the empirical data used to define the spring response were obtained for steel pipes with high flexural stiffness and the effectiveness of the resulting spring stiffness values for flexible pipes is questionable. This paper presents full-scale tests undertaken using a new split-box apparatus which permits the testing of pipes in dry sand subject to a normal fault with dip angle of 90°. Four polyvinyl chloride (PVC) pipes (various diameters), one instrumented with strain gauges and three instrumented with fibre optic sensors, were tested to provide experimental evidence for flexible pipes. The research includes confirmation of the effectiveness of fibre optic strain measurement, which has the advantage of providing much more data than the limited discrete values obtained from conventional strain gauges. However, the fibre optic strain sensing technique is limited to strain values below 1%. The prototype-scale testing permits assessment of the efficacy of the current design approaches, including the relative success of accounting for reduced spring stiffness or patterns of imposed deformation.