Cyclic and post-cyclic axial behaviors of steel pipelines buried in dense sand

The current design guidelines for underground pipelines do not consider cyclic axial soil-pipe interaction and its impact on post-cyclic pullout resistance, potentially leading to unsafe designs. This study conducted 12 large-scale physical model tests on steel pipes in dense sand to investigate their axial behavior during and after cyclic loading. A film-like sensor was employed to monitor soil-pipe interface contact pressure and earth pressure. The test program included different levels of pipe roughness, overburden pressure, and cyclic displacement. Given a cyclic displacement, the axial resistance in the first loading exceeds the guideline prediction, attributed to the increased interface contact pressures by constrained dilation. Subsequently, the axial resistance degrades over cycles. It stabilizes at a value that is roughness-dependent and smaller than the prediction because of the translation of the initial negative soil arching to positive soil arching on the pipe. The post-cyclic pullout resistance is smaller than the monotonic resistance without cycling when the cyclic displacement is relatively large (above 5 mm in this study). In contrast, the post-cyclic pullout resistance is above the monotonic resistance when the cyclic displacement is smaller due to cyclic loading-induced soil densification. The difference between post-cyclic and monotonic resistances for the rougher pipe is more significant.