Perturbation analysis for upheaval buckling of imperfect buried pipelines based on nonlinear pipe-soil interaction

Submarine pipelines are often operated under conditions of high temperature and high pressure, which may induce considerable axial compressive force. If the lateral movement is constrained, for instance, burying pipe or dumping gravel, upheaval buckling may happen. Pipe-soil interaction affects the upheaval buckling behavior of submarine pipelines. However, pipe-soil interaction models currently existing fail to reflect the drop process of uplift resistance when the vertical displacement is over mobilization distance. To solve this problem, a new nonlinear pipe-soil interaction model is presented and the governing differential equation of an imperfect pipeline on soft foundation is deduced. The solution to the governing differential equation is proposed based on nonlinear perturbation expansions. The effect of soil conditions, burial depth and initial imperfections on critical force as well as localization pattern of upheaval buckling are discussed. Results show that the capacity of pipeline against thermal buckling increases with the burial depth or maximum uplift resistance and decreases with the OOS of pipeline or mobilization distance. Critical buckling force is almost unaffected by pipe-soil interaction form, but the post-buckling response depends on pipe-soil interaction forms. The pipe-soil interaction model can be used not only in pre-buckling design but also in post-buckling control.