Limit analysis of large defomation of deep-water pipelines under cyclic vertical pipe-soil interaction

The vertical pipe-soil interaction is the key element to determine the installation depth and the fatigue life of deep-water pipelines. A sequential limit analysis (SLA) is performed on the monotonic and cyclic loading behaviours of a rigid pipe in undrained clay. The numerical model incorporates the effects of strain softening and strain rate on the soil strength and the extremely large deformation of soils during pipe displacement. Moreover, the transition of failure mechanism of soils, formation of trenchs, collapse and backfilling of soils as well as pipes breaking out from soils during uplift can all be satisfactorily captured by the model. The validity and suitability of SLA in modelling such problems are demonstrated through a comparison with laboratory and centrifuge tests. Following that, the development of vertical resistance and failure mechanism of soils are discussed for a number of cases with different cyclic loading paths. The present study aims to provide guidance for the establishment of a simplified nonlinear pipe-soil vertical interaction model, and to promote the application of SLA method to modeling complex large-displacement geotechnical engineering problems.