Probabilistic analysis of the uplift resistance of buried pipelines in clay

Uplift resistance provided by soil cover is a key aspect in the design of a buried offshore pipeline. The capacity must be sufficient to avoid upheaval buckling but prediction of the uplift resistance is complicated by disturbance of the soil structure during installation. Previous numerical investigations of pipeline uplift capacity in undrained clays have employed simple elasto-plastic models and consider a homogeneous clay. These simplifications neglect critical features of soil-pipeline interaction and may not describe the real mechanical behaviour. In this paper, an advanced kinematic hardening model implemented in a finite element code is used to capture the degradation of structure as a pipeline buried in a natural clay is lifted upwards. The spatial variability of clay structure is represented by a random field and Monte Carlo simulation used to characterise the response. This novel framework shows that clay structure has a significant effect on the failure mechanism and uplift capacity of a buried pipeline. The probabilistic approach accounts for the uncertainty in the condition of the clay backfill and reveals that the spatial distribution of intact and remoulded material can change the mode of failure, emphasising the importance of considering clay disturbance in design.