Effect of Drainage on Upheaval Buckling Susceptibility of Buried Pipelines

This paper investigates the effect of soil drainage on the uplift resistance of buried pipelines, and their susceptibility to upheaval buckling. The uplift resistance of buried pipelines is considered through analytical and numerical predictions for both drained and undrained conditions. Combinations of soil strength parameters for typical soils are estimated based on common correlations. For certain ranges of typical normally consolidated soil conditions, particularly those with high critical state friction angles, the drained uplift resistance may be lower than the undrained resistance. This observation is important because in typical practice only drained or undrained behaviour is considered depending on the general type of soil backfill used. In this case, the critical or minimum uplift resistance may be overlooked. Further, the changing undrained uplift mechanism between shallow and deep conditions is investigated. It is found that the common approach of considering the minimum of either a local (flow around) or global (vertical slip plane) failure can overestimate the uplift resistance in normally consolidated soils.