Finite element analysis of the vertical penetration of 'on-bottom' pipelines in clay

This paper reports a series of finite element analyses which were conducted to investigate the relationship between vertical pipeline load and pipeline burial for a pipeline resting on soft, undrained clay. The analyses investigated particularly the changes in deformation mechanism in the soil as burial increased and the effect of surface heave caused by the embedment on the bearing capacity. Results are presented from two different types of FE analysis. In one set, the pipeline was installed from above the soil surface using a large-strain formulation and soil heave occurred around the pipeline. In the second set of analyses, the pipeline was 'wished-in-place' at different embedment depths and penetrated vertically to failure using a smallstrain formulation. The vertical capacity penetration curves from the two sets of analyses are compared with each other and with previously published solutions. Results show that the effect of the surface heave is not significant, but the unit weight of the soil should be considered when calculating the penetration depth of a pipeline.