Pipelines in deep water are usually laid on the seabed, penetrating by a fraction of the pipe diameter, rather than being buried. Thermal expansion and contraction of the pipeline during operation can lead to lateral buckling. For a buckle to be initiated, the pipe must break out from the as-laid position. The seabed sediment found in deep water is typically soft clay, which remains undrained during pipe embedment and breakout. In this paper, finite element (FE) analyses of a shallowly-embedded pipeline under vertical and horizontal load are used to generate yield envelopes in V-H load space, indicating the load conditions that will lead to breakout. Two FE techniques are used: (i) conventional displacement FE analysis, using ABAQUS, and (ii) an FE-based limit analysis technique to produce upper bound plasticity solutions. In particular, these analyses examine the influence of separation between the pipe and the soil when tension is applied. Separate yield envelopes are derived for the cases involving separation (no tension) and full bonding (full adhesion / unlimited tension) at the pipe-soil interface. Simple curves are fitted to these envelopes in order for the results to be applied in the routine assessment of pipe breakout behaviour.
12th International Conference of International Association for Computer Methods and Advances in Geomechanics (IACMAG). Proceedings of the 12th International Conference of International Association for Computer Methods and Advances in Geomechanics (IACMAG) (Goa, India 1-6 October, 2008) p. 4249-4256