Lateral Breakout Resistance of Shallowly Embedded Offshore Pipelines

Abstract

Stresses induced by thermal expansion of unburied seabed pipelines can be designed to be relieved through controlled lateral buckling, which requires accurate and reliable assessment of the lateral breakout resistance. The lateral breakout resistance is strongly dependent on the pipe embedment, soil strength and loading history of the pipe. In addition, prediction of the pipe movement during the breakout process is essential as it subsequently determines the lateral resistance at large displacement. Theoretical solutions based on plasticity theory are available for combined vertical and horizontal loading on partially embedded pipes. These solutions however ignore the pre-failure pipe displacement and the associated change in soil geometry which could have significant influence on the failure load. A series of 1g model tests has been conducted to examine the lateral breakout resistance for a shallowly embedded pipe in a soft clay. Two types of tests, (1) sideswipe tests and (2) probe tests, were conducted to examine the effect of pipe embedments and loading history on the breakout resistance of a partially embedded pipeline. Results were compared with other proposed predictions in order to provide a more rigorous basis for the prediction of the breakout resistance of a partially embedded pipeline.