Optimisation of Rock Berm Shapes for Pipeline Protection

In shallow water rock dump berms are routinely employed for product protection. Conventional berm shape is based on a minimum 0.6m rock cover height, 1m wide crest and 1:3 slopes. This paper presents the results of physical model tests undertaken to assess the effectiveness of conventional berm design to mitigate trawl gear loads on rock-dumped pipelines and assess the benefits from adopting alternative berm shapes. Testing was undertaken at SINTEF's test facilities in Trondheim, Norway, and comprised a series of scale model tests to assess the impact of trawl gear on various rock berm configurations. Both the trawl gear and the berms were fully modelled allowing the true trajectory of the trawl to be assessed as it was pulled over the berms. Penetration of the trawl gear and the resultant loads imposed on buried pipelines during the trawl pull overs were captured. Comparisons between alternative and conventional rock berm configurations were made. The findings indicate similar levels of protection can be achieved by using alternative berm configurations. However, these alternative berm configurations offer significant reductions in rock volumes required to form the berms which first reduce their environmental impact and secondly reduce rock berm installation time and costs.