Soil cover, rock cover and a combination of soil and rock cover are common approaches to protecting pipelines, cables and umbilicals associated with offshore energy infrastructure. However, with the exception of a simplified rock cover case or a simplified sand cover case, there is limited published guidance with respect to this design consideration.
Based on a bearing capacity approach, geotechnical numerical analysis techniques have been used to investigate the protection provided by a range uniform and mixed cover scenario. Effects related to rock placement in a slot-shaped trench have also been investigated.
Relatively standard observations were noted with respect to the protection provided by uniform soil or rock cover cases, including noting the different behaviours associated with granular drained cover materials and cohesive undrained cover materials. Some significant observations were made concerning the mixed cover cases. Of particular note was the impact of very soft clay as a limitation on the protection provided by the rock material. The influence of adjacent soil conditions on the protection provided by a rock infilled slot-shaped trench was also noted from analysis results.