Stability of pipelines in trenches

The need for the study reported in this paper was originally identified during the engineering of the 24-inch West Sole
gas pipeline in 1980. The West Sole field is characterised
by high currents that generally flow across the pipeline
route. It had been found that it was not practicable to
apply adequate concrete coating to stabilise the 24-inch
pipeline on the seabed without incurring installation and
manufacturing difficulties. It was therefore decided to
achieve stability by trenching the pipeline, Previous
experience of pipeline burial in the West Sole field by the
then commonly used jetting technique had been found to be
generally unsatisfactory in the very stiff boulder clays
that predominated, BP subsequently trenched the 24-inch
pipeline in a l m deep trench, using the post-ploughing
technique and following a full-scale offshore trial in
seabed materials representative of the proposed pipeline
route. This was the first application of post-ploughing in
the North Sea.