Video Observations of Dynamic Embedment During Pipelaying in Soft Clay

The as-laid embedment of a pipeline is an important parameter that affects many aspects of pipeline design. Offshore pipelaying is a dynamic process that causes pipelines to embed deeper than predicted based on static penetration models. This additional embedment is due to cyclic pipeline motions at the seabed that soften and displace the soil. This study presents observations from an ROV-based video survey of dynamic pipeline motion and as-laid embedment. The pipeline had a diameter of 12 inches and was installed from a J-lay vessel in 140 m water depth onto soft clay. The observations illustrate typical trends of embedment and seabed disturbance. Different lay conditions were encountered including downtime events and laydown of the final section of pipeline using a chain. From these observations, the effect of the dynamic behavior is quantified. The results show that in this case dynamic lay effects resulted in an as-laid embedment that was an order of magnitude greater than that from the submerged pipeline self weight alone, and was up to five times greater than the static embedment accounting for the vertical stress concentration from the pipeline catenary.