Modelling the dynamic embedment of seabed pipelines

The as-laid embedment of a seabed pipeline is an important design parameter. As a pipe is laid on the seabed it oscillates, owing to vessel motion and hydrodynamic loading of the hanging pipe. This movement significantly increases the pipe embedment beyond the theoretical value related to the static pipe weight, even when corrected for any stress concentration caused by the hanging catenary. Dynamic lay effects are either ignored in practice, or are accounted for by scaling up the static embedment by an empirical factor, leading to significant uncertainty in this important design parameter. A series of centrifuge model tests has been conducted using two clays – kaolin and a high-plasticity natural clay – to simulate the dynamic embedment process. The results indicate that only a few cycles of small-amplitude oscillation (±0·05D) are required to double or triple the pipe embedment, owing to the combined effect of lateral ploughing and soil softening. In these experiments the pipe embedment increased to up ...