The upheaval capacity of pipelines in jetted clay backfill

Offshore pipelines are often placed in the seabed by the process called jetting, which has implications for the resistance of the soil to upward pipeline movements. A series of centrifuge model tests has been conducted to investigate the uplift capacity and the load-displacement behaviour of pipelines buried in recently liquefied clay. Undrained uplift capacities were seen to be lower than the drained capacities. Recently liquefied clay may still be consolidating when pipelines are commissioned; the effective stresses in the soil (and thus the shear strengths) at the expected switch-on time have to be calculated in order to calculate the uplift capacity of the pipeline. A simple method is presented which predicts uplift capacity from the average degree of consolidation of the backfill.