This paper describes a series of experiments to investigate the effects of water entrainment in soil around and beneath oscillating cylinders at the seabed. This knowledge is important in order to predict the as-laid embedment of pipelines laid on the seabed, and to model how risers and chains interact with the seabed during their design life. The experiments consist of harmonic vertical oscillation of a circular pipe section into and out of model seabeds of selfweight consolidated clay, followed by immediate measurements of the undrained soil strength with mini T-bar testing and water content in the pipe footprint. The paper confirms that water entrainment can increase the soil sensitivity significantly compared to the fully remoulded strength measured without water entrainment (i.e. that of a non-surface-breakaway T-bar cyclic test), and discusses the potential of using these findings to form a soil mechanics-based framework to predict the effects of water entrainment on the strength of soil around offshore infrastructure.
F. Sahdi, J. G. Tom, P. Watson, C. Gaudin and M. F. Bransby
Keywords: pipe-soil interaction, clays, softening, water entrainment
Publisher: DFI