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Interface Shear Testing Of Gulf Of Guinea Sediments: Implications For The Design Of Hot-Oil Pipelines And Suction Caissons

Published: Offshore Site Investigation and Geotechnics: Integrated Geotechnologies – Present and Future: Proceedings of the 7th International Conference, 12-14 September 2012, London, UK, Society for Underwater Technology, London

12 Sep 2012
MYH Kuo and MD Bolton (University of Cambridge), Alain Puech (Fugro)

Interface shear tests undertaken with a Cam-shear device have been conducted on very soft clay core samples from the Gulf of Guinea. These tests have been completed at normal effective stresses applicable to pipelines and suction caissons. Pipeline tests were conducted on rusted and coated steel, and on smooth and rough polypropylene interface material at speeds of 0.050mm/s and 0.001mm/s. Tests relevant to suction caisson installation and extraction were conducted on a rusted steel plate at shear rates of 1mm/s and 5mm/s. It is shown that the interface friction value is strongly influenced by both the shearing rate and the interface roughness, leading to the following conclusions. Firstly, rough and smooth interfaces produce comparable peak interface friction values. However, shearing on rough interfaces can produce lower residual friction values than on smooth interfaces. Secondly, slow shearing can produce residual interface friction values that are significantly higher than obtained during fast shearing. Thirdly, the apparent roughness of an interface is likely to be a function of the existing natural soil structure, which includes robust faecal pellets ranging in proportion from 20% to 50% by dry mass. The paper concludes by highlighting relevant implications for the design of pipe-lines and suction caissons located in similar sediments.


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