Kuo, MY and Bolton, MD The nature and origin of deep ocean clay crust from the Gulf of Guinea. Geotechnique: international journal of soil mechanics. (Unpublished)Full text not available from this repository.
Deep ocean sediments off the west coast of Africa exhibit a peculiar undrained strength profile in the form of a crust, albeit of exceptionally high water content, overlying normally consolidated clay. Hot-oil pipelines are installed into these crustal sediments, so their origins and characteristics are of great interest to pipeline designers. This paper provides evidence for the presence of burrowing invertebrates in crust material, and for the way sediment properties are modified through their creation of burrows, and through the deposition of faecal pellets. A variety of imaging techniques are used to make these connections, including photography, scanning electron microscopy and X-ray computer tomography. However, the essential investigative technology is simply the wet-sieving of natural cores, which reveals that up to 60% by dry mass of the crustal material can consist of smooth, highly regular, sand-sized capsules that have been identified as the faecal pellets of invertebrates such as polychaetes. Mechanical tests reveal that these pellets are quite robust under effective stresses of the order of 10 kPa, acting like sand grains within a matrix of fines. Their abundance correlates closely with the measured strength of the crust. While this can easily be accepted in the context of a pellet fraction as high as 60%, the question arises how a smaller proportion of pellets, such as 20%, is apparently able to enhance significantly the strength of a sediment that otherwise appears to be normally consolidated. A hypothesis is suggested based on the composition of the matrix of fines around the pellets. These appear to consist of agglomerates of clay platelets, which may be the result of the breakdown of pellets by other organisms. Their continued degradation at depths in excess of 1 m is taken to explain the progressive loss of crustal strength thereafter.
|Additional Information:||This paper presents a strongly interdisciplinary piece of research that addresses the biological origin (faecal pellets and associated agglomerates) of many offshore sediments which exhibit crust-like undrained shear strengths. This work is of key interest and concern for the offshore energy sector, particularly with the embedment of hot-oil pipelines directly into the crust material; and thus forms the basis for future collaborative research and potential publications relating to soil-structure interaction of existing and future offshore energy structures. This particular paper was written based on analysis of samples provided through a collaboration with BP Exploration, however, the findings presented herein are also relevant to other existing research collaborations including the CITEPH JIP (Total, Technip, Acergy, Schlumberger Fugro France) and proposed collaborations with Senergy and Petrofac.|
|Uncontrolled Keywords:||clay fabric/structure of soils laboratory tests microscopy offshore engineering pipelines|
|Divisions:||Div D > Geotechnical and Environmental|
|Depositing User:||Cron Job|
|Date Deposited:||04 Feb 2013 18:10|
|Last Modified:||18 Mar 2013 01:06|
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