A comparison study of soil-conductor stiffness from centrifuge and laboratory testing

onductors are the outer most casing in an offshore well, providing axial and lateral support to the inner strings andmitigating hole collapse during drilling at shallow depth. Recent studies have investigated the geotechnical response of a conductorsubject to cyclic lateral loading induced by environmental conditions. Originally based on a series of centrifuge tests reported by BP,and subsequently extended through the development of a laboratory scale testing apparatus (operated by NGI), the result is a growingbody of test data in this area. To extend and verify this experience for other soil types and a wider range of riser motion histories, anew research project was launched at The University of Western Australia, which explores the life cycle behaviour of conductors.The objective of this paper is to present a comparison between results from recent centrifuge testing and companion tests performedby NGI using the laboratory (p-y) apparatus. The tests were performed on reconstituted samples of kaolin clay and carbonate silt. Aparallel suite of simple shear tests at different strain rates was also performed. These are presented in a way that allows directcomparison to the centrifuge and p-y apparatus data. Where differences are observed, these are discussed and explanations proposed.The data obtained is also plotted against the recommendations in a recently published approach, to be used as the basis of a draftindustry standard – with an emphasis on identifying potential refinements of the method to capture soil-specific characteristics.