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Durham University

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Publication details for Professor Ashraf Osman

Smit, G., Jacobsz, S.W. Gaspar, T.A.V. & Osman, A. S. (2019), Centrifuge modelling of pile pull-out tests in expansive soil, 17th European Conference on Soil Mechanics and Geotechnical Engineering ECSMGE. Reykjavik, Iceland, Icelandic Geotechnical Society, Reykjavik, Iceland, 1-8.

Author(s) from Durham


Designing foundations of wind turbines in expansive soils present a challenge. Piled foundations are often used to mitigate some of the problems associated with construction on expansive soils. Swelling clays frequently occur in an unsaturated state in many arid and semi-arid areas of the world. Upon wetting, soil sur-rounding the pile shaft simultaneously undergoes softening and expansion. While swelling of adjacent soil will increase confinement and thus pull-out resistance, the softening caused by an increase in saturation could lead to a reduction in pull-out resistance. The conflicting consequences of these two mechanisms have been previously documented by independent studies reporting the results of in-situ concrete plug pull-out tests. The interaction between the pile shaft and soil and the resulting shaft capacity in this context are not well understood. It is therefore not clear whether tests conducted in the wet or dry season will result in conservative or non-conservative indications of pile shaft capacity. This article presents the results of centrifuge tests undertaken to investigate shaft friction mobilised on concrete piles subjected to pull-out tests in expansive soils under in-situ and saturated moisture conditions. A comparison of results from tests performed prior to and after swelling showed that pull-out loads were substantially reduced during wetting and swelling, implying that softening dominated over in-creased swell pressures.