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Microstructural study of the deformation zones during cone penetration in silt at variable penetration rates

Paniagua, P., Fonseca, J., Gylland, A. S. and Nordal, S. (2015). Microstructural study of the deformation zones during cone penetration in silt at variable penetration rates. Canadian Geotechnical Journal, 52(12), pp. 2088-2098. doi: 10.1139/cgj-2014-0498

Abstract

During conventional cone penetration testing in silt, the soil will normally be partially drained. If the penetration rate varies, time for drainage is altered and therefore the measured cone resistance and pore pressure will change. This paper studies the change in soil microstructure around the probe during cone penetration carried out at different penetration rates to investigate the failure mechanism and the processes controlling drainage in silt. Backscattered electron images of polished thin sections prepared from frozen samples at the end of penetration were used. Making use of advanced image processing techniques, the statistical distribution of particle orientations and the local porosity were investigated for the zones around the cone tip and the shaft. The spatial distribution of the measured microscale parameters in the region near the probe indicates that the soil deformation during CPTU in silt leads to the formation of both contractive and dilative zones. The macro response of the material, presented by the pore pressure and the cone penetration resistance measured during the test, results from the competition between these zones during penetration, which is shown to be dependent on the penetration rate.

Publication Type: Article
Publisher Keywords: Silts; Site investigation; Fabric/structure of soils; Microscopy; Cone penetration test
Subjects: T Technology > TN Mining engineering. Metallurgy
Departments: School of Mathematics, Computer Science & Engineering > Engineering
URI: http://openaccess.city.ac.uk/id/eprint/12316
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