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University of New South Wales (UNSW) 2011

The cone penetration test in unsaturated sands

Pournaghiazar, Mohammad

Titre : The cone penetration test in unsaturated sands

Auteur : Pournaghiazar, Mohammad

Université de soutenance : University of New South Wales (UNSW)

Grade : Doctor of Philosophy (PhD) 2011

Résumé
The cone penetration test (CPT) is widely used for in situ characterization of saturated or dry soils based on correlations developed for saturated/dry conditions. However, no methods currently exist for interpretation of CPT data in unsaturated soils. This study advances both experimental and theoretical bases for interpretation of CPT data in unsaturated soils.In particular, a calibration chamber has been designed and constructed to perform laboratory controlled cone penetration tests in unsaturated soils. The chamber allows the independent application of lateral and vertical pressures to an unsaturated soil specimen while suction is controlled using the axis translation technique. A unique feature of the chamber includes the specimen formation system, enabling dry pluviation, static or dynamic compaction to be used. The results of cone penetration tests conducted on saturated and unsaturated sand specimens are presented and the significant contribution of suction to cone penetration resistance is highlighted. In addition, a novel solution procedure for the problem of cavity expansion in finite soil media has been developed which enables evaluation of chamber boundary effects and the extension of CPT results from chambers to free field conditions. It is possible to use hardening/softening elastic-plastic constitutive models formulated in the critical state framework in the analysis for the first time. A simple method is then presented which enables either : i) the contribution of suction to the effective stress (χs) in an unsaturated sand to be estimated when results of CPTs are available for both saturated and unsaturated ground conditions ; ii) an equivalent saturated cone penetration resistance to be determined from a value measured for unsaturated conditions, provided that χs is known for the unsaturated conditions, permitting the use of established charts to estimate strength and stiffness parameters. Established CPT correlations for sands are extended to account for influences of suction. The extended correlations enable direct characterization of an unsaturated sand from CPT results provided the contribution of suction to effective stress (s) is known. It is shown that failing to account for χs in the mean (or vertical) effective stress when interpreting CPT results may result in significant and non-conservative misrepresentations in estimated sand parameters.

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