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Finite deformation simulation of CPTu tests in saturated structured clays

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conference contribution
posted on 14.05.2021, 08:49 by Kateryna Oliynyk, Matteo O. Ciantia, Claudio Tamagnini
In this paper a finite deformation version of an isotropic hardening elastoplastic constitutive model for bonded soils is used to reproduce the behaviour of a saturated soft structured clay during the penetration of a piezocone in standard CPTu tests. The formulation of the model is based on the multiplicative split of the deformation gradient and on the existence of a free energy function for the elastic behaviour. The model is equipped with two bonding–related internal variables which provide a macroscopic description of the effects of clay structure. The mechanical effects of structure degradation associated to the plastic deformations are quantified by suitable evolution equations. In order to deal with strain localization, typically observed in bonded geomaterials upon yielding, the model has been equipped with a non–local version of the hardening laws for the internal variables, which has proven to be capable of regularizing the pathological mesh dependence of classical finite element solutions in the post–localization regime. The results of the numerical simulations, conducted for different soil permeabilities and bond strengths, show that the model is capable of capturing: a) the development of plastic deformations induced by the advancement of the cone tip; b) the destructuration of the clay associated with such plastic deformations; c) the space and time evolution of pore water pressure as the cone tip advances. The possibility of modelling the CPTu tests in a rational and computationally efficient way opens a promising new perspective for their interpretation in geotechnical site investigations.

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