• Geomechanics and Engineering
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• v.18 no.2
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• pp.121-131
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• 2019

This article discusses the phenomenon of plastic volumetric deformation of naturally structured clays before virgin yielding, i.e., subyielding behavior. A simple approach representing both the compression and shear responses of the clays during subyielding is demonstrated. A new compression model for structured clays based on the theoretical framework of the Structured Cam Clay (SCC) model via incorporation of the subyielding behavior is presented. Two stress surfaces are introduced to distinguish the subyielding and virgin yielding. The hardening and destructuring processes of structured clays under isotropic compression and shear are the focus of this work. The simulations of the compression and shear of eleven natural clays are studied for validation. The proposed work can accurately predict the subyielding behavior of structured clays both qualitatively and quantitatively and can be used for modeling structured clays under compression and shear responses in geological and geotechnical engineering problems.

• Geomechanics and Engineering
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• v.7 no.2
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• pp.213-231
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• 2014

An elastoplastic model for structured clays, which is formulated based on the fact that the difference in mechanical behavior of structured and reconstituted clays is caused by the change of fabric in the post-yield deformation range, is present in this paper. This model is developed from an elastoplastic model for overconsolidated reconstituted clays, by considering that the variation in the yield surface of structured clays is similar to that of overconsolidated reconstituted clays. However, in order to describe the mechanical behavior of structured clays with precision, the model takes the bonding and parabolic strength envelope into consideration. Compared with the Cam-clay model, only two new parameters are required in the model for structured clays, which can be determined from isotropic compression and triaxial shear tests at different confining pressures. The comparison of model predictions and results of drained and undrained triaxial shear tests on four different marine clays shows that the model can capture reasonable well the strength and deformation characteristics of structured clays, including negative and positive dilatancy, strain-hardening and softening during shearing.

• Geomechanics and Engineering
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• v.8 no.5
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• pp.707-726
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• 2015

This paper investigates the time dependent behaviour of Haarajoki test embankment on soft structured clay deposit. Half of the embankment is constructed on an area improved with prefabricated vertical drains, while the other half is constructed on the natural deposit without any ground improvement. To analyse the PVD-improved subsoil, axisymmetric vertical drains were converted into equivalent plane strain conditions using three different approaches. The construction and consolidation of the embankment are analysed with the finite element method using a recently developed anisotropic model for time-dependent behaviour of soft clays. The constitutive model, namely ACM-S accounts for combined effects of plastic anisotropy, interparticle bonding and degradation of bonds and creep. For comparison, the problem is also analysed with isotropic Soft Soil Creep and Modified Cam Clay models. The results of the numerical analyses are compared with the field measurements. The results show that neglecting effects of anisotropy, destructuration and creep may lead to inaccurate predictions of soft clay response. Additionally, the numerical results show that the matching methods accurately predict the consolidation behaviour of the embankment on PVD improved soft clays and provide a useful tool for engineering practice.

• Geomechanics and Engineering
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• v.11 no.5
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• pp.725-738
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• 2016

A theoretical study of the behavior of structured soils is presented herein. By introducing the effect of soil structure and loading history into the Cam Clay model, a new model was formulated. The concept of differing void ratios was modified to combine structural parameters and the over consolidation ratio, and an evolution law was proposed. Upon introducing the concept of the subloading yield surface, a new two-yield surface model was obtained. The predicted results were compared to the experimental data, demonstrating that the new model provided satisfactory qualitative modeling of many important features of structured soils.