Nallathamby Sivasithamparam

Comparison of Anisotropic Rate-Dependent Models for Modeling Consolidation of Soft Clays

Two recently proposed anisotropic rate-dependent models are used to simulate the consolidation behaviour of two soft natural clays: Murro clay and Haarajoki clay. The rate-dependent constitutive models include the EVP-SCLAY1 model and the Anisotropic Creep Model (ACM). The two models are identical in the way the initial anisotropy and the evolution of anisotropy are simulated, but differ in the way the rate-effects are taken into consideration. The models are compared first at the element level against laboratory data and then at boundary value level against measured field data from instrumented embankments on Murro and Haarajoki clays. The numerical simulations suggest that at element the EVP-SCLAY1 model is able to give a better representation of the clay response under oedometric loading than ACM, when the input parameters are defined objectively. However, at boundary value level the issue is not as straightforward, and the appropriateness of the constitutive model may depend heavily on the in situ overconsolidation ratio (OCR).

Towards consistent numerical analyses of embankments on soft soils

A consistent automated parameter derivation method for an advanced constitutive model, Creep-SCLAY1S, which considers anisotropy, structure and creep in soft soil is presented. The algorithms are i...

The comparison of modelling inherent and evolving anisotropy on the behaviour of a full-scale embankment

The behaviour of a full-scale embankment constructed on a soft soil deposit has been studied using two different anisotropic elasto-plastic constitutive models, namely S-CLAY1 and Sekiguchi–Ohta (SO) inviscid, in order to investigate the influence of modelling (initial) inherent and evolving anisotropy on boundary value level simulations. The initial inherent anisotropy which is generally modelled by a rotated yield surface can also influence the model prediction capability. A Finnish test embankment known as Murro embankment was chosen for finite-element analysis using the two advanced soil models. The predictions of each model were studied and compared with measured field data. For the purpose of model comparison, the influence of evolution of anisotropy was further investigated by using only the inherent anisotropy feature of S-CLAY1 model, by setting the values of rational hardening parameters to zero. Overall, the S-CLAY1 model predictions are in good agreement with the measured data, which is due to the incorporation of a rotational hardening law (evolution of anisotropy) into the model in addition to the consideration of inherent anisotropy. However, the SO inviscid model predictions are less comparable with the measured data due to the consideration of only the inherent anisotropy into the model. The results clearly demonstrate the importance of including soil’s evolving anisotropy in the analysis and how the inherent anisotropy is modelled (i.e. the shape of yield surface).

A Constitutive Model for Soft Clays Incorporating Elastic and Plastic Cross-Anisotropy

Natural clays exhibit a significant degree of anisotropy in their fabric, which initially is derived from the shape of the clay platelets, deposition process and one-dimensional consolidation. Various authors have proposed anisotropic elastoplastic models involving an inclined yield surface to reproduce anisotropic behavior of plastic nature. This paper presents a novel constitutive model for soft structured clays that includes anisotropic behavior both of elastic and plastic nature. The new model incorporates stress-dependent cross-anisotropic elastic behavior within the yield surface using three independent elastic parameters because natural clays exhibit cross-anisotropic (or transversely isotropic) behavior after deposition and consolidation. Thus, the model only incorporates an additional variable with a clear physical meaning, namely the ratio between horizontal and vertical stiffnesses, which can be analytically obtained from conventional laboratory tests. The model does not consider evolution of elastic anisotropy, but laboratory results show that large strains are necessary to cause noticeable changes in elastic anisotropic behavior. The model is able to capture initial non-vertical effective stress paths for undrained triaxial tests and to predict deviatoric strains during isotropic loading or unloading.

Modeling Pile Setup in Natural Clay Deposit Considering Soil Anisotropy, Structure, and Creep Effects: Case Study

AbstractThis paper reports the results of a numerical investigation of the behavior of a natural soft clay deposit under the installation of a case study pile. The case study problem included installation of an instrumented close-ended displacement pile in a soft marine clay deposit, known as Bothkennar clay, in Scotland. The site has been used for a number of years as a geotechnical test bed site, and the clay has been comprehensively characterized with both in situ tests and laboratory experiments. The soft soil behavior, both after pile installation and subsequent consolidation, was reproduced by using an advanced critical-state-based constitutive model that accounts for the anisotropy of soil fabric and destructuration effects during plastic straining. Furthermore, a time-dependent extension of the model was used to study soil creep and the significance of its consideration in the overall pile-installation effects. The simulation results were compared against field measurements; furthermore, for compa...

Creep of geomaterials – some finding from the EU project CREEP

This paper gives a summary of some of the main findings of the EU founded project “Creep of geomaterials”, CREEP. CREEP was an Industry-Academia Partnerships and Pathways (IAPP) project funded from...

Comparison of anisotropic rate-dependent models at element level

Two recently proposed anisotropic rate-dependent models, EVP-SCLAY1 and ACM are used to simulate the stress-strain behaviour of Vanttila clay. The models are identical in the way the evolution of anisotropy is simulated, but differ the in way the rate-effects are taken into account. Based on numerical simulations against element level tests, using objective parameters, suggest that EVP-SCLAY1 is able to give a better representation of the clay response at element tests than ACM in 1D loading, but the latter gives a better prediction for undrained strength.