## 1 Introduction  
Prediction of the behavior of soil as a foundation for various man-made structures represents a very important part of geotechnical engineering. The types of soils and the natural ground conditions are so diverse that the task of determining how the soil will perform under an imposed load, or under various construction works, can be complex. Thus, the development and application of advanced constitutive soil models, which can include different aspects of soil behavior, is a very significant task for both researchers and geotechnical engineers. A soft soil deposit can be very demanding for modeling, design, and construction, even with the considerable developments in geotechnical engineering during the past several decades [1]. Overconsolidated soft clays are acknowledged as one of the most problematic soils because of their deficient mechanical properties [2]. The mechanical properties of overconsolidated soft clays depend on the causes of overconsolidation such as desiccation stresses due to moisture extraction by plant roots and surface evaporation, secondary consolidation, changes in static groundwater level, and the erosion of surface material [3]. Earthfill embankments, used for supporting roads, railroads and serving as floodwalls along riverfronts and coastlands, are often built on soft soil deposits [4]. In the past, embankments were built on firm soil in order to reduce construction costs, but in recent years, they are increasingly being built on sites consisting of soil layers with poor mechanical characteristics [5]. Because of such geotechnical conditions, it is very important to accurately assess the mechanical behavior of the soil, especially settlement. The use of numerical methods, such as the finite element method, requires the proper formulation of constitutive laws that can reproduce all of the important aspects of a soil's behavior. A good way to validate the suitability of the constitutive model used for clay soil is a comparison of the predicted and field-measured behaviors [6]. One of the most widely used elastoplastic soil constitutive models for modeling clays' behavior is the Modified Cam Clay (MCC) model [7]. Due to its simplicity, well established model parameters, and its ability to satisfactorily predict some facets of clayey soil's behavior, it is usually the first model of choice employed in numerical analyses [1; 6; 8; 9; 10; 11; 12; 13; 14; 15]. Although the MCC model can adequately describe the behavior of normally or slightly overconsolidated clay, it possesses certain drawbacks when used for overconsolidated clays [16; 17]. The Soft Soil (SS) constitutive model was developed for soft soils, such as slightly overconsolidated clays, clayey silts, and peaks, as a modification of the MCC model [9; 18]. The Soft Soil Creep (SSC) model is the improved SS model, with the ability to model creep behavior of soft clays susceptible to secondary consolidation using the logarithmic creep function [18; 19]. Both SS and SSC combine the Mohr-Coulomb failure criterion with the cap yield surface of the MCC model. One of the drawbacks of the previous three constitutive models is that they are isotropic yielding models. The S-CLAY1 and S-CLAY1S constitutive models are developed in the critical state framework, and can account for plastic strain induced anisotropy (S-CLAY1) and anisotropy combined with destructuration (S-CLAY1S) [9; 10; 20]. Application of the MELANIE model, which represents a modification of the MCC model for anisotropic conditions with a non-associated flow rule, can be found in [14; 21]. The MIT-E3 [22] constitutive model, based on bounding surface plasticity, has also been used to predict overconsolidated soft clays' behavior as an embankment base [21; 23]. The MIT-E3 model incorporates: anisotropic yield surface, kinematic plasticity, strain softening behavior under undrained conditions, small nonlinear elasticity using a closed loop hysteretic stress-strain formulation, and bounding surface plasticity [24].