Abstract
In this work, a constitutive model able to capture the strain rate dependency, small strain effects and the inherent anisotropy is proposed considering the influence of the overconsolidation ratio (OCR). Small strain effects are captured by using an extended ISA plasticity formulation (Fuentes and Triantafyllidis in Int J Numer Anal Methods Geomech 39(11):1235–1254, 2015). The strain rate dependency is reproduced by incorporating a third strain rate mechanism (in addition to the elastic and hypoplastic strain rate). A loading surface has been incorporated to define a three-dimensional (3D) overconsolidation ratio and to account for its effects on the simulations. Experimental investigations using Kaolin Clay and Lower Rhine Clay with horizontal bedding plane have shown that under undrained cycles of small strain amplitudes (<10^{-4}), the effective stress path in the p–q space is significantly inclined towards the left upper corner of the p - q plane. Consequently, a transversely (hypo)elastic stiffness has been successfully formulated to capture this behaviour. The performance of the model has been inspected by simulating the database of approximately 50 cyclic undrained triaxial (CUT) tests on low-plasticity Kaolin Clay (Wichtmann and Triantafyllidis) considering different deviatoric stress amplitudes, initial stress ratios, displacement rate, overconsolidation ratio and cutting direction. Furthermore, 4 CUT tests conducted on high-plasticity Lower Rhine Clay were simulated, whereby the influence of the displacement rate, as well as the deviatoric stress amplitude, has been analysed. The simulations showed a good congruence with the experimental observations.
Highlights
The prediction of the soils irreversible displacements is indispensible for the performance-based design of structures subjected to cyclic loading
The inherent anisotropy incorporated in the model requires the calibration of the material parameter a termed as anisotropic coefficient and the definition of the unit vector along the sedimentation axis ms
The present work proposes a constitutive model with some interesting capabilities, such as the simulation of the strain rate and time dependency and the incorporation of small strain and of inherent anisotropic effects, permitting the user to evaluate the influence of each effect on a simulation, without changing the model and keeping the same set of material parameters
Summary
The prediction of the soils irreversible displacements is indispensible for the performance-based design of structures subjected to cyclic loading. Most natural clays show anisotropic behaviour due to their mode of deposition and the elongated shape of the particles [3,4,5,6]. This anisotropy, known as inherent anisotropy, along with the time-dependent phenomena of soft soils, has practical consequences for, that is, the passive lateral thrust on piles, which has been the target of many investigations in the last decades. Uses projections in the stress space (similar to [5]) Without projections in the stress space Rate independent Inclusion of rate and time dependency Inherent anisotropy introduced
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