Abstract
Abstract This paper presents a new rate-dependent hypoplastic constitutive model for overconsolidated clays. The model is developed based on a basic hypoplastic model proposed recently for sand. New density and stiffness factors are introduced to account for history dependence. The Matsuoka-Nakai failure surface is incorporated for the limit stress criterion. With six constitutive parameters, the model is capable of predicting the hardening/softening, shear dilation/contraction, and asymptotic state for overconsolidated clays. Comparison between numerical predictions and experimental results shows this model can properly describe the main features of both reconstituted and undisturbed clays with different overconsolidation ratios.
Highlights
Constitutive modeling of overconsolidated (OC) clays has a long history, pioneered by the Modified Cam-clay (MCC) model based on the critical state concept [32, 33]
The first attempt to extend hypoplastic model for clay was made by Niemunis [26, 27], who combined the critical state concept with hypoplasticity to describe the behavior of OC clays
The first five have the same physical interpretation as those used in the MCC model: φc is the critical state friction angle; N is the value of ln(1 + e) at the isotropic normal compression line for p = 1 kPa; λ∗ is the slope of the isotropic normal compression line on the ln(1 + e) − lnp plane; κ∗ denotes the slope of unloading line in the same plane, and vi is ratio between the initial bulk and shear moduli
Summary
Constitutive modeling of overconsolidated (OC) clays has a long history, pioneered by the Modified Cam-clay (MCC) model based on the critical state concept [32, 33]. Herle and Kolymbas [14] modified the model by von Wolfferdorff [37] (VW model) for soils with low friction angle Based on these works, Masın [21] proposed the first hypoplastic model for clay (DM model), which employs a density factor to describe the consolidation history. Later Masın himself found that the DM model gives rise to an unrealistic asymptotic state boundary surface (ASBS) when a certain combination of parameters is used [23] The reason for this deficiency is that the adopted density factor is dependent on the consolidation history and related to other material parameters. Model performance is demonstrated by simulating several element tests, and comparing the prediction with experiments on different OC clays
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