Improvement to the intergranular strain model for larger numbers of repetitive cycles
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Improvement to the intergranular strain model for larger numbers of repetitive cycles J. Duque1 • D. Masˇ´ın1 • W. Fuentes2 Received: 2 June 2020 / Accepted: 12 September 2020 Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The analysis of geotechnical problems involving saturated soils under cyclic loading requires the use of advanced constitutive models. These models need to describe the main characteristics of the material under cyclic loading and undrained conditions, such as the rate of the pore water pressure accumulation and the stress attractors. When properly doing so, the models are expected to be reliable for their use in boundary value problems. In this work, an extension of the widely implemented intergranular strain model by Niemunis and Herle (Mech Cohes Frict Mater 2(4):279–299, 1997) is proposed. The modification is aimed to improve the capabilities of the model when simulating a number of repetitive cycles, where a proper reduction of the strain accumulation is expected. For validation purposes, the reference model and proposed improvement are compared against some monotonic and cyclic triaxial tests. The results indicate that the intergranular strain improvement model provides a more realistic prediction of the accumulation rates under cyclic loading, without spoiling the advantages of the original formulation. Keywords Constitutive modeling Cyclic loading Hypoplasticity Intergranular strain
1 Introduction Hypoplasticity for soils is a family of constitutive models with the following characteristics: (a) it can be written in a single tensorial equation, which interrelates the stress ten_ (b) it can be sor rate r_ with the strain tensor rate e, _ decomposed into a linear and nonlinear component in e, while the e_ is not decomposed into elastic and plastic parts, (c) it accounts for at least the stress-dependency (barotropy), and (d) it provides smooth responses envelopes. Different versions of hypoplasticity have been proposed in the literature for the simulation of granular (e.g., [1, 33, 40–42]) and fine-grained (e.g., [5, 9, 12, 15, 16, 18, 19]) soils. The experience with this model family is that it provides a good performance on monotonic loading, or equivalently, under medium and large strain amplitudes (k De k [ 103 ), but in the basic
& J. Duque [email protected] 1
Charles University, Prague, Czech Republic
2
Findeter, Bogota´, Colombia
form it presents some serious deficiencies when simulating cyclic loading where small strain effects take relevance [15, 24, 34, 40]. One can summarize the main limitations of hypoplastic models on cyclic loading as follows: (a) the inability to properly reproduce the increase in stiffness upon reversal loading, (b) excessive strain accumulation (ratcheting) upon cyclic loading and (c) lack of memory upon reloading paths [3, 4, 6, 24, 29]. In order to overcome these shortcomings, Niemunis and Herle [25] proposed the so-called Intergranular Strain (IS) t
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