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Numerous geotechnical applications are significantly influenced by changes of moisture conditions, such as energy geostructures, nuclear waste disposal storage, embankments, landslides, and pavements. Additionally, the escalating impacts of climate change have started to amplify the influence of severe seasonal variations on the performance of foundations. These scenarios induce thermo-hydro-mechanical loads in the soil that can also vary in a cyclic manner. Robust constitutive numerical models are essential to analyze such behaviors. This article proposes an extended hypoplastic constitutive model capable of predicting the behavior of partially saturated fine-grained soils under monotonic and cyclic loading. The proposed model was developed through a hierarchical procedure that integrates existing features for accounting large strain behavior, asymptotic states, and small strain stiffness effects, and considers the dependency of strain accumulation rate on the number of cycles. To achieve this, the earlier formulation by Wong and Mašín (CG 61:355–369, 2014) was enhanced with the Improvement of the intergranular strain (ISI) concept proposed by Duque et al. (AG 15:3593–3604, 2020), extended with a new modification to predict the increase in soil stiffness with suction under cyclic loading. Furthermore, the water retention curve was modified with a new formulation proposed by Svoboda et al. (AG 18:3193–3211, 2023), which reproduces the nonlinear dependency of the degree of saturation on suction. The model's capabilities were examined using experimental results on a completely decomposed tuff subjected to monotonic and cyclic loading under different saturation ranges. The comparison between experimental measurements and numerical predictions suggests that the model reasonably captures the monotonic and cyclic behavior of fine-grained soil under partially saturated conditions. Some limitations of the extended model are as well remarked. [ABSTRACT FROM AUTHOR]

A wide range of geotechnical structures founded in fine-grained soils are subjected to complex cyclic loading scenarios. The prediction of their behavior has motivated the development of several constitutive models for soils under different mathematical frameworks. Some success has been achieved under certain simplified cyclic conditions. However, the performance of the models is usually not satisfactory when dealing with a wide range of test conditions, such as variation of the loading amplitudes, initial effective stresses, initial stress ratios, overconsolidation ratios, direction of the loading with respect to the bedding plane, among others. Even though this issue is well-known by model developers, few efforts have been made in the literature to analyze and discuss this and other models' limitations. This article investigates the strengths and weaknesses of four advanced constitutive models for anisotropic fine-grained soils, namely: the anisotropic hypoplastic model by Fuentes et al. (Géotechnique 71(8):657–673, 2021), the SANICLAY-B elasto-plastic model by Seidalinov and Taiebat (Int J Numer Anal Meth Geomech 38(7):702–724, 2014), the constitutive Anamnesis model by Tafili (PhD thesis, Institute of Soil Mechanics and Rock Mechanics, Karlsruhe Institute of Technology, 2019) and the three surface kinematic hardening model proposed by Stallebrass and Taylor (Géotechnique 47(2):235–253, 1997) with transverse isotropic elasticity. In order to achieve that, simulation results with the models are qualitatively and quantitatively compared against a large number of experimental results under monotonic and cyclic loading on an anisotropic kaolin reported by Wichtmann and Triantafyllidis (Acta Geotech 13(5):1103–1128, 2018). [ABSTRACT FROM AUTHOR]

Numerous studies in the literature are concerned with proposing new constitutive models for sands to simulate cyclic loading. Despite considerable progress in this area, there are various limitations on their simulation capabilities that are either overlooked or not communicated clearly by the developers. A number of these limitations are rather crucial for the end users, and therefore, providing discussion and analysis of them would be of great value for both applications and future developments. The present work is devoted to discussing seven characteristic limitations, which are frequently observed in cyclic loading simulations. Four advanced constitutive models are considered in this study: two bounding surface elastoplasticity and two hypoplasticity models—with the models in each category following a hierarchical order of complexity. Relevant cyclic loading experimental test data on Toyoura and Karlsruhe fine sands support the analysis. The key issues discussed include stress overshooting, one-way ratcheting in cyclic strain accumulation, liquefaction strength curves, stress attractor in strain-controlled shearing, hypoelasticity, cyclic oedometer stiffness, and effect of drained preloading. The presented results elaborate on the specific limitations and capabilities of these rather advanced models in simulating several essential aspects of cyclic loading of sands. [ABSTRACT FROM AUTHOR]

The design of large diameter monopiles subjected to cyclic lateral loading is of interest in many applications, such as, for example, in the offshore wind energy industry. Engineering design methods to estimate the deflection of these structures are required for this purpose. In the present work, a p–y model for large diameter monopiles subjected to lateral loading is proposed. The model considers a pile in cohesionless soil subjected to static and long-term cyclic loading. Its formulation features the consideration of nonlinear relations for the ultimate soil resistance pu and the initial subgrade modulus Epy0 among the soil depth and a cyclic factor that accounts for the effect of the soil density and loading amplitude. A relation is also proposed to account for a base shear force at the tip of the monopile. The proposed relations were employed and solved under the beam on nonlinear Winkler foundation (BNWF) approach and were adjusted to simulate a number of three-dimensional (3D) finite-element (FE) models accurately, accounting for variations on pile geometry, soil properties, and loading conditions. In the end, the performance of the proposed relations was evaluated through the comparison with a field test and a centrifuge test. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The prediction quality of three of the most sophisticated constitutive models for sands has been examined based on a comparison of results from element test simulations and laboratory tests. Hypoplasticity with intergranular strain, the Sanisand elastoplastic model in the version of 2004 and the recently proposed ISA (intergranular strain anisotropy) model have been inspected. The laboratory tests performed on Karlsruhe fine sand used in the present study are freely available on the homepage of the first author. The model predictions have been inspected for drained and undrained monotonic triaxial tests with various densities and pressures and for monotonic tests with a few number of un- and reloading cycles. The main focus, however, lies on undrained cyclic triaxial tests with either stress or strain control and with different densities, initial stresses and stress/strain amplitudes. The strengths and weaknesses of the different constitutive models for various test conditions are worked out. • The parameters of three models have been calibrated for the same fine sand. • Different sets of parameters are necessary for monotonic and cyclic loading. • No liquefaction with hypoplasticity in case of stress or large strain cycles. • Buttery predicted by Sanisand for large strain cycles contrasts experiments. • All models work well for certain test types and show deficits for others. [ABSTRACT FROM AUTHOR]

The ISA-plasticity is a mathematical platform which allows to propose constitutive models for soils under a wide range of strain amplitudes. This formulation is based on a state variable, called the intergranular strain, which is related to the strain recent history. The location of the intergranular strain can be related to the strain amplitude, information which is used to improve the model for the simulation of cyclic loading. The present work proposes an ISA-plasticity-based model for the simulation of saturated clays and features the incorporation of a viscous strain rate to enable the simulation of the strain rate dependency. The work explains some aspects of the ISA-plasticity and adapts its formulation for clays. At the beginning, the formulation of the model is explained. Subsequently, some comments about its numerical implementation and parameters determination are given. Finally, some simulations are performed to evaluate the model performance with two different clays, namely a Kaolin clay and the Lower Rhine clay. The simulations include monotonic and cyclic tests under oedometric and triaxial conditions. Some of these experiments include the variation of the strain rate to evaluate the viscous component of the proposed model. [ABSTRACT FROM AUTHOR]

A sample of soil is subjected to multidimensional cyclic loading when two or three principal components of the stress or strain tensor are simultaneously controlled to perform a repetitive path. These paths are very useful to evaluate the performance of models simulating cyclic loading. In this article, an extension of an existing constitutive model is proposed to capture the behavior of the soil under this type of loading. The reference model is based on the intergranular strain anisotropy concept and therefore incorporates an elastic locus in terms of a strain amplitude. In order to evaluate the model performance, a modified triaxial apparatus able to perform multidimensional cyclic loading has been used to conduct some experiments with a fine sand. Simulations of the extended model with multidimensional loading paths are carefully analyzed. Considering that many cycles are simulated ( $$N>30$$ ), some additional simulations have been performed to quantify and analyze the artificial accumulation generated by the (hypo-)elastic component of the model. At the end, a simple boundary value problem with a cyclic loading as boundary condition is simulated to analyze the model response. [ABSTRACT FROM AUTHOR]

The authors welcome the note provided by Prof. Kolymbas regarding his analysis of the characteristic limitations using the Barodesy model. "Limitation 2": Similar to many other constitutive models in the literature, the Barodesy model does not accurately reproduce the reduction rate of pore water pressure toward liquefaction in the successive undrained cycles of shearing. [Extracted from the article]

While hypoplastic models have demonstrated accurate predictions of sand behavior under monotonic loading, their accuracy diminishes when applied to cyclic loading conditions. To address this limitation, the intergranular strain approach is used as an extension to the model. The current investigation focuses on the analysis of two variants: the original Intergranular Strain (IS) approach proposed by Niemunis and Herle (1997) and the Intergranular Strain Anisotropy (ISA) by Fuentes et al. (2019). Although both models have the same objective, they present distinct mathematical structures and therefore different repercussions on the simulations. In this study, sand Hypoplasticity is enhanced with IS and ISA, and employed to simulate a series of experimental tests conducted on Fontainebleau sand. These tests encompass isotropic compression, drained monotonic triaxial, and undrained cyclic triaxial tests, while considering different initial densities and test characteristics. Furthermore, the calibrated models were applied to simulate a series of centrifuge tests, involving a pile embedded in the same sand, which is subjected to various episodes of monotonic and cyclic lateral loading. A comparison and discussion of the similarities and differences in elemental and finite element predictions, arising from the two intergranular strain formulations is presented. • Hypoplastic models with intergranular strain or ISA realistically reproduce the soil behavior under triaxial conditions. • The accumulated displacements of piles under cyclic loading could be fairly well described considering hypoplastic models with IGS or ISA. • The evolution normalized stiffness observed in the centrifuge experiments was not reproduced by hypoplastic models. [ABSTRACT FROM AUTHOR]