This paper presents a novel micropolar-based hypoplastic model to reproduce the stress-strain relationship of face mask chips-sand mixtures (MSMs) and their localized deformation. Based on a critical state hypoplastic model, a non-polar hypoplastic model for MSMs is first developed with modifications and new features: (1) the cohesion induced by face mask chips is considered by introducing an additional stress tensor into the Cauchy stress tensor; (2) the initial stiffness variation in MSMs is described with a modified tangential modulus; and (3) the effective skeleton void ratio concept is introduced to capture the initial and critical void ratio variations in MSMs. The model is then extended to its micropolar terms by incorporating the micropolar theory, which includes an internal length parameter and a couple stress induced by particle rotation, with the advantage of overcoming the mesh dependency problem in the conventional finite element method (FEM) based simulations. Moreover, the new micropolar hypoplastic formulations are implemented into a FEM code. The onset and evolution of shear bands in MSMs are investigated by simulating a series of biaxial tests on both pure sand and MSMs. Numerical results are also compared to experimental observations, demonstrating that the developed micropolar hypoplastic model can adeptly capture the shear band propagation in MSMs and their mechanical responses.

This article presents the findings of a comprehensive assessment of the predictive capabilities and limitations of advanced geotechnical numerical tools utilizing two sophisticated constitutive models for sands: the hardening soil model with small strains and hypoplasticity with intergranular strain. The evaluation is based on simulations of laboratory and centrifuge tests under monotonic and cyclic loading conditions. Initially, these models were calibrated and assessed using an experimental database on Fontainebleau sand. This database encompasses a range of laboratory results, including isotropic compression, drained monotonic triaxial, and undrained cyclic triaxial tests with varying initial conditions. The models, in general, provided good representation for monotonic experiments while some discrepancies were observed in undrained cyclic experiments. Subsequently, the calibrated models were employed to replicate a series of centrifuge tests involving a pile embedded in the same sand. The pile was subjected to various episodes of monotonic and cyclic lateral loading. In general, the models accurately replicated the experimental observations from tests conducted under monotonic loading conditions. Some small discrepancies were found in pile tests subjected to cyclic loading, these were however minor when compared to issues in predicting cyclic element tests at undrained conditions.

Accurate modeling of soil behavior under seismic conditions is critical for understanding and mitigating earthquake-induced hazards. In this study, the Dyna-Simhypo model, an enhanced hypoplastic framework incorporating the intergranular strain tensor, is integrated with smoothed particle hydrodynamics (SPH) method for the first time to simulate co-seismic large deformation processes of slopes. The model's performance is validated through cyclic triaxial tests, seismic wave propagation analysis, and large-scale seismic slope simulations. Compared to the original Simhypo model, it eliminates ratcheting and reliably captures shear modulus reduction, damping buildup, and progressive soil degradation under cyclic loading. These advancements enable precise site response evaluations and accurate slope instability predictions, offering a robust tool for seismic hazard assessment.

Temperature effects become important in a number of geotechnical applications, such as nuclear waste disposal facilities, buried high-voltage cables, pavement, energy geostructures and geothermal energy. On the other hand, soft soils act time- and strain rate dependent. Both temperature and strain rate influence soil behavior, affecting stiffness, strength, and deformation even under constant stress levels. A model to predict temperature and loading rate effects on soil behavior is presented in this article. The model is based on a simple visco-hypooplastic model for clays and encompasses key aspects of coupled rate- and temperature-dependent soil behavior such as (partially irreversible) thermal expansion, heating-induced irreversible compression, stress history, drained heating/cooling cycles, as well as mechanical and thermal creep, incorporating isotachs, and isotherms.

Coupled nonlinear thermo-hydro-mechanical finite element simulations were carried out to investigate the behavior of energy micropiles subjected to thermal loading cycles. Two kinds of problems were analyzed: The case of an isolated micropile, for which comparison with previous research on medium-size isolated energy pile is provided, and the case of large groups of micropiles, with the aim of investigating the interaction effects. In both problems, micropiles were considered installed in a thick layer of very soft, saturated clay, characterized by isotropic or anisotropic hydraulic conductivity. Two advanced existing hypoplastic models, one incorporating the thermal softening feature, were used to describe the clay behavior in both problems. The settlements of the micropile head were found to increase during thermal cycles under constant mechanical load, showing a sort of ratcheting. For micropile groups, the settlement increase rate was faster as the spacing between micropiles was reduced. The excess pore water pressures developed at the micropile-soil interface played a significant role on the deformation and displacement fields of the soil-micropile systems, especially in the case of micropile groups, affecting the shear strength developed at the micropile-soil interface. The consolidation process was faster when the hydraulic conductivity was anisotropic, meaning that the development of excess pore water pressure was reduced in this case. As the spacing between the micropiles increased, i.e., as thermal interaction decreased, the heat flux exchanged by a micropile of the group during one cycle approached the heat flux exchanged by an isolated micropile in the same period.

Integral bridges with longer spans experience an increased cyclic interaction with their granular backfills, particularly due to seasonal thermal fluctuations. To accurately model this interaction behaviour under cyclic loading, it is crucial to employ appropriate constitutive models and meticulously calibrate and test them. For this purpose, in this paper two advanced elastoplastic (DeltaSand, Sanisand-MS) and two hypoplastic (Hypo+IGS, Hypo+ISA) constitutive models with focus on small strain and cyclic behaviour are investigated. The soil models are calibrated based on a comprehensive laboratory programme of a representative highly compacted gravel backfill material for bridges. The calibration procedure is shown in detail and the model capabilities and limitations are discussed on the element test level. Additional triaxial tests with repeated un- and reloading reveal significant over- and undershooting effects for the majority of the investigated material models. Finally, cyclic finite element analyses on the soil-structure interaction of an integral bridge are conducted to compare the performance of the soil models. Qualitatively similar cyclic evolution of earth pressures are detected for the soil models at various bridge lengths and test settings. However, a substantially different cyclic settlement behaviour is observed. Additionally, the investigation highlights severe overshooting effects associated with the tested hypoplastic soil models. This phenomenon is studied in detail using a single integration point analysis. Supplementary studies reveal that the foot point deformation of the abutment significantly influences the lateral passive stress mobilisation and the amount of its increase with growing seasonal cycles.

A critical investigation of three constitutive models for clay by means of analyses of a sophisticated laboratory testing program and of centrifuge tests on monopiles in clay subjected to (cyclic) lateral loading is presented. Constitutive models of varying complexity, namely the basic Modified Cam Clay model, the hypoplastic model with Intergranular Strain (known as Clay hypoplasticity model) and the more recently proposed anisotropic visco-ISA model, are considered. From the simulations of the centrifuge tests with monotonic loading it is concluded that all three constitutive models give satisfactory results if a proper calibration of constitutive model parameters and proper initialisation of state variables is ensured. In the case of cyclic loading, the AVISA model is found to perform superior to the hypoplastic model with Intergranular Strain.

Steel piles driven into the seabed for offshore structures regularly experience monotonic and cyclic axial loading. The bearing capacity of these piles under cyclic loading degrades with the number of cycles due to the reduction in skin friction. Limited experimental data has led to the development of interaction diagrams, which predict the number of loading cycles until failure based on the mean load and the amplitude of the cyclic load, both often normalized through the static pile bearing capacity. However, these diagrams do not account for varying soil conditions or pile geometries. In this paper, the authors extend the previously developed Capacity Degradation Method (CDM) by incorporating the hypoplastic material law, which accounts for loading and unloading paths, stress levels, and the change of soil void ratios. New interaction diagrams have been developed for different pile geometries. Additionally, the pullout capacities of piles with varying diameters and embedded lengths under different loading cycles are investigated.

The development of a constitutive model for soil-structure contact surfaces remains a pivotal area of research within the field of soil-structure interaction. Drawing from the Gudehus-Bauer sand hypoplasticity model, this paper employs a technique that reduces the stress tensor and strain rate tensor components to formulate a hypoplastic model tailored for sand-structure interfaces. To capture the influence of initial anisotropy, a deposition direction peak stress coefficient is incorporated; meanwhile, a friction parameter is introduced to address the surface roughness of the contact. Consequently, a comprehensive hypoplastic constitutive model is developed that takes into account both initial anisotropy and roughness. Comparative analysis with experimental data from soils on contact surfaces with diverse boundary conditions and levels of roughness indicates that the proposed model accurately forecasts shear test outcomes across various contact surfaces. Utilizing the finite element software ABAQUS 2021, an FRIC subroutine was developed, which, through simulating direct shear tests on sand-structure contact surfaces, has proven its efficacy in predicting the shear behavior of these interfaces.

Loosely deposited granular soils can be strengthened through cyclic loading, with vibrocompaction being a widely used and effective method. However, the lack of rational design methods stems from the complex interaction between soil and vibrator, as well as the inaccurate description of plastic accumulation caused by small strains in soil regions distant from the vibrator. In this work, we investigate Osinov's hypothesis which suggests that the soil densification primarily results from numerous cycles of small-amplitude strains rather than wave propagation effects (including reflection and dispersion). In this way, the complex dynamic interaction between vibrator and soil (contact forces, large deformations around the vibrator, high frequency waves emanating from the vibrator, resonance effects, soil flow, etc.) is replaced by the effect of the vibrator on the soil: cyclic deformations applied repeatedly to the soil, with amplitudes varying both spatially and temporally. Quasi static finite element simulations using a combined hypoplastic and high cyclic accumulation model, with a prescribed field of strain amplitudes, show that the proposed simplified approach is able to qualitatively capture in-situ observations. The impact of different factors such as probe spacing, insertion depth, probe movement, and even the sequence in which the probe are driven can be reproduced by the model. The model's predictions may complement on-line compaction control methods.