The hysteresis effect of unfrozen water during freeze-thaw cycles greatly influences the hydrothermal properties of soil. To better understand the hysteresis behavior of unfrozen water in the soil, this study utilized frequency domain reflectometry to measure the unfrozen water content variations in silty clay under both stepwise and rapid temperature change modes. The hysteresis effect of unfrozen water in soil was analyzed, also the underlying mechanism was revealed. The results indicate that unfrozen water content variations are consistent across the two temperature change modes, with hysteresis observed in both scenarios. This effect was more noticeable during the rapid temperature change mode, and soil samples with higher initial moisture content froze earlier and thawed more slowly in this mode. The hysteresis phenomena are mainly influenced by the ice crystal metastable nucleation, the blockage effect of pore ice crystallization, and the pore water pressure changes during phase transition. The main cause of unfrozen water hysteresis in soil during the initial freezing phase is the metastable nucleation process. In the later stages of freezing, the hysteresis effect is primarily driven by changes in capillary water curvature, induced by the blockage effect of pore ice crystallization, and shifts in pore water pressure during the ice-water phase transition. Also, a hysteresis model was proposed and validated against experimental data and existing models, demonstrating good performance and accurately predicting unfrozen water content under varying temperature conditions. This research enhances the understanding of the mechanism responsible for the hysteresis effect of unfrozen water content in frozen soil.

To establish the hysteresis model of EPS particles amended light weight soil under multi-step cyclic loading, the dynamic deformation characteristics of light weight soil were studied by consolidated undrained dynamic triaxial tests. The results showed that the backbone curve of light weight soil is hyperbolic and has strain hardening characteristics. With the increase of dynamic stress, the hysteresis curve shape of light weight soil gradually transforms from spindle-shaped to crescent-shaped, showing nonlinearity, hysteresis and strain accumulation. Based on the Hardin-Drnevich model and Masing rules, a modified unloading and reloading rule for the hysteresis model of light weight soil is proposed. The maximum dynamic shear modulus correction coefficient k1 and dynamic shear modulus attenuation coefficient k2 are introduced to establish the modified hysteresis model of light weight soil. Based on the modified hysteresis model, the physical meanings of k1 and k2 are defined. The influence of k1 and k2 values on the shape of hysteresis curve is discussed, and the empirical formulas of k1 and k2 about the dynamic shear strain are obtained. Through the verified dynamic triaxial tests of light weight soil by changing stress state, it is found that the relative error between the predicted values of modified hysteresis model and measured values is between 3.19% and 19.41%, which indicates that the model can describe closely the mechanical response process of light weight soil under complex dynamic conditions. The modified hysteresis model can predict the complex mechanical response mechanism in the progressive evolution of structural soil from convex to concave-convex hysteresis loop.

The degradation of subarctic peatland ecosystems under climate change impacts surrounding landscapes, carbon balance, and biogeochemical cycles. To assess these ecosystems' responses to climate change, it is essential to consider not only the active-layer thickness but also its thermo-hydraulic conditions. Ground-penetrating radar is one of the leading methods for studying the active layer, and this paper proposes systematically investigating its potential to determine the thermal properties of the active layer. Collected experimental data confirm temperature hysteresis in peat linked to changes in water and ice content, which GPR may detect. Using palsa mires of the Kola Peninsula (NW Russia) as a case study, we analyze relationships between peat parameters in the active layer and search for thermal gradient responses in GPR signal attributes. The results reveal that frequency-dependent GPR attributes can delineate thermal intervals of +/- 1 degrees C through disperse waveguides. However, further verification is needed to clarify the conditions under which GPR can reliably detect temperature variations in peat, considering factors such as moisture content and peat structure. In conclusion, our study discusses the potential of GPR for remotely monitoring freeze-thaw processes and moisture distribution in frozen peatlands and its role as a valuable tool for studying peat thermal properties in terms of permafrost stability prediction.

Stress-strain behavior of two different soil specimens subjected to cyclic compressive loading are studied herein, the goal being to present a simple dynamic uniaxial mem-modeling approach that aids physical insight and enables system identification. In this paper, mem stands for memory, i.e., hysteresis. Mem-models are hysteresis models transferred from electrical engineering using physical analogies. Connected in series, a mem-dashpot and mem-spring are employed to model inter-cycle strain ratcheting and intra-cycle gradual densification of the two soil specimens. Measured time histories of stress and strain are first decomposed so that the two modeling components, mem-dashpot and mem-spring, can be identified separately. This paper focuses on the mem-dashpot, a nonlinear generalization of a linear viscous damper. A mem-spring model is also devised built on an extended Masing model. Nonlinear dynamic simulations (with inertia) employing the identified mem-dashpot and mem-spring demonstrate how well the identified mem-models reproduce the measured early-time data (first 200 cycles of loading). Choices of state variables inherited from bond graph theory, the root of mem-models, are introduced, while MATLAB time integrators (i.e., ode solvers) are used throughout this study to explore a range of contrasting damper and spring models. Stiff solver and the state event location algorithm are employed to solve the equations of motion involving piecewise-defined restoring forces (when applicable). Computational details and results are relegated to the appendices. This is the first study to use single-degree-of-freedom (SDOF) system dynamic simulations to explore the consistency of mem-models identified from real-world data.

This paper quantitatively analyses the macroscopic characteristics of soil hysteretic curves under dynamic loading and examines the elastic properties, viscosity, meso-damage degree and energy consumption of soil from a macroscopic perspective. Given the lack of research on the hysteresis characteristics of bioenzyme-modified silty soil, a series of dynamic triaxial tests were conducted under varying bioenzyme dosages, confining pressures, loading frequencies, and other conditions. The analysis focused on several parameters: the slope of the major axis of the hysteretic curve k, the ratio of the major to minor axes alpha, the distance between the central points of adjacent hysteretic curves d, and the area enclosed by the hysteretic curve S. These were used for quantitative analysis of the morphological characteristics, influencing factors, and changing patterns of the hysteresis curve in bioenzyme-modified silty soil. The results showed that the hysteresis curve of the bioenzyme-improved silty soil resembled an inclined ellipse. Under the influence of different bioenzymes dosages, confining pressures, and loading frequencies, k and alpha decreased as dynamic stress increased, while d and S increased exponentially with rising dynamic stress. When the bioenzyme dosage was 0.01%, the k value was largest, and alpha, d and S were smallest. With increasing confining pressure, k increased, while alpha, d, and S decreased. As the loading frequency increased, k, alpha, and d decreased, while S gradually increased. At a bioenzyme dosage of 0.01%, the bioenzyme had the greatest effect on improving the silty soil.

change of unfrozen water content in pores of rock during freeze-thaw process is one of the key factors affecting its mechanical properties. In this paper, the sandstone is taken as the research object, and the pore water content of rock during freeze-thaw process (20, 0, -2, -4, -6, -10, -15, -10, -6, -4, -2, 0, 20 degrees C) is monitored by low-field nuclear magnetic resonance system (NMR), and the evolution law of unfrozen water content with temperature is analyzed. The influence of the evolution of unfrozen water content on the mechanical properties of rock during freeze-thaw process is also discussed. The research findings show that the pore water in rocks during the freezing-thawing process is significantly influenced by temperature, passing through five stages: supercooling, rapid freezing, slow freezing, slow melting, and accelerated melting. A distinct hysteresis phenomenon is observed in the rock during thawing. At identical temperatures, the unfrozen water content during freezing is notably higher than during thawing. Consequently, the peak intensity and elastic modulus during thawing are significantly greater than during freezing. The relationship between uniaxial compressive strength, rock elastic modulus, and unfrozen water content in freeze-thaw process can be expressed by exponential function. At the beginning of freezing, the change of rock mechanical parameters is mainly affected by the increase of pore ice content and the cementation effect of pore ice on rock particles. With the further decrease of temperature, the thickness of adsorbed water film decreases, and the adsorption capacity increases, so that the integrity between pore ice and rock particles is enhanced, and rock mechanical parameters further change.

Offshore wind turbines are subjected to long-term cyclic loads, and the seabed materials surrounding the foundation are susceptible to failure, which affects the safe construction and normal operation of offshore wind turbines. The existing studies of the cyclic mechanical properties of submarine soils focus on the accumulation strain and liquefaction, and few targeted studies are conducted on the hysteresis loop under cyclic loads. Therefore, 78 representative submarine soil samples from four offshore wind farms are tested in the study, and the cyclic behaviors under different confining pressures and CSR are investigated. The experiments reveal two unique development modes and specify the critical CSR of five submarine soil martials under different testing conductions. Based on the dynamic triaxial test results, the machine learning-based partition models for cyclic development mode were established, and the discrimination accuracy of the hysteresis loop were discussed. This study found that the RF model has a better generalization ability and higher accuracy than the GBDT model in discriminating the hysteresis loop of submarine soil, the RF model has achieved a prediction accuracy of 0.96 and a recall of 0.95 on the test dataset, which provides an important theoretical basis and technical support for the design and construction of offshore wind turbines.

Granite residual soil is widely used as a subgrade filler in highway construction. Dynamic loads induced by vehicles and earthquakes are complex and involve multidirectional loads, and the dynamic behavior of soil under multidirectional cyclic loading differs significantly from that under unidirectional cyclic loading. A series of horizontal cyclic direct shear tests under cyclic normal loading were conducted using a large-scale cyclic direct shear apparatus at different shear displacement amplitudes (1, 3, 6, and 9 mm) and normal stress amplitudes (0, 100, and 200 kPa). The test results indicate that under cyclic normal stress, the dynamic shear strength of granite residual soil increased during the forward shear process but decreased during the reverse shear process. The damping ratio increases with increasing shear displacement amplitude and normal stress amplitude. This behavior is associated with higher excess pore water pressure induced by greater normal stress amplitude and larger shear displacement, which drive the soil into the yielding phase. The Granite residual soil exhibited significant asymmetric hysteretic characteristics under bidirectional dynamic loading. However, no model has yet been found to describe the asymmetric hysteretic behavior of soil under bidirectional dynamic loading. To obtain the asymmetric hysteretic curve of granite residual soil under bidirectional cyclic loading conditions in the laboratory without the instruments for bidirectional cyclic direct shear tests, the Hardin-Drnevich model and the second Masing rule were extended to propose two asymmetric hysteretic curve models under bidirectional cyclic loading based on the tests. Both models fit with the test results well.

Fatigue damage accumulation for offshore wind turbines is highly dependent on damping of the structure and particularly on the soil damping contribution during idling conditions. This paper presents an efficient method to estimate soil damping specific to wind turbine design and offshore environmental conditions. The method assumes a narrow-banded response, suitable for turbines in low damping conditions. The proposed method demonstrates that soil damping varies significantly with load level and that predictions can be improved over the common industry practice of assuming a constant soil damping value. The fatigue damage predicted using this proposed method is calibrated using a multi-surface plasticity foundation model. The structural response with this plasticity model is also compared to linear elastic soil modelling without any soil damping. This analysis shows that significant reductions in damage may be observed when soil Masing behaviour is incorporated. Overall, this paper shows that soil plasticity, and its variation with load level, should be included within a design framework and suggests a straightforward way of doing so.

Climate-induced desiccation cracks exhibit a hysteresis behavior, referred to as crack dynamic hysteresis (CDH), where they display different geometric characteristics during the drying and wetting phases at constant soil water content. This phenomenon has a complex effect on slope stability, an aspect often overlooked in analytical and numerical methods. In this study, we conducted experimental and numerical analyses to provide new insights into the effects of the CDH on slope stability. A series of laboratory experiments on desiccation cracking under drying-wetting cycles were performed. The testing results were used to develop and validate an extended dynamic dual-permeability model. The proposed model was integrated into a set of slope stability analyses using the finite element method. The numerical model results show that CDH causes greater fluctuations in crack dynamics and increases soil water retention under drying-wetting cycles. Neglecting this phenomenon leads to underestimation of slope stability during dry conditions and overestimation during wet conditions, with these discrepancies becoming more pronounced as the cycles progress. Furthermore, CDH changes the mechanical properties of soil, transitioning relatively stable zones to regions prone to localized instability. These unstable zones present significant challenges for accurately analyzing and managing slopes with cracked soil layers. Monitoring groundwater fluctuations and local crack development after heavy rainfall events is essential for mitigating localized slope collapses.