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The efficiency of geosynthetics has been proven in stone column-reinforced foundations. In this paper, loading tests were conducted on three stone column-reinforced foundations, experiencing four freeze-thaw cycles. The effects of geosynthetic encasement and lateral reinforcement were investigated on the behavior of ordinary stone column (OSC) – reinforced and geosynthetic encased stone column (GESC) – reinforced foundation. The results showed that particles of OSCs spread into foundation soil during freezing and thawing, and top of OSCs were replaced by foundation soil. The temperature gradient along the depth in OSC-reinforced foundation was smaller than in GESC-reinforced foundations, resulting in a lower negative pore pressure at the beginning of freezing. However, it was found that geosynthetic encasement helped maintain the integrity of GESCs, and increased the stress concentration ratio (SCR) during thawing, which led to a lower excess pore pressure in GESC-reinforced foundations. The lateral reinforcement was also found to not only reduce the differential settlement between GESCs and soil during thawing, but also restrain the frost heave during freezing. The tensile membrane effect of lateral reinforcement redistributed the stress and the overburden pressure throughout the freeze-thaw process. More water moved upwards during freezing in the OSC-reinforced foundation, leading to a larger amount of frost heave. However, the moisture migration became complex in the OSC-reinforced foundation, as OSCs were damaged by freeze-thaw cycles. • This paper studied the behavior of GESC-supported embankment under freeze-thaw cycles. • The effects of geosynthetics encasement and lateral reinforcement were investigated in partially frozen ground. • Encasement helped keep entity of stone columns, and enhanced the bearing capacity. • Lateral reinforcement redistributed stress on column and soil in both freezing and thawing. • Lateral reinforcement restrained frost heave, and reduced differential settlement between column and soil. [ABSTRACT FROM AUTHOR]

In this paper, an experiment study was carried out to identify the fundamental behavior of geosynthetic-encased stone column (GESC) reinforced foundation under freeze-thaw cycles. Three loading tests under four freeze-thaw cycles were considered. A 10-m thick reinforced foundation unit consisted of four floating GESCs with 2.5-m underlain clay layer, and the foundations were preconsolidated to three different initial degrees of consolidation (U = 1.0, 0.6 and 0.3, respectively). The results showed that soil near GESCs had a larger frozen depth due to the excellent heat transfer ability of GESCs. An extra uneven subsidence of soil also appeared around GESCs. Voids could be found between foundation soil and the loading plate after thawing, which indicated that only GESCs carried the overburden pressure. The GESCs showed outward bending under lower initial degree of consolidation, while inward bending under higher one. A bulging failure was observed on frozen part of GESCs, especially at the connection of encasement in foundation with lower initial degree of consolidation. In the first freezing process, a rapid decrease in frost heave force was noticed, inferring the fracture of frozen soil. The stress on GESC was found to almost have no change until complete freezing, when the soil was freezing and the stress on soil exceeded that on GESC. Negative pore pressure was observed in the foundation soil, and the absolute value decreased with the increasing overburden pressure. Both the peak positive and negative pore pressures were reduced as the foundation was preconsolidated to a higher degree. The freeze-thaw cycles were also found to generate excess pore pressure in soil during thawing. Moisture migration was also analyzed using Electrical Resistivity Tomography (ERT) method, and the results showed that moisture tended to go upwards and outside the reinforced unit from thawing to freezing, while downwards and inside the unit from freezing to thawing. • This paper investigated the behavior of GESC-reinforced foundation under freeze-thaw cycles. • Significant differential settlement was observed in the foundation. • The deformation patterns of GESCs were influenced by the initial degree of consolidation. • Only GESCs carried overburden pressure by the rigid base during thawing, and SCR reduced to less than 0.5 during freezing. • Moisture migration was studied using ERT, and negative pore pressure was observed. [ABSTRACT FROM AUTHOR]

• A fractional-order viscoelastic model is used to simulate soil. • The time variation of engineering load is considered. • The layered property of soil is considered. • The influence of the bottom rock on the soil is considered. • The recovery of settlement after unloading is analyzed. Time-varying loading is a frequently encountered loading type in geotechnical engineering. As the deformation of viscoelastic soil is related to its loading history, studying the viscoelastic problems under time-varying loads has important practical engineering significance. In this paper, the stress and displacement of a layered soil with fractional-order viscoelastic model under time-varying loads were solved using the complex variable method and the corresponding principle. Under the assumption of quasi-static and linear elasticity, this paper derives the quasi-static elastic solutions of a layered soil under time-varying strip loads. By introducing the fractional-order viscoelastic model and using the corresponding principle, the Laplace-domain analytical solutions are obtained. Finally, numerical methods are utilized to perform the Laplace inverse transform and obtain the solutions in the physical domain. The correctness of this paper is validated by comparing the numerical results with the ANSYS software, as well as by comparison with previous literature. Based on the experimental data, the material parameters of frozen soil at two temperatures are fitted. The settlement patterns of soil under two engineering loads were analyzed through case studies. By controlling variables, the influence of parameters of the fractional viscoelastic model on elastic aftereffect was investigated. [ABSTRACT FROM AUTHOR]

Lined canals in cold regions often experience severe frost damage, posing a significant threat to the water supply safety. This paper proposes a modified analytical solution for the response of canal lining under soil frost heave, which is based on a Timoshenko beam on a Pasternak foundation considering tangential contact between the lining and frozen soil. This analytical solution can provide any solution using Timoshenko or Euler–Bernoulli beams on Pasternak or Winkler foundations with or without tangential contact. Then, the modified analytical solution, along with the traditional analytical solutions using Euler–Bernoulli beams on Winkle foundations, is compared against both model test and numerical simulation results. The modified analytical solution performs better than the traditional solution. Finally, the effects of foundation model, beam model, and tangential contact in simulating canal frost heave were discussed, and some measures to mitigate canal frost heave are proposed. The results show that solutions based on Winkler foundation overestimate frost heaves and tensile stresses of canal linings, and solutions without considering tangential contact only obtains overestimated frost heave. In addition, solutions based on Euler–Bernoulli beams underestimate frost heaves slightly and overestimate tensile stresses slightly. Therefore, the Pasternak foundation, Euler–Bernoulli beam, and tangential contact model can be used to simulate canal frost heave. The modified analytical solution directly uses field measurements of soil free frost heave to calculate canal frost heave, thereby enhancing result reliability. This analytical solution provides a simple method for canal frost heave design, and can be applied to frost heave analyses of flat and inclined structures. [Display omitted] • Propose analytical solution considering shear effects of the lining, frozen soil, and their tangential contact. • Perform model test and numerical simulation to verify the accuracy of the analytical solution. • Discuss the applicability of foundation and beam models on simulating canal frost heave. • Factors studied include the shear layer stiffness, and normal and tangential contact conditions. [ABSTRACT FROM AUTHOR]

The unfrozen water content (UWC) plays a crucial role in frozen soil engineering, however, traditional unfrozen water measurement or calculation methods are time-consuming and costly, and it is difficult to express the non-linearity among the influencing factors. Currently, LF-NMR is widely recognized as an effective tool for measuring unfrozen water. In this study, a calibration curve that can describe the relationship between the NMR signal and water content was derived. Moreover, the effects of temperature, initial water content, and soil height on UWC are explored along one-dimensional large-diameter columns based on LF-NMR data. Combined with the ML algorithm and the UWC test data under different factors based on LF-NMR, an intelligent prediction method that can consider the nonlinear characteristics of multiple factors is proposed. The results showed that the NMR accuracy is 176.64 semaphore per 1% water content, the error between the water content calculated from the calibration curve and that obtained from the drying method is small (average error is 0.97%), and the linearity degree of the calibration curve is good (R2 = 0.999). Moreover, due to the strong correlation between unfrozen water and temperature, initial water content, and other factors, the results indicated that the GPR model can better describe this correlation and has the best prediction effect, which was evaluated with the quantitative indicators: R2 = 0.96, RMSE = 1.07, MAE = 1.00, and again verifies the superiority of this model in combination with other literature data. Overall, this paper offers a technical basis for controlling and preventing freezing and thawing disasters in cold regions and artificial freezing engineering projects. • Machine learning method is applied to predict the unfrozen water content of artificially frozen clay. • Three machine learning models, GPR, BPNN, and SVM are used to study. • Comparison shows that GPR has a good prediction performance of UWC of artificially frozen clay. • The internal relation between unfrozen water content and the influencing factors is explored. [ABSTRACT FROM AUTHOR]

[Display omitted] • Complete phase diagram of pore solution at icing stage was presented. • Freezing point of saline soils was estimated with equivalent solute concentration. • Calculation method for eutectic temperature of saline soils was proposed. • Criteria for judging saline soils with one or two freezing stages was proposed. • SFCC shape index varying with soil matrix and initial solute concentration was found. Soil freezing characteristic curve (SFCC) describes the relationship between unfrozen water and subzero temperature, which is of significance for the simulation of heat, water, salt migration in cold regions. There are two phase transition stages in some saline soils, which is often explained by the phase equilibrium of bulk solution. However, the second phase transition and chemical characteristic of solute are ignored in the current coupling numerical models for freezing-thawing soils. The newest SFCC methods considering abovementioned two items are not applicable to numerical models due to complex calculation or irregularly changeable parameters. To solve those problems, a simple model was proposed in this paper. Firstly, the complete phase diagram of pore solution at icing stage was speculated from published experimental SFCCs of saline soils. Then, the temperatures of saline soils at freezing and eutectic points were quantitative expressed with phase diagram of bulk solution and SFCC of nonsaline soil, and the criteria determining whether single icing stage or icing-eutectic stage occurs in saline soils was proposed. A synthetic index was used to describe the effects of soil matrix and initial solute concentration on the exponent. Only three constant parameters were introduced to reflect the soil matrix effect on phase transition points of pore solution and the influence of chemical characteristic of solute on pore water freezing process. Finally, the model was validated by the experimental data of saline soils and showed good results and ease of use compared to a widely used theorical model for saline soil with single freezing stage and other two models both considering two phase transitions. The work provides a deeper view of freezing process in saline soils and promote the improvement of numerical simulation effect for heat, water and salt migration in seasonal freezing-thawing areas. [ABSTRACT FROM AUTHOR]

This paper presents the establishment of a macro-mesoscopic constitutive model based on poromechanics for investigating the mechanics of warm frozen soil. The elastic parameters of warm frozen soil are influenced by the ice content variations during the loading process, considering the pressure melting characteristic of warm frozen soil. Through the integration of poromechanics and mesomechanics, a macro-mesoscopic constitutive model incorporating the pressure melting effect is developed to characterize the mechanical properties of warm frozen soil. The proposed model establishes a relationship between the elastic modulus at the mesoscopic and macroscopic scales of warm frozen soil.To validate the model, a comparison is made between the model predictions and experimental data obtained from warm frozen silt. The results demonstrate that the model effectively captures significant mechanical performance of warm frozen soil, including strain soft and dilatancy phenomena under various confining pressure conditions. Furthermore, the proposed model enables the prediction of freezing temperature, unfrozen water saturation, unfrozen water pressure, ice pressure, and porosity changes in warm frozen silt samples during the loading process. • A new constitutive model for warm frozen soil is proposed at mesoscopic scale. • The model can model the mechanical behaviors of warm frozen soil well. • The model can predict ice pressure and water pressure within warm frozen soil. [ABSTRACT FROM AUTHOR]

• A 3D cyclic stress fields were simulated by frozen hollow cylinder apparatus. • The deformation behaviors were investigated under 3D cyclic stress states. • The damage developing is strongly dependent on the 3D stress characteristics. • A fatigue damage evolution model considering the 3D effect is proposed. The fatigue and damage characteristics of frozen soil under cyclic loading are highly dependent on the three-dimensional (3D) stress state, due to the anisotropic properties of the ground. Measuring and researching the deformation behavior and fatigue failure characteristics of frozen soil under complex 3D cyclic stress states are significant for the stability assessment of frozen soil when it is subjected to earthquakes and vehicular traffic. In this paper, a hollow cylindrical apparatus was used to simulate a cyclic stress state with constant values of principal stress direction angle (α), coefficient of intermediate principal stress(b), and amplitude of the first principal stress under −6℃ conditions. The influences of 3D stress parameters (α and b) on the deformation behavior, damage evolution, and fatigue failure characteristics of frozen silty clay were systematically investigated. The results indicated that the deformation of the samples was dominated by axial strain, when α < 15° and b = 0. Furthermore, as the value b increased, both the accumulated axial strain and accumulated torsional shear strain exhibited a decreasing-then-increasing trend. When 30°≤α ≤ 60°, the deformation feature is primarily dominated by torsional shear direction. With the increase of the value b, the accumulated torsional shear strain increased rapidly, while the axial strain gradually decreases, and then in turn to compressive elongation deformation. The increase of 3D stress parameters leads to a decrease in accumulated torsional shear strain, absolute value of accumulated axial strain, number of cycles, and accumulated torsional shear dissipated energy density at the failure of frozen soil. This indicated that under cyclic stress conditions, the increase of 3D stress characteristic parameters accelerates the damage evolution and fatigue failure process of frozen soil samples. Essentially, the increase of 3D stress parameters accelerates the damage of soil particle and ice lens structures in horizontally layered and the growth of micro-crack of frozen soil, thereby reducing the transverse shear resistance of frozen soil samples. [ABSTRACT FROM AUTHOR]

Temperature changes may cause irregular soil uplift or thawing settlements in frozen soil areas, potentially affecting the safe operation of High-Speed Railways (HSR). Analyzing and predicting these deformation characteristics is thus critical. However, the conventional forecasting and analysis techniques rarely considered factors such as dynamic parameter variations, uncertainties, and measurement errors, which hinder accurate regional scale forecasting. To bridge this gap, this paper introduces a novel time-series coupling method, which integrates post-processing deformation from Interferometric Synthetic Aperture Radar (InSAR) with a frost heave model (FHM), facilitated by the ensemble Kalman filter (EnKF) assimilation algorithm. We obtained deformation observations along the HSR using Persistent Scatterer InSAR (PS-InSAR) technology in combination with time-series post-processing techniques. Considering the causative factors for deformation, we structured the FHM. By integrating FHM with observational data using the EnKF algorithm achieved an efficient upgrade of the posterior distribution of model parameters. This integration significantly improves the predictive accuracy, it facilitates an efficient update to the posterior distribution of model parameters, leading to enhanced prediction accuracy of our model. Our experimental results indicate that the effectiveness of this approach, with observational data assimilation into FHM reducing the average Root Mean Square Error (RMSE) to a mere 0.247 mm. Concurrently, both the Normalized Reduction Error Index (NER) and the Assimilation Efficiency Factor (EFF) values surpassed 0.60 and 0.84 respectively. These underlines signify a successful update of our model parameters, which in turn elevates the accuracy of future deformation predictions, thereby promising safer railway operations. • a time series coupling method based on data assimilation is proposed by considering the triggering factors of deformation. [ABSTRACT FROM AUTHOR]

• Ground deformation of thermokarst landform increased dramatically within ten years. • The area of thermokarst landform has increased about 4.42 km2 from 2009 to 2018. • The seasonal deformation pattern shows obvious four-stage characteristic. • InSAR shows significant potential in thaw slump disaster monitoring. Due to the effects of global climate change, the permafrost temperature in the Qinghai-Tibet Plateau (QTP) has rapidly increased over the past decades. The development of thermokarst landforms is one distinctive indicator of permafrost degradation, while the change of the rate of permafrost degradation in recent 10 years has not been systematically investigated in QTP. In this paper, the annual average growth rate (AAGR) of ground deformation, the change of thaw slump areas, and the change of active layer thickness (ALT) of thermokarst landforms are monitored integrating SAR (synthetic aperture radar) and optical images for years 2007 to 2020 in Qilian Mountain, northern QTP. The ground deformation rate and seasonal amplitude were estimated by InSAR method, and the descending and ascending InSAR data are compared the validate the results. Based on the deformation results, AAGR was introduced to evaluate the permafrost degradation degree. Moreover, the ALT were estimated based on the seasonal deformation amplitude and Stefan model. The spatio-temporal characteristics of ground deformation and its relationship with thaw slump and temperature are explored. Experimental results show that the deformation rate increased about 150 % from 2007 to 10 to 2017–20. The maximum AAGR of deformation rate in the study area can reach 20.6 %. The thaw slump area has an obvious trend of expansion from 2009 to 2015, and its distribution agreed well with the deformation map. The ALT results ranged from 0.5 m to 2.8 m, indicating an obvious increase trend from 2007 to 2020. Based on the estimated increased ground deformation, thaw slump area, and ALT, it is inferred that frozen ground was undergoing serious degradation in the last 10 years. This study demonstrates the capability of multi-temporal InSAR in observing the accelerated permafrost thaw-freezing process and monitoring the permafrost parameters. [ABSTRACT FROM AUTHOR]

A large part of the earth's surface is covered by seasonally or permanently frozen soils. Considering the negative impact of climate change, future development of such regions can be underpinned by mathematical methods for accurate analysis of heat and moisture transport in freezing and thawing soils. Reported in this paper is a novel non-local formulation of water and heat transport in unsaturated soils. The formulation uses bond-based peridynamics (PD) and consists of a set of integral–difference formulations of energy and mass conservation. Specific features of freezing/thawing soils are incorporated by a combination of van Genuthcen and Clausius–Clapeyron relations. Computational results are compared with four sets of laboratory experiments to demonstrate the efficiency of the developed approach. The model can be used to analyse the effect of water flow on heat transfer in soils during thawing of permafrost soils. Further, it can be applied in modelling climate change effects, and can be used for construction of coupled physically justified models of frost heave. • A general form of energy and water mass conservation equations is proposed. • A new bond-based Peridynamics model of unsaturated frozen soil is developed. • Agreement between the developed PD solutions and experimental results is demonstrated. [ABSTRACT FROM AUTHOR]