Infrastructure In Cold Regions Research Articles

Study on the effect of strain rate on the bond performance between GFRP bars and ECC after seawater freeze-thaw cycles

With the increase in marine and coastal infrastructure in cold regions, freeze-thaw damage and dynamic loads will reduce structural performance. However, the dynamic bonding performance of seawater sea sand ECC and glass fiber-reinforced polymer (GFRP) bars after freeze-thaw cycles is still unclear. In this paper, the mass loss rate, dynamic elastic modulus, and compressive strength of seawater sea sand ECC were studied through freeze-thaw cycle tests. The bonding properties of seawater sea sand ECC and GFRP bars were examined under two freeze-thaw environments (Seawater environment, Freshwater environment), four freeze-thaw cycles (0, 50, 100, and 150), and four strain rates (2.63 × 10−5s−1, 2.63 × 10−4s−1, 2.63 × 10−3s−1, and1.32 × 10−2s−1) using pull-out tests. Additionally, the microstructure was analyzed using SEM. The results show that compared with the freshwater freeze-thaw cycle, the seawater freeze-thaw cycle deteriorates the surface peeling resistance and mechanical properties of seawater sea sand ECC. Compared with the non-freeze-thaw specimens, the failure mechanism after freeze-thaw cycles changed from the gradual increase of bond strength with the increase of strain rate to the gradual decrease. Compared with the dynamic elastic modulus, compressive strength, and bond strength freeze-thaw damage model based on the Weibull distribution, it was observed that the predicted life of compressive strength is overestimated, while the predicted life of bond strength is underestimated. The bond strength and slip calculation models for freeze-thaw cycles and strain rates have been established. This provides a theoretical foundation for predicting the structural service life and conducting durability research on ECC and GFRP bars in seawater and sea sand.

Investigating the Constitutive Model of Frozen Supersulfate Saline Soil: Insights from Fractional Calculus

The study of the mechanical properties of frozen saline soil is one of the key issues in addressing the design of infrastructure in cold regions. This research focuses on the supersulfated saline soil of the Ningxia Yellow River Irrigation Area in China, conducting triaxial tests under negative temperatures (−5, −10, −15 °C, and − 20 °C) with varying water contents (12%, 16%, 20%). Based on fractional calculus theory and incorporating an exponential decay factor, this study proposes a novel fractional-order constitutive model for a unified description of the softening and hardening behaviors in frozen saline soil. The model treats frozen saline soil as a composite blend of ideal solids and ideal fluids in varying proportions, taking into account the material's inherent time-dependency and non-linear stress-strain relationships. Finally, the validity of the model is verified by the calculated values of the model and the triaxial tests. The results indicate that, based on preliminary judgment, due to the presence of salt solutes, a large amount of liquid water remains in the supersulfated saline soil at temperatures ranging from 0 to −10 °C, forming an unstable state called “warm frozen saline soil”. The mechanical properties of frozen saline soil depend on the relative content of unfrozen water, ice crystals, and salt crystals and the formation of ice and salt crystals significantly enhances the strength of frozen saline soil. The computational results of the improved fractional constitutive model align well with experimental results, effectively describing the stress-strain relationship of frozen supersulfate saline soil. In the model, the parameter κ functions analogously to an elastic modulus and exhibits a linear relationship with temperature, and the parameter α characterizes the strain hardening of saline soil, while β describes its softening behavior. The proposed fractional constitutive model, with only three parameters having clear physical significance, is convenient for practical engineering applications.

Electrical Resistivity Behavior of Saline Soil under Low-Temperature Conditions

Freeze-thaw cycling of frozen soils is known to be the cause of various engineering failures of infrastructure in cold regions. Researchers found that electrical resistivity methods outperform traditional ground surveying methods in frozen soils for their greater convenience and cost-effectiveness. However, detailed investigation into the relationship between the electrical resistivity of soil and a variety of soil properties is still needed. In this study, a series of laboratory experiments using the Wenner method were conducted to determine the relationship between soil electrical resistivity and soil geotechnical properties such as initial water content and pore fluid concentration under freeze-thaw conditions. Cylindrical soil samples undergo artificial freeze-thaw cycles to a temperature as low as −70°C, and electrical resistivity and temperature values are recorded simultaneously. Measurement results are summarized for curve fitting, and a statistical model showing relationship between electrical resistivity and temperature during freezing and thawing was given. Above freezing point, the log of electrical resistivity had a linear relationship with temperature. Below freezing point and above −15°C, the log of electrical resistivity had a square root relationship with temperature. Different trends in electrical resistivity change in extremely low-temperature regions (from −15°C to −70°C) are also discussed. In extremely low-temperature regions, the electrical resistivity of frozen soils did not monotonously increase with lower temperature, which may be because of increasing salt concentration in the unfrozen water phase. The findings of this study are expected to bring more insights to frozen soil structure, and assist in geophysical surveying in cold regions and construction methods utilizing ground freezing.

Evolution and prediction of static and seismic properties in diatomite-incorporated concrete members exposed to freeze-thaw cycles

Freeze-thaw cycles induce substantial durability concerns for concrete infrastructures in cold regions. Traditional approaches to assess freeze-thaw degradation in concrete necessitate extensive environmental and mechanical testing, which are both resource-intensive and time-consuming. This paper introduces a concrete freeze-thaw damage constitutive model, designed for the accurate and efficient quantitative evaluation and prediction of the evolution in concrete's mechanical properties post freeze-thaw cycles. This model specifically considers the impact of supplementary cementitious materials, like diatomite. A numerical program was then developed to simulate the stress-strain responses of both diatomite-enhanced and ordinary concrete under freeze-thaw conditions. Based on these insights, the model was extended to structural members, creating a seismic and static finite element simulation methodology. The findings demonstrate the improvements in the mechanical performance of diatomite- incorporated concrete subjected to both static and seismic loads. This model offers theoretical support for predicting the mechanical behavior evolution of concrete materials and structures in cold climate regions.

Psychrophiles to control ice-water phase changes in frost-susceptible soils

The phase changes of soil water or porous media have a crucial influence on the performance of natural and man-made infrastructures in cold regions. While various methods have been explored to address the impacts of frost-action arising from these phase changes, conventional approaches often rely on chemicals, mechanical techniques, and the reuse of waste materials, which often exhibit certain limitations and environmental concerns. In contrast, certain organisms produce ice-binding proteins (IBPs) or antifreeze proteins (AFPs) to adapt to low temperatures, which can inhibit ice crystal growth by lowering the freezing point and preventing ice crystallization without the need for external intervention. This study explores the potential of three psychrophilic microbes: Sporosarcina psychrophile, Sporosarcina globispora, and Polaromonas hydrogenivorans, to induce non-equilibrium freezing point depression and thermal hysteresis in order to control ice lens growth in frost-susceptible soils. We hypothesize that the AFPs produced by psychrophiles will alter the phase changes of porous media in frost-susceptible soils. The growth profiles of the microbes, the concentration of released proteins in the extracellular solution, and the thermal properties of the protein-mixed soils are monitored at an interval of three days. The controlled soil showed a freezing point of − 4.59 °C and thermal hysteresis of 4.62 °C, whereas protein-treated soil showed a maximum freezing point depression of − 8.54 °C and thermal hysteresis of 7.71 °C. Interestingly, except for the controlled sample, all the protein-treated soil samples were thawed at a negative temperature (minimum recorded at − 0.85 °C). Further analysis showed that the treated soils compared to porous media mixed soil freeze (1.25 °C vs. 0.51 °C) and thaw (2.75 °C vs. 1.72 °C) at extensive temperature gap. This freezing and thawing temperature gap is the temperature difference between the beginning of ice core formation and completed frozen, and the beginning of ice core thawing and completed thawed for the treated soil samples selected from different incubation days. Overall, this study presents a novel bio-mediated approach using psychrophilic microbes to control ice formation in frost-susceptible soils.

Evaluations of low-temperature mechanical properties and full-range constitutive models of AA 5083-H112/6061-T6

The low-temperature mechanical properties of aluminium alloys (AAs) are important for the analysis and design of infrastructures in cold regions and LNG storage tanks made of AAs. This paper investigated the stress-strain behaviours of AA 5083-H112/6061-T6 materials through conducting tensile tests on 32 AA coupons at 20 ℃ ∼ −165 ℃. All the tested AA coupons exhibited ductile failure modes. Their results showed that the stress-strain curves of AA 5083-H112 exhibited the Portevin-Le Chatelier effects that gradually weakened with the decreasing temperature. Reducing the temperature from 20 ℃ to −165 ℃ increased the elastic modulus, yield and ultimate strengths of AA 5083-H112 (or 6061-T6) by 5.1% (6.5%), 8.7% (12.0%) and 7.8% (13.1%), but reduced the fracture strain by 16.4% (12.4%). The fracture surfaces of all AA 5083-H112 and 6061-T6 coupons displayed localised cross-sectional area reductions and substantial plastic deformation. Meanwhile, precipitation-hardened AA 6061-T6 exhibits a more pronounced enhancement compared to strain-hardened AA 5083-H112. Furthermore, regression analyses were performed to establish prediction equations for the low-temperature mechanical indexes of AAs. Subsequently, a full-range constitutive model was proposed to estimate the stress-strain behaviours of AA 5083-H112 and 6061-T6. Validations against reported experimental observations demonstrated that the developed model reasonably described the stress-strain responses of AA 5083-H112 and 6061-T6 from 20 ℃ to −165 ℃.

Macro-micro behaviors and failure mechanism of frozen weakly cemented mudstone

Understanding the mechanical properties and multiscale failure mechanism of frozen soft rock is an important prerequisite for the construction safety of tunnels, artificially frozen ground and other infrastructure in cold regions. In this study, the triaxial compression test are performed on mudstone in the weakly cemented soft rock strata in the mining area of western China, and the mechanical characteristics and failure mechanism of weakly cemented mudstone are systematically investigated under the combined action of freezing and loading. Furthermore, the quantitative relationship between the microstructural parameters and the macroscopic strength and deformation parameters is established based on fractal theory. Thus, the failure mechanism of frozen weakly cemented mudstone is revealed on both micro- and macro-scales. The results show that temperature and confining pressure significantly affects the elastic modulus and peak strength of weakly cemented mudstone. With decreasing temperature, the compressive strength increases, while the corresponding peak strain decreases gradually. On the deformation curve, the plastic deformation stage is shortened, and the brittle fracture feature at the post-peak stage is more prominent, and the elastic modulus correspondingly increases with decreasing temperature. Under low-temperature conditions, most of the weakly cemented mudstone undergoes microscopic shear failure along the main fracture surface. The micro-fracture morphology characteristics of weakly cemented mudstone under different temperatures are quantified via the fractal dimension, and an approximately exponential relationship can be obtained among the fractal dimension and the temperature, compressive strength and elastic modulus.

Using computer vision to monitor ice conditions in water supply infrastructure: a study of salient image features

Abstract Ice condition monitoring (ICM) is critical for the operation and maintenance of water supply infrastructure in cold regions. Existing approaches either depend on ground-level sensors or satellite photography for ICM, which suffer from high maintenance costs or inadequate precision. Computer vision (CV) has the potential to tackle the limitations by providing a precise and scalable solution based on near-shore cameras and increasingly affordable drones. To explore the potential of CV for ICM, this paper presents a systematic study of salient image features for differentiating typical ice evolvement phases throughout the freeze–thaw cycle. First, ice condition during the freeze–thaw cycle is studied to provide a categoric system of typical ice stages. Second, multiple image feature descriptors are proposed to characterize the distinction between different ice conditions. Finally, with the proposed descriptors as input, two support vector machines (SVMs) are trained to classify the ice condition for automatic ICM. Experiments have been implemented to identify salient features for ice characterization. It was found that the SVMs can achieve 71.9 and 77.3% accuracy for the prediction of ice stage and ice flow strength, respectively. Future research is suggested to develop the research findings into practical solutions for webcams or drone-based automatic ICM.

Subsurface Porewater Flow Accelerates Talik Development Under the Alaska Highway, Yukon: A Prelude to Road Collapse and Final Permafrost Thaw?

AbstractThe presence of taliks (perennially unfrozen zones in permafrost areas) adversely affects the thermal stability of infrastructure in cold regions, including roads. The role of heat advection on talik development and feedback on permafrost degradation has not been quantified methodically in this context. We incorporate a surface energy balance model into a coupled groundwater flow and energy transport numerical model (SUTRA‐ice). The model, calibrated with long‐term observations (1997–2018 on the Alaska Highway), is used to investigate and quantify the role of heat advection on talik initiation and development under a road embankment. Over the 25‐year simulation period, the new model is driven by reconstructed meteorological data and has a good agreement with near surface soil temperatures. The model successfully reproduces the increasing depth to the permafrost table (mean absolute error <0.2 m), and talik development. The results demonstrate that heat advection provides an additional energy source that expedites the rate of permafrost thaw and roughly doubles the rate of permafrost table deepening, compared to purely conductive thawing. Talik initially formed and grew over time under the combined effect of water flow, snow insulation, road construction and climate warming. Talik formation creates a new thermal state under the road embankment, resulting in acceleration of underlying permafrost degradation, due to the positive feedback of heat accumulation created by trapped unfrozen water. In a changing climate, mobile water flow will play a more important role in permafrost thaw and talik development under road embankments, and is likely to significantly increase maintenance costs and reduce the long‐term stability of the infrastructure.

Experimental Study on the Dynamic Characteristics of Frozen Silty Clay and Its Influencing Factors

Frozen soils are widely distributed in the seismically active regions of northwest China. Under the background of global warming, the study of the dynamic characteristics of frozen soil is very significant for the sustainable development of engineering in cold regions. In this study, the silty clay in the Lanzhou area of northwest China is selected to investigate the dynamic characteristics and its influence factors by dynamic triaxial tests. Various influence factors were considered, including confining pressure, soil temperature, soil water content and loading frequency. The dynamic elastic modulus ratio and reference dynamic strain amplitude increase as confining pressure and soil temperature decrease, and they also increase as soil water content and loading frequency increase. With an increase in confining pressure, soil water content, loading frequency, and a decrease in soil temperature, the damping ratio decreases but the maximum dynamic elastic modulus increases. With an increase in dynamic strain amplitude, the dynamic elastic modulus ratio has a decreasing trend, while the damping ratio has an increasing trend. It was found that the dynamic behaviors are most sensitive to the soil temperature. In addition, the comprehensive influence effect of soil water content, confining pressure, soil temperature, and loading frequency on the maximum dynamic elastic modulus, maximum damping ratio, and reference dynamic strain amplitude of frozen silty clay are analyzed, and the quantitative relationships between them are established. The results can provide evidence for seismic design and safe operation and maintenance of infrastructure in cold regions.

Dynamic mode I fracture properties of saturated white sandstone under ambient sub-zero temperatures

Dynamic fracture properties of frozen rocks are essential for better designs of rock engineering infrastructures in cold regions. Thus, a dynamic-cryogenic testing system combined with a high-speed camera is adopted to conduct dynamic tests under ambient room and sub-zero temperatures (20 °C, −10 °C, −20 °C, and −30 °C). A porous white sandstone (WS) is used to fabricate notched semi-circle bend (NSCB) specimens for mode I dynamic fracture tests. The percentage of ice and unfrozen water in rock pores under different temperatures is quantified using the nuclear magnetic resonance (NMR) method. For comparison purpose, dry specimens are also tested under the same ambient temperatures. The results show that the dynamic fracture toughness (DFT) for two sets of specimens all show obvious rate dependency. Except for −30 °C, DFTs of dry specimens are marginally influenced by the sub-zero temperatures. On the contrary at a given loading rate, DFT of frozen saturated specimens first drops to the lowest value at −10 °C before further increasing with the dropping ambient temperature. Compared with dry specimens, saturated specimens show lower DFTs and crack propagation velocities that are quantified with the digital image correlation (DIC) method. The experimental results are explained invoking the rock weakening and enhancing mechanisms of the ice and unfrozen water mixture in rock pores. These results are useful to blasting designs in cold areas.

Pore microstructure and mechanical behaviour of frozen soils subjected to variable temperature

Mechanical behaviour of frozen soils is of great concern in the design and construction, and maintenance of the railways, highways, airports, pipelines, and other major infrastructure in cold regions. The micro-structural behaviour of the frozen soils such as porosity, particle morphology, arrangement pattern, contact connection, and particle trajectory can be susceptible to variable temperature. The paper investigates the microstructure characteristic and mechanical behaviour of the frozen soils caused by different temperature gradients. The soils differ in both water content (5% ∼ 20%) and temperature range (−15 °C ∼ 0 °C) under cold environment. The purpose of the study is to evaluate the mechanical behaviour of frozen soils based on a mathematical model and observe the microstructure behaviour using scanning electron microscopy (SEM) equipped with particles (pores) crack analysis system (PCAS). The mathematical model can well simulate the stress-strain relationship of frozen soils. The porosity of the frozen soils increases with the decrease of the temperature, and the distribution of the particles triggered by different temperature gradient. Furthermore, micro-structural behaviour has potential applications in micro- and macroscopic mechanical behaviour of the frozen soils in cold region engineering.

Experimental and numerical analyses of soil electrical resistivity under subfreezing conditions

The engineering behavior of frozen soils is critical to the serviceability of civil infrastructure in cold regions. Among various geophysical techniques, electrical resistivity imaging is a promising technique that is cost effective and provides spatially continuous subsurface information. In this study, under freeze–thaw conditions, we carry out lab–scale 1D electrical resistivity measurements on frost–susceptible soils with varying water content and bulk density properties. We use a portable electrical resistivity meter for temporal electrical resistivity measurements and thermocouples for temperature monitoring. Dynamic temperature-dependent soil properties, most notably unfrozen water content, exert significant influences on the observed electrical resistivity. Below 0 °C, soil resistivity increases with the decreasing temperature. We also observe a hysteresis effect on the evolution of electrical resistivity during the freeze–thaw cycle, which effect we characterize with a sigmoidal model. At the same temperature, electrical resistivity during freezing is consistently lower than that during thawing. We have implemented this sigmoidal model into a COMSOL finite element model at both laboratory and field scales which enables the simulation of soil electrical resistivity response under both short–term and long–term sub–freezing conditions. Atmospheric temperature variations induce soil temperature change, and thereby phase transition and electrical resistivity change, with the rate of change being a function of the depth of investigation and soil properties include initial water content and initial temperature. This study advances the fundamental understanding of the electrical behaviors of frozen soils and enhance the application of electrical geophysical investigations in cold regions.

Construction and structural analysis of an arched cellulose reinforced ice bridge for transportation infrastructure in cold regions

While floating ice covers have been leveraged to traverse water bodies during cold months, ice has seen little use as a stationary, free-standing bridging material for transportation routes. To address this knowledge gap, an arched bridge made from ice reinforced with 0.3 wt% cellulose was constructed using a spray deposition method. The bridge was built over a constructed gap (3 × 3 × 1 m) in a temperature-controlled facility and was able to support the static and dynamic loading of military-grade vehicles (up to 3050 kg) with no apparent damage to the bridge. Flexural and compression testing of ice specimens extracted from the bridge post traverse indicated that the cellulose reinforced ice is approximately 2× greater in strength compared to pure ice. Microstructural analysis showed a layered structure with smaller ice grains in layers with more cellulose. To assess the utility of the arched cellulose reinforced ice bridge (ACRIB) as a technology, we built a computational model using a conservative approach with pure ice material properties and only short-term elastic loading. We probed the loading capacity of the ACRIB as built and with design modifications. The model results predicted that the ACRIB as built could support up to 16,800 kg of static loading, which is safely in the range of military tactical vehicles (e.g., M1083, 13,480 kg) and commercial vehicles (e.g., Ford F150, 2300 kg). Increasing the curvature of the bridge effectively increases the load capacity of the ACRIB by approximately 50%, while larger gaps and widths are still able to support vehicles up to 3050 kg if the ice is thickened by 50%. The versatility of this new approach is of high impact to both civilian and military mobility in cold regions, adding a critical new tool to the cold regions engineering toolbox.

Inexpensive Anti-Icing Concrete Material for Application to Tunnel and Slope Engineering Infrastructures in Cold Regions.

The formation of ice hangings on the surfaces of concrete tunnel linings and sloped rock masses in cold regions endangers railroad and highway traffic. However, an inexpensive anti-icing material that meets both performance and cost requirements has not yet been developed for application in tunnel and slope engineering infrastructures in cold regions. Most current advanced anti-icing materials are expensive, and fabrication and spraying are both cumbersome, which limits their widespread application to tunnel and slope engineering. Because concrete is a widely used construction material owing to its excellent mechanical properties and low cost, we developed an inexpensive, environmentally friendly anti-icing concrete material (AICM). The AICM can be easily fabricated and sprayed onto the surfaces of large-area concrete or rock substrates and exhibits excellent superhydrophobicity (CA: 151°, SA: 6.7°), surface robustness, water resistance, chemical durability, good anti-icing, easy deicing (deicing stress: 0.06 MPa), and excellent long-term durability in freeze-thaw cycles in low-temperature environments. In addition, a novel fractal theory-based model of ice adhesion shear stress was developed and revealed the mechanism through which an AICM with a composite micro/nanostructure easily deices. The AICM has good application prospects and serves as an important guide for mitigating the formation of ice hangings in tunnel and slope engineering infrastructures in cold regions.

Neutron scattering quantification of unfrozen pore water in frozen mud

The Earth's polar regions are experiencing a greater frequency of freeze-thaw events throughout the polar summer, contributing to atmospheric methane and destabilising clay-rich sediments. Clays in soils tightly bind pore water and thus substantially modify freeze-thaw events. While temperatures of phase transitions for confined pore water may be precisely assessed using calorimetric or thermal analyses to −30 or −40 °C, neutron scattering directly probes how pores in clay minerals control ice formation and melting to lower temperatures. We apply elastic neutron scattering to accurately quantify the unfrozen water content of clay gels and unambiguously identify different pore-water environments by their freezing temperatures. Using this approach, we conclude that cryosuction controls water mobility in frozen soils in the absence of soluble salts to much lower temperatures than observed by other techniques. Dyanmics determined from neutron scattering indicates that water in clay gel pores thaws at much lower temperatures than currently considered, and thus pose potential risks for contaminant migration at sub freezing temperatures. The general poor strength of wet clays can significantly impact infrastructure in cold regions undergoing an increased frequency of freeze-thaw events. Different pore water environments in clay gels can be identified and quantified by inelastic neutron scattering. • Cryosuction removes interlayer water from clay gels hydrated to near saturation. • Cryosuction requires capillary connectivity to operate in clay gels. • Considerable interlayer water remains unfrozen in clay gels to below −80C. • Freezing characteristic curves can be used to identify pore environments.

Mechanical behavior of frozen soils: Experimental investigation and numerical modeling

The mechanical behavior of frozen soils plays a central role in the design, construction, and maintenance of buildings and infrastructure in cold regions. We present and discuss the main results of an experimental campaign focused on the mechanical behavior of frozen soils from Alaska. The data set is unique because it involves natural frozen soils and covers a wide range of temperatures (i.e., from −6 °C up to −26 °C) and confinements (i.e., from unconfined conditions up to a cell pressure of 54.6 MPa). An elastoplastic model for frozen soils is presented and validated based on the test results. The elastoplastic model accounts for the effects of temperature and cryogenic suction on key properties associated with frozen soil behavior, namely, increase of preconsolidation pressure, stiffness, and strength with the decrease of temperature. Other aspects such as the volumetric behavior of frozen soils at different temperatures and the smooth transition between elastic and plastic states are also qualitatively well captured by the model. We implemented the constitutive model in a fully coupled thermo-hydro-mechanical simulator and we analyzed the behavior of a foundation in a thawing ground. The proposed approach is able to capture the main feature of frozen soil behavior.

Risk assessment of potential thaw settlement hazard in the permafrost regions of Qinghai-Tibet Plateau

Climate warming could exacerbate the occurrence of thaw settlement hazard in the permafrost regions of the Qinghai-Tibet Plateau (QTP), which would threaten the stability of engineering infrastructure in cold regions. The risk associated with permafrost settlement, valuable for the regional sustainable development, remains poorly assessed or understood on the QTP. In this study, three common Geo-hazard indices were used to assess the settlement risks in the permafrost regions of the QTP, including the settlement index, the risk zonation index, and the allowable bearing capacity index. However, large spatial differences existed in simulating the risk maps by using the abovementioned Geo-hazard indices. Hence, we developed a combined index (Ic) by integrating the three indices to reduce the uncertainty of the simulations. The results indicated that the ground ice is a critical factor for assessing the settlement risk in permafrost regions. We also applied the Ic to assess the settlement risk along the Qinghai-Tibet Railway (QTR). The proportion of low-risk area along the QTR would be the highest (45.38%) for the future periods 2061–2080 under Representative Concentration Pathway 4.5. The medium-risk area combined with the high-risk area would be accounted for more than 40%, which were located at the boundary of the present permafrost regions. Therefore, the corresponding adaptation measures should be taken to reduce the potential economic losses caused by the high-risk regions to the infrastructure. Overall, the results would present valuable references for engineering design, construction and maintenance, and provide insights for early warning and prevention of permafrost thaw settlement hazard on the QTP.

Electrical conductivity and ground displacement in permafrost terrain

Permafrost and ground ice are important features of the landscape that can significantly affect infrastructure in cold regions. Information on thaw susceptibility is important for predicting the behaviour of permafrost as an engineering substrate. We compare apparent conductivity surveys to ground displacement obtained from differential interferometric synthetic aperture radar with the objective of establishing apparent conductivity as an indicator of thaw susceptibility for regional characterization of terrain stability and permafrost conditions along the western coast of Hudson Bay, Nunavut. For field conditions where ground displacement and conductivity are influenced by surficial geology, there is a correlation between high seasonal and inter-annual subsidence and low apparent conductivity, and between high seasonal and inter-annual subsidence and high seasonal conductivity ratio, inferred to be indicative of high ice content and thaw-related displacement. For field conditions with no strong influence of surficial geology, a clear correspondence between subsidence and apparent conductivity does not exist. Nevertheless, the geophysical data are useful in identifying relevant factors for characterization of terrain stability such as saline permafrost and an ice-rich top of permafrost that experience significant seasonal fluctuations in unfrozen water content. When utilizing low-induction number electromagnetic surveys in permafrost terrain, apparent conductivity must be corrected for a depth-dependent temperature profile. For this study, correction factors of 6–13% are required to compensate for temperature variation, or 2.1% per °C at half-depth, but this is not necessarily applicable to other temperature profiles.

Solute strongly impacts freezing under confinement

The presence of liquid water in frozen media impacts the strength of soils, the growth of frost heave, plant life and microbial activities, or the durability of infrastructures in cold regions. If the effect of confinement alone on freezing is well known, water is never pure and solutes depressing the freezing point are naturally found. However, the combination of confinement and solute is poorly understood. Here, we study in situ the freezing of water in a model porous medium made of densely packed particles with various salt (KCl) concentrations. We demonstrate a synergistic effect of solute with confinement: the freezing front, initially heterogeneous due to confinement, drives solute enrichment in the remaining liquid, further depressing its freezing point. This increases the local freezing point depression and results in much larger mushy layers where ice and liquid water coexist. We compare our experimental freezing profile with theory and estimate the local solute concentration to increase by more than one order of magnitude through the freezing process. These results imply that even low solute concentrations may have important effects on the distribution of water in frozen porous media and should help explain the variety of freezing patterns observed experimentally. This may be critical for cryo-tolerance of construction materials and organisms and will help understanding solute precipitation and redistribution in soils.