Journal of Cold Regions Engineering

Abstract

Global warming is causing unprecedented changes to permafrost regions with amplified effects in the Arctic through a phenomenon known as Arctic amplification. This intensified climate warming thaws both the discontinuous and continuous permafrost resulting in changes in the mechanical properties of the soils found in these regions. Since permafrost regions constitute nearly 24% of the Northern Hemisphere, understanding the strength of soils in thawed conditions is essential to analyze the stability of existing structures, and to design safer and more economical infrastructure in these regions. Specifically, thawing of the permafrost is causing considerable reductions in its strength of soils, which may lead to massive landslides, foundation failures, and so forth. Since frozen soil is a multiphase structure that consists of soil particles, unfrozen water, ice, and air, each constituent will influence the mechanical properties. This paper reviews the current state of knowledge of the impact of temperature, volumetric ice content, unfrozen water content, and frozen density on the compressive strength, peak shear strength, residual shear strength, undrained shear strength, and tensile strength of soils. The undrained shear strength of soil is said to have a linear correlation with temperature. In addition, the undrained cohesion of soil was found to depend on the temperature, whereas the undrained friction angle of soil was significantly influenced by volumetric ice content. An increase in the volumetric ice content up to 80% to 90% will cause a reduction in the peak and residual deviatoric stresses. In addition, an increase in volumetric ice content resulted in an increase in the compressive strength of the soil. The tensile and compressive strengths were found to be functions of the unfrozen water content.

Practical Applications

Global warming is causing the temperature of the permafrost, which is permanently frozen ground, to rise. This paper provides valuable insights into the impact of the changes in this ambient temperature on the strength of frozen soils in permafrost regions for a wide range of applications. Such insights are crucial for the design of resilient and stable infrastructure, such as foundations, embankments, and retaining walls, in which consideration of the reduced strength of thawed soils due to climate change will be necessary. In addition, the knowledge will allow for better management of vulnerable areas prone to landslides and erosion caused by the weakened soil strength permitting the implementation of mitigation measures before lives are lost and costly economic damages are incurred. Finally, this information will aid in early warning systems, emergency planning, and decision making to minimize the impact of hazards on human settlements and infrastructure. In this paper, a review of the current state of knowledge regarding the strength of frozen soils and the associated fluctuations in these strengths because of a rise in temperature are presented. Guidelines on the best practices for sample preparation and testing along with correlations to estimate various strength parameters are also provided.

Abstract

Snow and ice route removal activities play an essential role in travelers’ safety and roadways’ reliability. They often require the deployment of a large number of snowplow trucks on a vast maintenance area and involve a set of vehicle routing problems with multiple objectives and constraints. Many transportation agencies have limited resources and budgets for snow and ice route removal activities during winter maintenance operations. The objective of this paper is to propose a constraint-based snowplow optimization model to accommodate vehicle routing problems and justify the optimized fleet size for achieving the maximum level of service in snow and ice route removal. The proposed snowplow optimization model was developed using the geographic information system (GIS) base maps created by using ArcGIS Pro (version 2.7). After the model was tested and verified by experts in the Kansas Department of Transportation, it was applied to the snow and ice route removal activities in a district in Kansas as an illustrative example. The optimization results showed that the level of service could be increased up to 81% with an average route removal efficiency of 86% and the total travel time required to treat all snow routes in the selected district can be reduced by approximately 29 h for one treating iteration. The proposed model contributed to the winter operation maintenance body of knowledge by providing an efficient approach to snow and ice route removal activities. The findings of this study also may assist transportation agencies in optimizing their snow route removal practice in winter maintenance operations.

Practical Applications

This study developed a snowplow route optimization model using a geographic information system (GIS)-based software platform to enhance the efficiency of snow removal of Departments of Transportation of states in their winter maintenance. The model outcomes provided a detailed set of optimized snowplow route maps with time-related parameters (e.g., total travel time, plowing time, and deadhead time), snowplow route efficiency, and percentage of level of service (LOS) satisfaction of snow removal. Then, transportation agencies can utilize the optimized routing networks to monitor their resources spent on snow and ice control activities and increase the LOS in their maintenance operations. The results of this study enable transportation agencies to effectively justify the fleet size required at each service area and efficiently allocate limited resources to maintain all roadways in an economic, safety, and reliability manner. This study also facilitates the automation of snowplow optimization processes using GIS to provide satisfactory services during snow and ice events. The proposed model can serve as a tool to assist the agencies in directing any future facility locations and capacities for their winter maintenance.

This study presents a systematic literature review of ice load measurements on dams. Several hypotheses about the relationship between the maximum ice load and external variables are tested using regression analysis on the data collected from the literature. The performed tests show that ice thickness, water level change category, and dam height are factors that have a significant and relevant relationship with the magnitude of all measured ice loads. The ice thickness is the only tested variable that also shows a significant and relevant relationship with differences in ice load between winters at one dam. The variation in recorded ice load from several sensor positions at one dam during the same winter is considerable. Generally, the difference between the sensor area and the structure–ice interaction area is large, resulting in extensive extrapolation and uncertainties regarding the representativeness of the measured results.

Premature degradation of concrete, caused by frost damage, has been associated with inadequate transport properties and poor resistance to deicing salt. In this study, transport properties and deicing salt resistance of various kinds of ultrahigh-performance concrete (UHPC) containing Type V portland cement, fly ash, and microsilica were investigated. Seven combinations of cementitious materials (one reference, three binary, and three ternary) were used to batch UHPCs using a water-to-cementitious material ratio (w/cm) of 0.21. The aggregate-to-cementitious material ratio (V_a/V_cm) of 1.20 was kept constant for all mixtures. The investigated transport properties included water absorption, volume of permeable voids, water penetration, rapid chloride penetration, and surface resistivity. The transport properties of the plain UHPCs were also compared to those of the corresponding steel fiber–reinforced UHPCs. The test results showed that the transport properties and deicing salt resistance of the studied binary and ternary UHPCs improved with the inclusion and increases in microsilica, replacing a portion of cement. The addition of steel fiber had a minor effect on strength and transport properties and a moderate increase in deicing salt resistance of the studied UHPCs. While rapid chloride penetration and surface resistivity tests were found appropriate to assess chloride transport through the studied plain UHPCs, both tests were deemed unsuitable for the companion steel fiber–reinforced UHPCs.

This study aimed to present the effect of mixture proportions (including coarse-to-fine aggregate ratio and water-to-binder ratio) and mixture compositions (including the addition of different supplementary cementing materials and fibers) on the impact resistance and mechanical properties of concrete cured in cold temperatures. The impact resistance was evaluated using drop-weight and flexural impact tests conducted on concrete samples cured in different curing conditions. The studied parameters included coarse-to-fine aggregate (C/F) ratio (0.7 and 1.2), water-to-binder (w/b) ratio (0.4 and 0.55), type of supplementary cementing materials (SCMs) [20% metakaolin (MK) and 10% silica fume (SLF)], and the addition of steel fibers (0.35%) (SFs). The studied mixtures were cured under different curing conditions, including moisture condition at 23°C, air condition at 23°C, +5°C curing condition, and −10°C curing condition. The positive effect of using SFs and SCMs (MK and SLF) on enhancing the impact resistance and splitting tensile strength (STS) was more pronounced in samples cured at normal curing temperatures compared to samples cured at low temperatures. The mechanical properties and impact resistance of mixtures developed with higher C/F and w/b ratios were more affected by the low-temperature curing condition compared to the control mixture (with lower C/F and w/b ratios). The results also showed that low-temperature curing had a more pronounced negative effect on the impact resistance and STS than the compressive strength.

The axial compression performance of confined reinforced concrete columns in cryogenic temperature environments is affected by the mechanical properties of reinforcement and concrete materials. The properties of reinforcement and concrete material vary greatly in cryogenic environments. To investigate the axial compression behavior of confined reinforced concrete columns at cryogenic temperatures, specimens with stirrup-confined and carbon fiber–reinforced polymer (CFRP) confined were simulated respectively, considering the impact of cryogenic temperatures on material properties. The various stirrup and CFRP ratios were applied at different temperatures from 20°C to −120°C. The results indicate that decreasing temperature improves the peak load and initial stiffness while reducing peak strain and ductility. The ductility of specimens improves with the increasing stirrup and CFRP ratios, while the increment at cryogenic temperatures is less than that at 20°C. At −120°C, the hoop strains at the peak point and descending branch are greater than those at 20°C. The confined strength increases linearly with the increasing confinement ratio, while the decreasing temperature reduces the growth rate. The confinement effects are weakened as temperature drops. Based on the numerical results, a compression model that can reflect the influence of cryogenic temperatures was established. The model can provide better predictions of confined strength, peak strain, and stress–strain curves of confined reinforced concrete columns under axial compressive load and cryogenic temperatures.

This study focuses on the investigation of the electromagnetic properties of multiphase inorganic materials (i.e., soils) in changing subsurface environmental conditions that are induced by climate warming. Subsurface warming in cold regions exacerbates the spatial and temporal evolution of frozen soil properties; therefore, an accurate characterization of the unfrozen water and ice content of frozen soils under different thermal conditions has become a pressing need. Several studies focused on the effect of the initial hydraulic properties on the electromagnetic properties of soils. However, detailed systematic studies on the influence of the combined effects of temperature, initial degree of saturation, applied frequency fields, and experiment scales are limited. This study aims to characterize the dielectric and electrical behavior of ice-bearing inorganic soils under the coupled effects of thermal, hydraulic, and electromagnetic conditions. A series of laboratory experiments were performed on soil samples that had different initial degrees of saturation and dry density values by electromagnetic impedance spectroscopy (EIS) and time domain reflectometry (TDR) between −10°C and 5°C. The results from the experiments revealed that the dielectric constant of the inorganic soils decreased with increasing frequency, decreasing initial volumetric water content (VWC), and temperature. The electrical resistivity values decreased with increasing frequency values, initial water content, and temperatures. In addition, the unfrozen water contents at different temperatures were calculated using a modified power law that accounts for the temperature-dependent dielectric permittivity of water and was compared with the TDR measurements. The outcomes of this study could help elucidate the intricate mechanisms of the particle–water–ice interface and their influence on the behavior of frozen soils that are needed for sustainable built and natural environments in cold regions.

In cold regions, the frequent occurrence of frost damage seriously affects the safety and stability of tunnel projects during construction and service time. Analyzing the formation mechanism of ice congestion in the drainage channel is of great significance for reducing the risk of frost damage. For this purpose, a mathematical model was proposed in the present work to investigate the freezing properties of water flow in the drainage channel. In this model, the latent heat of the water–ice phase change was taken into account to describe the formation process of frazil ice. Combined with the method of energy conservation, the critical distance of water freezing was derived theoretically. The field experiment and computational fluid dynamics (CFD) simulation were carried out to verify the accuracy and effectiveness of the proposed model. It showed that the estimated critical position of water freezing agreed well with the experimental and simulation results. Subsequently, the effects of hydraulic and thermodynamic factors on the freezing process of water flow were further discussed. As a practical application, the proposed mathematical model is utilized to evaluate the safety of the drainage channel of a railway tunnel in cold regions. The results demonstrate that when the flow discharge is smaller than 2,600 m³/day, there is a risk of ice congestion in the drainage channel within a range of about 960 m from the water outlet. Therefore, freeze-proof measures such as (1) thermal insulation cover plate, (2) electric heat tracing system, and (3) ground-source heat pump system should be employed in this range.

Abstract

For evaluating the resistance performance of cement-stabilized soils in cold regions, the variation of the strength of the cemented sand–gravel (CSG) mixture concerning the hydration process should be explored. This paper aims to study the effect of freeze–thaw (F–T) cycles on the strength and microstructure of a CSG mixture with 10% cement that is subjected to 12 cycles of freezing at a temperature of −23°C for 24 h and then melted at room temperature of 24°C for the next 24 h. The uniaxial compressive strength (UCS), California bearing ratio (CBR), and weight volume loss of the samples were measured after individual F–T cycles. Furthermore, the change in the microstructure of the CSG mixture in various F–T cycles was explored. The results showed a considerable reduction in the UCS up to Cycle 3, then a slight increase for Cycles 3–6, and finally a gradual decrease for further cycles. However, the CBR and weight loss slightly fluctuated up to Cycle 6, and then gradually decreased for subsequent cycles. The majority of compounds of hydrated cement were damaged in the first three cycles. In the following cycles, between Cycles 3 and 6, the portlandite compound was dissolved and recrystallized within the microvoids. Depending on the environmental conditions, carbonation may be generated from the hydrated cement fraction, which fills the microvoids and improves the strength and structure of the mixture. During further cycles after the sixth cycle, the mechanical action of the ice lenses coupled with the disintegration of the hydrate compounds imposed many new microvoids and cracks with considerable length and width, which intensified the strength reduction of the moisture and weakened the adhesion between grains.

Practical Applications

Since cement is widely used in pavement and dam engineering for stabilizing soils, the durability of cemented soils is of prime concern. This study may help improve the durability and resistance of cemented soils in cold climates. The F–T action not only influences the macrostructure of cement-stabilized soils by imposing a wide crack and ice lens but also induces a considerable change in the complexes existing in the hydrated cement paste of the mixture. Three patterns govern the change of the mixture microstructure in various F–T cycles that correspond to the observed trend in strength. The mentioned trend for the microstructure change and, consequently, the strength variation of the CSG mixture are associated with many factors such as pH, cement content, CO₂ content, moisture content within the mixture, and relative humidity within the environment. Accordingly, the pattern of microstructural changes in the CSG mixture after the middle F–T cycles may vary depending on environmental conditions.

Low-temperature curing significantly affects the performance of concrete. This study explored the mechanical and microstructural characteristics of concretes modified with three kinds of nanoparticles [i.e., nano-CuO (NC), nano-SiO₂ (NS), and nano-TiO₂ (NT)] at curing temperatures of −6°C, −2°C, 2°C, and 6°C. The results indicated that the compressive strength of concrete cured at positive temperatures was higher than that of concrete cured at negative temperatures. Variations in the stress–strain relationships for the specimens were similar, of which the strain of concrete modified with NT was higher than those modified with NC and NS. At positive curing temperatures, the peak stress of concrete specimens modified with NC and NT first increased and then decreased as the nanomaterial content was raised, and the peak stress reached its maximum value when the nanomaterial content was 2%. However, at negative curing temperatures, the peak stress reached a maximum value when the NC content was about 3%. Besides, in terms of the compressive strength of nanoconcretes, the optimum contents of the nanomaterials to resist external loads and the optimal contents for NC, NS, and NT cured at negative temperatures were 3.0%, 1.0%, and 3%, respectively. Moreover, compared with the controlled group of ordinary portland cement without nanomaterials, for concretes with added nanomaterials, the nanomaterials can significantly fill the internal pores of the concrete, which can inhibit the development of cracks. Furthermore, low-temperature curing can inhibit hydration reactions, and the resistance to negative temperatures for concretes modified with NT was better than that for concretes modified with other nanoparticles. This study will help us better understand the influence mechanism and degree of low-temperature curing on the behavior of nanoconcrete and provide guidance for engineering construction in cold regions.

In this paper, fiber Bragg grating (FBG) sensors were applied to investigate the frost resistance of C60 concrete. First, the growth of both the static and dynamic elastic modulus of C60 concrete with curing age was investigated using an FBG, the standard method, and the resonance method, respectively. Second, to simulate the freezing and thawing conditions in cold regions, the concrete specimens were subjected to air freezing and water thawing using the slow freezing method. The authors explored the effect of freeze–thaw cycles on the mechanical properties of concrete and established a mathematical model relating its mechanical properties to freeze–thaw cycles based on an FBG sensor. Meanwhile, its compressive strength, dynamic elastic modulus, and mass loss rate were tested. Finally, the interface morphology and hydration products of concrete were observed using a scanning electron microscope (SEM) after freeze–thaw cycles. The results indicate that both the static and dynamic elastic modulus of C60 concrete increase with curing age. Its elastic modulus measured by FBG is approximately the same as that measured by the standard method, confirming the viability of using an FBG sensor to measure its elastic modulus. Furthermore, the authors highlighted the dependence of its compressive strength on the freeze–thaw cycles. The relationship of the static elastic modulus to freeze–thaw cycles is similar to that of the dynamic elastic modulus and mass loss rate. A static elastic modulus achieved from an FBG is proposed here to characterize the frost resistance of C60 concrete.

The Qinghai–Tibet Plateau shows an obvious trend of warming and humidification, and the increased rainfall is mainly concentrated in the summer. There have been few reports on the effects of summer rainfall variations on the hydrothermal states of embankments in permafrost regions. Therefore, based on an indoor embankment-scale model experiment, the effects of increased summer rainfall on the surface energy, temperature, and water fields of highway embankments in permafrost regions were investigated. The results showed that increased summer rainfall led to an increase in surface net radiation. However, the increase in summer rainfall led to a decreasing trend in the pavement temperature and shallow heat flux of the embankment, indicating that increased summer rainfall could effectively inhibit the increase in pavement temperature. Simultaneously, the increased summer rainfall also increased the shallow water content at different locations of the embankment in the following order: natural site > shoulder > slope > pavement. The maximum increase in water content at the natural site was 6.7% after a twofold increase in the summer rainfall. In addition, the temperature within the embankment exhibited a decreasing trend with an increase in summer rainfall. Compared to other parts of the embankment, although the increased summer rainfall led to a relatively small increase in water content in the lower part of the pavement, the asphalt concrete pavement had a higher temperature. Therefore, when rainfall acts as an energy cold pulse on the pavement, the temperature of the lower part of the pavement decreases more significantly than that of the other parts of the embankment. The increased summer rainfall affected the cooling range of different parts of the embankment in the following order: pavement > natural site > shoulder > slope. The increase in summer rainfall had a hysteresis effect that affected the water and temperature fields within the embankment in autumn.