Soil Ice Research Articles

The Relation between Soil Moisture Phase Transitions and Soil Pore Structure under Freeze–Thaw Cycling

The process of soil moisture phase transitions (SMPT) under freeze–thaw cycling is considered a key factor driving changes in soil pore structure. However, there is still no consensus on which indicators related to SMPT affect the soil pore structure. The objectives of this study were to compare SMPT and soil pore characteristics under freeze–thaw cycling, and to analyze the inherent relationship between them as affected by different bulk densities. Hence, we employed thermal pulse time-domain reflection technology (T-TDR) and X-ray CT scanning technology (X-CT) to quantitatively study the process of SMPT and pore characteristics of soil core samples (60 mm diameter, 100 mm height) repacked with three different bulk density levels: 1.10 g·cm−3 (NC), 1.30 g·cm−3 (LC) and their combination (1.10 g·cm−3 for upper half, 1.30 g·cm−3 for lower half, SC) under freeze–thaw cycling. Our results showed that compared with NC, the porosity of LC’s 0–5 cm soil column decreased by 0.070 cm3·cm−3, the imaged porosity (ϕ>60μm) decreased by 0.034 cm3·cm−3, and the maximum soil ice content (MIC) decreased by 0.030 cm3·cm−3. The pores within the range of 200−300 mm (ϕ2) and 300–400 mm (ϕ3) contribute the most significantly to ϕ>60μm (50–60%). Soil initial moisture content (IMC) and MIC explained 50.1% of the change in ϕ2, and the bulk density explained 49.3% of the change in ϕ3. During the melting process, higher moisture content promotes the thaw collapse of soil particles, resulting in a decrease in ϕ>60μm. The mean pore radius of the limiting layer (MRLL) and the hydraulic radius (HR) show that changes in bulk density from 1.10 g·cm−3 to 1.30 g·cm−3 do not have significant differences. Our results show the relationship between SMPT and pore structure change during freeze–thaw cycles as affected by initial soil bulk density and moisture condition.

Retrogressive thaw slump susceptibility in the northern hemisphere permafrost region

AbstractMean annual temperatures in the Arctic and subarctic have increased in recent decades, increasing the number of permafrost hazards. Retrogressive thaw slumps (RTSs), triggered by the thawing of ground ice in permafrost soil, have become more common in the Arctic. Many studies report an increase in RTS activity on a local or regional scale. In this study, the primary goals are to: (i) examine the spatial patterns of the RTS occurrences across the circumpolar permafrost region, (ii) assess the environmental factors associated with their occurrence and (iii) create the first susceptibility map for RTS occurrence across the Northern Hemisphere. Based on our results, we predicted high RTS susceptibility in the continuous permafrost regions above the 60th latitude, especially in northern Alaska, north‐western Canada, the Yamal Peninsula, eastern Russia and the Qinghai‐Tibetan Plateau. The model indicated that air temperature and soil properties are the most critical environmental factors for the occurrence of RTSs on a circumpolar scale. Especially, the climatic conditions of thaw season were highlighted. This study provided new insights into the circumpolar susceptibility of ice‐rich permafrost soils to rapid permafrost‐related hazards like RTSs and the associated impacts on landscape evolution, infrastructure, hydrology and carbon fluxes that contribute to global warming.

Are Northern Hemisphere boreal forest fires more sensitive to future aerosol mitigation than to greenhouse gas-driven warming?

Considerable interest exists in understanding how climate change affects wildfire activity. Here, we use the Community Earth System Model version 2 to show that future anthropogenic aerosol mitigation yields larger increases in fire activity in the Northern Hemisphere boreal forests, relative to a base simulation that lacks climate policy and has large increases in greenhouse gases. The enhanced fire response is related to a deeper layer of summertime soil drying, consistent with increased downwelling surface shortwave radiation and enhanced surface evapotranspiration. In contrast, soil column drying is muted under increasing greenhouse gases due to plant physiological responses to increased carbon dioxide and by enhanced melting of soil ice at a depth that increases soil liquid water. Although considerable uncertainty remains in the representation of fire processes in models, our results suggest that boreal forest fires may be more sensitive to future aerosol mitigation than to greenhouse gas-driven warming.

Climate change will reduce North American inland wetland areas and disrupt their seasonal regimes

Climate change can alter wetland extent and function, but such impacts are perplexing. Here, changes in wetland characteristics over North America from 25° to 53° North are projected under two climate scenarios using a state-of-the-science Earth system model. At the continental scale, annual wetland area decreases by ~10% (6%-14%) under the high emission scenario, but spatiotemporal changes vary, reaching up to ±50%. As the dominant driver of these changes shifts from precipitation to temperature in the higher emission scenario, wetlands undergo substantial drying during summer season when biotic processes peak. The projected disruptions to wetland seasonality cycles imply further impacts on biodiversity in major wetland habitats of upper Mississippi, Southeast Canada, and the Everglades. Furthermore, wetlands are projected to significantly shrink in cold regions due to the increased infiltration as warmer temperature reduces soil ice. The large dependence of the projections on climate change scenarios underscores the importance of emission mitigation to sustaining wetland ecosystems in the future.

Assessing hydrothermal changes in the upper Yellow River Basin amidst permafrost degradation

Since the 20th century, the temperature on the Qinghai–Tibetan Plateau (QTP) has increased at a rate of 2–3 times that of global warming. Consequently, the soil temperature and active layer thickness have also increased, which have directly caused severe degradation of the frozen ground on the QTP. Using a hydrological model driven by climate and vegetation forcing, the spatial and temporal changes in the hydrothermal characteristics of the Upper Yellow River Basin (UYRB) from 1960 to 2019 were modeled and the mechanism of the changes was analyzed. During the past six decades, the soil temperature in the UYRB exhibited an increasing trend. The degradation of permafrost in the UYRB was accompanied by thickening of the active layer, a reduction of the maximum depth of the seasonal frost penetration, and continuous extension of the basin thawing time. This degradation was also associated with the increase in the soil moisture content and decrease in the soil ice content, resulting in degradation of the permafrost area by one-tenth of the total area in the UYRB. The reduction of the permafrost area and the thickening of the active layer can profoundly impact hydrological processes and ecosystems. These findings play a critical role in designing efficient strategies to manage and protect frozen ground and serve as a valuable reference for understanding the consequences of frozen ground degradation globally.

Characteristics of ground surface heat flux for alpine vegetation in freeze-thaw cycles in the three river source region

Ground surface heat flux (G0) is a key component of surface energy flux and serves as a reliable parameter for assessing shallow geothermal energy. Using the observations from four sites and a novel method, we investigated the daily, monthly, and diurnal characteristics of G0 across various types of land cover in the Three River Source Region. The contribution of soil heat flux at 5 cm or 7.5 cm (Gsoil) to G0 was found to be only between 1/2 and 2/3, with the remaining portion being attributed to changes in heat storage of soil and liquid water (Δssoil), heat storage of soil ice (Δsice) and latent heat of ice phase change (ΔsLH). The characteristics of G0 exhibited significant variations in response to different land-covered vegetation during daily, monthly, and diurnal cycles, as well as two freeze-thaw stages. The alpine marsh-covered soil had the largest annual amplitude in G0 on both daily and monthly averages but showed the smallest diurnal amplitude in G0. In the frozen stage (FS), G0 played a significant role as a supplement to net radiation (Rn) in TRSR, particularly in the alpine marsh region where it accounted for approximately −22 % to −80 % of Rn from November to February.

Numerical simulation revealing the impact of drilling-based mining equipment structure on water ice extraction from lunar soil

In the context of space exploration, the in-situ utilization of lunar water ice holds principal significance. A variety of techniques have been suggested for water ice mining. However, the impact of mining equipment structure on water ice extraction has been rarely reported. Here, we used numerical simulations to study the impact of drilling-based mining equipment structure on water extraction from icy soil, by comparing two designs: Corer and Auger. The impact of water ice on deep lunar drilling missions was explored. The results showed that the mining equipment structure significantly affects vapor flow, phase transitions, and water ice extraction efficiency. The Auger's design allows for higher water vapor content and enhanced heat transfer within the icy soil, while the Corer's design reduces vapor flow and performs better during the initial mining stage. It is believed that this work will provide theoretical guidance for designing high-performance mining equipment in further lunar water ice utilization. We also highlighted the potential role of water ice in lunar soil for enhancing heat dissipation in deep drilling missions, protecting the drill bit from potential damage due to elevated temperatures. The insights gained from this study offer valuable contributions to the design of drilling tools for future lunar missions and the exploration of other icy celestial bodies.

Impacts of seasonally frozen soil hydrothermal dynamics on the watershed hydrological processes inferred from a spatially distributed numerical modelling approach

The freeze–thaw cycle over the surface seasonally frozen soil is an important soil hydrothermal dynamic process linking land surface processes and climatic changes in the cold regions. With the advancement of frozen soil hydrothermal dynamic studies and remote sensing technology, the simulation of frozen soil hydrological processes based on the distributed numerical model has become a hotspot to better understand the impact of frozen soil hydrothermal dynamics on the watershed hydrological processes in the cold regions over a large spatial scale. However, the quantitative analysis of the impact of seasonally frozen soil hydrothermal processes on watershed runoff at long-term time scales remained an unsolved issue in the field of frozen soil hydrology. Under the framework of the watershed distributed eco-hydrological model ESSI-3, a fully distributed frozen soil hydro-thermal processes integrated modeling system (FFIMS model) was established based on the coupled water and heat transferring mechanism for frozen soil hydro-thermal process simulations in the frozen surface or at a certain depth of a watershed. By coupling the FFIMS model with the distributed eco-hydrological model ESSI-3, the impacts of seasonally frozen soil hydrothermal processes on hydrological processes were investigated from the perspective of temporal-spatial domain with the simulated hydrothermal and hydrological processes for a long-term period from 2008 to 2016 over a watershed located in the cold region of Northeastern China. The results suggested that the soil freeze–thaw cycling posed different impacts with limited significance throughout the whole hydrological processes of the watershed in different seasons. Significant impacts on the hydrological processes were particularly observed in the thawing period of a year, when soil ice meltwater contributing to the discharge of the study watershed reached to about 35% in average in this period. ESSI-3 coupled with the FFIMS modelling system obviously improved the performance of the original ESSI-3 in cold region watershed simulations, and the averaged Nash efficiency coefficients obtained increased from almost 0 to 0.77 in the thawing period of a year. The study demonstrated the importance of application of spatially distributed numerical model with physical mechanism for seasonally frozen soil water and heat transfer process simulations.

Evaluation of Parameterization Schemes for Matric Potential in Frozen Soil in Land Surface Models: A Modeling Perspective

AbstractSoil matric potential (SMP) is an important variable in land surface models (LSMs) for regulating soil hydrological processes and highly influenced by soil ice in frozen ground. In this study, four SMP parameterization schemes that incorporate different effects of soil pore ice were separately integrated into the Simultaneous Heat and Water (SHAW) model and evaluated for their ability to simulate heat and water transport at a permafrost monitoring site at the Tanggula Mountain Pass on the inner Qinghai‐Tibet Plateau based on the same data and model settings. The schemes differed in their treatment of pore ice effects, including effective porosity and cryosuction. An identifiability analysis of SMP‐related parameters for each scheme was performed, based on 1,000‐fold random parameter sampling. The scheme that considered both effects performed best, accurately simulating both soil moisture content and temperature in the active layer. The schemes that considered only one effect of pore ice showed limitations, with the effective porosity scheme underestimating unfrozen water content and the cryosuction scheme seriously overestimating it, and both schemes leading to large discrepancies in simulated soil temperature. The scheme that ignored both effects performed better than the partially considered schemes due to a compensating effect of reduced effective porosity and increased cryosuction in the presence of pore ice, but not as well as the scheme that considered both effects, particularly in simulating soil temperature during freezing periods and estimating unfrozen water content near the mid‐depth of the active layer.

Reclamation effects of distinct volumes and concentrations of CaCl2-amended brackish ice in different saline-sodic soils

The proper usage of marginal soil and water resources has major implications for the sustainability of agriculture, such as brackish water and saline-sodic soils. The saline soils can be ameliorated though melting process of calcium-containing brackish ice, however, the optimum concentration and volume of brackish ice (water) for the reclamation of different saline-sodic soils remain to be determined. In this study, 108 soil columns representing four Ice salinity levels (16, 26, 36, 46 mmolc L−1) and three Pore Volumes (2/3, 1.5, 2.5 PV) of calcium-amended brackish ice were tested to reveal the reclaiming effect on a range of saline-sodic soils. The linear mixed model (LMM), multiple regression equation, and principal coordinate analysis (PCoA) were applied to calculate the amelioration effect in terms of three factors: Ice volume, Ice salinity and Column depth. Our results showed that the soil salinity and sodicity generally decreased with increasing Ice volume and Ice salinity, and the saline-sodic soils with low exchangeable sodium percentages (i.e. ESP 20) were more sensitive to Ice salinity, with high salinity (26–46 mmolc L−1) and large volume (2.5 PV) of brackish ice reaching a better amelioration effect. The effect of Ice volume became more dominant in medium and high ESP soils (ESP 40 and ESP 70), whereas the high salinity combined with low volume of brackish ice would lead to worse soil properties, especially at the bottom layers. Meanwhile, the Column depth factor had a considerable effect on the soil chemical properties, with the variance explained ranging from 18.6% to 36.0%. These results provide theoretical guidance in the rational use of calcium-amended brackish ice and highlight the necessity to take layer effect into consideration for reclaiming saline-sodic soils.

Drying of tundra landscapes will limit subsidence-induced acceleration of permafrost thaw

We used a model for permafrost hydrology informed by detailed measurements of soil ice content to better understand the potential risk of abrupt permafrost thaw triggered by melting ground ice, a key open question associated with permafrost response to a warming Arctic. Our spatially resolved simulations of a well-characterized site in polygonal tundra near Utqiaġvik, Alaska, agree well with multiple types of observations in the current climate. Projections indicate 63cm of bulk subsidence from 2006 to 2100 in the strong-warming RepresentativeConcentration Pathway 8.5 climate. Permafrost thaw as measured by the increase in active layer thickness (ALT)-the thickness of the soil layer that thaws each summer-is accelerated by subsidence, but the effect is relatively small. The ALT increases from the current-day value of approximately 50cm to approximately 180cm by 2100 when subsidence is included compared to about 160cm when it is neglected. In these simulations, previously identified positive feedbacks between subsidence and thaw are self-limiting on decadal time frames because landscape runoff and increasing evapotranspiration result in drier tundra with weaker surface/atmosphere coupling. These results for a tundra site that is representative of large swathes of the Alaska North Slope suggest that subsidence is unlikely to lead to abrupt thaw over large areas. However, subsidence does have significant effects on the hydrology of polygonal tundra. Specifically, subsidence increases landscape runoff, which helps maintain streamflow in the face of increased evapotranspiration but also causes drier tundra conditions that could have deleterious effects on sensitive Arctic wetland ecosystems.

Discrimination Between Dry and Water Ices by Full Polarimetric Radar: Implications for China’s First Martian Exploration

China’s first Mars rover named “Zhurong” has begun its exploration at the surface of the Utopian Plain in the Martian northern hemisphere on May 22, 2021. Mars rover penetrating radar (RoPeR) is one of the key payloads onboard the Zhurong rover and one of its prima scientific objectives is to detect potential water ice and/or dry ice in the subsurface soil at the landing site. The high-frequency channel of RoPeR, which is equipped with a fully-polarized antenna array with a center frequency of 1.3 GHz, can record full polarimetric radar reflections from subsurface anomalies. In this article, a radar system with a polarimetric antenna array the same as RoPeR was set up and carefully calibrated. Laboratory experiments were carried out to test the feasibility of RoPeR in the detection and discrimination of potential dry ice and/or water ice in Martian soils. The experimental results indicate that the reflection signals from the bottom of the dry ice and water ice samples present different polarimetric scattering characterizations. The characteristic polarimetric scattering features of dry ice and water ice revealed in this article would guide the analysis and interpretation of the real data acquired by RoPeR on Mars.

Experimental study on shear characteristics of the silty clay soil-ice interface

During the spring thawing, the decrease of soil-ice interface strength by temperature may lead to slope instability. For this reason, some researchers have explored the relationship between temperature and soil-ice interface strength. However, previous studies have not systematically explored the change law of strength at the soil-ice interface from negative temperature to 0 °C. Therefore, direct shear tests were conducted at different shear temperatures and different moisture contents. The effects of temperature and moisture content on strength, cohesion, and internal friction angle are analyzed, while the shear failure mechanism of specimens at different temperatures is discussed according to the location of the shear failure surface. The results show that: Shear properties of soil ice specimens are related to the unfrozen moisture content. The strength of the sample decreases with increasing temperature, and the change in strength is most significant from − 2 to − 0 °C. The strength reduction in this range is from 21.8 to 74.8%, and the higher the moisture content the more obvious this phenomenon is. The shear index tends to decrease with the increase of unfrozen water content, and the greater the increase of unfrozen water, the faster the decrease of both, especially in stage 2. When the temperature is higher than − 5℃, the failure surface is located above the soil-ice interface, and the strength of the specimen is similar to that of the frozen soil. When the temperature is − 10℃, the shear damage surface appears at the soil-ice interface, and the strength of the specimen is determined by the strength of the soil-ice interface.

Impact of profile-averaged soil ice fraction on passive microwave brightness temperature Diurnal Amplitude Variations (DAV) at L-band

The dynamic change of frozen soil is crucial to land-surface modeling, carbon feedback studies, ground engineering (e.g., constructions), and microwave remote sensing. L-Band satellite missions Soil Moisture and Ocean Salinity (SMOS) and Soil Moisture Active Passive (SMAP) are currently exploited to characterize soil into freeze or thaw (FT) states. However, brightness temperatures (TB) at L-band contain more information besides the FT state, particularly over permafrost or seasonally frozen soil, which has not been explored via current retrieval algorithms. To examine the potential for L-band TB observations, we define an index called Profile-Averaged Frozen Soil Fraction (Ff) related to Diurnal Amplitude Variation (DAV) of TB (i.e., ΔTB) based on the optical depth of the frozen soil column. We evaluated Ff inferred from the 0th-order microwave transfer model with the SMAP L1c product, the ground-based European Space Agency L-Band Radiometer III (ELBARA-III) TB observations, and temperature profiles collected at the Maqu station in northeastern Tibet. While there is a clear relationship between Ff and ΔTB, no apparent link exists with the ice content fraction (Ffi) within a fixed-depth soil column. The proposed model certifies that the profile-averaged soil ice content Ff relates to the dynamic microwave penetration depth by math and field measurement. The model reproduces well ΔTB in Period Freezing but has problems in Period Thawing when melted surface water obstruct the microwave signals. Our findings can be used to exploit ΔTB between 6 am and 6 pm, as a typically overpassing time by the SMOS and SMAP satellites, for estimating Ff, which can be further applied in weather/climate forecasting and for improving land-surface modeling.

A repository of measured soil freezing characteristic curves: 1921 to 2021

Abstract. Soil freeze–thaw processes play a fundamental role in the hydrology, geomorphology, ecology, thermodynamics, and soil chemistry of cold regions' landscapes. In understanding these processes, the temperature of the soil is used as a proxy to represent the partitioning of soil ice and water content via a soil freezing characteristic curve (SFCC). This mathematical construct relates the soil ice content to a specific temperature for a particular soil. SFCCs depend on many factors, including soil properties (e.g., porosity and composition), soil pore water pressure, dissolved salts, (hysteresis in) freezing/thawing point depression, and the degree of saturation, all of which can be site-specific and time-varying characteristics. SFCCs have been measured using various methods for diverse soils since 1921, but, to date, these data have not been broadly compared. This is in part because they had not previously been compiled in a single dataset. The dataset presented in this publication includes SFCC data digitized or received from authors, and it includes both historic and modern studies. The data are stored in an open-source repository, and an R package is available to facilitate their use. Aggregating the data has pointed out some data gaps, namely that there are few studies on coarse soils and comparably few in situ measurements of SFCCs in mountainous environments. It is hoped that this dataset (https://doi.org/10.5281/zenodo.5592825; Devoie et al., 2022a) will aid in the development of SFCC theory and improve SFCC approximations in soil freeze–thaw modelling activities.

Freezing‐induced stiffness and strength anisotropy in freezing clayey soil: Theory, numerical modeling, and experimental validation

AbstractThis paper presents a combined experimental‐modeling effort to interpret the coupled thermo‐hydro‐mechanical behaviors of the freezing soil, where an unconfined, fully saturated clay is frozen due to a temperature gradient. By leveraging the rich experimental data from the microCT images and the measurements taken during the freezing process, we examine not only how the growth of ice induces volumetric changes of the soil in the fully saturated specimen but also how the presence and propagation of the freezing fringe front may evolve the anisotropy of the effective media of the soil–ice mixture that cannot be otherwise captured phenomenologically in the isotropic saturation‐dependent critical state models for plasticity. The resultant model is not only helpful for providing a qualitative description of how freezing affects the volumetric responses of the clayey material, but also provide a mean to generate more precise predictions for the heaving due to the freezing of the ground.

Prediction of the unfrozen water content in soils based on premelting theory

The variation of unfrozen water content with temperature has a significant effect on the coupled heat-water transport in freezing soil, which can cause the frost heave and thaw settlement, and thus influence the stability of infrastructures. The premelting theory for water–ice in soils is developed to study the unfrozen water variation in freezing soil. The developed theory integrates the interfacial premelting of contact ice, the soil particles, the melting of the ice surface, and the premelting induced by impurity and curvature. A model to predict the unfrozen water content is then established by considering the change of unfrozen water film. The equivalent grain size is introduced to improve the solving efficiency in the calculation. Finally, the proposed analytical model is verified by the test data. The results indicate that the thickness of water film in soils increases when the surface charge density and the impurity concentration increase under the same supercooling degree. The surface melting on the interfaces of soil particle and the pore ice has key influence on the variation of the liquid water content. Meanwhile, the unfrozen water content increases with the increasing impurity concentration and surface charge on soil particles. Besides, the unfrozen water content also increases with the decreasing radius of soil particles.

Water Migration and Segregated Ice Formation in Frozen Ground: Current Advances and Future Perspectives

A characteristic of frozen ground is a tendency to form banded sequences of particle-free ice lenses separated by layers of ice-infiltrated soil, which produce frost heave. In permafrost, the deformation of the ground surface caused by segregated ice harms engineering facilities and has considerable influences on regional hydrology, ecology, and climate changes. For predicting the impacts of permafrost degradation under global warming and segregated ice transformation on engineering and environmental, establishing appropriate mathematical models to describe water migration and ice behavior in frozen soil is necessary. This requires an essential understanding of water migration and segregated ice formation in frozen ground. This article reviewed mechanisms of water migration and ice formation in frozen soils and their model construction and introduced the effects of segregated ice on the permafrost environment included landforms, regional hydrological patterns, and ecosystems. Currently, the soil water potential has been widely accepted to characterize the energy state of liquid water, to further study the direction and water flux of water moisture migration. Models aimed to describe the dynamics of ice formation have successfully predicted the macroscopic processes of segregated ice, such as the rigid ice model and segregation potential model, which has been widely used and further developed. However, some difficulties to describe their theoretical basis of microscope physics still need further study. Besides, how to describe the ice lens in the landscape models is another interesting challenge that helps to understand the interaction between soil ice segregation and the permafrost environment. In the final of this review, some concerns overlooked by current research have been summarized which should be the central focus in future study.

Improving Ground Heat Flux Estimation: Considering the Effect of Freeze/Thaw Process on the Seasonally Frozen Ground

AbstractAn inadequate understanding of the changes in water and heat of the soil is likely a potential reason for the nonclosure of the surface energy balance. During the freeze/thaw period, the large volumetric heat capacity of ice and the latent heat of soil ice phase change had a specific influence on the estimation of ground heat flux (G0). However, the effects of the freeze/thaw process on G0 estimation were not well quantified using field observations. The improvements of G0 estimation by adding the soil ice heat storage (Δsice) and the latent heat of soil ice phase change (ΔsLH) were evaluated during the freeze/thaw period at two sites (Madoi and Maqu) on the eastern Tibetan Plateau. During the freeze/thaw period, both Δsice and ΔsLH had important influences on the reasonable determination of G0. Adding ΔsLH increased G0 at the daytime peak by 34.4 W/m2 (Madoi) and 9.3 W/m2 (Maqu). During the completely frozen stage, the contributions of Δsice to G0 ice + LH (adding both Δsice and ΔsLH) were higher than those during other freeze/thaw stages at both sites, and ΔsLH also made a significant contribution to G0 ice + LH. Therefore, the daily freeze/thaw cycles cannot be ignored during the completely frozen stage in the estimation of G0. The G0 ice + LH approach improved the G0 estimation more than G0 ice (adding Δsice) approach during the freezing and thawing stages. The improvements of G0 estimations increased the energy closure status and reduced the daily average of imbalance.

An implicit Heat-Pulse-Probe method for measuring the soil ice content

• Ice content measurement in soil is essential and challenging, and the thermal response of frozen soil mainly depends on the pore ice content. • The pore ice content can be measured by its thermal response. • An implicit heat-pulse method is proposed to measure soil ice content. • T rela characterizes soil thermal response upon heating. • Ice content θ i affects soil thermal properties and thermal response T rela . • A standard calibration is proposed to determine the relation between T rela and θ i . • The average errors of θ i from the new method are around 3%. Soil ice content increases with time during the freezing process, thus frequently causing severe frost heave of subgrade or foundation in the cold region. It is a lasting challenge to implement real-time monitoring of soil ice content. In this study, a new heat-pulse method with an average accuracy of around 3% was proposed to measure soil ice content. This method was implemented by the following steps: (1) A heat pulse method with a double-probe sensor, i.e., one heating probe and one measurement probe was used; (2) In the calibration, the relation area after a heat-pulse action was measured on four samples with different initial water contents and at eight negative environmental temperatures. (3) On the calibrated data, an approximate function was fitted to characterize the monotonic relation between the relation area and soil ice content; (4) In application, the relation area value and environmental temperature were measured for each frozen sample, and the measurements were substituted into the approximate function to calculate the soil ice content. The effectiveness of the new method was verified by the test on three types of soil, including a silty clay, a sand loam, and a sand.