Frost Depth Research Articles

Frost protection mechanism based on rubber airbag interlayered composite lining system for cold-region tunnels

To solve the problem of freezing damage in cold-region tunnels, this study proposed a rubber airbag interlayered composite lining system, and tested its performance of buffering, pressure adjustment, waterproofing, and heat preservation by simulating a low-temperature environment in an artificial freezing chamber. The experiment results show that the frost-heaving force exerted on the lining can always be lower than 1.69 kPa by constantly adjusting the airbag pressure, and the maximum frost-heaving force can reach 28.25 kPa without the airbag. In addition, the airbag also has good waterproof performance. Finally, the airbag can significantly improve the temperature field of the surrounding rock and reduce the freezing depth (6.75 cm < 17.25 cm). The insulation effect of the airbag is positively correlated with its thickness and negatively correlated with the thermal conductivity of the filling gas. The insulation effect of CO2 is better than that of air. The rubber airbag interlayered composite lining system provides a new scheme for freezing damage control in cold-region tunnels.

Spatial and Temporal Changes in Soil Freeze-Thaw State and Freezing Depth of Northeast China and Their Driving Factors

It is necessary to further investigate the spatial considerations, temporal characteristics, and drivers of change affecting the beginning and end of soil freezing and thawing, including the maximum depth of the seasonal freezing (MDSF) and the active layer thickness (ALT) in Northeast China. Hourly soil temperature, among other data, from 1983–2022 were investigated, showing a delay of about 6 days in freezing. In contrast, thawing and complete thawing advanced by about 26 and 20 d, respectively. The freezing period and total freeze-thaw days decreased by about 29 and 23 days, respectively. The number of complete thawing period days increased by about 22 days, while the MDSF decreased by about 25 cm. The ALT increased by about 22 cm. Land Surface Temperature (LST) is the main factor influencing the beginning and end of soil freezing and thawing, MDSF and ALT changes in Northeast China; air temperature, surface net solar radiation, and volumetric soil water content followed. The influence of the interacting factors was greater than the single factors, and the interactive explanatory power of the LST and surface net solar radiation was highest when the soil started to freeze (0.858). The effect of the LST and the air temperature was highest when the soil was completely thawed (0.795). LST and the volumetric soil water content interacted to have the first explanatory power for MDSF (0.866) and ALT (0.85). The results of this study can provide scientific reference for fields such as permafrost degradation, cold zone ecological environments, and agricultural production in Northeast China.

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.

Simulation of Temperature Field in Railway Embankment Filling in Seasonal Frozen Areas

In order to examine the temperature field changes of railway roadbed in seasonal frozen areas under different filling heights, a typical cross-sectional model of Chagan Lake Station railway was established using the finite element numerical simulation software ANSYS. The temperature parameters of the roadbed were calculated based on the atmospheric temperature of local meteorological data, and the temperature fitting curve was used as the temperature boundary condition. Under different filling quantities, the temperature field of the roadbed was simulated for a freeze-thaw cycle, and the temperature curve changes were analyzed. The results indicate that as the filling height increases, the freezing depth line also increases accordingly. When the filling height is 2.5m, the maximum freezing depth at the roadbed is 1.7m. In a freeze-thaw cycle, the freezing process of soil develops from top to bottom, and the melting process develops in two directions: from top to bottom and from a certain depth of soil upwards, with the characteristics of "unidirectional freezing and bidirectional melting". The freezing period starts from early December of each year to the end of March of the following year, and completely melts until the end of April. Melting develops faster than freezing.

Are the Noah and Noah-MP land surface models accurate for frozen soil conditions?

The accurate prediction of frozen soil conditions is a critical component of dynamic terrain characterization for engineering operations in cold regions. Currently the trusted resource for dynamic terrain within the US military uses gridded global soil conditions (i.e., temperature and moisture) generated by the Land Information System (LIS) architecture. LIS combines static terrain data with trusted surface weather information into the Noah land surface model to generate a continuous representation of the global surface conditions. Both the input weather data and the model output land surface state are adjusted to match the observed state using an advanced ensemble Kalman filter data assimilation technique to incorporate in situ and remote sensing observations. While this product has been robustly evaluated under unfrozen conditions only sporadic studies have investigated its ability to accurately simulate freeze/thaw cycles, and soil temperature and moisture under frozen conditions. Here, we present a broad comparison and evaluation of the simulated soil state against an in situ network of soil temperature and moisture distributed across the Continental United States that focuses on the winter season. This comparison includes both the Noah and the newer Noah with multi-parameterization (Noah-MP) land surface models. A comparison of the two models reveals substantial differences in simulated soil moisture, frozen content, and frozen soil strength. In general, Noah predicts colder soils with deeper frost depths, and frozen soils that are slightly stronger than Noah-MP. Initial results evaluating Noah and Noah-MP against in situ observations show that both models have significantly degraded model performance for frozen soil conditions compared to their performance for unfrozen soil. In particular, Noah has a significant and persistent cold bias of approximately −3 K when the soil temperature is below freezing. This cold bias is not present in Noah-MP and further analysis shows that this improvement was almost entirely caused by a better representation of thermal conduction through snow in Noah-MP. Specifically, we find that the bulk effective thermal conductivity of a snowpack is 2× greater in Noah, which allows for greater surface heat loss during the winter and, consequently, lower soil temperatures. This analysis reveals that the more advanced multi-layer snow model in Noah-MP substantially improves the representation of soil temperature during the cold season.

Simulations and Prediction of Historical and Future Maximum Freeze Depth in the Northern Hemisphere

AbstractThe maximum annual freeze depth (MFD) is a primary indicator of the thermal state of frozen ground, affecting ecosystems, hydrological processes, vegetation growth, infrastructure, and human activities in cold regions. It is thus important to quantify the past, present, and future spatial and temporal variability of MFD at the hemispheric scale. We develop a data‐driven MFD simulation method within a machine learning framework, integrating MFD observations from meteorological stations and several environmental predictors, to analyze past and future scenarios in the Northern Hemisphere (NH). Based on ERA5 reanalysis estimates and historical to future CMIP6 scenarios, the NH MFD averaged 133 cm (ERA5) and 131 cm (CMIP6) during 1981–2010, and will vary 81–112 cm during 2015–2100 depending on the emission scenario. During 1950–2013, MFD decreased by 0.37 cm/a (ERA5) versus 0.22 cm/a (CMIP6), and is projected to decrease 0.16–0.69 cm/a by 2100. During 1981–2010, MFD decreased by an average of 19.1% (ERA5) and 13.9% (CMIP6), with a net change of −17 cm (ERA5) and −13 cm (CMIP6). Depending on the emission scenario, MFD will decrease 11% (−12 cm) to 42% (−19 cm) between 2015 and 2099 relative to the 1981–2010. Warming, increased moisture, warmer cold seasons, warmer warm seasons, shallower snow depths, and increased vegetation cover all lead to a reduction in MFD. The results from this novel machine learning approach provide useful insights regarding the fate of future frozen ground changes.

NEOWISE Observations of Distant Active Long-period Comets C/2014 B1 (Schwartz), C/2017 K2 (Pan-STARRS), and C/2010 U3 (Boattini)

Hyperactive comet activity typically becomes evident beyond the frost line (∼3–4 au) where it becomes too cold for water-ice to sublimate. If carbon monoxide (CO) and carbon dioxide (CO2) are the species that drive activity at sufficiently large distances, then detailed studies on the production rates of these species are extremely valuable to examine the formation of the solar system because these two species (beyond water) are next culpable for driving cometary activity. The NEOWISE reactivated mission operates at two imaging bandpasses, W1 and W2 at 3.4 μm and 4.6 μm, respectively, with the W2 channel being fully capable of detecting CO and CO2 at 4.67 μm and 4.23 μm in the same bandpass. It is extremely difficult to study CO2 from the ground due to contamination in Earth’s atmosphere. We present our W1 and W2 photometry, dust measurements, and findings for comets C/2014 B1 (Schwartz), C/2017 K2 (Pan-STARRS), and C/2010 U3 (Boattini), hereafter, B1, K2, and U3, respectively. Our results assess CO and CO2 gas production rates observed by NEOWISE. We have determined: (1) comets B1 and K2 have CO2 and CO gas production rates of ∼1027 and ∼1029 molecules s−1, respectively, if one assumes the excess emission is attributed to either all CO or all CO2; (2) B1 and K2 are considered hyperactive in that their measured Af ρ dust production values are on the order of ≳103 cm; and (3) the CO and CO2 production rates do not always follow the expected convention of increasing with decreased heliocentric distance, while B1 and K2 exhibit noticeable dust activity on their inbound leg orbits.

Study on the effect of step ratio to temperature field of cut-fill transition in deep seasonal frozen soil region

The existing studies lack numerical simulation of the temperature field in the cut-fill transition of the deep seasonal frozen soil regions. The ratio effect of steps in the backfill area of cut-fill transitions has also been little studied. Therefore, this paper establishes a numerical model based on some geological and meteorological data of Yichun City, China. It simulates the temperature field process of the cut-fill transition for the next 10 years under three ratio step conditions: 1:1, 2:3, and 1:2. The results show that the temperature field of the subgrade corresponding to different working conditions varies relatively significantly in terms of maximum freezing depth and frozen layer morphology. The law shows that in the cut-fill transition section, the gentler the step gradient is, the deeper the maximum freezing depth is, and the larger the frozen layer retained area in the thaw period. The retention of frozen interlayers is likely to cause differences in subgrade stiffness and exacerbate the “thaw-basin” phenomenon. Therefore, this study recommends 1:1 ratio of steps as the optimal program for the construction of backfill area, and can be targeted according to the numerical results of this paper in the arrangement of drainage, insulation and other measures.

Температурный расчет грунтового основания в геотехнических программных комплексах

A crucial step in addressing the challenge of constructing shallow foundations on seasonally freezing heaving soils is performing temperature calculations of the soil foundation. The software packages Frost 3D and QFrost can be used for conducting these temperature calculations. This research compared the results of calculating frost penetration depths of a test site’s soil foundation using Frost 3D and QFrost with data from geotechnical monitoring. The test site was located in Tyumen, in the vicinity of the Bereznyaki settlement. The study found that using Frost 3D and QFrost software packages for modeling the soil foundation allows for determining frost penetration depths with an error of up to 3.5 %, indicating the reliability of the results and the possibility of using these software packages for performing temperature calculations.

Experience in construction and operation of sewerage networks in areas with deep seasonal ground freezing across different regions of the Russian Federation

Reviewing the experience in construction and operation of sewerage networks in areas with deep seasonal ground freezing across different regions of the Russian Federation. Methods: analyzing the sewer pipeline laying, in-situ observations of wastewater temperature regime at sewer outlets from residential buildings. Results: designs of sewer pipelines laid in different regions are presented, as well as their dependence on the depth of seasonal ground freezing in different regions of the Russian Federation. The actual values of sewage water temperature at sewage outlets from residential buildings are established. Practical significance: In a number of regions the laying of sewerage pipes at a depth of 1.5-1.8 m led to normal and stable operation of sewerage pipelines. In terms of capital expenditures, sewer pipelines account for more than 50% of the estimated cost of the entire wastewater disposal system. Their operation claims a significant share of the costs.

Selection and validation of release sites for conservation translocations of temperate-zone snakes

Poor habitat quality is one of the most important reasons for reintroduction failure of reptiles; therefore, release site suitability ought to be evaluated prior to conducting conservation translocations. In temperate zone snakes, translocations have failed due to high overwinter mortality, so practitioners have recommended that release sites be located near suitable hibernacula. The presence of a Life Zone (LZ), the underground space above the groundwater table and below the frost line, may indicate the presence of suitable hibernation habitat. Identification and validation of sites with LZ, however, is challenged by the dynamic nature of groundwater and frost levels, coupled with the secretive nature of hibernating snakes. In this study, our goals were to 1) identify potential reintroduction sites for the globally imperiled Eastern Massasauga (Sistrurus catenatus) in southern Canada based on the presence of a LZ, 2) to validate the suitability of those reintroduction sites by hibernating a surrogate species (Eastern Gartersnake, Thamnophis sirtalis) in constructed hibernacula, and, 3) to determine if two separate measures of LZ were associated with the survival of individual gartersnakes to the end of hibernation. Four 1-ha study grids, each consisting of multiple groundwater and frost monitoring stations, were surveyed from 2015 to 19. Release sites were identified in each grid where a LZ of ≥ 10 cm was observed consistently for at least 2 full winters, and gartersnakes were successfully hibernated therein and at 2 reference sites over 3 winters. Overall, survival of subadult/adult snakes was very high (100 %; n = 20), regardless of site, whereas juvenile survival was lower (78 %; n = 93). A Kaplan-Meier test indicated that juvenile survival differed significantly among sites, and ranged from 60 % to 100 %. GLMM analysis indicated that mass at ingress had a significant positive effect on snake survival during hibernation. The temporary loss of a LZ did not impact snake survival. Contrary to our expectations, snake survival in hibernacula was negatively associated with both minimum LZ size and LZ frequency (i.e., the % of sampling occasions when LZ size ≥ 10 cm). Hibernating snakes can tolerate periods with a very small or non-existent LZ, but a large LZ may become unsuitable to juveniles, possibly due to a lack of moisture. Our results will guide the selection of release sites for Massasauga reintroductions, and for the development of a rigorous release site selection process for temperate zone snakes.

Experimental study on solar heating system based on heat pipe technology for mitigating subgrade frost heave

Subgrade frost heave is the main reason that affects the safe operation and comfort of trains during the cold season. Solar heating system based on heat pipe technology is a promising method to mitigate the frost heave by raising the subgrade temperature. In this paper, a field experiment was conducted to evaluate the heating performance of the solar heating system based on heat pipe technology in the cold season. In addition, the heat collection performance and stability of the system are compared with other solar heating systems. Finally, its applicability is discussed. Experimental results revealed that the solar heating system based on heat pipe technology can effectively raising the soil temperature and mitigate the frost heave of subgrade. During the experiment period, the soil temperature at the depth of −0.5 m in the experiment site was 5 °C higher than that of the comparison site, and the maximum freezing depth was 0.4 m, which was 56 % lower than that of the comparison site. The mean daily temperature of heat collection units (HCUs)fluctuated around 30 °C, and the mean daily temperature of the two-phase closed thermosyphons (TPCTs) fluctuated between 15 °C and 30 °C. The heat transfer efficiency of System 1 and System 2 is greater than 0.5, and the total effective heat transfer during the experiment period is 512 MJ and 283 MJ, respectively, and the heat transfer difference is about 2 times. Compared with other solar heating systems, the system proposed in this paper has good heat collection performance and more superior system stability. The mean daily heat transfer of System 1 and System 2 is 6.4 MJ and 3.71 MJ, respectively, which is 62.9 % higher and 5.6 % lower than the mean daily heat loss of subgrade of 3.93 MJ, respectively. The system has the application prospect of low maintenance cost and good long-term anti-frost heave effect.

Thermal performance of wedge pile slab foundation without frost protection insulation and highly insulated slab on ground floor – first year measurements

In the Nordic countries frost insulation is necessary if the foundation is above the frost-free depth. The thermal performance of the pile foundations is between a shallow ground foundation and a frost wall foundation. The pile ends extend below the frost line to help insulate the ground beneath a building’s foundation. The ends of the piles extend below the frost line to prevent the foundation of the building from frost heaving. However, there may be a risk that the ground below the slab on ground may freeze and frost heaving may occur there. The risk of frost below the slab on ground floor and/or basement increases because increasing thickness of floor insulation remarkable influences frost insulation dimensioning. In this study a 6.5 × 17-meter size uninsulated wedge pile slab foundation with highly insulated (U=0.07 W/(m2·K)) slab on ground floor was constructed for a heated building and equipped with temperature, soil moisture, relative humidity, and heat flux sensors. Seven temperature measurement piles below the building and one for reference 8 meters far from the building reached a depth of up to 3.2 meters, which is deeper than the usual 1.4 m depth to avoid freezing in foundation design. In three places, the temperature below the insulation of slab on the ground is measured at 0.5 meters step up to 3 meters from the outer wall of the building. The first-year measurement results showed that temperature did not drop below the zero degree below the foundation and floor. Even though during winter the daily average absolute minimum temperature was -24 °C the sum of degree hours below the zero degree was -7300 °Ch. The historic 50-year absolute sum of minimum degree hours below the zero degree was -28600 °Ch. In addition to real measurement results this three-dimensional temperature sensor field helps to calibrate and validate dynamic model for temperature simulation of thermal performance of wedge pile slab foundation without frost protection insulation and highly insulated slab on ground floor.

Calculation of stress in excavation support structures in seasonal frozen soil areas under temperature effects

In seasonally frozen soil regions, the excavation engineering is significantly inflenced by temperature, making it challenging to determine the stress and deformation of excavation support structures under the combined effects of thermal expansion/contraction and frost heave. In this study, a calculation method for the analysis of stress and deformation in excavation support structures in seasonally frozen soil regions is proposed based on the Winkler foundation model. This method considers the interaction between soil frost heave deformation and load constraints, taking into account factors such as the coordination deformation between soil and support structures, elastic resistance of the soil, air temperature, support material and arrangement, soil moisture content, and frost depth. Verification of the calculation method was performed using field monitoring data with two calculation approaches: the single-factor stepwise solution method and the dual-factor solution method. The monitoring values and calculated values of maximum axial force changes in three layers of support differed by 9.12%, 4.61%, and 9.43% for the single-factor method, and by 9.08%, 6.79%, and 9.43% for the dual-factor method, respectively. The results indicate that the proposed calculation method exhibits good applicability.

Modelling forest road trafficability with satellite-based soil moisture variables

ABSTRACT Recent decades have seen increased temperatures and precipitation in the Nordic countries with long-term projections for reduced frost duration and depth. The consequence of these trends has been a gradual shift of delivery volumes to the frost-free season, requiring more agile management to exploit suitable weather conditions. Bearing capacity and trafficability are dependent on soil moisture state and in this context two satellite missions offer potenially useful information on soil moisture levels; NASA’s SMAP (Soil Moisture Active Passive) and ESA’s Sentinel-1. The goal of this pilot study was to quantify the performance of such satellite-based soil moisture variables for modeling forest road bearing capacity (e-module) during the frost-free season. The study was based on post-transport registrations of 103 forest road segments on the coastal and interior side of the Scandinavian mountain range. The analysis focused on roads of three types of surface deposits. Weekly SMAP soil moisture values better explained the variation in road e-module than soil water index (SWI) derived from Sentinel-1. Soil Water Index (SWI), however, reflected the weather conditions typical for operations on the respective surface deposit types. Regression analysis using (i) SMAP-based soil dryness index and (ii) its interaction with surface deposit types, together with (iii) the ratio between a combined SMAP_SWI dryness index and segment-specific depth to water (DTW) explained over 70% of the variation in road e-module. The results indicate a future potential to monitor road trafficability over large supply areas on a weekly level, given further refinement of study methods and variables for improved prediction.

Centrifuge modelling of axially loaded steel piles in cold and thawing frozen sand

Foundations in northern climates are founded under ground conditions that are certain to change due to climate warming. Piled foundations situated in permafrost are designed to resist loads by mobilising the shaft friction from adfreeze strength that is attributed to the ice–soil bonds in contact with the pile. Design considers ground warming causing thawing over time and normally specifies a thermal condition whereby mitigation measures, such as thermosyphons, need to be implemented. While pile design and analysis for completely frozen and thawed profiles are defined in terms of pile capacity, the intermediate condition, during transition from frozen to thawed, is not well examined. In this study, centrifuge modelling is utilised to quantify the reduction in pile capacity and foundation stiffness under an axial monotonic loading as initially frozen sand profiles warm and thaw depth increases. The results show agreement between the physical models and analytical methods for piles in fully frozen and thawed ground. A marked decrease in pile capacity occurs as ground temperatures approach freezing and thaw depth increases. The results are the first comprehensive physical model testing programme aimed at quantifying pile performance in frozen and warming ground under field-realistic stress conditions.

Unified strength-based elastoplastic solution for frost heaving force of cold-region tunnels considering dual non-uniform frost heaving of surrounding rock

Precise evaluation of the frost heaving force and surrounding rock plastic zone is an important basis of the prevention of freezing damage in cold-region tunnels. The temperature gradient along the radial direction of cold-region tunnels surrounding rock results in the dual non-uniform frost heaving of surrounding rock, namely, the gradual change of frost heave ratio along the radial direction and the unequal frost heaving deformation in the circumferential and radial directions. A new elastoplastic solution of tunnel frost heaving force considering double non-uniform frost heave and intermediate principal stress was derived based on the elastoplastic mechanics theory, thick-cylinder theory, and unified strength theory to better guide the frost resistance design of tunnels in cold regions. The rationality and advantages of the unified plastic solution of tunnel frost heaving force were verified by model tests and engineering examples. Results showed that the theoretical calculation value of frost heaving force was in good agreement with the measured value. When the gradual change in the frost heave ratio of surrounding rock in the radial direction was ignored, the frost heaving force and radius of the surrounding rock plastic zone were large and conservative. The solution in this paper can accurately evaluate the tunnel frost heaving force and surrounding rock plastic zone. Finally, this paper studies the influences of intermediate principal stress coefficient, the frost heaving coefficient of unit temperature of frozen surrounding rock, non-uniform frost heaving coefficient in different directions, and maximum freezing depth on the evolutionary law of frost heaving force and plastic zone of cold-region tunnels are studied.

Experimental study on frost heave characteristics and micro-mechanism of fine-grained soil under dynamic load for heavy-haul railway subgrades in seasonally frozen regions

In seasonally frozen regions, there is frequent uneven frost heave of heavy haul railway subgrades, which reduces the smoothness of the track and affects the operational safety of trains. To clarify the frost heave characteristics and micro-mechanism of subgrade filling under the action of unidirectional freezing and dynamic loading, unidirectional freezing tests were performed on a fine-grained subgrade filling under open conditions, and the frost heave characteristics under different initial water contents and dynamic loads were analyzed. The particle image velocimetry (PIV) technique was applied to analyze the development of local deformation at different locations in the samples. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) were performed on the samples before and after freezing to reveal the development mechanism of the microstructure. The test results showed that with the increase in the initial water content and load amplitude, the frost heave increased, while the water replenishment and frost depth decreased. Combined with the PIV results, it was found that the soil in the frozen and unfrozen areas exhibited frost heave and compressive deformation, respectively, during the freezing process, further revealing the local deformation law of the soil. The samples mainly contained small pores and micropores before freezing and small pores and medium pores after freezing, indicating that the effect of freezing and swelling had the greatest influence on the small and medium pores inside the soil. The higher the initial water content, the higher the porosity of the sample after freezing; with the increase in the load amplitude, the porosity of the frozen samples decreased. The negative temperature effect of the change in phase from water to ice drove the particle movement, thereby increasing the inter-particle pore space, leading to a macroscopic frost heave deformation of the soil samples. Our results can serve as a basis in the maintenance and safety of railway subgrades in cold regions.

Pavement freezing depth estimation using hybrid deep-learning models

Predicting pavement temperature by depth is crucial for road design, analysis, and maintenance. However, current methods predominantly utilize regression and/or open-form solutions focusing on highways. Additionally, most machine-learning models focus on asphalt layers and do not extend to deeper pavement layers. Therefore, this study provides deep-learning models using weather parameters to predict pavement temperature from surface to sublayers and estimate pavement freezing depth for developing massive apartment complexes. Temperature-by-depth data collected from thin pavements from three locations in South Korea were used. Comparative analyses of long short-term memory (LSTM), convolutional neural network-LSTM (CNN-LSTM), and convolutional LSTM were performed. Results showed that CNN-LSTM model performed better with coefficients of determination ( R2) of 0.965, 0.987, and 0.981. Additionally, the CNN-LSTM predicted freezing depth with 0.3%–13.1% error margins outperforming the LSTM, Aldrich’s, and Korean Ministry of Transport approaches. The proposed approach shows that deep-learning models better estimate the freezing depth of pavements than existing approaches.

Study on the geothermal environment of urban building in permafrost regions of Northeast China

The geothermal environment of urban buildings is critical to the structural stability of urban buildings in permafrost regions, which is directly related to the safety of human settlements. However, existing studies have not been able to obtain the 3D geothermal field of building subgrades and its evolution during operation, due to a lack of continuous geothermal data. In this study, thermistor sensors were installed inside pile foundations during the construction, providing valuable data for geothermal field analysis. Based on long-term in-situ monitoring data, this paper studied the evolution of the geothermal field of urban building in permafrost regions of Northeast China. The results indicate that excavation and cast-in-place foundation construction cause irreversible degradation of the warm permafrost. When the building is vacant, the subgrade is frozen in the winter, with a maximum frost penetration depth of 6 m. When heated in winter, the frost penetration depth decreases year by year and the ground becomes warmer. The ground temperature within the monitoring depth (i.e., the bearing layer of the pile foundation) increases to above 0 °C. The mean annual ground temperature within the 0–4 m depth of the subgrade increases significantly, while that at depths below 7 m exhibits slight fluctuations. The 3D geothermal field and its evolution of the building subgrade are obtained for the first time. It was also found that the sunny-shady effect induces asymmetry of the geothermal field of the building, which increases the risk of uneven settlement of the building. In addition, the seasonal frost penetration on the northern side reaches 3 m, which can cause frost-heaving damage to buildings. These findings provide scientific evidence for risk assessment, disaster prevention, and control of building in permafrost regions under the scenario of climate warming.