Precision of determination of thawing depth of the frozen rocks

An important quantity determining the choice of technical solutions in design of both surface and underground structures in the permafrost area is the thawing depth of the rocks. To obtain simple analytical relations to determine the thawing depth over time, a simple assumption is used: that the initial temperature of the rocks is equal to the melting temperature of ice. The aim of the present work was the assessment of impact of this assumption on the forecast precision. For a quantitative assessment, a simple typical formula recommended by construction norms was used. Functional dependence of the density of the rocks and their heat capacity on the fraction of ice content was considered in the formulas. A rock consisting of a combination of quartz sand and ice was used as an example.Multiple variant calculations were done according to the formulas and their results presented in the form of charts. It was shown that the relative error in determination of thawing depth depends solely on the Stefan criterion and is independent of the thawing duration, thermal conductivity coefficient of the thawing rocks and the air temperature during the thawing. A relation was obtained which allows to quickly assess at which initial values (temperature and ice content of the frozen rocks) it is possible to use the formulas obtained from the simplified calculation models with the assumption that the temperature of the rocks is equal to the melting temperature of ice.

Soil cryogenesis as a natural risk factor for gas pipelines in the permafrost zone during modern warming

The paper summarizes the experience of studying the effect of modern warming on the thawing depth of sandy and loamy soils in the permafrost zone. The definition of soil cryogenesis as a natural process and facies as the end result of soil cryogenesis as a process is given. The effect of soil cryogenesis facies on stress corrosion cracking of gas pipes of the Gazprom system in cold and warm seasons has been studied. It was found that the facies of soil cryogenesis are interconnected by the process of energy and mass exchange. It is shown that in the annual cycle, each facies formed by soil cryogenesis is the basis for the development of stress corrosion cracking of gas pipelines.

Evaluation of a permissible roadbed thawing depth in permafrost

Roadbed thermal conditions in permafrost are subject to seasonal changes affecting roadway resilience. A roadbed thawing depth is important for road base processing, especially in permafrost. This research had the purpose of evaluation of a permissible roadbed thawing depth based on the Biot number reflecting general thermal resistance of roadbed layers. These results will contribute to understanding road bed thermal resistance and selection of roadway construction materials.

A Distributed Temperature Profiling System for Vertically and Laterally Dense Acquisition of Soil and Snow Temperature

Measuring soil and snow temperature with high vertical and lateral resolution is critical for advancing the predictive understanding of thermal and hydro-biogeochemical processes that govern the behavior of environmental systems. Vertically resolved soil temperature measurements enable the estimation of soil thermal regimes, freeze/thaw layer thickness, thermal parameters, and heat and/or water fluxes. Similarly, they can be used to capture the snow thickness and the snowpack thermal parameters and fluxes. However, these measurements are challenging to acquire using conventional approaches due to their total cost, their limited vertical resolution, and their large installation footprint. This study presents the development and validation of a novel Distributed Temperature Profiling (DTP) system that addresses these challenges. The system leverages digital temperature sensors to provide unprecedented, finely resolved depth-profiles of temperature measurements with flexibility in system geometry and vertical resolution. The integrated miniaturized logger enables automated data acquisition, management, and wireless transfer. A novel calibration approach adapted to the DTP system confirms the factory-assured sensor accuracy of +/−0.1 °C and enables improving it to +/−0.015 °C. Numerical experiments indicate that, under normal environmental conditions, an additional error of 0.01 % in amplitude and 70 seconds time delay in amplitude for a diurnal period can be expected, owing to the DTP housing. We demonstrate the DTP systems capability at two field sites, one focused on understanding how snow dynamics influence mountainous water resources, and the other focused on understanding how soil properties influence carbon cycling. Results indicate that the DTP system reliably captures the dynamics in snow thickness, and soil freezing and thawing depth, enabling advances in understanding the intensity and timing in surface processes and their impact on subsurface thermal-hydrological regimes. Overall, the DTP system fulfills the needs for data accuracy, minimal power consumption, and low total cost, enabling advances in the multiscale understanding of various cryospheric and hydro-biogeochemical processes.

Ways to Increase the Efficiency of Thermopressiometry

Purpose. The purpose of the work is to identify the ways to increase the efficiency of engineering research, based on the significant amount of exploration work required in the creation of modern man-made objects, taking into account the shortcomings of existing instruments and equipment used to measure soil stress, and in relation to the need to improve the design of thermopressiometers, which are aimed to facilitate the study of frozen soils. Methodology. The ways to improve the blade thermopressiometer for the study of frozen soils with different aggregates were selected by the comparative-analytical method and the method of analogy. Thawing depth, absolute soil sediment, deformation modulus etc. were determined by thermal-technical calculations. Findings. The application issues of concern of the existing thermopressiometers (limited research of soils of a certain type, complexity and insufficient accuracy of readings) identified can be overcome by the proposed improved design of a blade thermopressiometer for testing frozen sandy-clay soils. It is based on the improved heating circuit, the applicationd of quality materials and changing the form of the blades and body. The device is intented for use on permafrost and natural frozen soils of the world, including Ukraine. Originality. For the first time we offered a model of an advanced thermopressiometer with an improved body shape made of high-quality corrosion-resistant materials, including non-metallic ones. It has the reduced number of blades to one retractable sector blade-stamp (square or round) and one heating blade-stamp. A special probe design with mechanical/hydraulical sensor drive with a thermocouple (or with two fork probes to improve the measurements) was proposed. It was also recommended to introduce an electric conductive system designed for thawed soils, with a rod for measuring the retractable blade-stamp. The possibility of using a thermopressiometer during the study of seasonally frozen soils is established. Practical value. Improving the device model should facilitate its application in engineering and geological research for various types of construction, including transport, hydraulic engineering, which use the methods of deep freezing of weak and unstable soils.

Observational variations in the seasonal freezing depth across China during 1965-2013

Long-term changes in the soil freezing-thawing depth are an important indicator of climate change. Based on data from 764 meteorological stations across China, we analysed the climatology and variability in the seasonal freezing depth (SFD) during 1965-2013 and investigated the connections among changes in the SFD, meteorological factors (temperature, precipitation, snow depth, freezing index and thawing index) and atmospheric circulations (East Asian winter monsoon [EAWM] and North Atlantic Oscillation [NAO]) in each of 4 sub-regions: northwestern China (W), the Tibetan Plateau (TP) and eastern China (E1 and E2). In addition, the contributions of 2 different factors to variation in the SFD were quantified. The results revealed that during 1965-2013, the SFD noticeably changed from positive to negative anomalies in approximately 1988 for all of the studied regions, exhibiting a significant decreasing trend at rates (mean ± SE) of 0.23 ± 0.03, 0.08 ± 0.01, 0.26 ± 0.03 and 0.24 ± 0.03 cm yr-1 in E1, E2, W and TP, respectively. The air freezing index was strongly correlated with the SFD in the E2 and TP regions, and accounted for 82.6 and 84.9% of the change in SFD, respectively. Snow depth showed a significant association with the variability in SFD only in the E1 region. Compared to the NAO, the EAWM plays an important role in changes in SFD. These findings have implications for further understanding the mechanisms of cold environment changes across China.

Arctic greening, Arctic browning or Arctic drowning?

<p>Thawing of permafrost and the resulting decomposition of previously frozen organic matter constitute a positive feedback to global climate. However, contrasting mechanisms are at play. Gradual increases in thawing depth and temperature are associated with enhanced vegetation growth, most notably in shrubs (“greening”). In ice-rich permafrost, abrupt thaw (thermokarst) results in disturbance of vegetation and surface wetting, which may result in an opposing trend (“browning”).</p><p>We determined the balance of shrub decline and expansion in an ice-rich lowland tundra ecosystem in north-Eastern Siberia using vegetation classification and change analysis. We used random forest classification on 3 very high resolution commercial satellite images gathered between 2010 and 2019 (GeoEye-I and WorldView-II). To mitigate (slight) differences in sensor properties and vegetation phenology, a spatio-temporal implementation of Potts model was used to utilize both spectral properties of a pixel and its degree of correspondence with spatially and temporally neighbouring pixels. This reduced artefacts in change detection substantially and improved accuracy of classification for all three images.</p><p>We found that shrub vegetation declines in this lowland tundra ecosystem. Areas of thaw features (thermokarst ponds, thermoerosion gullies) and aquatic plant types (sedges and peat mosses) however show an increasing trend. Markov Chain analysis reveals that thaw features display a succession from open water / mud to sedges to peat moss. </p><p>This transition from shrub dominated to wetland species dominated tundra may have important implications for this ecosystem's greenhouse gas balance and is indicative of wetter conditions. Thermokarst may be an important driver of such change, as thaw features are found to expand at the expense of shrub vegetation and show rapid colonization by aquatic species. </p>