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There are many experimental methods for determining the strength of frozen soils. However, the experimental period is always much shorter than the period of infrastructure facilities operation on permafrost. Hence, one of the main tasks of the frozen soils mechanics is the development of methods for prediction of long-term strength. The aim of the research is selection of equations for long-term strength prediction of frozen saline soils. The selection is carried out based on spherical template indenter test (STI) using artificial samples of two soil types (fine sand, loam) with different salinity (from 0.07% to 1.42%), water content and temperature (-2°C, -4°C,-6°C). There were 200 experimental tests. Two approaches with 10 empirical equations and time analogy method were used for long-term strength prediction. As a result, only four equations satisfied the selection criteria and can be used for the long-term strength calculations. Our studies have shown the possibility of using the time analogy method for saline frozen soils. Calculated values of equivalent cohesion for a saline-time analogy as well as for a temperature-time analogy were within confidence interval: 90% and 80% of values respectively.

This article summarises a laboratory program involving over 100 tests that were performed to study the influence of soil type, temperature, water content and salinity on the strength and creep of frozen soils under uniaxial compression and shear tests. Analyses of experimental data allowed to get equations for predicting strength and creep parameters depending on the temperature and salinity using generalising parameters for frozen soils (freezing point and the concentration of pore solution). These parameters reflect the total impact of all factors (soil type, salinity and water content) in forming a single pattern for all types of soil. The developed theory of searching for generalised dependencies showed a good convergence for predicting the strength and creep characteristics of frozen soils. [ABSTRACT FROM AUTHOR]

An increase in air temperature leads to a significant transformation of the relief and landscapes of the Arctic. The rate of permafrost degradation, posing a profound change in the Arctic landscape, depends on air temperature, vegetation cover, type of soils, surface and ground waters. The existing international circumpolar programs dedicated to monitoring the temperature state of permafrost TSP (Thermal State Permafrost) and active layer thickness CALM (Circumpolar Active Layer Monitoring) are not sufficient for a comprehensive characterization of geocryological conditions. Yet, no standardized protocol exists for permafrost monitoring and related processes. Here, we propose a novel multi-parameter monitoring protocol and implement it for two sites in the European part of the Russian Arctic: the Yary site along the coast of the Baydaratskaya Bay in the Kara Sea (68.9° N) within the continuous permafrost area and the Hanovey site in the Komi Republic (67.3° N) within the discontinuous permafrost area. The protocol includes drilling boreholes, determining the composition and properties (vegetation cover and soils), snow cover measurement, geophysical imaging, active layer estimation and continuous ground temperature measurements. Ground temperature measured in 2014–2020 revealed that amplitudes of surface temperature fluctuations had no significant differences between the Yary and Hanovey sites, while that the mean annual temperatures between the areas had a considerable difference of greater than 3.0 °C. The period of the presence of the active layer changed with the year (e.g., ranging between 135 and 174 days in the Yary site), showing longer when the air temperatures in summer and the preceding winter were higher. Electrical resistivity tomography (ERT) allowed determining the permafrost distribution and active layer thicknesses. Thermometry results were consistent with our geophysical data. Analyzing the composition and properties of frozen soils helped better interpret the data of geophysical and temperature measurements. By integrating the study of the soil properties, ground temperatures, and ERT, our work allowed us to fully characterize these sites, suggesting that it helps better understand the thermal state at any other research sites in the European north of Russia. Our suggested monitoring protocol enables calibrating and verifying the numerical and analytical models of the heat transfer through the earth's surface. [ABSTRACT FROM AUTHOR]

Hydrochemical and geophysical data collected during a hydrological survey in September 2017, reveal patterns of small-scale hydrological connectivity in a small water track catchment in the north-European Arctic. The stable isotopic composition of water in different compartments was used as a tracer of hydrological processes and connectivity at the water track catchment scale. Elevated tundra patches underlain by sandy loams were disconnected from the stream and stored precipitation water from previous months in saturated soil horizons with low hydraulic conductivity. At the catchment surface and in the water track thalweg, some circular hollows, from 0.2 to 0.4 m in diameter, acted as evaporative basins with low deuterium excess (d-excess) values, from 2‰to 4‰. Observed evaporative loss suggests that these hollows were disconnected from the surface and shallow subsurface runoff. Other hollows were connected to shallow subsurface runoff, yielding d-excess values between 12‰and 14‰, close to summer precipitation. 'Connected' hollows yielded a 50% higher dissolved organic carbon (DOC) content, 17.5 ± 5.3 mg/L, than the 'disconnected' hollows, 11.8 ± 1.7 mg/L. Permafrost distribution across the landscape is continuous but highly variable. Open taliks exist under fens and hummocky depressions, as revealed by electric resistivity tomography surveys. Isotopic evidence supports upward subpermafrost groundwater migration through open taliks under water tracks and fens/bogs/depressions and its supply to streams via shallow subsurface compartment. Temporal variability of isotopic composition and DOC in water track and a major river system, the Vorkuta River, evidence the widespread occurrence of the described processes in the large river basin. Water tracks effectively drain the tundra terrain and maintain xeric vegetation over the elevated intertrack tundra patches. [ABSTRACT FROM AUTHOR]

The technique of an exergy analysis concerning various circuits of biogas units, which allow replacing traditional energy resources and improving environmental conditions, has been presented. The heat balances of biogas units were proposed, and analysis of their effectiveness was made. The comparison of different cycle parameters of various biogas units (i.e. a combustion turbine unit, a combined cycle gas turbine unit with gas discharges into the boiler and a combined cycle gas turbine with a high-temperature vapor generator and a reheating stage) was made, and the comparison of their exergy characteristics was carried out. The exergy analysis has shown that the cycle of biogas CCGT (combined cycle gas turbine) with a reheating stage and using a high-pressure steam generator is the most effective, that can be explained by the fact that the temperature energy proportions of combustion products, accounting for the steam cycle and the gas cycle are approximately equal, comparing to conventional combined cycle gas turbine units. [ABSTRACT FROM AUTHOR]

Correct understanding of the ignition and combustion processes in the combustion chambers are critical for modeling advanced schemes of engines of high-speed aircraft and promising spacecraft. Moreover, experimental data on the ignition delay time are a universal basis for the development and testing of combustion kinetic models. Moreover, the higher the temperature of the fuel mixture, the smaller this time value and the more important its correct determination. The use of a thermoelectric detector allows to measure ignition delay times and record heat fluxes with a high time resolution (to tenths of μs) during ignition in propane–air mixtures. Due to the faster response time, the use of it allows refining the ignition delay time of the combustible mixture, and the detector itself can serve as a useful device that allows a more detailed study of the ignition processes. [ABSTRACT FROM AUTHOR]