Testing Deformation and Compressive Strength of the Frozen Fine-Grained Soils with Changed Porosity and Density

Current paper focuses on the laboratory experiments performed wit aim to test the deformation in the frozen loam soil specimens. Loam frozen soils are subject to the external effects, such as climate and environmental impacts including temperature changes. Soil heave is one of the key features restraining possible area development: construction of buildings, roads and railways. Necessarily, this requires the improvements of methods of the assessment of heave. This research evaluated the compressive strength and deformation in several specimens of the frozen soil. The approach included varying load and physical properties of soil specimens: porosity, pore filling, moisture, density of soil particles and dry soil density. Besides during the experiment, the external conditions were changed: decreased temperature and increased load pressure. The experiment is based on the UPG-MG4-01. The paper presented the laboratory tests of heave and compressive strength of the frozen soils using applied geotechnical methods.

The Influence of Hydrogeological Factors on the Railway Stability in the Areas of Island Permafrost Distribution (by the Example of the Trans-Baikal Railway, Russia)

Changes in the geocryological situation at the road base and in the adjacent territory should be predicted based on an analysis of regional features of the “climate – landscape – cryolithozone – construction” system. These relationships are manifested in various ways across various cryolithozone regions, with these differences being rather poorly understood. In this regard, in 2019, the Melnikov Permafrost Institute (Yakutsk, Russia) and the Northwest Institute of Eco-Environment and Resources of the Chinese Academy of Sciences signed an agreement on joint research work in order to elucidate the evolution of frozen soils, as well as to justify the application of certain measures to stabilise the permafrost environment. These projects aim to study the cryolithozone response along the routes of projected high-speed highways and existing railway tracks. Since 2019, the Institutes’ representatives along with specialists from the Tynda permafrost station (the branch of Russian Railways), North-Eastern Federal University (Neryungri, Russia), Zabtransproekt (Chita, Russia) and the Institute of Natural Resources, Ecology and Cryology of the Siberian Branch of RAS (Chita, Russia) have been investigating individual sections of the Far Eastern and Trans-Baikal railways in Russia. Some areas here are characterised by the continuous distribution of permafrost soils, while others – by island permafrost distribution. These areas share such common features, as the significant lifetime of linear structures (lasting for several tens of years) and the presence of deformations of the railway track, which appeared in the first years after construction. Railway track sections installed in high-temperature frozen soils are of particular interest for monitoring. However, the construction deformations are not always caused by frozen soil degradation. This article presents the results of surveys at one of such objects – a section of the track confined to the Chernovskaya station of the Trans-Baikal railway.

Radiophysical methods for modelling frozen soils dielectric permittivity in the southern Vitim plateau (Eastern Siberia, Russia)

The article presents the results of applying the radiophysical method for modelling the dielectric permittivity on the example of Haplic Chernozem Molliglossic soils in the south of the Vitim plateau, depending on VHF and UHF wavelengths, temperature, and soil moisture. Depending on the heterogeneity of moisture reserves and heat content, the soil is considered as a three-layer medium with different soil characteristics. A difference in the frequency dispersion of the complex dielectric permittivity over the entire soil profile in the VHF and UHF ranges has been established.

Pore-water pressure development in a frozen saline clay under isotropic loading and undrained shearing

A systematical testing program on frozen Onsøy clay under isotropic loading and undrained shearing at different temperatures (− 3 ~ − 10 °C), strain rates (0.2~5%/h) and initial Terzaghi effective stress (20~400 kPa) was conducted with the focus on pore pressure development. It is meant to increase the understanding and facilitate the development of an ‘effective stress’-based model for multi-physical analysis for frozen soils. This study adopted the pore pressure measurement method suggested by Arenson and Springman (Can Geotech J 42 (2):412–430, 2005. https://doi.org/10.1139/t04-111) and developed a new testing procedure for frozen soils, including a ‘slow’ freezing method for sample preparation and post-freezing consolidation for securing hydraulic pressure equilibrium. The B-value of frozen soils is less than 1 and significantly dependent on temperature and loading history. The dilative tendency or pore pressure development in an undrained shearing condition is found to be dependent on both unfrozen water content and mean stress, which is consistent with unfrozen soils. Besides, the experimental results reported in the literature regarding uniaxial tests show that the shear strength does not share the same temperature- and salinity-dependency for different frozen soil types. The rate dependency of frozen soils is characterized between rate dependency of pure ice and that of the unfrozen soil and is therefore highly determined by the content of ice and the viscous behavior of ice (through temperature dependency). This paper also explains the pore pressure response in freezing and thawing is dependent on volumetric evolution of soil skeleton.

Experimental Studies on Frozen Soil

Various studies have been carried out for soils at normal room temperature but the studies on frozen soils are meagre. For every construction, soil investigation is the most important and the primary step for a site. For constructions at normal room temperature, there is plenty of experimentation and research data on soil is available. But lack of research data for colder regions, where the ambient temperature is below zero degrees Celsius for most of the time. It is therefore the need to study soil under the iced condition to get a better idea about the behaviour of frozen soils. There is little research on the construction and mechanical behaviour of frozen soil but no study on the very basic parameters like void ratio, bulk density, porosity, and the degree of freezing and how these parameters change as the soil temperature changes from normal room temperature to negative values. The main emphasis is on the study and experimentation of frozen soil and the formulation of different relationships between individual soil parameters at various temperatures. The methodology used is to model the soil surface (open grounds in colder regions) by taking sand as the soil after sieving. The model samples are taken into beakers with different bulk densities to replicate real site conditions in the freezer. Then by calculating factors like density, porosity, void ratio, etc at negative temperature (-5, -10, -15, -20 degree Celsius) and forming a relationship with the same parameters as that on room temperature. The experimental data obtained is used in “Eureqa software” that will utilize the input so provided and will find mathematical relations that exist in the soil parameters.