Purpose: Definition of the most effective methods and components for strengthening weak Yoldian clays used in the creation of transport routes in the North regions. Methods: The definition of the main physical-mechanical characteristics of clay soil was carried out in accordance with the requirements: of GOST (Russia State Standard) 12536—2014 “Soils. Methods for laboratory determination of granulometric (grain) and microaggregate composition”; GOST 25584—2016 “Methods for laboratory determination of the filtration coefficient”; GOST 22733—2016 “Soils. Method for laboratory determination of maximum density”; GOST 5180—2015 “Soils. Methods of laboratory determination of physical characteristics”; GOST 25100—2020 “Soils. Classification”. It is shown that the effective strengthening of weak clay soil is achieved as a result of its preliminary stabilization with the help of granulated blast-furnace slag or natural limestone of ≈2.5 mm fraction. The rational amount of granulated blast-furnace slag or limestone is 15 wt.% of the soil mass and at the same time, clay soil has the highest strength value — (2.25–2.45) MPa. The difference in strength indicators in favor of limestone constitutes 9.0%. It has been experimentally established that in order to increase reinforced clay soil strength it is effective to use granulated blast-furnace slag in combination with finely ground blast-furnace slag which rational amount of is 10 wt.% of soil mass which achieved strength of corresponds to M20–M25 grade. It has been defined that for comprehensive improvement of the indicators as strength, density, and frost resistance it is necessary to introduce additionally to clay soil, reinforced with blast-furnace metallurgical slag as reactive components which it’s effective to use Portland cement in amount of not more than 5 wt.% of soil mass in combination with dry complex chemical additive “PRA” which rational amount of constitutes 2.0 wt.% by weight of (Portland cement + finely ground blast-furnace slag). Practical significance: Stabilized and comprehensively strengthened weak clayey soil is characterized by the following actual indicators: M50 F35 K10 — 0.026 m/day which can be used as a base at construction of transport routes of local importance in the regions of the North.

Purpose: To assess the current ecological condition of the survey site located in the Republic of Karelia and intended for laying a non-public railway track. To analyze the component of the environment — the soil, for compliance with the requirements of regulatory documentation. To establish the category of soil pollution in accordance with Sanitary and Epidemiological Standards and Regulations SanPiN 2.1.3684 and the rules for further use in accordance with SanPiN 2.1.3685. Methods: To assess the degree of soil contamination with heavy metals and organic ecotoxicants, samples have been taken from 14 test sites. Assessment of the degree of soil contamination with heavy metals and benz(a)pyrene has been carried out in accordance with SanPiN 1.2.3685. The assessment of the degree of contamination of soils with petroleum products has been carried out in accordance with a letter from the Ministry of Natural Resources and Environment of the Russian Federation. The assessment of the danger of soil pollution has been carried out according to several indicators (Tables 4.3–4.5 of SanPiN 2.1.3685): –- a complex of metals for public health is made according to the indicator of total pollution (Zc); –- the presence/absence of excess over the established maximum permissible concentrations (MPC) and approximately permissible concentrations (APC). The pollution category is determined by the worst indicator. When establishing pollution categories worse than “permissible”, recommendations have been developed for the further use of contaminated soils (Appendix No. 9 to SanPiN 2.1.3684). Results: As a result of the tests conducted, it was determined that the soil samples collected from the survey area for the construction of a non-public railway section comply with the soil pollution category of “Permissible” and, according to the rules of further usage, fall under the classification of “Unrestricted Use”. Practical Significance: The investigated soils meet all the requirements of the regulatory documentation and can be used without restrictions for the construction of the non-public railway section.

Purpose: To create highly effective heat-insulating structural concrete, recommended for insulating and preventing permafrost soil thawing. Methods: When conducting research, we used GOST (Russia State Standards) 25820-2014 “Lightweight concrete. Specifications”, GOST 25485—2019 “Cellular concrete. General technical conditions”. Determination of strength and processing of results according to GOST 10180-2012 “Concrete. Methods for determining strength upon control samples”; thermal conductivity coefficient was determined according to GOST 7076-99 “Construction materials and products. Method for determining thermal conductivity and thermal resistance at stationary thermal regime”; frost resistance of concrete according to GOST 10060-2012 “Concrete. Methods for determining frost resistance”; density of concrete in natural moisture state- according to GOST 12730.1-2020 “Concrete. Density determination methods”. It has been established experimentally that in order to create highly efficient heat-insulating-structural concrete, it is advisable to use as a filler a foam glass of fraction 1.25–2.5 mm, D250, λ ≈ 0.06 W/ m · °C, and for to create strong and reliable matrix on cement basis it’s effective to use finely dispersed microsilica in combination with complex chemical additive on polycarboxylate basis, modified with nano-dispersions of silicon dioxide, SiO2. Results of physicalmechanical studies have confirmed that it is effective to use particles of silicon dioxide together of micro- and nano-size in combination with surfactants represented by polycarboxylate polymers, meanwhile, foamed glass concrete with the best compressive strength and tensile strength at bending a rises significantly, coefficient of resistance to cracks of nanomodified foam glass concrete, Ktr. = Rbend./Rcompress. = 3.6/13.3 = 0.27, has rather high value which should provide for increased resistance to cracks and for reliability for a protective coating. In order to increase density/strength without deteriorating heat-insulating indicators it is advisable to use additionally a finely-ground blast-furnace slag as a filler which a rises cohesion of foam glass concrete mixture and strength of foam glass concrete. Practical significance: Rational ratio of components of nanomodified foam glass concrete mixture ensures the creation of highly mobile foam glass concrete mixture with good workability, and on the mixture basis, a unique heat-insulating-structural material is formed with the following characteristics: D900; λ = 0.14 W/m·°C, B12, Btb2.9 F1300 that defines it as a thermal insulation material of increased reliability and durability, which is advisable for recommendation for the Arctic harsh regions.