CONSTRUCTION AND GEOTECHNICS

The article discusses a method of strengthening pile foundations with contour reinforcement. Armoelements are solid injection bodies formed by group high-pressure injection. To determine the effectiveness of various contour reinforcement schemes, the soil base stress-strain state numerical calculations were performed in the MIDAS GTS NX 2019 software package (v1.1). Several reinforcement schemes are considered: continuous and intermittent contour reinforcement along the entire perimeter of the pile bush; continuous and intermittent contour reinforcement along two opposite sides of the pile bush. For each case, variants with 8-, 6-, 4- and 2 levels of reinforcement are calculated: to a depth of l from the sole of the grillage, 0.75 l , 0.5 l and 0. 25l , where l is the length of the piles. It is concluded that any contour reinforcement scheme has a positive effect on the stress-strain state of the base, while the specific reinforcement efficiency decreases along with an increase in the number of reinforcement elements. The effectiveness of reinforcement is estimated by the coefficient of reduced material consumption KPRM , equal to the ratio of the volume of solids used in cubic meters to the difference between the foundation sediment with and without reinforcement, expressed in centimeters - that is, the required volume of reinforcement elements in cubic meters to reduce the foundation sediment by 1 centimeter. It is recommended to strengthen pile foundations in stages - increasing the number of reinforcement elements: from intermittent contour reinforcement to solid reinforcement or from reinforcement along two opposite sides to reinforcement along the entire perimeter of the grillage. At the same time, the need for subsequent work should be determined by the results of monitoring the development of deformations during and after the completion of each stage of work.

Lightweight concrete has recently interested researchers as an alternative structural material in the construction of buildings and structures. Due to its small own weight and a simple process of changing the structure, it was very interesting to customers and proved to be very popular in construction. The multicomponent composition of such concrete is constantly being improved and leads to the production of high-quality samples. Special attention is paid to the resistance of lightweight concrete to high temperatures and increased fire safety. A promising direction in the field of research is the determination of strength characteristics in the case of changes in structural components under different temperature conditions. The aim of the work was to conduct an experiment on samples using steel fibers and nano-silica. As part of the study, the processes of physical reactions of light concrete and general patterns of destruction of the tested samples were identified. The positive effect of nano-silica on the microstructure of concrete has been shown, which made it possible to increase the compressive strength and elastic modulus of the material. According to the research results, it was found that only a limited content of steel fibers leads to a decrease in the level of crack propagation and improves the tensile properties of concrete. Changing the composition by the complex inclusion of additives at different temperature conditions led to an improvement in the mechanical properties of the samples. Lightweight concrete has received an additional strength resource, which can be used in building structures under strong thermal influences in the event of a fire-hazardous situation. The research results are applied in nature and are aimed at developing a comprehensive methodology for improving the strength characteristics of lightweight concrete as a structural material of buildings and structures at high temperatures.

The peculiarities of the Russian Federation geographical location predetermine the need to develop infrastructure in the territories composed of permafrost soils. At the same time, the construction of buildings and structures in the permafrost zone is associated with the presence of additional risk factors due to the development of deformation processes in the foundations under the condition of changes in their temperature regime. Thawing of permafrost soils is accompanied by the destruction of the natural structure of soil bases and leads to a sharp increase in deformations of buildings and structures erected in areas of permafrost soil distribution. The article is devoted to the determination of thawing deformations and represents an overview of existing methods for calculating the thawing settlement of permafrost soils. The basic principles of calculating thawing bases are considered and the factors influencing the complexity of predicting thawing deformations are revealed. On the basis of the existing mathematical dependencies, the main components of thawing deformations are identified. The existing analytical and numerical methods of calculation of thawing deformations have been analyzed, and the applicability of the existing calculation methods has been assessed. On the basis of existing studies the basic principles of stress-strain state changes of soil during thawing have been revealed. The physical and mechanical processes occurring in thawing foundations at the micro- and macro level have been considered. The influence of these processes on strength, deformation and filtration properties of soils during thawing has been analyzed. The main stages of development of thawing deformations in the soil mass have been identified. The prerequisites have been considered and the basic principles of solving the problems of foundations thawing by numerical methods have been described. The analysis of existing models of thawing of permafrost soils has been carried out. The basic principles of formation of computational models of freezing and thawing of soil foundations have been highlighted