Construction and Geotechnics

When karst deformations are formed at the base of bridge supports, additional loads are transferred to the piles, and the bearing capacity of the base decreases. The article proposes methods for determining additional loads on the piles and the bearing capacity of piles, depending on the type of karst deformations. A method for numerical variation calculations based on the analysis of the change of shear stresses on the lateral surface of the piles at different stages of loading with the growth of a cavity in karst soils. The correct design model and criteria for evaluation the stability of the arch over the cavity were selected. A series of numerical calculations were performed. Analytical solutions to determine the additional load on the pile depending on the distance from the bottom of the pile to the roof of karst soils and the predicted diameter of the cavity in karst soils were obtained.

The practical experience to dig an excavation shows that this process is extended in time and can last for several months engulfing different seasons. An additional accounting of processes occurring in excavation shoring and surrounding soil body during wintertime, when the air temperature drops below zero, is important in such circumstances. This paper describes the results of a field survey of shoring of a deep excavation, soil body and buildings of a surrounding development as the air temperature was changing during the 2020-2021 winter. The survey was performed by monitoring the horizontal and vertical positions of structures using inclinometers and tacheometers. The heaving properties of the clay soil positioned at the excavation digging level were determined in laboratory conditions. The soil frost depth was determined by a numerical simulation of temperature distributions in the "atmosphere-excavation-soil body" system. All this helped understand the nature of the processes observed. The observation results showed that, as the temperature was decreasing, the excavation shoring structures moved into the excavation to a distance of up to 8 mm, and the surrounding development buildings shrank by up to 5 mm. The laboratory study results showed in this context that soils bordering on the shoring structures and foundations of surrounding buildings were not heaving. Thereupon, the strains, which were registered in this actual situation, can not be explained by the frost-heaving phenomenon. The observed strain can be explained by shrinkage of the sprung structure material resulting from a decreasing mean daily air temperature. This effect was confirmed by test results and several surveys presented in the paper. Based on the study conclusions practical guidelines were formulated for excavation digging with consideration to seasonal air temperature fluctuations causing shrinkage and expansion of sprung structures in the shoring structures of excavation of any depth.

Modern cities have a multi-level structure of technological systems that functionally and organizationally meet the needs of consumers. The development of urban areas requires an integrated approach. Heat and gas supply systems are the main element of energy systems. In accordance with the economic, social and technological conditions, heat and gas supply systems undergo organizational and structural transformations. The purpose of the study is to develop promising schemes of heat and gas supply systems for territories based on mutual influence. Methods. Based on the analysis of the functional and planning zoning of urban areas, the calculation method provides options for the development of heat and gas supply schemes. The implementation of modern standards of heat supply is possible due to multivariate approaches. The reliability of the research results is ensured by the use of proven calculation methods. Residential neighborhoods with a load on heat supply and household consumption are considered as the main consumers. Small industrial and municipal facilities are taken into account when planning the use of energy resources in the considered territory. Industrial consumption, as a rule, has an independent system of heat and gas supply. The method for determining loads is based on specific normative indicators. When developing the gas distribution scheme for urban areas, the possibility of spreading the load on the heat supply is taken into account. Results. On the one hand, the developed variants of heat and gas supply schemes were considered as alternative ones. Both the scheme of the main heat supply networks and the gas distribution scheme will be able to perform functional tasks to provide subscribers with resources for the considered design area independently. On the other hand, at different stages of system development, alternative options can complement each other, according to the periods of phased development, taking into account the criteria of reliability and cost-effectiveness. Conclusions. The variants of heat and gas supply systems allowed us to identify the main linear parameters for different building densities. The general material criterion for heat and gas supply systems is the material characteristic. The development of heat and gas supply schemes, taking into account the mutual influence, ensures a stable and economical development of the territory.

Object of research: acid-resistant tiles obtained on the basis of unenriched kaolin and waste of non-ferrous metallurgy - slag from the production of metallic chromium, non-ferrous metallurgy wastes occupy the second place after chemical production waste in terms of the amount of especially harmful various pollutants. Various environmental pollutants, such as dust and slag, containing very harmful substances (especially hexavalent chromium, antimony, arsenic, lead and mercury) have a very negative impact on the health of people living within a radius of 50 km from metallurgical plants. The use of large-tonnage waste of non-ferrous metallurgy - aluminum-containing slag from the production of metallic chromium in an amount of 40 % allows to obtain acid-resistant tiles with high physical, mechanical and chemical parameters at a firing temperature of 1300 °C and reduce environmental stress in the area of non-ferrous metallurgy production. Studies have shown that it is impossible to obtain acid-resistant tiles from non-enriched kaolin clay containing less than 18 % A12O3 even at a firing temperature of 1300 °C. The introduction of an optimal amount of chamotte (40 %) into the ceramic mass allows to obtain acid-resistant tiles that meet the requirements of GOST for physical and mechanical parameters at a firing temperature of 1300 °C. The use of aluminum-containing slag from the production of metallic chromium in ceramic compositions in an amount of 40 % (as well as chamotte) allows to obtain products with high physical, mechanical and chemical parameters at a firing temperature of 1250 °C. The introduction of alumina-containing aluminum-containing slag from the production of metallic chromium into the compositions of ceramic masses contributes to the formation of corundum. Corundum is characterized by high chemical resistance to acidic and alkaline reagents. At this temperature, even HF practically does not affect it.