Construction and Geotechnics

To achieve effective thermal insulation of enclosing structures, it is necessary to increase the resistance to heat transfer through the use of advanced thermal insulation materials. A promising heat-insulating material is foam glass, which has a low thermal conductivity, high mechanical strength, frost resistance and low density. The physical properties of foam glass are determined by the structure of its macro- and microstructure, which depend on the temperature regime of synthesis and composition components. In the work, the choice of the optimal compositions of foam glass for correct comparison was carried out, a physicochemical model was developed, the qualitative and quantitative phase composition of foam glass samples was determined using the method of X-ray phase analysis to verify the results obtained. Based on the performed calculations of the composition of phases and components that are formed during the synthesis of various modifications of foam glass, the possible phases were determined using physicochemical models and methods for minimizing thermodynamic potentials. These methods make it possible to determine the equilibrium composition of a heterogeneous system and the thermodynamic parameters of processes. The reliability of the model is confirmed by the results of X-ray phase analysis, which showed the presence of phases obtained by calculation. The scientific novelty of the study lies in determining the features of the formation of crystalline phases during the synthesis of foam glass, taking into account the temperature-time conditions and composition. The study showed that the formation of the mineral composition of foam glass in the considered modifications is significantly affected by Na2B4O7∙10H2O and natural chalk. Additionally, microimpurities affect the formation of new aluminosilicate phases and the redistribution of the main chemical elements between the mineral components of foam glass. This also leads to changes in the density and composition of amorphous phases. An efficient model has been developed using the Gibbs isobaric-isothermal potential minimization method, numerical values of the number of probable phases and components formed during the synthesis of foam glass material have been obtained.

The article presents a generalization of the results of experimental and theoretical studies on the intensive thermal effect on the surface of foundations from cohesive soils (as opposed to deep heat treatment) using an electric arc generator of low-temperature plasma (plasmatron). A plasmatron with massive consumable electrodes made of borosilicated graphite and a wide "blurred" plasma torch was used for heat treatment. Physical and mathematical modeling of the thermal effect on the surface of clay soil by a moving high-temperature source has been performed. For the first time, a special installation was manufactured and experimental studies were carried out on the heat treatment of ground surfaces on the site with an electric arc plasma torch. It is established that the effective heat flux density reaches 2.5-.3.5 kW/cm2. The main part of the thermal energy for the used plasmatron enters the material due to radiant heat transfer. An analytical mathematical model of the temperature field of a three-dimensional semi-bounded body in the technological process under consideration is given by an essentially nonlinear boundary value problem for a nonlinear heat equation with nonlinear boundary conditions of the second kind. When solving thermophysical problems, the ground semi-bounded space was considered as a quasi-homogeneous medium having a constant initial temperature and initial thermophysical parameters that change in the process of temperature increase. The effective values of the thermophysical characteristics were determined on the basis of experimental data. Calculations and experiments have shown that the temperature boundary leading to significant changes in the structural properties of soils drops to a depth of 4-6 cm from the surface, despite the boiling of the ground melt with a temperature of 2500 ...2800 K on the ground surface. Therefore, a new technological principle of heat treatment is proposed, which consists in building up the ground melt in layers of 4-5 cm up from the initial surface. The impossibility of obtaining a positive effect even with the use of a powerful high-temperature source of exposure in the case of traditional surface heat treatment technology has been confirmed. The new plasma technology of surface heat treatment of ground surfaces to the stage of silicate melt allows to obtain a common layer of the required thickness. At the same time, the efficiency of surface heat treatment is significantly increased. The new technology of layer-by-layer surface deposition reduces cracking in the layer when the melt cools, but does not eliminate this negative process.

The method of high frequency vibratory driving and extraction of sheet piles is frequently utilized in the conditions of structurally unstable soils in St. Petersburg. However, with this method of installation (extraction) of sheet piles in the surrounding soil mass it arises oscillations that are transmitted to nearby buildings and housing, capable of causing dangerous phenomena in their undergroud and aboveground structures, mainly related to differential settlement of foundations. The prediction of additional settlement of buidings in the surrounding area from vibro-driving/extraction of sheet piles is a complex, multi-factor task, and the level of the structural displacement of building, which is the main controlled parameter for the influence of dynamic loading on the foundation soil, according to the current regulatory documents Territorial Building Codes50-302-2004, Departmental Building Codes490-87, Russian State Standard 52892-2007 is merely an indirect criterion for assessment. To obtain a more accurate assessment of the development of additional settlements in buildings during high-frequency vibratory pile driving and sheet pile extraction, it is necessary to take into account not only the duration and frequency of the impact, but also the properties and type of soil itself. The purpose of this reseach was to study changes in the strength parameters of silty-clay soils depending on the time of dynamic loads impact, the type and consistency of the soil itself, as well as changes in parameters depending on the “rest” time of the soil base after exposure to vibration. The article presents the results and shows the tendency to reduce the parameters of soil strength after the application of dynamic load and the dependence of their change on the time of impact, on the type and consistency of the soil. It has been determined the dependence of changes in the strength parameters of the soil conditionally upon the "rest" time of the soil mass as a result of thixotropic re-storation, which will determine the economic attractiveness for the accident-free technology of this method.