Construction and Geotechnics

Moving transport is one of the main sources of technogenic vibration impact on nearby buildings and structures. But there is a problem when trying to take into account the impact of vehicles in various calculations. It is lack of rationing of the vibration impact of motor transport in Russia presently. Therefore, the study of the impact of vehicles on the foundations of buildings and structures is relevant. During the research, the goal was to build an adequate numerical model of the dynamic impact of a single vehicle on an existing building using data obtained by express methods of multichannel analysis of surface waves. The results of numerical modelling are compared with the data of field studies to verify the adequacy of the numerical model. In general, the results are close to full-scale values: the arrangement is not more than 14 % for the maximum vertical component of the acceleration and not more than 5 % for the maximum horizontal component for a cargo vehicle and a bus. Additional studies of calculation of the dimensions of wheel contact spot are required to obtain more accurate results of numerical modelling. The developed model is adequate for a single vehicle of large mass.

In the foundations of the foundations of buildings in the historical part of St. Petersburg, as well as in a large number of cities in the north-west of our country, there are soft water-saturated siltyclay soils, and there are inclusions of peat with different degrees of decomposition. With the development of such a metropolis as the city of St. Petersburg, there is an urgent need for a controlled transformation of the properties of weak base soils and giving them the necessary properties: increasing the strength and modulus of deformation, reducing water permeability. Fixing soils by jet carburizing is a technological process that involves a whole complex of special works to create a geomass with the necessary properties. They include the following basic operations: Lead drilling of wells with washing of drill cuttings with water or mortar, mixing of the foundation soil of the site, usually with cement mortars with chemical additives, then reinforcement of the well. Injection technology has been used in St. Petersburg since the mid 90s of the 20th century, first one-component, and then two-component. When using one-component technology of soil stabilization, a jet of cement mortar is used, and with a two-component jet of a solution in the ground, it is fed under the protection of a coaxial jet of air. Obviously, with the use of this technology of soil consolidation, the range of application of cementation of soils of various granulometric composition to clays and biogenic soils has expanded. In connection with the optimization of the cost of works of the “zero” cycle, using the practice of import substitution of materials and technologies, the application of jet technology is now becoming even more urgent for its active use in underground construction.

In the Russian practice of engineering surveys, traditional methods of research are used, including field testing of soils with the selection of samples and their subsequent study in laboratory conditions. Performing surveys using these methods is a labor-intensive and long-term process that requires considerable material costs. Therefore, there is a need to apply express methods. One of the most common express methods is the method of cone penetration test (CPT). In Russia, CPT is most often used only as a duplicating method, since it is difficult to obtain accurate data in interpreting the results, which is associated with old equipment for engineering surveys. Therefore, in practice, sounding is most often used to determine the bedding, determine the bearing capacity of piles and to determine the strength characteristics of soils with high reliability. At present, electric cones with pore pressure sensors have found wide application in foreign practice. These cones make it possible to increase the accuracy, determine the soil type and evaluate the soil filtration parameters from the dissipation test data. In the article the authors will consider the application of the cone penetration test with the measurement of pore pressure to find the filtration coefficient of clay soil. The results of trough and field tests on immersing the cone in clay soil are presented. On the basis of the experimental data, a numerical model of probe immersion has been developed and a sequence of its calibration is presented with the aim of finding the soil filtration coefficient.

At present, there is a need to develop a methodology for calculating the reinforcement of slab foundation by piles. The need for reinforcement arises when adding of additional floors of a building under construction or reconstruction of an existing one. The use of soil-cement piles has certain advantages.In addition to the small and stable projected lead times, reinforcement with piles can be carried out in limited basements due to compact equipment. In the normative documents there are no recommendations on such calculations.When calculating the reinforcement of the slab foundation with ground-cement piles, the load is determined at the operational stage, which is compared with the permissible load on the pile (by the ground and by the material). Simulation of such staged processes by modern software is possible, however, rather laborious. Practical methods of reinforcing foundations with piles do not take into account many important factors: in what stress-strain state is the foundation and structure of the structure, at what moment of construction is the strengthening, etc. An important role is played by the features of the structure and the foundation: the thickness of the foundation slab, the number of storeys, and the physical and mechanical properties of the soils. Parameters of soil-cement piles also have a significant influence: space, length, diameter. The reinforcement of the slab foundation with soil-cement piles can be carried out in two schemes: with uniform placement of piles over the area of the slab and with local arrangement around the supporting structures (walls and columns). The article presents the results of numerical studies of the interaction of the slab foundation with ground-cement reinforcement piles. A local arrangement of reinforcement piles near the main supporting structures-columns and walls-has been adopted. Certain regularities in the load variation on the pile are obtained depending on the thickness of the foundation slab, the diameter of the piles, the length of the piles, and the time at which the reinforcement is performed.Based on the results obtained, a technique for designing the reinforcement of a plate foundation with piles is proposed. This takes into account the loads perceived by the base of the plate before the amplification is performed. The proposed methodology was used in designing the reinforcement of the slab foundation of a 13-storey residential building, for which the construction of three additional floors was planned.

The article presents the results of a study of the mutual influence of the work of two energy-efficient piles as ground heat exchangers. Energy-efficient piles differ from other types of energy-efficient foundations that work as separate heat exchangers as part of a single foundation, influencing each other. This fact should be taken into account when calculating the work of piles as part of an energy efficient pile foundation. In the course of the study, the value of the decrease in the heat flux density through the surface of the constant piles with soil was estimated when operating as ground heat exchangers. The study was carried out by performing a series of numerical calculations. The main factors that were varied during the calculations were the diameter of the piles and the distance between them. Numerical calculations were carried out in the TEMP module of the GeoStudio software package. A numerical model has been created to carry out the calculations: the geometric dimensions of the model, the initial and boundary conditions, the minimum necessary for a long numerical simulation have been determined. The initial and boundary conditions for modeling were adopted for the climatic conditions and temperature conditions of the Perm soil. The studies were carried out during the operation of energy-efficient piles in clay soil. The results of numerical simulation were processed using mathematical statistics. As a result, the dependence of the heat flux through the surface of the constant piles with the soil is obtained when they work as ground heat exchangers from the diameter of the piles and the distance between them. Graphically, the dependence is presented as a nomogram. An analysis of the obtained dependence made it possible to draw the following conclusions: the magnitude of the drop in the density of the heat flux decreases with increasing distance between the piles; The magnitude of the drop in the density of the heat flux increases: at small distances between the piles, with a decrease in the diameter of the piles, at large - with increasing.

The article analyzes the effect of deformation anisotropy on the stress-strain state of the soil basement on the basis of a numerical experiment using the ANSYS software package. Strain properties of environment are determined by strain module Е and Poisson's ratio µ. Degree of stress-strain anisotropy was evaluated based on ratio of deformation modules in vertical Ez and horizontal Ex directions ka = Ez / Ex . Resulting from calculation experiments, transverse-isotropic environments were concerned with coefficients of stress-strain anisotropy ka = 0.5; 0.75; 1.33 and 2 and additional coefficients α ' are obtained, which are used in determining vertical stresses from the additional load. Based of obtained results a method is proposed for calculating the additional stresses of the anisotropic basement of the foundations of the existing building from the buildings and structures being erected. The calculation is based on the Lyave problem using the scheme of a linearly deformed medium. The anisotropic properties are taken into account by introducing an additional coefficient α ' , which depends on the degree of anisotropy of the soil basement ka and the geometric dimensions of the foundation. The obtained results of the studies show that taking into account the anisotropic properties of soils has a significant effect on the stress-strain state of the soil basement and allows the most reasonable approach to predicting the settlements of foundations. It is particularly important to consider deformation anisotropy when design of reinforced soil basement with the creation of induced anisotropy, including construction new facilities near existing building.

The osmotic, hydraulic and self-healing efficiency of bentonite based barriers (e.g. geosynthetic clay liners) for containment of polluting solutes are governed both by the chemico-physical intrinsic parameters of the bentonite, i.e. the solid density (ρ sk ), the total specific surface ( S ), and the total fixed negative electric surface charge (σ), and by the chemico-mechanical state parameters able to quantify the solid skeleton density and fabric, i.e. the total ( e ) and nano ( en ) void ratio, the average number of platelets per tactoid ( Nl,AV ), the effective electric fixed-charge concentration and the Stern fraction ( fStern ). In turn, looking at saturated active clays only, the state parameters seem to be controlled by the effective stress history ( SH ), ionic valence ( νi ) and related exposure sequence of salt concentrations in the pore solution ( cs ). A theoretical framework, able to describe chemical, hydraulic and mechanical behaviours of bentonites in the case of one-dimensional strain and flow fields, has been set up. In particular, the relationships, linking the aforementioned state and intrinsic parameters of a given bentonite with its hydraulic conductivity ( k ), effective diffusion coefficient osmotic coefficient (w) and swelling pressure ( usw ) under different stress-histories and solute concentration sequences, are presented. The proposed theoretical hydro-chemico-mechanical framework has been validated by comparison of its predictions with some of the available experimental results on bentonites (i.e. hydraulic conductivity tests, swelling pressure tests and osmotic efficiency tests).