The article considers innovative pile technologies that can significantly increase the load-bearing capacity of reinforced concrete piles by increasing the friction forces on the side surface of hanging piles. The authors developed designs of modular reinforced concrete piles for the perception of various combinations of external influences, and also studied the influence of the granulometric composition of the soil adjacent to the pile body on its load-bearing capacity. The study included dynamic tests of t-shaped and square piles, theoretical studies of the interaction of t-shaped piles with clay soil by mathematical modeling, and the selection of the composition and distribution of coarse-grained filler around the pile developed by the authors with “pockets” (cavities) during its driving. The developed innovative solutions allow increasing the angle of internal friction of the soil adjacent to the reinforced concrete pile, while increasing the load-bearing capacity.

The paper discusses the methods of erecting sunk wells and pile foundations, which consist in regulating the frictional forces of soils: lowering along the lateral surface when sinking wells and increasing when erecting pile foundations. The developed method of sinking wells provides for the application of two types of effective antifriction coatings along the lateral surface: along the cutting edge of the structure and above the cutting ledge. At the same time, the coefficients of reducing the friction forces by these coatings for various types of soils have been established, and a method for calculating sunk wells for lowering is proposed, taking into account the use of the developed submerging method. To increase the friction forces on the lateral surface of the driven piles and to increase their bearing capacity, modular piles with a developed lateral surface of the T-section have been developed and introduced. The areas of rational use of these piles are established depending on the types of soils (clay and sandy) and the depth of their penetration.

The molecular-mechanical (adhesion-deformation) theory of friction with respect to a dispersed medium was confirmed in the article on the basis of theoretical and experimental soils external friction studies. At the same time, the soil particles interaction calculated model of a spherical shape with a smooth polymer surface was developed and an expression for determining the area of their actual contact with a solid surface under the action of a load N was obtained. The calculated contact area results‘ comparison for coarse and fine sand showed satisfactory convergence with the experimental data (discrepancy does not exceed 8-10%). The particles behavior analysis of the dispersed medium adjacent to a solid smooth surface under shear, presented in the computational model, was confirmed by the experimentally obtained and fixed plastic deformations of the polymer surface layer. The experimental studies using a soil tribomer allowed to determine the deformation proportion and adhesive components in the external friction force of sandy and clay soils. Using the obtained dependencies for calculating and contacting soil particles with a solid surface, a method for calculating the coefficient of external friction of the soil based on the molecular-mechanical theory of friction is proposed.

The results of the studies are presented which is an extension of the earlier authors’ work of combined bolted-welded joints for building steel structures. Data on the parameters of the stress-strain state of finite-element models of physical specimens of bolted, welded and bolted-welded connections are given. These specimens are manufactured and are being prepared for testing. There are some special features of design of physical specimens and numerical models: the conditions which have been created for realization of limit state, conditioned by crushing of bolt edge of a hole in a thinner piece and its consequent breaking (poking out). Subsequently, it is supposed to compare data on the parameters of the numerical models and physical samples. Considering computer modeling of bolted-welded specimens, it is assumed that welds are made (imposed) after a finite-element model of the bolt connection has been loaded to a certain part of its bearing capacity according to the crushing criterion. Such conditions correspond to the operation of a bolted joint reinforced at partial unloading by welds. Thus, it is assumed that the bolted joint will be deformed largely before it is reinforced with welds. According to the authors' hypothesis, it will create favourable conditions for joint operation of the bolted joint and welds during its loading after reinforcement. The generally obtained numerical simulation data confirm the above hypothesis on the possible joint operation of welds and bolted joint, in which the limiting state in terms of buckling is realized and which is reinforced by partial unloading with welds.

оболочка опускного колодца, технология погружения, усилия, напряженно-деформированное состояние, свая, момент, радиус.