"Вестник МГСУ"

The author considered the results of the numerical studies of stress-strain state of a 100 m high rockfill dam with a reinforced concrete face. In the analysis, the dam construction sequence and loads applied to it were considered; it was assumed that the reinforced concrete face was constructed after filling the dam. The calculations were carried out in the elastic formulation at various moduli of deformation and Poisson’s ratio. It was revealed that at rockfill settlement under the action of hydrostatic pressure the reinforced concrete face not only bends but also is subject to longitudinal force. The development of these forces is connected not only with rockfill shear deformation in horizontal direction. Depending on the value of rockfill Poisson’s ratio these longitudinal forces may be both compressive and tensile. At the Poisson’s ratio exceeding 0.25 the longitudinal forces are tensile, and when it is equal to 0.2 - they are compressive. Evidently these particular longitudinal forces are the course of crack formation in reinforced concrete faces of a number of constructed dams. The indirect confirmation of the development of tensile forces on the face is the fact that actually in all the dams with reinforced concrete face opening of perimeter joint was observed. Thus, in order to provide the strength of reinforced concrete it is important to increase rockfill shear modulus. Only the decrease of stone compressibility (i.e. increase of linear deformation modulus E) will slightly improve the stress state of the face, as the value of E has less effect on settlements and shear of the dam than Poisson’s ratio. High rockfill dams with reinforced concrete face may have a favorable stress state only at narrow site when the face horizontal displacements are inconsiderable and due to the settlements of rockfill in the face the forces are compressive but not tensile longitudinal forces.

Subject: at the present time, the active interaction of various elements of combined piled-raft foundation (CPRF), erected in the conditions of distribution of collapsible soils, has not been sufficiently studied. The subject of the study is technological parameters and design schemes of the combined piled-raft foundation installation. We evaluate the effect of soil compaction of the foundation with ground piles on the formation of stress-strain state of the system (slab-pile-ground base). Research objectives: to reduce the cost and timing of construction of foundations, develop effective design techniques, an assessment was made of the implementation of integrated CPRF technology in the construction of a high-rise building in the conditions of distribution of collapsible soils. Materials and methods: field and laboratory data for determination of physical and mechanical properties of ground soils (humidity, specific and volume weight, humidity at the borderline of rolling and fluidity), grain (granulometric) and micro aggregate composition, swelling and shrinkage characteristics, strength and deformability characteristics (single-plane section, consolidated drained tests), characteristics of subsidence, filtration coefficient; soil testing with static indentation and pull-out loads; computer simulation of stress-strain state of the foundation with the software package Plaxis 2D. Results: field and laboratory experiments resulted in the implementation of integrated technology of construction of the piled-raft foundation on collapsible soil in the conditions of dense urban development. Conclusions: the proposed design method of the piled-raft foundation has allowed us to improve construction properties of soil, considerably increase the pile bearing capacity, reduce depth of piling and effectively include the ground-soil of a longitudinal part of the foundation into work. This method gives considerable economic effect and reduces the construction duration.

ABSTRACT Introduction. The article considers results of research of reinforced-concrete face stress-deformation state depending on availability of the reinforcement. At some ultra-high reinforced-concrete faced rockfill dams (CFRD) the transversal (horizontal) cracks were developed in the seepage-control element. It is supposed that the cause of the crack formation is high values of tensile stresses. In this connection, opinions are expressed about the necessity of strengthening the face reinforcement. However, in accordance with the experience gained, in real dams the reinforcement, as a rule, is arranged in one row with reinforcement percentage 0.35 to 0.5 %. The urgent issue of CFRD studies is assessment of impact of the concrete face strengthened reinforcement on enhancement of its reliability. Materials and methods. The studies were conducted for different variants of rock fill deformation properties on the example of 100 m high rockfill dam. The reinforced concrete face was adopted to be wide (1 m thick). The reinforcement was adopted to be two-row one, with reinforcement percentage of 1.5 %. The study was conducted using the finite element method. The reinforcement was simulated using bar finite elements. Results. To reveal the role of reinforcement, analyses of the stress-deformation state were conducted for two cases. In one case it was assumed that reinforcement is absent and in the other case consideration was made for the face with steel reinforcement. Stresses in concrete and steel reinforcement were analysed. Stresses acting along the upstream slope were considered. Conclusions. It was revealed that due to the reinforcement of steel-bar reinforced concrete face it was impossible to provide decrease of tensile stresses in the face concrete down to the permissible level. Reinforcement may play a significant role in the face stress-deformation state only at the moment of forming transversal cracks in the face concrete, but such a case is inadmissible.