Stress-strein state of weak and filled soils reinforced with reinforced concrete and soil piles, respectively

Introduction. The overwhelming majority of construction areas are characterized by difficult engineering and geological conditions, represented by the presence of weak soils at the base. There are construction sites on which a large thickness of fill soil is observed. In these conditions, designers apply: soil consolidation, soil reinforcement, significant deepening of the underground part of buildings, etc. This article presents the formulation and solution of the problems of interaction of reinforced concrete piles with weak soils, as well as the interaction of soil piles with bulk soils as part of a pile-slab foundation, which allow one to determine the reduced deformation modulus and the bedding value. Materials and methods. To describe the change in shear stresses depending on depth, a law was adopted in the form τ(z)=τ0е–αz. The solution is presented by analytical and numerical methods. The results obtained were compared by the analytical solution of the problem with the results obtained in the PLAXIS 3D software package. Results. Regularities of the distribution of the total load on the pile-slab foundation between the pile field and the grillage have been obtained. The analytical solutions in the article are supported by the graphical part, performed using the Mathcad program. Numerical simulation of the problem was carried out in the PLAXIS 3D software package. The dependence of the settlement on the load, calculated by analytical and numerical methods, is shown. An expression is obtained for defining the stresses in different sections of the pile shaft and under the grillage slab. The theoretical and practical aspects of the construction of crushed stone piles are considered. The theoretical substantiation of compaction of bulk soils with crushed stone piles using a special technology is given. A dependence is obtained for determining the reduced modulus of deformation for bulk soil mass reinforced with soil piles. Conclusions. Comparative evaluation of the results of solutions obtained by analytical and numerical methods showed good convergence. The solutions obtained can be used to preliminary determination of the settlement of piles as part of a pile-slab foundation. Selection of the optimal ratio of the pile length and its diameter allows the most effective use of the bearing capacity of the pile. For bulk soils, reinforced with soil piles, it is possible to select the optimal reduced modulus of deformation by varying the pitch of the soil piles.

Ensuring the reliability of pavements in the repair and reconstruction of existing cement-concrete pavements destroyed by vibroresonance on a weak basis

Repair and reconstruction of existing ce-ment-concrete pavements of hard pavements should be performed based on the results of the assessment of the condition of the pavement, assessment of their suitability as a basis for new layers and especially when reinforced with asphalt concrete layers. The article presents a method of determining the actual total modulus of elasticity of pavement, using static and dynamic stamping equipment and evaluating the results of measuring the modulus of deformation and elasticity of the concrete base at different passes of the vibrating cavity to decide on the method of re-pair. It is concluded that with a weak base, the vibroresonance method is unsuitable and stress relief should be used with a minimum number of passes of destructive equipment.

Filter leaching of salt soils of automobile roads

Globally, in arid regions, due to the irrational use of water resources for irrigating plants, salinization of soils occurs, which causes significant damage to the country's economy. In particular, recently in some regions of Uzbekistan, there has been a rise in groundwater and flooding of territories. In these areas, where the soil bases of highways contain such readily soluble salts as: NaCL, Na2SO4·10H2O, MgSO4·7H2O, MgCL2·6H2O, CaCL2·6H2O, NaHCO3, Na2CO3·10H2O, CaCO3 and CaSO4·2H2O, additional suffusion precipitation is often observed which lead to deformations of road surfaces. Additional precipitation is due to the dissolution of salt crystals upon ingress of moisture during filtration leaching. Filtration leaching of soils was carried out in the F-1M device according to the upward flow pattern. To determine the amount of leached salts during the experiment, the infiltrate was taken, its volume and mineralization were recorded. At the end of the tests, the soil was tested according to the general scheme. To assess the influence of the leaching process on the strength indices of the studied soils by the methods of consolidated and fast shear, tests of pre-leached samples were performed. When testing soils, samples were cut, pre-compacted with the same specified load, and leached for a month. In laboratory conditions, the deformation modulus was determined by performing compression experiments. In connection with a sharp change in the modulus of deformation of soils during moistening, the tests were carried out at two values of humidity: at natural and after water saturation without the possibility of swelling. The study results show that the deformation modulus of water-saturated loams satisfactorily correlates with the value of the initial porosity coefficient and decreases as a result of water saturation and leaching. The degree of decrease depends on the value of the initial deformation modulus: the higher it is, the more significant its change. The value of the coefficient of weakening of the soil structure depends on the effective average pressure. The criterion for the permissible salt content in the base of the roadbed of highways should be taken not only the value of the degree of salinity but also the change in the indicators of the mechanical properties of soils used in the design of the construction of the roadway during soaking and leaching.

The development of stamp points displacement mathematical model by static tests of road structures

In various static stamp tests methods, both foreign and Ukrainian, it is foreseen to use a different number of sensors for stamp settlement measuring. Austrian method with three displacement sensors allows to reveal the stamp warping while loading, but it is unclear how to determine the settlement in the stamp center, when the sensor readings at the moment of warping will be completely different. The German method with a single displacement sensor is much simpler, but does not consider the stamp warping. The use of Ukrainian methodology is not appropriate at all, because two displacement sensors do not allow to observe the stamp warping. The article is focused on mathematical model for the displacement of stamp points in road structures static testing development with theoretical justification of necessary and sufficient number of sensors for stamp settlement measuring. Initially, the stamp displacement under warping in a flat deformed condition is considered as a rotation on a certain angle α and a parallel transfer. It has been established that in this case, the stamp settlement with enough accuracy for engineering practice can be measured with a single displacement sensor installed in the stamp center. In fact, the stamp can rotate not only around the axis Oy, but also around the Ox axis. Therefore, a separate mathematical model is constructed and describes the process of stamp displacement while it’s warping in a volumetric deformed condition. The developed mathematical model provides an opportunity to determine the settlement in the stamp center, necessary for the modulus of elasticity calculation or modulus of deformation in the case when the stamp at the warping moment will rotate both around the axis Oy and around the Ox axis, and the rotation angles α and β will be significant.

Overview of the Quaternary sediments deformation modulus dependence on testing methodology

The surface of earth on the territory of Lithuania is covered by sediments of the Quaternary system, which are the object of human economic activities. Reliable assessment of sediment deformations is an important task of modern engineering geology and geotechnical engineering. The deformation of sediments is most often described using the modulus of deformation. The current article overviews different methods employed in deformation moduli determination and their application possibilities. The deformation moduli, which are used in various calculations, are usually calculated using correlation formulas and empirical coefficients. Thus, the obtained results may be inaccurate or completely unsuitable for further interpretation of the numerical situation. This article presents recommendations with regard to the use of various calculated deformation moduli in interpreting Lithuanian Quaternary system sediments.

THEORETICAL SUBSTANTIATION OF THE MECHANISM PATTERNS OF THE MANMADE BASE “STRUCTURAL GEOTECHNICAL SOLID”

When building on weak water-saturated soils, manmade base in the form of a "structural geotechnical solid" are increasingly used. The article provides a theoretical substantiation for the use of a model of a transversally isotropic material with the given deformation characteristics for the design of such structures. The problem of determining the radius of a rigid cylindrical element during its formation in an elastic-plastic porous medium under normal pressure of jet-grouting of soil is considered. A method is proposed for determining the effective modulus of deformation of a "structural geotechnical solid" with the allocation of a representative volume - a periodicity cell, within which the geometric averaging of deformation characteristics is performed depending on the volume contribution of its components. Analysis of the results of modeling the joint operation of the base-building system using the proposed base model showed the effectiveness of its application.

APPLICATION OF ROLLER-COMPACTED CONCRETE IN FREIGHT TERMINALS

In these days constantly being looking for solution to reduce construction costs, the amount of materials used and the negative impact on the environment. Designing pavement structures with top layer of traditional concrete, the structures become very massive because of variation of concrete thickness from 20 cm to 29 cm according to the standard structures with concrete which are given in KPT SDK 19. An alternative to traditional concrete is roller-compacted concrete, the concrete with significantly larger fine aggregates which lead concrete mix to be non-slip. The roller-compacted mix can also achieve high concrete density and consolidation by rolling. The experimental studies were performed according to the guidelines of the “Guide for rollercompacted concrete pavements” and the automated StreetPave program. Twelve different variants of the pavement structure were used in the calculations, in which the main variables were: the modulus of deformation (Ev2), the thickness of stabilized layer (CTS) and the modulus of elasticity (E). Calculations were also performed for two scenarios, assuming that the amount of cracks appearing on the surface of the top layer after the design period would be 5% and 10%.