"Вестник МГСУ"

In the article the authors present the data of laboratory researches of geosynthetic grid samples based on polyamide-6, taken from the embankment slopes constructions of different light after 9 years of operation. The samples of geosynthetic grid EnkamatS20 were selected from the ground constructions of Svyataya Kanavka (Holy Groove) in the South of the Nizhny Novgorod region, the village of Diveevo, constructed in 2003 for the erosion preventive fixing of the slopes of the ditch and a shaft. The village of Diveevo is situated in a zone of clearly expressed continental climate, characterized by hot summers and cold winters. In the process of exploitation of ground structures in the period from 2003 to 2012, there was a decline in the protective properties of the lawn and turf, which was reflected in violation of the integrity of cover, including on the slopes of the ditch and of a shaft of a southern exposure, which are not sheltered from the direct streams of the sun. The similar situation was observed on deeply shaded slopes of a Northern exposure covered with trees and shrubs, as well as on the slopes of the bottom of the ditch, where the sun streams didn’t reach. From these mostly unprotected places in 2012 samples of geosynthetic grid Enkamat-S20 were selected in order to define the influence of the lighting conditions of slopes on the operational properties of Enkamat-S20 for 9 years of operation. According to the obtained data the residual tensile strength for each series of samples of geosynthetic grid Enkamat-S20 was identified. The influence of light intensity on the operational properties was evaluated by the highest residual tensile strength of the investigated samples compared to the passport strength value of geosynthetic grid Enkamat-S20. As a result of the research it was established, that the deeply shaded areas for 9 years of operation the reduction of tensile strength for samples of geosynthetic grid Enkamat-S20 amounted to 4.5 % and 6 % respectively. In the intensively lighted area the strength loss amounted to 39.5 % due to destruction of synthetic fiber. In the conditions of partial shadow the strength loss amounted to 25 %. As a result of the studies the authors offer the data on the lighting conditions impact on the operational properties of geosynthetic grid on the example of Enkamat-S20 upon condition disturbing the integrity of the lawn and turf, which are a natural protective shield.

In the article the authors estimate the possibility of building a high (100 m high) stone dam with clay-cement concrete diaphragm. This diaphragm is used as an antifiltering element and it is made of secant piles method of clay-cement concrete (method of "slurry wall"). This diaphragm should be constructed in several phases, in our example example in three stages. Numerical studies of the stress-strain state of such a dam show that considerable compressive stresses can appear in the diaphragm. These stresses can be significantly (3...4 times) greater than the strength of clay-cement concrete in compression. However it should be taken into consideration that the diaphragm of such a high dam will be crimped by horizontal stresses, i.e. clay-cement concrete will operate in the triaxial compression. Under these conditions the strength of clay-cement concrete will be significantly higher, therefore, the diaphragm reliability might be provided with a margin. For this reason, the most important issue in the engineering of a high dam with such type of diaphragm is to select the required composition of clay-cement concrete. Increasing its strength by extension of the cement fraction could increase modulus of deformation. Therefore it could lead to compressive stress increase and the strength state degradation. Hydrostatic pressure generates the areas of tensile stresses in the clay-cement concrete diaphragm due to the arising bending deformation. It threatens the formation of cracks in the clay-cement concrete, especially in the nodes interface diaphragm queues. It is recommended to match the diaphragm queues using ferroconcrete galleries. This should ensure flexibility of deformation between the gallery and the diaphragm.

Process of downfall of frozen ground overhanging above a thermoabrasion cave under its own mass forms the cycle of thermoabrasive destruction of sea shores and reservoir banks in the cryolite zone. Russian and foreign papers on arctic coastal dynamics merely state the existence of thermoabrasion caves, but quantitative measurements of the collapsed frozen ground overhanging the caves have never been done. It is difficult to measure parameters of this process under natural conditions, therefore, physical tests were carried out. Testing was performed at freezing air temperatures and comprise several steps. Blocks of frozen ground were manufactured in forming boxes. Blocks were placed in a cartridge on a table, a console imitating frozen ground overhanging a cave was pulled out, a load was applied. Moments of load application and the console failure were registered. In this way there were tested 24 blocks with various length of console of loam, sand, and pebble. Presented are test results and physical properties of the frozen soils under investigation, graphs of their breaking strength plotted on the basis of test data. The simulation has revealed the following: console failure is caused by the rupture of frozen ground along a surface which is almost vertical; breaking strength value at the moment of the console failure is smaller than that at the uniaxial tension of frozen soils, but this difference is negligible for engineering calculations; coarse frozen ground (pebble) shows lower breaking strength as compared with fine one (sand); when the thermoabrasion caves in the shores are formed quickly (during a few hours of storm), the probability of overhanging ground failure should be evaluated by the value of frozen ground breaking strength, which is intermediate between the instantaneous and prolonged strength values. The obtained data may be used in engineering calculations of arctic thermoabrasion shore downfall.

The article deals with the results of the numerical analysis of the stress-strain state of a 50 m high earthfill cofferdam. A geocomposite membrane (geo-membrane and geotextile layers) in its upper part (20 m) serves as a seepage control element. The grout curtain is installed in the lower part of the cofferdam and in the foundation. The cofferdam design implements the idea of using riprap to reduce the weight of the geocomposite membrane.The analysis proves that the high weight of the membrane considerably worsens the stress state of both the membrane and the whole dam. First of all, the load causes additional deflection of the membrane and consequently increases tensile stresses inside it. Second, due to the low value of the friction coefficient (approximately 0.3 0.4) in the point of contact between the geocomposite membrane and soil the dam upstream shell may slide down along the geocomposite membrane. Additional dam displacements may cause considerable tensile forces in the geomembrane. Their maximum values are comparable to the strength of the polymer material used for the manufacturing of the membrane. Any rupture of the membrane and geotextile layers may be expected. The analysis proves that it is necessary to get compensators in the polymer membrane allowing for the extension of the membrane absent of any tensile forces.The analysis proves that the geocomposite membrane does not affect the stressstrain state of the earth fill due to its small thickness. Non-linear effects of “earth – geomembrane” contacts are to be taken into account, because tensile forces appear inside geo-membranes due to the presence of friction forces.

Reinforced concrete is uninterruptedly developing progressive type of building materials. One of the most important advantages of reinforced concrete is the possibility of using it with reinforcing steel or composite materials of increased and high strength.As a result occurs substantial permanent growth in production, increase in strength and other service characteristics of steel rolling used for reinforcing concrete.Production and application of the modern types of reinforcement in our country started not long ago, much later, than in the USA and European countries. Until 1950 deformed reinforcement was not produced and used in our country; the production of hot-rolling reinforcement of the A400 (A-III) class started only in 1956.But already in 1960 the application of this reinforcement was 1.0 million tons a year, and in 1970 — 3.4 million tons a year.Up to the year 2012, the production and application of the deformed reinforcement of the classes A-400, A-500C and A-600C of all kinds exceeded 8.0 million tons. In order to ensure economic efficiency and competitive ability of national construction, the process of increasing the strength and workability of domestic reinforcing bar is continuously taking place. The results of this process in respect of the common untensioned reinforcement of reinforced concrete structures are discussed in the present article.We suggest to consider the mechanical and service characteristics of deformed reinforcement, which is manufactured according to the standards of our country GOST P 52544, classes A500C and B500C, GOST 5781, class A400, and Technical specifications 14-1-5596—2010, class Ан600С, grade 20Г2СФБA.For the comparative analysis we use the standard data for similar reinforcement established by EN 10080-2005 and Eurocode 2, as well as by standards ÖNORM B-420 of Austria, BC 4449/2005 of Great Britain, DIN 488 of Germany, A706M of the USA and G3142 of Japan.The standards of the above-mentioned countries slightly differ from the standardsEN 10080 and Eurocode 2, and from the Russian standards.We consider the statistical data of the real properties of hot-rolling, coldolling and thermo mechanically strengthened deformed reinforcement manufactured and certified according to GOST R 52544 and GOST 5781, produced in Russia, Byelorussia, Moldavia, Latvia, Poland, Turkey and Egypt.The fundamental difference of modern European standards from Russian standards and the standards of other countries considered in this article is that the requirements of EN 10080 and Eurocode 2 are unified for all reinforcement with the yield point of 400 to600 H/mm2 regardless of its production method.At the same time it is stated, that the actual properties of reinforcement of all groups according to EN 10080, differ essentially from those specified by this Standard and they better correspond to the Russian, Austrian and German standards.The Standard EN 10080 in the version of the year 2005 is inconvenient, because it does not determine technical classes. As a result, many European countries use their own, but not the European standards.Conclusion.The comparative analysis of our national and foreign standards of deformed rolled steel used for reinforcing concrete demonstrates that the physical and mechanical properties of the Russian and European reinforcing steel are almost the same, but for the following facts:Standard requirements established according to GOST 5781, GOST 10884 andGOST R 52544 are a bit higher than the standards of EN 10080;Reinforcement of the classes A400, A500 B500C and A600C, manufactured according to the Russian standards, can be used without recounting instead of reinforcement of the same strength classes according to EN 10080 and to the standards of other countries all over the world.