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15
Section 9. Technical sciences
Arifjanov Aybek Muxamedjanovich, d.t.s. prof. (TIIAME) Jurayev Sherali Sharipovich, s.teacher. (NamEBl) E-mail: [email protected]
ANALYSE OF WATER PERMEABILITY OF SOILS USED FOR DAMB CONSTRUCTION
Abstract. In this article discusses the results of analysis of permeability of soils. In the practice ofhydro technical construction, widespread impervious devices made of clay soils. When constructing them, it is very important to correctly assess the permeability of the soil. Based on experimental studies, the filtration coefficient of bentonit was determined and recommendations and practical use were developed.
Keywords: permeability, bentonite, filtration coefficient, pressure, flow rate, soil, sand, water, suffusion.
In the practice of hydro technical construction, anti-filtration devices which made of clay soils (ponures, screens, cores, etc.) are widespread. When constructing them, it is very important to correctly assess the permeability of the soil. The overestimation of this value leads to excesses in the construction and unproductive expenditures of material resources, and an understatement leads to higher filtration losses [1; 2].
Bentonite clay - is one of the valuable fossil materials that has found it's widely application in various fields of human activity. Its other name is cloth clay, which is used for degreasing cloth. In modern industry, bentonite clay is used mainly in metallurgy to form iron ore pellets and to make molding sands. Equally important is the use of bentonite clay in the preparation of drilling and mortar, cleaning products for petroleum products, and also as a raw material for the production of heat and waterproofing materials.
Conducting these analysis is necessary, since there is still no clear indication in the literature about the most appropriate method for determining the filtration coefficient of low-permeable bentonite. Moreover, some authors even doubt about the possibility of determining it directly, in connection with which they recommend to study this important soil characteristic indirectly according to other analyze methods [3].
Fractional analysis of bentonite is refers to clay rocks, since the content of particles with diameter d < 0.005 mm is more than 30%.
The article deals with the analyse of the permeability of bentonite of a broken structure, taking into account some additives that are recommended for reducing the permeability of the soil used as an impervious material. In modern literature and regulatory documents, a significant number of various devices have been proposed to determine the filtration coefficient [3; 4]. However, their application in the study of clay soils in the field requires some features. To this end,
we have developed a device design for analysing bentonite. The instrument for determining the filtration coefficient of bentonite includes the following elements: Compression filtration device, which allows conducting analysis close to natural conditions. The composition of the compression-filtration device should include: mesh with filter, providing free flow of water to the sample and its withdrawal; roof on the device; choke connector; Libra; stopwatch; thermometer; scales and others.
In the implementation of field studies, based on the design of the available instruments, new installations were created to determine the filtration coefficient of bentonite. According to GOST 25584-90, the preasure on the stamp should be no more than 0.0025 MPa or 2.5 kPa in order to prevent soil swelling. Taking this factor into account, a soil from local sand was installed in a cylindrical chamber (d = 150 mm). The density of the soil was fi = 1.42 g/cm3
According to preliminary calculations, it was established that the flow of water through bentonite is Q < 10-3 cm3/s.
To assess the permeability of bentonite, it is necessary to determine the filtration coefficient of the sand which the dam body of the reservoir is built. To determine the filtration coefficient of sands, we use the Kamensky device in field conditions [5].
The filtration coefficient is determined by the formula:
K = - é T
V ho J
(l)
where: h0 - initial pressure; S - level drop;
l - the length of the filtration path (the height of the column of sand in the tube). T - filtration time;
Temperature correction to the value of the filtration coefficient:
T= 0.7 + 0.03 -t (2)
The results of the experiment are summarized in (Table 1).
ANALYSE OF WATER PERMEABILITY OF SOILS USED FOR DAMB CONSTRUCTION
Table 1. - Sand filtration coefficient
№ Soil h0, sm S, sm T, c ^S) h0 l, sm K, sm/s t T K - k K10 - — T
1 Sand 86 35.3 540 0.41 15 0.014 18 1.24 0.011
2 Sand 39 11.5 300 0.346 15 0.017 18 1.24 0.0137
3 Sand 28.5 9 300 0.315 15 0.015 18 1.24 0.0121
4 Sand 50.5 13.8 300 0.273 15 0.0136 18 1.24 0.011
Based on the results of research about permeability of sand, the body of the dam and bentonite made the following conclusions:
• When testing bentonite clays in order to reduce the time to determine the filtration coefficient, it is necessary to create a large head;
• When determining the filtration coefficient of bentonite, the time factor is essential, i.e. the duration of the experiment;
• Determination of the filtration coefficient of bentonite samples with a broken structure should be carried out at high pressure gradients, which makes it possible to drastically reduce the duration of experiments, reduce the spread of experimental values and improve the accuracy of determination;
• According to research results, the value of the filtration coefficient is on average 0.4 * 10-7 cm/s;
• It should be noted that the tests were carried out without taking into account chemical phenomena
in the filtration process, nature of bentonite has not yet been fully studied;
• The tests did not take into account the phenomenon of suffusion, which occur during insufficient compaction of soils.
According to the results of studies of the water permeability of bentonite in the form of a powder, it was established that without creating a shell around bentonite, the phenomenon of mechanical suffusion is possible, which creates the risk of compromising the safety of a pressure hydraulic structure. Analysis of the results of laboratory studies showed that with an increase in the pressure of water from the pressure tank, the filtration of water through bentonite increases and the time of the experiment decreases, depending on the pressure. The tests did not take into account the phenomenon of mechanical suffusion, which occur during insufficient compaction of soils. As well as resistance to effects on bentonite, the presence of salts contained in water.
References:
1. GOST 25584-90. Soils. Laboratory methods for determining the filtration coefficient. 1998.
2. Zamaleev Z. Kh., Posokhin V. N., Chefanov V. M. Fundamentals of hydraulics and heat engineering: a manual. -St. Petersburg: Lan, 2014.- 352 p.
3. Arifjanov A., Juraev S. Methods for studying filtration properties bentonites in hydraulic structures. Subscribe to the Fergana Valley report on the theme of "Fergana Valley" on October 27-28, 2018.- P. 271-273.
4. Sologaev V. I. Filtration calculations and computer modeling in the protection against flooding in urban construction: Monograph.- Omsk: SibADI Publishing House, 2002.- 416 p.
5. Kolomensky N. V. Engineering geology.- M.: Gosgeoltehizdat, 1956.
6. Arifjanov A., Jurayev S. "The value of bentonite in the study of the filtration process in hydraulic structures". Fer PI scientific and technical journal. 2012.- No. 3.- P. 14-17.
7. Arifjanov A., Jurayev Sh. KaTTa OaproHa Ba KaTTa ahah^oh KaHAAapnga ^нAтpbaцнfl ^apaeHHHH ypraHHm 6yHHna oah6 6opuAraH H3AaHnrnAap Ta^AHAH Ba TaBcaaAap - "Modern problems, soil mechanics and complex rheological systems" materials of the international scientific and technical conference - Samarkand 2013.- P. 16-16.
