The study results of the filtration process in the ground dams body and its chemical effect on piezometers

The article describes the definition of filtration flow gradients in the dam's body on the example of the Kattakurgan reservoir, the analysis of the reasons for their change in cross-section. Evaluation of the aggressiveness of the filtration flow in the dam's body plays an important role in ensuring the stability of the reservoir dam and its parts. To assess the aggressiveness of the filtration flow in the dam's body, it is necessary to know the action pattern of the filtration water in the reservoir dam and its effect on the elements of the dam. In addition, the chemical composition of the water in the piezometers was analyzed in the laboratory to determine the aggressive effect of sulfate elements on the piezometers and their corrosion. Measures on the observations of systemic piezometers were also mentioned.


Introduction
The research aims to determine filtration flow gradients in the dam body, analyze the reasons for their change by cross-section, estimate water filtration effect on structure elements at the example of Kattakurgan reservoir dam. To estimate the aggressiveness of filtration flow in the dam body, it is necessary to know the movement pattern of filtration water in the reservoir dam and its effect on the dam elements. The results of the analysis gain importance in providing the stability of the reservoir dam and its parts [1][2][3][4][5][6]. Filtration water in the reservoir dam body usually moves in chaotic flow. In particular, filtration flow is non-pressure flow. In non-pressure flow, filtration flow has an open surface and moves towards the side from the upper part of the dam to its lower part. The head difference is ΔH = H 1 -H 2 Filtration flow gradient (J) is the ratio of the head difference of filtration flow in the dam body (ΔH = H1-H2) to the length of the filtration path:

= ∆
Filtration flow in the dam body follows the Darcy's law. Such movement can be thoroughly observed in the base soils and in the dam body, including sands, loams, and sandy loams [7,8].
Filtration flow discharge in the dam body can be determined by the following equation according to the law of the French scientist Darcy: where: is filtration flow discharge, i.e., amount of filtrated water through soil in a unit of time, m 3 /day; is filtration coefficient, i.e., the amount, expressing the ability of the dam soil pass water through itself, m/day; is filtration flow zone cross-section area, m 2 ; is filtration flow path length, m; is head difference of the head race and the tail race, m; By dividing both sides of the equation by ( ), we can determine filtration velocity = . Thus, by Darcy's law, it is considered that the velocity (v) of filtration or water movement in the soil composing the dam body is proportionate to filtration head gradient (J) and filtration coefficient. In cases when head gradient = ∆ = 1, the equation = becomes = , i.e., filtration coefficient will be equal to filtration velocity concerning numerical value [9]. While estimating the filtration stability of the earth-fill dam and its antifiltration elements, the following conditions must be met: Were: , is mean gradient of the dam design element; ɣ is dam rehabilitee coefficient (I-class-1.25; II-class-1, 2; III-class-1.15; IV-class-1.1); is mean filtration gradient allowable for earth fill dams.

Results and Discussion
The soil of the Kattakurgan Reservoir dam consists of homogeneous local soil, and there is cover drainage in the lower partThe average gradient of filtration pressure for such reservoirs is calculated by the following formula.
, =tg = (4) Here: is the angle of the depression curve relative to the horizontal line; is pressure affecting the dam ( = 1 − 2 ); is the distance between the calculated sections.
Based on field research, gradients have been calculated between piezometers 1, 2, 3, 4, and 5, located at section № 9 (ПК 20+00) of Kattakurgan reservoir dam and the results are shown in Table 1 and Figure 2 [13,14]. Tashkent reservoir dam cross-section is shown in Figure 1.  The analysis shows that filtration water movement velocity and head differences are large according to the design results, and the filtration path is short in the section between piezometers 15 and 2. Still, in the section between piezometers 17, 18, and 19, filtration water movement velocity and head differences are low and filtration path is long. As a result, in the section between piezometers 17, 18, and 19 head gradient sharply decreases. Water stability is observed in the piezometers if the amount of gradient is very low [19][20][21][22][23][24][25].
On the results of the research, it is considered that the movement of soil filtration is unsteady. The unsteadiness depends on the amount of gradient between piezometers located in the dam, i.e., if the gradient is at a normal level, then the change of filtration movement will comply with the pattern, and if the amount of gradient is too low, then water level stability is observed in piezometers.
Quality change analysis was conducted for the water samples taken from the Kattakurgan water reservoir basin and tail race drainage to determine the state of changes mentioned above within the research and estimation of water filtration effect on the structure elements (Table 2 and figures 3 and 4).   In estimating the filtration water aggressiveness stability of the dam elements in the reservoir, it is necessary to consider the soil filtration coefficient. The aggressive effect of water on the elements located in soils, where the filtration coefficient is large, can also be high. Based on this, water aggressiveness has also been estimated for concrete structures in the head race of the Kattakurgan water reservoir basin (Table 3). Also, the aggressiveness of water has been specified for concrete structures and piezometers located in the body of the dam (Table 4) [26][27][28][29][30][31].

Conclusions
Filtration flow in the body of the Kattakurgan water reservoir dam is sulfate aggressive about concrete and metal structures; it accelerates the corrosion of piezometers in the dam. It requires taking measures to process the concrete surfaces and joints on the headrace of the Kattakurgan water reservoir dam with hydroisolation materials and providing good operation of drainage in the tailrace of the dam. The sensitivity of piezometers in the water reservoir dam must be checked; during the process of checking, the sensibility piezometers must be filled with water and then emptied, thus providing the process of water replacement in them. As a result, filtration flow water aggressiveness will decrease concerning piezometers.