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13Central Asian Research Journal For Interdisciplinary Studies (CARJIS)
ISSN (online): 2181-2454 Volume 2 | Issue 8 |August, 2022 | SJIF: 5,965 | UIF: 7,6 | ISRA: JIF 1.947 | Google Scholar |
www.carjis.org DOI: 10.24412/2181-2454-2022-8-65-73
ASSESSMENT OF THE RISK CATEGORY OF A HYDRO SCHEME. CASE STUDY UPPER-CHIRCHIK HYDRO SCHEME
M.R.Bakiev, O.Kadirov, Kh.Khasanov, I.Primbetov
E-mail: bakiev1947@rambler.ru, kh.khasanov@mail.ru National Research University "Tashkent Institute of Irrigation and Agricultural Mechanization Engineers" (NRU TIIAME)
ABSTRACT
Hydraulic structures are the most common types of structures, with very important functions that have a great impact on the economy, environmental and social spheres, so the issue of their safe and reliable operation is of relevance. Currently, it is of concern that most of them are undergoing aging processes as a result of more than 30-40 years of their operation, a change in their technical parameters. Including, we conducted research Upper-Chirchik hydro scheme complex. It was put into operation in 1958. The accepted scoring system for assessing the risk category depends on the main parameters of the structures (filling volume, dam height, potential hazard) and downstream evacuation requirements. The risk category is determined by the sum of points for the hydro scheme complex. The results of the study, based on field observations, show that the erosion of the Chirchik riverbed downstream of the existing drop continues. The erosion has reached critical values, and the following shortcomings have been identified during the examination of the complex of structures of the hydro scheme complex.
Assessment of the safety category of a structure based on the calculation of so-called risk factors or scores, by analogy with the methodology adopted in international practice (materials of the Congress on large dams). According to this method, the Upper-Chirchik hydro scheme complex is assigned to the I - the lowest category. As for the risk of accidents that may occur with structures, they are assessed on a scoring system according to the methodology attached below in three tables. But if the above-mentioned shortcomings are not eliminated, it may lead to an increase in risk category.
INTRODUCTION
Uzbekistan is a predominantly arid region where evaporation exceeds
Central Asian Research Journal For Interdisciplinary Studies (CARJIS)
ISSN (online): 2181-2454 Volume 2 | Issue 8 |August, 2022 | SJIF: 5,965 | UIF: 7,6 | ISRA: JIF 1.947 | Google Scholar |
www.carjis.org DOI: 10.24412/2181-2454-2022-8-65-73
precipitation and annual precipitation is less. Therefore, agriculture cannot produce without irrigation. Therefore, the irrigation system is one of the main factors that ensure economic development, population employment and food security in Uzbekistan [1]-[3].
The construction of reservoir hydrosystems for the use and use of water resources, as well as for the implementation of measures to protect against the destructive effects of water flow, has developed significantly in Uzbekistan. This is mainly due to the fact that in the last century, the construction of water reservoirs has increased and, accordingly, the danger that may arise from them has increased [2], [4], [5]. During the design, construction and operation of hydrosystems, ensuring their safety, durability and stability is one of the most important tasks [6]-[8].
Hydraulic structures are the most common types of structures, with very important functions that have a great impact on the economy, environmental and social spheres, so the issue of their safe and reliable operation is of relevance. Currently, it is of concern that most of them are undergoing aging processes as a result of more than 30-40 years of their operation, a change in their technical parameters associated with siltation processes, seismic, landslide, mudflow and avalanche phenomena, movements of pulsating glaciers and other geodynamic impacts, the insufficient level of development of emergency warning systems at large hydraulic structures. In the Republic, large water management facilities have been built with a large number of run-of-river and bulk reservoirs for complex purposes. There are also more than 90 hydroelectric facilities, more than 100 long main canals, and 45 hydroelectric power stations [1], [9], [10].
The Upper-Chirchik hydro scheme complex is located in the Bostanlyk district of the Tashkent region. It was put into operation in 1958 and is intended for water intake into the canal of the Left-bank Karasu, which irrigates the lands of 4 districts of the Tashkent region with an area of 157.0 thousand hectares. Class of structures of the hydroelectric complex - II. The unit includes a shield dam on the Chirchik River, a canal regulator of the Left-bank Karasu and jet-directing dams. The capacity of the
-5 "5
dam for normal operating conditions is 1350 m /s, for emergency 1600 m /s. The shield part of the dam has a total width of 116.2 m. It is divided along the length by gobies 1.4 m thick into 14 bays 7.0 m wide. The calculated maximum capacity of the regulator is 180 m /s. The left-bank dam, 750m long, is lined with concrete on a 500m section. The right-bank dam, 1410m long, is lined with concrete for the first 470m.
Central Asian Research Journal For Interdisciplinary Studies (CARJIS)
ISSN (online): 2181-2454 Volume 2 | Issue 8 |August, 2022 | SJIF: 5,965 | UIF: 7,6 | ISRA: JIF 1.947 | Google Scholar |
www.carjis.org DOI: 10.24412/2181-2454-2022-8-65-73
Figure 1. Satellite imagery of the hydro scheme complex. 1 - Shield dam, 2 -Canal regulator of the Left-bank Karasu, 3 - drop, 4 - Canal of the Left-bank
Karasu
METHOD
In the process of research, statistical data from literature reviews, data from field surveys and theoretical processing of research results were used. For hydroelectric facilities, the impact of changes in water management conditions on their safety was assessed; clarified and substantiated criteria value of controlled parameters; simulation of scenarios, occurrence of accidents; the factors defining reliability and safety are established; safety criteria for each hydroelectric complex have been developed; the results of the research were summarized and a methodological basis for the development of safety criteria for hydro scheme complex was created[11]-[13].
Currently, there are no norms for assessing the category of risk (hazard) of structures, reservoirs and canals in the Republic. For an approximate assessment of the consequences of the destruction of structures, a system of approximate factors or risk scores was adopted, similar to those adopted in international practice.
The accepted scoring system for assessing the risk category depends on the main parameters of the structures (filling volume, dam height, potential hazard) and downstream evacuation requirements. The risk category is determined by the sum of
Central Asian Research Journal For Interdisciplinary Studies (CARJIS)
ISSN (online): 2181-2454 Volume 2 | Issue 8 |August, 2022 | SJIF: 5,965 | UIF: 7,6 | ISRA: JIF 1.947 | Google Scholar |
www.carjis.org DOI: 10.24412/2181-2454-2022-8-65-73
points.
Calculating risk scores
Table 1
For Upper-Chirchik
Indicators Points hydro scheme
Indicators Points
Volume, mln.m3 >120(6) 120-1(4) 1-0.1(2) <0.1(1) <0.1 1
Dam height >45(6) 45-30(4) 30-15(2) <15(1) <15 1
Requirement for >1000 (12) 1000-100 (O) 100-1(4) < not(0) Not 0
Potential Hazard High (12) Medium (O) Low (4) Not (0) Low 4
Sum of points 6
Risk category
Table 2
Sum of points Risk category
36-31 IV (High)
30-19 III (Medium)
1O-7 II (Low)
6-0 I (lowest)
In connection with the construction of the Charvak HPP with a reservoir of many years of regulation, the Khodjikent and Gazalkent HPPs with reservoirs of daily regulation, the flood discharges of the Chirchik River and the mudflows of the Ugam and Aksakatasai began to be transformed by the reservoirs of the named HPPs and through the shield dam of the Hydroelectric Complex instead of the estimated discharge of 1700.0 m3/s can pass a maximum flow rate of more than 1300.0 m3/s. Consequently, the safety of this hydro scheme complex is ensured and it cannot create a breakthrough wave by itself. Based on the foregoing, this hydro scheme complex, by analogy with the accepted assessment of the risk category, can be attributed to I (the lowest).
RESEARCH RESULTS
Analysis of the refinements made to the project during the construction and operation period, assessment of their impact on the safe operation of the Upper-Chirchik hydro scheme complex project. After the drafting of the hydro scheme
Central Asian Research Journal For Interdisciplinary Studies (CARJIS)
ISSN (online): 2181-2454 Volume 2 | Issue 8 |August, 2022 | SJIF: 5,965 | UIF: 7,6 | ISRA: JIF 1.947 | Google Scholar |
www.carjis.org DOI: 10.24412/2181-2454-2022-8-65-73
complex project, over 5 years of construction (1953-1958) and 5 years of operation, the river bottom behind the shield dam dropped by 4.0 m. This circumstance and the ongoing lowering of the river bottom made it necessary at the beginning to reconstruct the spillway of the shield dam (to deepen it by 5.0 m) in 1959, and in 1964 to build a drop structure with a water break threshold 4.4 m below the water break of the shield dam. The arrangement of the water slope threshold 2 m above the threshold of the shield dam springboard toe made it possible to have a flooded surface jump on the ledge of the shield dam's water slope when maximum discharges are missed, and the presence of a drop structure below the shield dam forever eliminated the risk of lowering the river bottom behind the water outlet of the shield dam's water slope.
The presence of an active quarry of inert materials in the downstream of the hydro scheme complex during the passage of floods contributes to a further lowering of the river bottom below the overfall structure. In this regard, it is necessary to move the existing quarry of inert materials in the bed of the Chirchik River downstream at a distance of at least 5 km.
The operating mode and throughput capacity of the hydro scheme complex during the operation period did not change compared to the design values. Under the changed operating conditions (construction of the Charvak, Khodzhikent and Gazalkent hydroelectric power plants), the values of possible maximum flow rates do
"5
not exceed the calculated values (1700 m /s) and, therefore, there is no threat of water overflow through the top of the jet-directing dams in the supply channel and in the downstream of the shield dam.
At present, all shutters, electric motors and sensors of DPZ-500 are in working order. The moving parts of the mechanisms are lubricated, covers of hydromechanical equipment, gates, railings and stands are painted.
In addition, the results of the study, based on field observations, show that the erosion of the Chirchik riverbed downstream of the existing drop continues. The erosion has reached critical values, and the following shortcomings have been identified during the examination of the complex of structures of the hydro scheme complex:
- increased wear of concrete in certain sections of the spillway part of the dam;
- there is a destruction of seams and fastening plates in the downstream of the spillway dam;
- there is an uneven passage of water along the front of the dam. This is one of
Central Asian Research Journal For Interdisciplinary Studies (CARJIS)
ISSN (online): 2181-2454 Volume 2 | Issue 8 |August, 2022 | SJIF: 5,965 | UIF: 7,6 | ISRA: JIF 1.947 | Google Scholar |
www.carjis.org DOI: 10.24412/2181-2454-2022-8-65-73
the reasons for the existing damage;
- electric drives and lifting mechanisms of the gates of the dam and the regulator are outdated, they pose a danger during operation;
- Erosion of the channel of the Chirchik River continues in the downstream of the spillway dam behind the existing drop. Erosion has reached critical values;
- destruction of the surface layer of concrete of the water slope at three right-bank spans on an area of about 30 m2 with a cover depth of 0.2 - 0.3 m;
- in the shield concrete dam there is filtration through the side and bottom seals when the gates are closed;
- no geodesic markers have been installed on the structures of the canal regulator of the Left-bank Karasu;
- monitoring of the opening of expansion joints at the hydroelectric complex is not carried out, because slot gauges not installed;
- the construction of an emergency spillway structure has not been completed;
- there is no backup power supply;
- the actual maximum throughput of the hydroelectric complex is unknown
destruction of seams and concrete of destruction of the anchorage and erosion fastening slabs of the tailwater
Figure 2. The spillway dam of the Upper-Chirchik hydro scheme complex (view
from the downstream)
Central Asian Research Journal For Interdisciplinary Studies (CARJIS)
ISSN (online): 2181-2454 Volume 2 | Issue 8 |August, 2022 | SJIF: 5,965 | UIF: 7,6 | ISRA: JIF 1.947 | Google Scholar |
www.carjis.org DOI: 10.24412/2181-2454-2022-8-65-73
Figure 3. Downstream damage behind Figure 4. Drop in the downstream of spillway dam the spillway dam
CONCLUSIONS
Description of possible emergencies of Upper-Chirchik hydro scheme complex, clarification of safety criteria.
Scenarios of possible emergency situations of structures.
1-scenario. Exceeding the maximum water level in front of the hydroelectric complex above the marks established by the project and possible overflow through the top of the jet guide dams. Overflow can occur:
a) during the passage of the estimated maximum water flow due to insufficient throughput capacity of the openings of the shield dam and at the lateral water intake structures located above;
b) in the event of the destruction of the Charvak hydroelectric complex located above the earthen dam and the summation of flood and breakthrough water flows.
2-scenario. Destruction of the downstream waterworks.
In this case, an emergency situation occurs with deep local erosion caused by improper maneuvering of gates, uneven distribution of flow rates, the occurrence of whirlpool zones and stall currents, as well as intense general erosion behind the hydroelectric complex.
3-scenario. Suffosion-filtration destruction of the base of the hydro scheme complex, the occurrence of concentrated filtration flows bypassing structures or at the "concrete-soil" contact.
In this case, as a result of the removal of small suffusion soil particles in certain sections of the hydroelectric complex, uneven settlement of individual
Central Asian Research Journal For Interdisciplinary Studies (CARJIS)
ISSN (online): 2181-2454 Volume 2 | Issue 8 |August, 2022 | SJIF: 5,965 | UIF: 7,6 | ISRA: JIF 1.947 | Google Scholar |
www.carjis.org DOI: 10.24412/2181-2454-2022-8-65-73
elements of the structure, distortion of shield boxes, opening of expansion joints, formation of unacceptable cracks in concrete, etc. may occur.
4-scenario. Destruction of a hydro scheme complex as a result of sabotage (for example, at the site of a road crossing along a shield dam).
In this case, the accident can be of a different nature, up to the occurrence of a catastrophic situation, especially during the period when flood flows are missed.
5-scenario. Natural phenomena (seismic, physical and geological, etc.)
Basic provisions for determining the risk assessment of various accidents and clarifying the criteria for the safety of structures.
To determine the risk assessment of various emergencies that may occur and for the overall assessment of the safety level of a structure, it is necessary, first of all, to have a normative risk level or safety criteria.
Assessment of the safety category of a structure based on the calculation of so-called risk factors or scores, by analogy with the methodology adopted in international practice (materials of the Congress on large dams). According to this method, the Upper-Chirchik hydro scheme complex is assigned to the I - the lowest category. As for the risk of accidents that may occur with structures, they are assessed on a scoring system according to the methodology attached below in three tables. But if the above-mentioned shortcomings are not eliminated, it may lead to an increase in risk category.
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ISSN (online): 2181-2454 Volume 2 | Issue 8 |August, 2022 | SJIF: 5,965 | UIF: 7,6 | ISRA: JIF 1.947 | Google Scholar |
www.carjis.org DOI: 10.24412/2181-2454-2022-8-65-73
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