Investigation of spatial displacements of hydroelectric power plant dams in Ukraine
Students Name: Bisovetskyi Yurii Anatoliiovych
Qualification Level: magister
Speciality: Space Geodesy
Institute: Institute of Geodesy
Mode of Study: full
Academic Year: 2023-2024 н.р.
Language of Defence: ukrainian
Abstract: Nowadays there are more than 35 thousand large dams with a height over 15 meters built worldwide. Statistical analysis, aiming to analyse dam accidents and damages, carried out by the International Commission on Large Dams (ICOLD) [1], has identified main patterns and trends. Thus, the average annual frequency of concrete dam failures ranges from 1/20,000 to 1/5,000 per year. It is important to mention, that the main reason of 80 % of catastrophic failures of river hydro structures are floods and the rapid rise of water in reservoirs. Furthermore, the probability of dam failure increases during long-term operation of these structures, especially after the age of 40-50 years. The age of Ukraine’s Dnieper and Dniester Cascade dams exceeds 40 years, which indicates the relevance of monitoring their displacements and deformations. The hydrological regime of the river and the cascade hydraulic system could be considered as the most influential factor on the operational reliability of the structures of the cascade hydraulic units [2]. Spring floods cause specific danger for hydrotechnical structures in Ukraine. The issues of the hydrological regime of rivers are considered in the context of operational reliability of reservoirs of hydroelectric units of the Dnieper and Dniester cascades of hydroelectric power stations. Necessity in increase of safety of dams has become the reason for specific measures, introduced by PJSC “Ukrhydroenergo”. Thus, automated systems for monitoring the state of hydrotechnical structures were implemented at all subordinate hydroelectric systems, replacing the traditional control methods used at the structures during their operation [3]. Such automated systems consist of geotechnical sensors installed at various points of hydraulic structures, local commutators, data collection systems, communication channels, servers for data collection and specialized software for processing the received information. In addition, Permanent Deformation Monitoring Systems (PDMS) were implemented at 4 HPPs, namely at Kaniv HPP, Seredniodniprovska HPP, Dnipro HPP and Dnister HPP [3]. These installed PDMS are complex systems, allowing real-time monitoring of the hydraulic structures of the Dnipro and Dnister cascades of hydroelectric power plants, thereby ensuring their operational reliability. In this master`s thesis were analysed PDMS of 4 HPPs on the territory of Ukraine: • Kaniv HPP; • Seredniodniprovska HPP; • Dnipro HPP; • Dnister HPP. Displacements of the base points of the Kaniv and Dnipro networks were usd as an example to show, that the timely introduction and monitoring of changes caused by the influence of geodynamic and seismic factors will allow obtaining reliable results of the displacements of the control points of the PDMS of HPP. These results confirm the need for constant geodynamic monitoring of the base points of the PDMS [4]. On the basis of the results of the GNSS processing of the measurements made during the period of 2014-2020, the displacements` time series of the control points of the Kaniv, Seredniodniprovska, Dnipro and Dnister HPP-1 PDMS were determined. For the most of points of all HPPs, systematic spatial fluctuations over a period of one year were observed. A detailed analysis of the data identified that almost every year the maximum deviations occur in the first decade of February and the first decade of August. Within these periods, the trend of displacement follows a linear law. It was identified that directions of horizontal vectors in the first and the second half of the year are opposite. In the first half of the year the body of the dam expands radially from the centre of the dam towards the reservoir. However, during the second half of the year, radial compression of the dam towards the lower pool can be obseved. At the Kaniv and Dniester HPPs, in the first half of the year, the horizontal displacement vectors diverge radially from the centre of the dam towards the reservoir, and in the second half of the year, on the contrary, they are directed radially towards the central part of the lower pool. For the Dnipro and Serednyodniprovska HPPs it was observed, that the directions of the velocity vectors in the first and second half of the year are almost opposite, creating the 70-80° angle with the dam axis. The reason of observed patterns could be both the dam structure and the arched shape of the Dnipro HPP dam. As a result of the research, the specific features of seasonal displacements of control points and deformations of dam crests of Ukrainian HPPs were identified and analyzed, which are characterized by the corresponding vector field and the magnitude of absolute spatial displacements. The created schemes of the vectors of horizontal and vertical displacement velocities of the PDMS of HPP control points can be the basis for comprehensive analysis of the displacements vector field of the control points. Thorogh assessment of such schemes enable to identify the magnitudes of irreversible movements that may cause the internal stresses, exceeding the design levels and formation of cracks in the body and dam foundation. Also, the main problems, in the implementation of the PDMS were identified, which require the elimination of measurements distorted by gross errors and the assessment of the influence of seismic, global and regional geodynamic processes [4]. Study object– Permanent systems for monitoring of spatial displacements of hydraulic structures in Ukraine. Scope of research–study of crest deformations of HPP dams of Ukraine according to GNSS data. Goal of research – to analyze the results of the Kaniv, Serednyodniprovska, Dnipro and Dniester HPPs according to GNSS data and to establish the features of the deformations of the dam crests and the influence of geodynamic and seismic factors on the PDMS. Research results – The specific features of the implemented PDMS of Kaniv, Dnipro? Serednyodniprovska and Dniester HPPs have been studied. The main issues of the implemented PDMS were identified, which require the elimination of measurements distorted by gross errors and the assessment of the influence of seismic, global and regional geodynamic processes. Schemes of vectors of horizontal and vertical velocities of displacements of control points of PDMS of HPP in Ukraine were constructed. Seasonal periods of changes in the direction of displacement vectors, which are different in direction and magnitude for each of the dams, have been established.