After a twenty-year operation, the Slovak Power Stations, Ltd., Water Power Stations Co. in Trencin decided to perform complete reconstruction of the asphalt concrete (AC) casing of the upper reservoir of the Cierny Vah WPS. It was based on the information from operation and performance of the technical and safety supervision (TSS) in the dam. The basic data on the Cierny Vah WPS:
The Cierny Vah WPS consists of four main groups of objects:
- upper reservoir (UR)
- conduits and access tunnel
- lower reservoir (LR)
- water power station (WPS)
a) Upper reservoirs – main parameters:
- maximum operation level, water level 1,160.0 m a.s.l.
- minimum operation level, water level 1,135.0 m a.s.l.
- effective volume of reservoir 3,700,000 m3
- total area of sealing 194,500 m2
The upstream slope of the reservoir in the gradient 1:2, as well as the bottom are built with asphalt concrete casing sealing with the corresponding drainage system. The AC casing is 16 cm thick.
b) Conduits
They create a hydraulic connecting way between the upper and the lower reservoir. The inflow of water to the power station is effected by three underground pressure conduits with inside diameter of Ø 3.8 m. Each of the three pressure conduits is connected to two hydropower units of 122.4 MW. The steel jacket piping of the conduit divides in the ball branch with diameter of 5.6 m into two branches to the turbine and two branches to the pumps.
c) Lower reservoir
The dam of the lower reservoir is made of reinforced concrete and consists of the individual functional blocks, as well as the blocks of the dam. The dam crest is in the altitude of 735.50 m.
Main parameters:
- maximum operation level, water level 733.45 m a.s.l.
- minimum operation level, water level 726.00 m a.s.l.
- effective volume of reservoir 3,700,000 m3
d) Water Power Station
The water power station consists of the assembly block, three power double-blocks, and the block for revision of transformers. The lower part of the power station is a strong reinforced concrete structure, forming also a part of the body of the dam of the lower reservoir.
Development Preceding the Repair of the AC Casing
Every year, upon closing the winter operation, during inspections, the condition of the AC casing was reviewed – especially existence of any cracks. They occurred only in winter time at extreme temperatures and sudden fall of the water level in the upper reservoir, thus causing the so-called thermal shocks. The crack in the AC casing was immediately manifested by seepage through the drainage system. Gradual degradation of the surface of the sealing was also affected by sudden changes in temperature (within a short time by 25°C). The loss of the original properties of the AC casing (embrittlement of the built-in asphalt concrete joints) was reflected in material change in the shortness point, softening point, and subsequently not only deformation of the surface thereof (sagging), but also increased seasonal seepage to the controlling channel. In the banks and background layers of the AC sealing, the consolidation is completed, and on the other hand, degradation of its surface area continues, manifested by sagging on the slope and local break-ups of its surface by small horizontal cracks, and subsequent break-up of surface of the AC casing. These cracks are principally of different character and scope than the mentioned cracks occurring during winter operation.
Repair of Asphalt Concrete Sealing of the Upper Reservoirs of WPS in 2001
The obtained information led to the decision to perform overall repair of the asphalt sealing, by laying a new sealing layer of modified water construction asphalt dense concrete (ADC).
The repair of the asphalt concrete sealing of the upper reservoir included:
- cleaning and removing the sediments from the bottom of the reservoir
- removing the original asphalt concrete sealing on the slopes of the upper reservoir, in its whole thickness (min. 8 cm)
- cleaning the ground and spraying by asphalt emulsion
- injecting the concrete of the inflow object – repair of seepage
- laying of a new layer of the ADC
- binding the asphalt concrete sealing to the bottom of the upper reservoir and the dam crest
- applying an asphalt sealing to the new ADC sealing and performing control tests
- renewal of the controlling and measuring points for deformation measurement of the technical and safety supervision.
Renewed Operation of the WPS
After filling-in the upper reservoir, the Cierny Vah WPS was renewed without any limitations. From the measurements made in the upper reservoir during the technical and safety supervision – monitoring deformations, water levels, levels of ground and seepage waters, greatest attention was paid to the evaluation of seepage volume to the control channel below the upper reservoir. For recording the seepage, there is a system of drainage tubes below the asphalt concrete sealing of the bottom and the reservoir slopes, ending in the control channel. In spite of the fact that the average seepage and outflow volumes have not been materially reduced, positive effect of the repair of the asphalt concrete sealing was manifested mainly in that, contrary to the preceding years, no cracks in the casing were caused by frost, and no seepage was recorded from the drainage tubes due to leakage in the AC sealing.
In: XXVIII. Dam Days 2002 – Conference with international participation, Bratislava, June 4 – 6, 2002
Information & Contact
Peter Panenka,
Vodohospodarska vystavba, s.p.,
Bratislava – zavod TBD a spec. merani,
Nobelova 7,
83102 Bratislava,
Tel: +421 2 44453494,
Fax: +421 2 44453492
