One of the alternatives is the use of a waterproof synthetic geomembrane directly to the existing lining made of z asphaltic concrete, which shall be anchored both vertically and horizontally (circumpheral anchoring). Continuous monitoring of the efficiency of the whole waterproof system by the monitoring system. All components shall be made-to-measure in advance in a controlled environment. The individual belts of the geomembrane shall be welded on the site by hot-air aggregates. This system allows to make the repair in several stages.

Another alternative is the use modified water construction asphalt exposed aggregate finish. In the first stage of repair, the existing layer of the AB coat would be removed. On the prepared area, a network of sensors would be placed for monitoring the efficiency of the new sealing, and they the layer of the modified water construction concrete 8 cm wide in favourable climatic conditions, i.e. the daily air temperature exceeding 10°C, i.e. during the period between May and September. This alternative is a standard solution in repair of AB coats.

For repair of the AB coat, also coated synthetic geomembranes may be used, which may be made from chemical liquid components directly in the site. They are spayed in hot or cold condition on the prepared surface, however, the homogenity of the coat and the constant width of 3-7.5 mm are more difficult to guarantee.

The experience with using the coated geomembranes for water reservoirs which are similar to the Black Vah PWPS is limited. The results of the several year testing of various types of such membrane on the La Girotte dam in France were published in the Study of Waterproof Linings of Water Slopes of Concrete Dams (Hydro-Quebec Research Institute, Canada 1995) – proved to be unsuitable.

The results of regular measurements, controlling tests of the sealing coat, and the information available to the operator of the upper reservoir of the Black Vah PWPS show ageing and gradual degradation of the asphaltic concrete sealing. The proposals for repair of the AB sealing coat account for the structure of the upper reservoir, the scope of repair, material which may be used for the given structure of the reservoir, climatic condition in the given location, the time period for repair, in view of the fact that this power station is irreplaceable in the electric system of the Slovak Republic.

The Black Vah PWPS is built in the protected area of the Low Tatras National Park. The works connected with the repair are subject to the provisions of the Building Law No. 50/1976 Coll., as amended, which may be of importance for selecting the solution of repair.

J. VORLICEK - In: Water Management Journal. - Year 42, No. 12 (1999), p. 10-11.

Information & Contact:

Research Institute of Water Management,
Nabr. arm. gen. L. Svobodu 5,
811 02 Bratislava,
tel.: 00421 (2) 59343111,
fax: 00421 (2) 54415743