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Beli Iskar Dam - Repair Works 1-st Stage

1997 - 1999

Employer: Sofiyska Voda AD.

Annual volume of water used from the "Beli Iskar" dam is 32 million cubic meters and provides water to all settlements along the Rila pipeline and Sofia's Southwest Qarters. The water storage basin's volume is 15.3 million cubic meters and the submerged area is 800 decares. In order to secure the dam wall's water tightness, the water angle of repose was lined with a high technology PVC geo-membrane with a total area of 15 000 square meters with a warranty term of 20 years.

The construction works of "Beli Iskar" dam began in 1936 and ended in 1947. The water from the snowmelt in the dam's cup derived from the melting of the snow along the geological area containing granites is aggressive and extracts the free lime - calcium from the conrete in the dam wall's composition. The research conducted by specialists from "Energoproekt" - Sofia have proven that about 5% of the total volume of concrete in the dam wall body was destroyed as a result of the prolonged extraction processes. The main construction works for the rehabilitation of the wall "Beli Iskar" dam include the construction of a weighty steel reinforced concrete slab at the wall's toe and removal of the alluvium with a thickness of 6-7 meters. The following works were executed:

  • Construction of diverting structures - cofferdam, dike and channel as well as a pipeline connected to the Dam bottom outlets;
  • Upgrading of the water - intake structures of the Dam, erection of new metal closing gates and installation of steel pipeline to ensure water supply during works; 
  • Grouting of the foundation (granite) from a reinforced concrete slab built at the upstream heel of the Dam in two stages (one stage at the beginning before the foundation grouting and one stage after the installation of the geocomposite system);
  • Consolidation of the Dam body by grouting;
  • Construction of the drainage collector for geo-membrane system;
  • Supply and installation of a water tightening barrier by means of a flexible polyvinylchloride (PVC) geocomposite system mechanically fixed over the entire upstream face;
  • Supply and installation of a comprehensive instrumentation network;

The wall's water tightness is provided by the use of a geo-composite membrane layer constructed of flexible polyvinyl chloride geo-composite containing no substances harmful to human health and possessing sufficient elasticity at temperatures from -30°C up to +50°C. The applied geo-membrane can withstand ultraviolet rays, periodic ice presence, alkaline media of the submerged concrete, and in the event of contact with organic or bacterial growth.