Construction of the first line of the Nurek hydroelectric station dam

Abstract

Natural Condkions and Characteristics of Hydro Development. The Nurek hydroelectric station* is the fourth hydroelectric station on the Vakhsh River (after the Golovnaya, Perepad, and Tsentral'naya). The site of its dam is located in the Pulisanga canyon of the Vakhsh River. The Vakhsh River is fed by glaciers and snow melt. The drainage area is 30,700 km z and the average runoff is 20.5 km s. The daily discharge ranges from 120 to 3900 mS/ sec. More than I00 m/ilion tons of suspended load pass through the region of the site during the year.The hydro development structures are located in a narrow canyon composed of Cretaceous rocks and represented by a formation of sandstones and s/irstones. The beds have a 30-80 ~ dip toward the upper pool. In some places the rocks are covered with Quaternary deposits 13-20 m thick. The construction site is located/n a zone of magnitude 8 seismic activity. The hydro development consists of an earth darn, spillway structures located on the left bank, and a powerhouse complex on the right bank. The installed capacity of the station is 2700 MW (9 x 300); annual production is 11.2 billion kwh.The dam will create a 10.5-kin s reservoir with a 70-1an backwater; the usable storage of the reservoir is 4.5 kmS; surface area 98 kmZ; annual drawdownis 53m. The dam, with a height of 300 rn, base width of 1440 m, and crest length of 704 m, is being constructed oflocalmaterials, thetotalvolumeoffillis 56 rnillionm s. Thedam ( For the gravel shoulders and rock surcharge stripping is being done by ~KG-4.6 excavators, then final excavation is done by machines to the reek foundation. The deluvium is removed mainly during the construction of the dam and, as a rule, is reworked into the dam shoulders, i.e., is spread there on the gravel layer and compacted. The particle-size distribution of deluvium is the same as the gravel, only with larger inclusions of rock fragments. This necessitates stripping, for which the ~KG-4.6 excavator has to be used on the dam, running it from Rank to flank, although such use of the machine is not profitable and increases the cost of the works.To obtain a smoother dam foundation within the limits of the loam core, the downcut for the core has been designed and is being made in a configuration sim/Iar to a parabola with agope approximating to unity; for this reason the depth of the downeut reached 20 m in some places. At the lower levels, where there were deluvial soils, and also in the river bed, stripping was begun after damming and diverting the water into the first temporary diversion tunnel. At this time approach roads were constructed and drnl~ug operations begun for smooth shearing and loosening of the rooks on the banks from the intermediate elevations of the first line of the dam.Drilling for smooth breaking was carried out from special contour umnels by means of descending and ascending holes up to 40 m long. The distance between holes was 0.7 m. By means of the first massive blast, carried