The Atbashi hydroelectric station

The Atbashi hydroelectric station with an installed capacity of 40,000 kW was put into operation in early 1970; the total capacity of its reservoir is 9.58 million m s, the useful capacity is 4.34 million m 3 at the normal pool level (NPL) of 154 m, and the dead storage level (DSL) is 145 ms The structures of the hydrostation include [i]: a gravel--pebble earth dam with a height of 79 m with a grouting gallery and grout curtain (Fig. !), operating tunnel spillway Qdes = 330 m3/sec, intake and power tunnel d = 5 m, I = 300 m, powerhouse with four units, grouting adits in the rock walls located at two levels ( Fig. 2), access adits, and a diversion tunnel. The hydrostation is located in the high-mountain region of Central Tien Shan on the Atbashi River, a left-bank tributary of the Na~/n River.The region of the hydrostation site has complex toBographic and engineering-geologic conditions: the foundation and bank abutments of the dam are composed of marmorized limestones whose permeability is characterized by permeability coefficient 0.2-0.01 m/day.The numerous fractures in the limestones are mainly of a tectonic origin. The bank release fractures with an open width to 50 cm, usually filled with sand--clay material or calcite, extend tens and hundreds of meters~The developed ancient karst has cavities from several millimeters to tens of meters.The groundwater level is 15-18 m below the water level in the river. The seismicity of the region is intensity 8. The climate is markedly continental: the mean annual air temperature is +2.5~ with an absolute maximum of +34 ~ and minimum of --38 ~ The mean annual discharge of the Atbashi River is 32.8 m3/sec, the sediment load varies from 0.I to 5.8 million m31yr, and the volume of runoff of shuga reaches 5.6 million m3/yr. At the present-day level the minimum storage of the reservoir for daily and weekly regulation needed for the Atbashi hydrostation to eliminate the weekly nonuniformity of the load is 1o7 million m 3. Since the volume of sediment and shuga [spongy ice lumps] far exceeds the indicated quantity, for providing operation of the hydrostation it was necessary to specify --for the first time in our country for a reservoir on a mountain river --deep (more than 40 m) annual flushing with complete drawdown of the reservoir during recession of the flood and brief stopping of the hydrostation.Such flushing was planned in stages with alternation of a partial rise of the water level in the reservoir and discharge of the clarified water for washing out the deposits formed in the lower pool during flushing into the Naryn River (a distance of about 4 km).Periodic deep flushings are supplemented by constant flushings in the su~er and fall by discharging surplus water at the 145-m DSL.For deep flushing, the inlet structure of the operating tunnel spillways has a number of special features (Fig. i): the sill of the radial gate is located 42 m below the NPL and the three-level intake openings, in the event of clogging of the lower opening by sediments, make it possible to flush ...

On-site observations at the Atbashi hydroelectric station

Sakharov¹,

Zhirkevich²,

Chichasov³

et al. 1982

Construction of an earth dam with a grout core and polyethylene film diaphragm without draining the foundation pit

Zinevich¹,

Kuperman²,

Kuz'min³

et al. 1973

At the end of 1970 the dam of the Atbashi hydroelectric station [1] on the Atbashi River, a left-bank tributary of the Naryn River, filled to the head of the first stage of construction. The dam, designed for a head of 75 m, is constructed in the high-mountain, difficultly accessible region of Tien Shan with extremely complex seismic and geologic conditions. The dam site is located in a narrow rock canyon, in the lower part of which is a cut in the rock 30 m deep and 8-10 m wide; in the upper part to a height up to 200 m above the water level the steepness of the rock banks is 72-76*. The rocks consist of strong but fissured karstified limestones. The rock jointing is quite substantial, the joints being mainly of tectonic origin. Bedding joints and flank release joints are also noted.Of greatest danger as possible routes of seepage were the flank release joints dipping at an angle of 60-70* toward the right flank, extending parallel to the river for tens and hundreds of meters, and having openings as great as 50 era. Most of the joints are filled with compact sand-clay material or calcite. Along the leR flank many of the joints wedge out along the trend toward the surface owing to the curved arrangement of the channel. In all limestone members there are ancient karst forms with cavities measuring from several millimeters to tens of meters. Under these conditions the permeability coefficient of the rocks varies widely (0.2-0.01 m/day) and the groundwater level is located 15-18 m below the water level in the river. Percolation of the surface waters from the channel into the water-bearing horizon under natural conditions is insignificant. A layer of alluvial and coarse-fragmental materials with a thickness of 6-8 m is situated in the river channel. The seismieity of the construction region is 8.In selecting the type of dam the complexity of delivering building materials to the region, which is difficultly accessible and far from the railroad, was taken into account and therefore a concrete dam was rejected and it was decided to construct an earth dam with shoulders of gravelly earth. With consideration of the complexity of pumping water from a foundation pit and the available experience on compacting and solidifying alluvial soils by grout injection it was decided to place the dam on an undrained foundation with subsequent grouting of the alluvial deposits. A grout core in alluvial deposits can be linked reliably with a grout curtain in a rock foundation and in the flanks.On analyzing the construction conditions it was also recognized that the construction of cut-off devices in the dam in the narrow, deep, and difficuR1y accessible canyon by conventional methods with the construction of

Construction of impervious membrane elements for dams and cofferdams

Glebov¹,

Lysenko²

1973

Experience with the construction of impervious membrane elements on the upstream cofferdam at the Toktogursk hydroelectric plant, a head-producing dam on the Kara Su River , the dam at the Atbashinsk hydroelectric plant (1969)(1970)(1971), and the cofferdam at the Ust'-Khantaisk hydroelectric plant (1970) [1-3] as well as with laboratory work carried out at the B. E. Vedeneev All-Union Scientific-Research Institute of HydrauUc Engineering (VNHG) has indicated the need for developing simple and technically adequate elements, for improving their reliability, for justifying the methods of analysis of such elements, and for determining the durability of the materials used for these elements.