In May 1978 at the construction site of the Kurpsa hydroelectric station the Naryn River was switched into a temporary tunnel constructed on the right bank.Cofferdams are being constructed in the channel for passage of the river discharges during the construction period: an upper one with a height of 33 m and lower one with a height of 20 m, and the temporary tunnel operating in a variable regime (Fig. i). The design maximum discharge (3680 m'/sec) of 0.01% probability with consideration of transformation of the flood in the Toktogul reservoir passes through the dewatering outlet (1030 m'/sec), tunnel spillway (1680 m'/sec), and units of the hydroelectric stations (970 m'/sec).The discharge capacity of the temporary tunnel in the contract design was assumed equal to 1800 m'/sec (1% probability). However, since the Toktogul reservoir by the start of construction of the Kurpsa station was not filled, the design capacity of the tunnel was reduced to I100 mS/set. MAIN DESIGN VOLUMES OF WORKS ON THE TUNNELOpen excavation, I0" m' 9.5 Open concrete, i0 a m a 4.2 Underground excavation, l0 s m' 68.5 Underground concrete, 10' m" 10.1 Gunite 8-14 cm thick, 103 m s 1.6 Concrete of plugs (in access tunnels), I0" m' 0.5 Borehole drainage, i0 a m 2.3 Steelwork of entrance portal, tons 284.1The temporary tunnel with a total length of 634 m occurs in bedrock composed of intercalating strata of thin-, medium-, and thick-layered sandstones and argillites whose beds intersect the river valley in a transverse direction with a 40-70 ~ dip toward the upstream pool. Sandstones account for 70-75% of the thickness of the rock strata, and argillites 25-30%. The rocks are broken by tectonic joints of various systems and orders.According to the data of englneerlng-geologlc surveys, the strength coefficient on M. M. Protod'yakonov's scale ranges from 2 to 8, cohesion in the rocks is from 0.12 to 0.3 MPa, the rocks are not slakable. The open width of the tectonic joints ranges from 1 to 300 mm, the joints are mainly filled with gouge. Zones of increased fracturing with a thickness from 0.3 to 5 m are traced along the joints.The temporary tunnel is made up of the following structures: entrance portal, tunnel, and exit portal.The construction and assembly works were carried out from March 1977 to May 1978 --14.5 months.The tunnel was constructed by the mining method by driving with two benches. Two approach tunnels were constructed to accelerate the works: No. 1 in the region of the exit portal with a cross section of 22 m a, length 30 m, and No. 2 in the region of the upstream cofferdam with a cross section of 25 m 2, length 163 m. Tunnel No. 2 was originally made at
Construction has presently begun on the Papana reservoir on the Akbura River in the Kirgiz SSR, which is designed to increase the water supply to irrigated lands in the Osh region and to the city of Osh. The storage capacity of the reservoir will be 200 million m 3. The construction site is located in the middle course of the Akbura River, in the Papana basin, extending along the northern slope of the Alai Range. The planned dam is sited in the narrow Katar canyon, cut into the mountain massif by the river. Its depth is 400 m, bottom width 15-20 m, top width about 400 m, length of the canyon 4 km, and steepness of the walls 60-90 ~ .The construction site is located in a single structural tectonic block composed of crystalline limestones of medium and coarse lamination.The compressive strength of the rock in a specimen is 950 kg/cm 2. Here and there the limestones are broken by tectonic and exogenic fractures.The greater part of the tunnel is located in strong limestones of good preservation, unaffected by pressure release.M. M. Protod'yakonov's strength coefficient is from 4 to 9 and the modulus of deformation is from 45,000 to 90,000 kg/cm 2.An exploratory tunnel driven in the vicinity of the exit portal revealed an intensely karstified stretch about 80 m long. A high degree of karstification of limestones is a result of bypass seepage around the obstruction in the valley of the Akbura River that existed in Upper Quaternary time. The karst cavities revealed areofrom 0.01 to 1-1.5 m wide and up to 15-25 m long. There are several types of filling material in the karst cavities: sandy loam--loam material; and rubble--block material from caving of the walls and roof of the cavities.
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