Temporary tunnel with a lightweight lining at the Kurpsa hydroelectric station

Abstract

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