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
At the present time, several high concrete dams are being constructed in the Soviet Union: gravity, Toktogul'sk, Us~,-Ilimsk; gravity-arch, Sayano-Shushensk; arch, Ingursk, Chirkeisk. In this connection, investigations and tests are being carried out on the most rational types of formwork for the different types of dams and climatic conditions. Now in the testing and introduction stages are cantilever forrnwork for the dams at the Ust'-Ilimsk and Ingursk hydroelectric plants, a perimetric self-lif~ng formwork for the Chirkeisk hydroelect_,ic plant, and a cantilever self-lifting formwork for the Toktogul'sk hydroelectric plant [1].Cantilever formwork is widely used for arch dams in foreign countries because of the ability of this type of formwork to produce with sufficient accuracy the required orientation and rigid fixing of the complex shapes of arch dam surfaces, which vary with their height [2,3]. The favorable characteristics of the use of canti/ever formwork are the following.I. Design of the formwork permits varying in a simple manner the dimensions of thee sheathing in the longitudinal direction immediately after its position is established in the block; as a result, a large proportion (950 and over) of the concreted structure having variable cross sections can be covered with stock fonnwork.2. For convenience in carrying out the construction work at the hydraulic development, under the restraints of mountain conditions, the possibility of repeated turnover, and utilization of a single set of forms for several hydraulic projects, the cantilever formwork is fabricated and assembled using sheathing having the required dimensions and made from simple fiat elements which can be easily stored and transported. These elements are the following: cantilever braces, brace planking, fiat ribless forrnwork panels, embedded anchor parts, and Pestle elements. These elements, transported in sets to the assembly area in the concreting block, are used to erect formwork of the required dimensions, with different numbers of braces. The maximum number of braces is limited by the lifting capacity of the crane. During the concreting process, the edge (comer) sheathing in the formwork can be easily shortened or lengthened, depending upon the changes in the dimensions of the blocks to be concreted when passing to the upper tier. Each cantilever brace, secured at two points to the concrete of the lower tier. and constructed with sufficient rigidity also in the plane of the formed surface, is a three-dimensionally invatiable component which does not require any additional connection to withstand the load transmitted by the concrete. However, for displacement of the formwork in the vertical plane from tier to tier, it is sufficient to connect several cantilever braces together by the planking and trestle elements, and by means of quickly demoun•ble connections. In addition to the excellent adaptability of this formwork to the variable shape of the blocks being concreted, there is the possibility of quickly replacing the fonnwork pan...
In the last few years sharp problems have arisen in connection with reconstruction of hydraulic developments built during the pre-and postwar years, intended for increase in the capacity of hydroelectric plants, improvement of their operating reliability, and restoration of structures damaged in the process of prolonged operation. For reconstruction, as a rule, in addition to the need for replacing the hydropower, hydromechanical, and electromechanical equipment because of obsolescence and physical wear, in many cases it is necessary to change the configuration of the internal passages of a hydroelectric plant, its repair with full or partial replacement of the metal liners, and repair of individual, heavily loaded elements of the components of basic structures, in particular: spillays, penstocks, concrete in the zone of variable water level, etc. Installation of modern electrical engineering equipment calls, in many cases, for changes in the planning of auxiliary rooms, by removing different walls or floors.At the present time, design, preparatory, and in several cases basic construction-erection work is being carried out for In the engineering practice of this country, such work is not of a massive nature, and until recently it was carried out basically by hand, using pneumatic drills, concrete breakers, and other similar tools. This calls for substantial time expenditures (according to the ENiP Norms and Rules, the demolition of 1 m 3 of reinforced concrete requires up to 40 manhours, the actual time expenditures being even higher). Moreover, prolonged work with manual pneumatic tools adversely affects human health. Taking into account the massive nature of reinforced concrete demolition work in the process of reconstruction and repair of hydraulic developments, as well as the short periods established for the carrying out of this work, the need has arisen for mechanization of these processes, using Russian and foreign experience with similar work or with work in related branches, in particular in rock excavation.
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