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

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...

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For tunnels constructed in rock wide use should be made of progressive types of linings in which the bearing capacity of rock of medium and high strength is utilized to the maximum possible extent.Such linings include, in particular, a new type made of a cavitationand wear-resistant material --pneumatic concrete with a geometrically accurate and smooth surface. The formless technology for construction of such linings makes it possible to obtain high-quality permanent linings of practically any small thickness (5-20 cm). This type of lining may have a minimal thickness, it is characterized by absence of contact grouting, and it has high density, strength, and imperviousness, as well as better conditions for joint operation with the rock.The use of permanent penumatic-concrete linings is possible in tunnels driven by the shield and combined methods, as well as by the drilling --blasting method with smooth breaking of the outline; and in combined linings, when pneumatic-concrete or reinforced Gunite shells are constructed on primary linings made of prefabricated, cast-ln-place, and cast-inplace --pressed concrete. However, the basic condition for applicability of such linings in hydraulic tunnels is the solution of the problem of building them with regular geometric shapes and a smooth surface characterized by a roughness coefficient of 0.011-0.012.

Linings which seal the excavated rock arc required in the majority of cases to insure normal operating conditious of transport and hydraulic tunnels driven under various geological conditions. The now widely-used linings of monolithic concrete, reinforced concrete, prefabricated reinforced-concrete elements, and tubing have many structural and production defects and are also highly labor-consuming and costly.In rccent years work has been done in the Soviet Union on the development of more progrcssive and economical types of linings of transport and hydraulic tunnels made of extruded concrete (when driving with shoring in soft and medium hard formations) and by grouting (when driven by the mining and aggregate methods in hard and medium formations). Linings of extruded concrete make it possible to mechanize the placement of concrete of high density and strength in the space behind the forms without leaving voids in the value space, thus eliminating the need for additional grouting. The stress in the concrete produced by extrusion results in a closing up of the formation and in an increase in its bearing capacity, which make possible the use of linings of smaller, more economical thickness. According to data of TsNIIS [1], the cost and labor expenditure of constructing a tunnel with a lining of monolithicextruded concrete are respectively, 50 and 40% smaller than with a prefabricated lining. However, as of now, a complex of mechanisms for the production of extruded linings has not yet been created. Thus, for instance, a. lining of high quality extruded concrete made in 1968-1969 on one of the sections of the Tbilissi subway has considerable (up to 50 ram) and frequent (0.6 m apart) projections, which are inadmissible for hydraulic tunnels. The used cyclic end method of placing the concrete does not insure a uniform closing up along the tunnel and is not too effective in tightening the formation of the excavation. Moreover, the achieved tempo of 100-120 running meters per month of erecting such a lining is also insufficient. One of the principal defects of the existing type of concrcting complex of extruded linings is also the use of small cross section, movable forms, the operation of which in the extrusion cycle is labor-and time-consuming. Finally, linings of extruded concrete arc as yet not applicable with the drilling-blasting method of tunnel driving because there is no method of compacting the clearance between the extruding unit and the uneven outline of the rock.