Reviewed by K. A. Mal'tsovThe first five chapters of the book present a substantiation of the fundamental aspects of the method adopted and describe its use on the construction of the Toktogul hydroelectric station dam. The sixth chapter contains essentially all recommendations which the builder or designer needs to use the method at a hydro development. The area of use of the method is given, the requirements imposed on structures are presented, the technology of concreting and temperature regime of the masonry are described, and the basic requirements imposed on the concrete and its components, on concreting, and on regulation of the temperature regime are formulated. Problems of concreting in the winter, characteristics of checking concrete work, some characteristics of sealing the vertical joints, and the overall economic effectiveness of the concreting method used are also presented.
The Toktogul'sk Hydrocenter* is located on the Naryn River in a narrow canyon with steep (60-78*) slopes rising to 1200-1300 m above the dam's crest. The canyon's geological structure consists of limestones with developed lateral release cracks (to a depth of 50 m) and a system of intersecting tector~ic cracks. The high seismicity of the construction region (force 9-10) and the presence of potentially unstable blocks on the slopes required the implementation of a complex of undertakings [1] before the main work of excavating the foundation pit and of pouring the concrete into the structure could proceed. The sharply continental climate of the region with a long-term temperature range of 84"C and a mean annual temperature of + 8.4~ is, unlike that of Siberia and the North, characterized by sharp fluctuations in mean daily temperatures in the fall-winter-spring periods and in diurnal temperatures reaching 20-25"C [2].The concrete-gravity dam is 215 m high, 40 m long at the base and 300 m at the crest, and will contain 3,200,0O0 m 3 of concrete. During the erection of the hydrocenter, construction discharges are passed through a diversion tunnel with a system of check dams. Because of the difficult topographic and mining-geologic conditions, the auxiliary enterprises are located on individual construction platforms along both banks of the Naryn and on the floodplain terraces of its tributaries, the Karasu, Karskol, and Keinda.The concrete works, located on the Naryn's left bank 5.5 km from the hydrocenter site, include: a 220-m3/h concrete plant with eight 2400-hp concrete mixers; a cement warehouse; an installation for storing ice; an air compressor; a refrigeration station for water cooling and ice making; installations for cooling coarse aggregates; asteam ejector installation for cooling or heating sand; a boiler room, etc. The gravel-grading plant is located on the same bank 11.5 km from the site. The raw material from a gravel pit is transported 2-5 km to the gravel-grading plant, whence the gravel and sand are carried in dump trucks to the bunkers of the concrete works, 6 km away. The concrete mix is transported 5.5 km to the dam site in KrAZ-256 dump trucks on the right-bank road. In the immediate vicinity of the dam site the transportation system changes as the dam rises. Difficult natural geologic, topographic, and climatic conditions necessitated the development of new methods of concreting, which along with rapid concrete placement ensured a monolithic and crack-proof dam. In considering numerous methods of operation, cable and turret cranes were rejected because of the impossibility of approaching the dam near the crest level and of placing the required number of concrete-pouring machines at the level of the s~ucture's base or near it. Building concretecarrying trestles under the natural conditions of a narrow canyon also proved irrational. The principal features of the concreting technology developed and mastered in the dam's construction is the complex mechanization of the delivery, unloading, spreadi...
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
A distinguishing feature of the concreting method used at the Toktogul'sk plant is the placing of the concrete in blocks of large areas, 32 x 60 m and 32 x 75 m in plan, and larger, and 0.5-1.0 m high. This feature leads to full mechanization of the concreting operations, as well as a considerable reduction in the number of vertical joints. This in turn, improves the monolithic nature of the structures [1,2]. At the same time, the number of horizontal construction joints is significantly increased.Horizontal construction joints are weakened sections in the concrete, which are inferior in strength and imperviousness to the monolithic parts. Observations on completed structures at the Bratsk, Bukhtarminsk, Uch-Kurgansk, and other hydroelectric plants, have revealed that the joints, together with the thermal cracks, are the main leakage paths.The degrees of weakening of the concrete at the joints depends upon the composition of the concrete mix, the texture of the joint surface, the degree and quality of removal of the cement firm, the interruptions in placing adjacent layers, the temperature-moisture regimen of the concreted blocks, etc. The effects of the horizontal construction joints upon the nature and distribution of the stresses in the structural elements depends upon their static behavior and operating conditions. The number of joints is determined basically from the adopted height of the concreting blocks and is usually increased somewhat by changes in the periods between covering of the concrete layers, owing to unforeseen construction difficulties and delays.Different technical and constructional methods have been worked out to improve the horizontal construction joints. In recent years, the following solutions have been applied in the hydraullc construction field to increase joint strength and imperviousness: a) removal from the joint surface of the cement film formed on the concrete during its setting, as well as sandblasting of the surface when it becomes dirty foLlowing prolonged exposure of the blocks; b) removal from the joint surface by means of an air jet of the debris and dust deposited immediately after concreting, and subsequent moistening; c) placing, when the concreting is resumed, of a 1-P. cm thick underlying mortar layer, or placing of a first layer of plastic. "soft~" fine-grained concrete; this measuse is not applied when concrete mixes having a slump of over 5-6 cm am used; d) construction in the horizontal joints of keys which increase their shearing strength.All these operations are carried out basically by hand; their effectiveness depends upon the careful execution of the work, and their quality (with the exception of the keys) cannot be adequately controlled. Despite the high labor costs involved in construction of the joints, the cohesion strength between the old and the new concrete under construction conditions seldom reaches 30-40 % of the tensile strength of monolithic concrete [3-5, etc.].In the construction of horizontal joints, in all traditional concreting methods, the blo...
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