Formwork operations on the construction of the arch dam of the Chirkey hydroelectric station

Abstract

Construction of the Chirkey hydroelectric station dam is approaching completion; its height as of January 1, 1975, was 190 m (versus 231 m according to the design). During 10 months in 1973 and 9 months in 1974 the dam's height was increased, respectively, 60and 65 m. The high rate of construction of such a complex structure, which is being built for the first time in Soviet practice, is due to the efficient organization of work and introduction of a number of new designs, equipment, and methods developed during conSraction of the arch dam, particularly the use of a new complex of formwork operations.From the very start Of constructing the hydro development great attention was devoted to the sdeetion of type of formwork, size of panels, and methods of shifting them, and, for all that, placement of concrete in the dam began with the use of six types of formwork and 10 models of panels, which effectively reduced the concreting rate and labor productivity.A study of Soviet and foreign experience led to two directions in the improvement of formwork operations: the creation of self-lifting types of formwork (Limberg arch dam in Austria and Dworshak in the USA) and improvement of the anchorage of the guide structures and use of polymeric material in the cantilever formwork (Glen Canyon and Libby in the USA; Mauieonagan-5 in Canada, etc.). Both directions pursue the same goal -to free heavy cranes from formwork operations and to reduce labor required for reassembling the forms in blocks.Only two types of formwork were supposed to be used in constructing the arch dam of the Chirkey station ( Fig. 1): self-lifting perimetral for the advancing seetious and cantilever, transposed by a truck-mounted crane, for the Iagging sections. A fundamentally new type of cantilever formwork was developed at the site, a multilift type, which subsequently permitted (since February, 1973) using a single formwork design that was the most effective with respect to initial labor expenditures for its manufacture and subsequent operation.The usual "classical" cantilever formwork (single-lift with cantilevers projecting beIow the deck) has a number of shortcomings which become worse when constructing a high dome dam: the need for high accuracy of placing the anchor connections or anchor key'ways; the location of the assembler on the panel being transposed when removing the anchor support and iustalling and aligning the panel; large expenditures of crane time. Among the shortcomings is the formation of beading and niches on the concrete surface along the interlift joint owing to loose fitting of the bottom of the panel to the concrete surface formed by the upper part of this panel. In addition, when constructing dome dams, i.e., when it is necessary to form a spherical surface, in order to create an incLination of each lift of panels to the preceding one it is necessary to have a special reguiating device for bending the cantilever or for turning the panel about the horizontal axis, which complicates the design and reassembly of the panels. In ...