The unreliability of the work of shaft waterbars of wide expansion joints of high-head hydraulic structures, the complexity of their design, and the labor intensity of their manufacture compel searching for ways to simplify them without loss of reliability. One such way is to replace the costly and complex designs of shaft waterbars by more simple and reliable membranes of rubber and polymer materials. However, these membranes as a consequence of a limited load-bearing capacity cannot cover expansion joints with a width of more than 4 cm. The author developed a design of a sealing device for expansion joints of high-head hydraulic structures, consisting of a sealing membrane in which this shortcoming is eliminated. The sealing device (Fig. 1) is installed in adjacent sections 1 of the hydraulic structure and includes a watertight elastic membrane 2 and a flexible netting 3 (for example, Rabitz wire netting). The transition part of the waterbar 4 between sections 1, made with a bend, increases the reliability of the work of the seal at high heads and considerable displacements of the sections of the structure. To protect the membrane 2 from mechanical damages by floating objects, a protective plate 5 performing the role of a contour permeable waterbar is installed on the upstream side. During construction of the hydraulic structure, at the time of preparing the blocks of the first section the concrete-embedded netting 3 and membrane 2 are passed through the formwork and secured on it by means of rods, bolts, or anchors. After concreting and striking the formwork from the blocks of the first section the embedded elements of the seal are staightened and put into the blocks of the second, adjacent section with the use of templates duplicating the prescribed bend of the membrane and netting, providing in so doing joining of the netting to the elastic membrane. They are fastened to the formwork of the second section in the same way as to the first. The sealing device works in the following way. The watertight elastic membrane 2 is pressed by the seepage pressure of water against the concrete surface of sections 1 of the hydraulic structure and against netting 3. Netting 3, embedded into the concrete of the sections 1 being joined, absorbs the seepage pressure of the water being transmitted by elastic membrane 2 performing the role of a seal in the device. The netting 3 made in the cavity of the joint with a bend duplicating the bend of the elastic membrane has a considerable degree of freedom of deformation, which enables it to work without breaking during nonuniform settlement of the sections 1 of the hydraulic structures. The presence of netting 3 makes it possible to cover expansion--settlement joints by means of rubber or polymer membranes of any required width. In addition to this, it is possible to use less strong, but more elastic membranes made from comparatively cheap rubber or polymer materials. As shown by the experience in using rubber and polymer membranes in the USSR and abroad (in foreign countries elastic membranes have been used since 1935), in such seals the reliability against seepage of water increases and the seals are simpler to make, which affects the quality of making them, and also the operating expenses are reduced to a minimum. Laboratory investigations conducted before the industrial use of rubber membranes on the Imperial Dam (USA) determined that the increase of stiffness of the rubber after 20-yr operation of the seal did not exceed 10% and during long operation all rubber seals worked satisfactorily. In hydrotechnical construction practice there is a tendency toward replacing complex, expensive, and not always reliable asphalt waterbars by simpler and more reliable elastic membranes. Example of Calculation. Use of the proposed device instead of the Nos. 12 and 14 shaft waterbars of the Lower Kama hydrostation. The cost of 1 m of shaft waterbar of the Lower Kama hydrostation according to catalog No. 4-77 of additional unit price rates, referred to the local conditions of the construction of the Lower Kama hydrostation, is equal to 243 rubles (collection No. 37, price list No. 37-Dy-12-72). The cost of 1 m of the vertical seal of an expansion joint made of a rubber membrane according to building code SNiP V-5-82, p. IV, collection 41, chap. 5, price list 41-51 is equal to 12.65 rubles.
Read full abstract
Aug 19, 2024
José Reginaldo De Arruda Cavalcanti + 3
Open Access
