Experience in the construction and operation of hydraulic structures showed that concrete dams, even of an old construction, have a very high seismic stability. Of the more than 100 dams that endured strong earthquakes, only a few received any noticeable damage [1].As is known, the Koyna dam in India, constructed from rubble concrete in 1963, suffered most seriously from an earthquake. This dam with a height of 103 m and crest length of 853 m was designed for a maximum acceleration of 0.05 g, but in 1967 was subjected to an earthquake with an acceleration 10 times greater than the design one, with a magnitude of 6.5 on the Richter scale. The nearby city of Koynanagar was practically completely destroyed, 180 people perished, about 2000 persons were injured.The dam withstood the earthquake without loss of water, but horizontal cracks appeared on the faces of its nonoverflow sections adjacent to the overflow dam: 18 cracks on the upstream face and seven on the downstream face. There were no cracks on the overflow sections located in the central part of the dam (with a length of 91 m) and in the lower bank parts of the dam. The occurrence of cracks in the Koyna dam is explained first of all by the rough calculations in evaluating the seismic stability of the region of its construction. At the same time a substantial role was played by the design and technological solutions, which were to some extent consequences of this calculation.Special features of the profile of the nonoverflow sections of the dam are the presence of a sudden change in the slope of the downstream face (37 m below the crest) and massive head, the crest width of which is about 15 m. This change, in the zone of which the cracks appeared, caused stress concentration, which in combination with the considerable inertia of the head led to very high tensile stresses during the earthquake (according to calculations, more than 3.5 MPa on the upstream face and more than 6.9 MPa on the downstream face), which the rubble concrete, having as well an increased unit weight and reduced tensile strength compared with ordinary concrete, could not withstand.The cracks were grouted, and the zone of the sudden change in the profile of the downstream face was strengthened with concrete buttresses. The Koyna dam is operating in this form to this day, and the lessons learned from its experience were assimilated by hydraulic engineers of all countries.In recent decades the design and construction of earthquakeproof dams have risen to a considerably higher level. The new, more modern design and technological solutions used in creating them were the result of investigations in the area of construction and materials, technological developments, and appearance of construction machines and mechanisms with far greater technical possibilities than earlier.The greatest progress was made in this direction in [1970][1971][1972][1973][1974][1975][1976][1977][1978][1979][1980] in Japan, where a special technology of constructing earthquakeproof dams of roller-compacted concrete (rol...
