Durability of dams and estimation of their behavior

Abstract

The problem of estimating the behavior of dams of various types after a certain interval of their operation attracts continously the attention of designers and constructors all over the world. At the Ninth International Congress on Large Dams*, 53 papers from 26 countries were presented on this problem (No. 34), which was the subject of a detailed discussion. The papers examined concrete as well as earthfill and rockfill darns. The most compreheusive was the analysis of problems of concrete deterioration. From the USSR a paper was presented by S. Ya. Eidelman (VNIIG) devoted to the results of instrumental observations at the Bratsk Hydroelectric plant,"The 50th Anniversary of the Great October." The problem was examined at the Congress under various aspects, most important of which were the design of dams, the observation of dams during the period of operation, repair and reconstruction, and the general problems of organizing and systematically controlling the behavior of dams of various types.As noted in a series of papers and emphasized by the general reporter D. Bullet (U.S.A.), the causes of deterioration and premature wear of dams are generated by insufficient investigation and poor study of the construction region, and also by design deficiencies, and particuiarly, by the incorrect selection of the dam type, and by the lack of adjustment of the dam to the actual conditions in which the construction works. Thus, according to the Czechoslovak National Committee, during the last 15 years several failures involving dams of heights between 5 and 21 m occurred because of the poor study and insufficient bearing capacity of the foundations. A failure involving a flood protection dike of 5.1 m height on the Danube occurred for the same reason.The comprehensive consideration of the climatic and operation factors which produce deterioration of the concrete in the operation process is very important. The modern state of the science of concrete and the level of knowledge of its properties make it possible to ensure a long and safe life service of hydraulic structures. However, 11 papers reported the destruction of concrete by frost because of interaction between the cement alkali and the aggregate, incorrect selection and specification of concrete requirements, and poor quality of concrete preparation and compaction during execution of the work. The papers emphasized that these destructive processes can be reduced to a minimum by the correct selection of the cement, aggregate, and additives, the ratio between the component parts of the concrete mix, careful casting, compaction, and curing of the concrete. The papers stressed especially the requirements of using aggregates of high quality and air entraining agents, and also of thermal protection of the concrete in the earlier stages to eliminate possible damage during the construction period.