Soil foundations for concrete and reinforced-concrete hydraulic structures

Abstract

The work of Section IV of the Eighth Congress "Soil foundations of concrete hydraulic structures" was devoted to investigations of the foundations of hydro developments. In addition, a number of problems pertaining to investigations of the foundations of hydraulic structures figured in the topics of plenary meetings of the Congress. The first plenary meeting was devoted to "Latest methods of investigating the strength and deformability of soih," the second to the -Interaction of foundations and structures," and the fourth to "Problems of soil mechanics and construction on weak clay and structurally unstable soils." Special Section 11 was devoted to "Problems of nonlinear soil mechanics."The characteristics of concrete and reinforced-concrete hydraulic structures on soil foundations consist in large areal dimensions of the foundations, and in the soils' bearing not only vertical but also horizontal loads commensurable with them, being under the effect of water pressure and seepage forces.The main topics of Special Section IV were the following: I) strength of foundations and stability of concrete hydraulic structures on soft clays (methods of research, design, and calculation with consideration of the time factor); 2) methods of calculating settlements and horizontal displacements of concrete hydraulic structures; 3) methods of increasing the shear resistance of concrete hydraulic structures and the bearing capacity of their soil foundations (anchorage, drainage, grouting, etc.). This article presents the main points of the general paper of S. Broms (Eweden), chairman of Section IV.The speaker expanded the subject matter of his paper, having included in it also elements concerning the design of concrete hydraulic structures on rock foundations (the 284-m-high Dixans dam in Switzerland and 280-mhigh Inguri dam in the USER). In presenting the world experience in the construction of gravity dams, B. Broms cited the USER experience (Lower-Svir, Uglich, Ivankovo Rybinsk, Tsimlyansk hydroelectric stations) which was known to him from the papers of O. A. Rou~eaux and V. P. Lichachev [I, 2]. The speaker indicated that the number of gravity and buttress dams being constructed is decreasing owing to their high cost in comparison with arch and earth dams. On the basis of the data of Hupner et al. [3], B. Broms reported th/t the cost of arch dams is 40-70% of the cost of gravity dams. This statement can be referred only to cases of the construction of dams on sufficiently strong rock foundations and at comparatively narrow sites.in the USA more than 90% of recently constructed dams were built from earth materials, whereas in Switzerland 90% of the dams are concrete [4]. The prevalance of earth dam construction, including very high ones of large mass (Omville, H = 224 m, V = 61 million mS), is due to the development of powerful machinery (heavy-duty excavators, trucks, heavy rollers, etc.).Failure of concrete dams as a rule resu/ts from defects in the foundation and not from loss of concrete strength. According to the literatu...