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In subsequent investigations the main parameters of the stilling basin and waterway of the service spillways were substantiated on three-dimensional models (scale 1:120) and on partial models (1:60 and 1:50) and in the design work carried out in close relationwith them. The characteristics of the hydrodynamic effects were also established.

On May 23-P.s 1976, the 4thCoordinating Conference onLimidng State of Hydraulic Structures was held in the city of Narva of the Estonian SSR. The Conference was attended by 82 specialists from 14 design institutes, scientific-research organizatiom, and higher educational institutions. They heard and discussed nine papers and 30 reports on results of investigations of plain and reinforced-concrete hydraulic structures, the basic concepts of the new SNiP chapters on design of these structures, and ways of improving the methods for their limiting state design.At the Conference it was stated that during the 9th Five-Year Plan significant successes had been achieved in carrying out investigations connected with analysis and design of elements of hydraulic structures, which have made it possible to substantiate the changeover to limiting state analysis and design of arch. gravity-arch, buttress, and gravity concrete dams. On the basis of the generalization and analysis of results of investigations of different types of structures, normative instructions included in the draft chapters SNiP ]I-54-76, II-56-76, and II-16-75 were drawn up.The paper "Basic concepts of Chapter SNiP 17-56-76 and ways of improving further the limiting state design of elements of hydraulic structures," presented by Candidate of Technical Sciences, A. V. Shvetsov (VNIIG). reflects the fundamentally new design concepts of the drawn up norms: changes in the classifications of limiting states; regulation of the new system of design coefficient~ carrying out of analyses of structural elements according to two groups of limiting states (for loss of carrying capacity or unfitness for operation, and for unfitness for normal operation); introduction of new requirements for establishing the normative strengths of the concrete and steel reinforcement with a given probability equal to 0.95 and with the system, recommended in the norms, of safety factors for the materials and of coefficients of working conditions of the concrete and reinforcement; and use of a unified system of combination coefficients and of overload coefficients, regulated for all types of structures and foundations in Chapter SNiP 11-50-74. The draft chapter SNiP II-56-76 develops and defines more precisely instructions for determining the uplift pressures exerted by water on concrete, and of the relations for t~mding the normative and design strengths of concrete under aU-around compression. The instructions for analysis of cracking and opening of cracks in reinforced-concrete elements, as weil as for analysis of action of cutting forces, have been substantially modified. Some changes have been introduced in the sections dealing with analysis of structural elements under temperature-moisture action.The "Basic concepts of the norms SNiP II-16-76 and ways of improving further the analysis and design of foundations" were described in a paper presented by Engineer T. F. Lipovetskaya, Candidate of Technical Sciences D. D. Sapegin, and Candidate of Technical Sciences R. A. Shiryaev (VNIIG). I...

The bearing capacity of dams, especially in the case of arch dams, depends upon the strength and structure of the material forming the gorge. Hence, a designer has to devote considerable attention to the study of the geological structure of the rock mass and the engineering measures introduced for ensuring combined functioning of the dam and the foundations. If the designed system cannot be satisfactorily assessed by calculations alone the design assumptions may be substantiated by experimental investigations.At the Vedeneev All-Union Scientific-Research Institute for Hydmgeology experimental investigations were set up on brittle models for assessing the deformability and stability of rock mass in the right bank abutment of the Toktogul dam.In the region under investigation the foundation consists of metamorphosed limestone in layers 1.5-2 m thick. The layers dip 70-75 ~ towards the upstream side while the bedding planes are inclined at an angle of 40-45 ~ to the river bank. The limestones are traversed by wide tectonic joints dividing the rock mass into blocks 50-60 m apart, which, in turn, are further subdivided into smaller blocks by a system of thinner joints. In most cases the width of the tectonic joints does not exceed 1 ram. Scales of calcite are often observed on the joint wails, from which it may be concluded that these joints may not have a significant effect on the mass functioning as a dam foundation.