CHARACTERISTICS OF THE MECHANICAL PROPERTIES OF ROCKS T. F. Lipovetskaya

UDC 624.131.43

Standardization of investigations of the characteristics of the mechanical properties of soils and the selection of the design values of these characteristics should be determined in the following way. When determining the composition and extent of investigations it is necessary to take into account not only the class of the structure but also the stability, strength, or deformations. For example, if the necessary degree of stability of the structure is knowingly provided even for the lowest values of the strength characteristics possible for the given type of foundation soils and the dimensions and design of the structure depend only on other factors, the extent of investigations of strength characteristics can be reduced. Investigations of the soils of a given object should not be the end in itself. Having outlined the composition of the complex and costly investigations of soils of the foundations or body of the structure, one must have a clear idea where the results obtained will be specifically used. Thls also pertains to experiments related to the development and substantiation of new methods of investigation and calculation, testing of which should be carried out primarily on structures already constructed and operating successfully. In this case it is necessary to treat with particular caution the introduction into design and construction practice any methods which necessitate an increase in the weight of these structures. Acting in this direction, one can reduce the time and cost of surveys without detriment to the quality of the structures.

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Fig. i. Characteristics of the shear strength of soils of the shoulders of the Nurek dam: a) ox=f (03); b) T=f(o); i) standard lines; 2) calculated lines according to the recommendations of SNiP II-16-76; 3) calculated lines according to the recomendations of the commission of the Science and Technology Council of the Ministry of Power and Electrification of the USSR; 4) broken lines according to the values of ~ used in the design.

Translated from Gidrotekhnicheskoe

0018-8220/83/1706-0281507.50

Stroitel'stvo, No. 6, p. 6, June, 1983.

9 1983 Plenum Publishing Corporation

281

When substantiating the designs of earth dams, especially when designing high and very high dams in seismic regions, the calculated values of the strength characteristics of the soils composing them have decisive importance, The methods of determining =he calculated values of the characteristics of soll strength from the results of experimental investigations are standardized by eonstruction specifications and regulations SNiP 11-16-76. If the values of the strength characteristics obtained in conformity with the requirements of this standard were used in the calculations, one could design dams of a sufficiently compressed profile. However, oneusuallyacts differently. Having obtained the calculated values of strength characteristics by means Of methods of mathematical statistics, one arbitrarily reduces themi and so moch[s0 th&t s a@e substantlally different from theresults of investigations. In=thls c~se various design measures are stipulated for ensuring stability of the dam slopes with knoWinglyminlmizedsoll characteristics, i.e., creative efforts are aimed at overoomingnonexistling diff~r For example, aS a resu!t 0f uslng minlmlzed strength characteristics of the gravel-pebble soils of the Nure~ (Fig. i)so-called reinforced-concrete belts were place in t~is dam. The greatest danger consists in that subsequently the arbitrarily reduced values of the strength characteristics of the given type of soil will be taken as th e actual ones and will be recommended for use as analogs. Thus it Is clear that it is necessary to use more completely the real properties of soils for reducing the cost of construction.

RELIABILITY OF ROCK FOUNDATIONS OF CONCRETE DAMS ~. S. Kalustyan

UDC 627.8.058.4

In recent years the statistics of the risk of occurrence of various natural catastrophes have been studied in connection with the introduction of probabilistic methods of calculation. Analogous work in the field of hydrotechnical construction made it possible to establish also the reliability of the rock foundations of concrete dams against destruction (0.9972) and damage (0.985). Such estimation became possible in connection with ICOLD's publication of extensive data on their failures and damages [i]. Next year's 100th anniversary of the construction of the small Psyrtskha arch dam in Novyi Afon, which withstood three earthquakes, serves as confirmation of the long life of dams. It is necessary to preserve a dam by imparting to it a form more accessible for inspection [2]. The problem of the reliability of rock foundations is presently acquiring ever more urgency, since the majority of failures known by their tragic consequences are related to dam foundations. In connection with the development of hydrotechnical construction on rock foundations in our country it is important to assess qualitatively the reliability of dams and their foundations on the basis of the existing world experience, to select and evaluate the significance of individual acting factors, and to determine on their basis the most dangerous ones for the purpose of their redundancy. Such an evaluation, in our opinion, can be made on the basis of ICOLD's statistical data already available for 1974 and 1979 [3]. The significance of the analysis increases with the selection of a general approach taking into account the possible relations between individual factors and their interdependence, which ultimately permits evaluating the directions and role of redundancy in increasing the reliability of the dam--foundation system. For such an evaluation it is necessary to isolate from the set of all acting factors the external actions causing failures and the elements of the subsystem with which this failure is associated [4]. Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 6, pp. 7-8, June, 1983.

282

0018-8220/83/1706-0282507.50

9 1983 Plenum Publishing Corporation