Construction of large hydraulic engineering installations and particularly high-head dams in folded mountain rock has placed fresh requirements on engineering geology. The calculation of dams on rock foundations, i.e., on elastic homogeneous and isotopic media with such heavy loadings on the foundation as represented by modern installations, results in big errors in evaluating stability and stress of the installations, in stability calculations for large rock slopes and the banks of reservoirs, in addition to several other important problems. Consequently, various types of models are being used increasingly in engineering geology for reproducing the different properties of the foundations. At a certain stage of accumulation of data, the investigator finds it necessary to generalize, in order to appreciate the nature of the relationships and interaction between the separate factors, the foundation and the engineering installation, etc. These interrelationships and interactions are represented in the form of circuit diagrams, in the natural physical or mathematical form, i.e., in the form of models providing a simplified representation of the object studied. In order to resolve engineering-geologic problems, models are set up which, depending on the form in which the data relating to the natural phenomenon or installation is expressed, may be to scale (graphical, natural, or of equivalent material), physical (hydrochemical, optical, etc.), or conceptual and mathematical (determinate, statistical).Engineering-geologic models must conform to the following requirements: simplicity of construction and sufficiently accurate representation over the whole range of measurements; a high degree of adequacy of the natural system or structure modeled; suitability for use in the design of planned installations and their foundations by existing methods of the mechanics of deformed media and hydromeehanies.The scale model is the most common and useful, the prototype of the object being subdivided into sections, reduced for ease of investigation and simple representation. Included are models of dam foundations, bridges, reservoir banks, etc.Physical models (electro-hydrodynamic, hydrochemieal, optical) simulate the geologic phenomena on the basis of generalization of their physical nature. This type of modeling is based on the principles of similarity, for example, between the laws of motion of water and an electric current.Conceptual models represent the conceptual image of some natural phenomenon, i.e., schematic models expressed in the form of various diagrams, mutual relationships, and variants. Such models express certain phenomena in the form of a hypothesis. An example of this type of model in soil mechanics is that of various types of rock. Conceptual models are qualitative and help largely in the study of complex geologic processes and bodies, and are a necessary stage in their study.Approaching the investigation of a given phenomenon by means of scale, physical, and conceptual models, data is obtained, allowing generaliz...

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The prediction of the development of slumps and slides on high mountain slopes and the evaluation of their stability are complex and insufficiently studied problems. The use of the method of natural analogues for estimating the stability of slopes appears to be promising. The prediction of the development of deformations in mountain slopes by the method of natural analogues is based on the engineering-geologic analysis of the natural setting and of the combined action of different factors.The development and stability of slopes may be predicted and evaluated with different degrees of accuracy, depending upon the stage of the engineering-geologic investigations, the complexity of the geologic structure of the slopes, the types of slumps and slides, and the type of construction and the uses of the given area. Different mathematical methods are used for processing the data from engineering-geologic surveys and map~ of the slidingcaving-in slopes. During the preliminary project stage, when there are data from engineering-geologic surveys of the tiver-valley slopes to scales 1:25,000 and 1: 50, 000, as well as of separate typical portions to larger scales, it is possible to formulate a tentative prediction. During the stages of the investigations for the technical project, which include large-scale surveying, (scale 1: 1000-1: 500) drilling, mining, geotechnical, geophysical, laboratory, and experimental-modeling work, it becomes possible to formulate an accurate prediction on the basis of ali the characteristics of the rock in the different decompression and weathering zones.

The state of the hydraulic structures is given according to the data of the commission of the USSR Ministry of Reclamation and Water Management (Minvodkhoz), which inspected 16 dams between February 15 and March 3, 1989. Four dams are under construction.The Getik dam under construction on the Chichkan River was designed for an intensity 8 earthquake with a frequency of once in 1000 years (building code SNiP II-7-81, seismic regionalization map of the USSR). According to the scheme of isoseisms of the Spitak earthquake, the hydraulic structures of the dam are located near an intensity 9 isoseism. The design height of the earth dam is 61 m and the reservoir storage 35 million m 3. At the time of the inspection the foundation pit for the dam was excavated in tuffstones and the irrigation outlet was made.The upper face of the right-bank abutment of the dam is in a zone of large (in volume) slides due to creep with an approximate thickness of 50 m and most probable volume of one-time displacements of several hundred million m 3. During the Spitak earthquake there occurred within the body of ancient slides, about 500 m from the dam site, a rapid movement of the blocks and packets of tuffstones, tuff-argillites, and tuffites with a total approximate volume of more than 10 million m 3 and horizontal displacement of several tens of meters. Activation of landslides with a rate considerably exceeding the present annual average rate of several tens of centimeters observed before the December earthquake is possible during filling of the reservoir and its rapid drawdowns. The given landslides can dam the valley, force the water out of the future reservoir and cause an overflow wave, and partially destroy the right-bank part of the dam with breakthrough of the water from the reservoir bowl.The Karnut dam was constructed in 1968. It is located in an intensity 8 earthquake zone (according to SNiP II-7-81 and the isoseisms of the Spitak earthquake). The homogeneous loam dam has a height of 35 m and length of 740 m. Its upstream slope has a steepness of 1:3, is stabilized by precast reinforced-concrete slabs in the form of hexahedrons, and the downstream slope with a steepness of 1:2.5 is covered with vegetation. The dam slopes are stabilized at the base by a stone berm. The water is let out through a 1420-ram-diameter steel pipe with a discharge of 7.6 m3/sec. It was established during the inspection that the gate-operating tower was displaced 10-15 crn during the earthquake (relative to its supports). The design storage capacity of the reservoir is 24.7 million m 3. During the main shocks the water level in it was 12 m below the normal pool level (NPL). A longitudinal (toward the dam axis) crack with a length of 15 m and width of 4 mm was found on the dam crest near the edge of its downstream slope. Mats of the vegetation layer of the soils were noted in the zone of the crack. Through cracks fracture the parapet in the right-bank abutment of the dam. No visible earthquake damages are noted on the other hydraulic structures.The Kh...