The impervious curtains, screens, and upstream aprons of most of the existing dams were designed and constructed by taking into account, to a greater or lesser extent, the engineering-geologic and hydrogeologic conditious which characterized the seepage through the rock in contact with the structure. However, in most cases, the evaluation of these conditions was mainly of a qualitative nature. The writer does not know of any dams for which the parameters of the impervious elements, and primarily of the impervious curtains, could have been determined analytically. In the best cases modeling by the electrohydrodynamic analogy method was used, but. as is natural, with significant averaging of the seepage characteristics and schematizing of the boundary conditions. Since this approach is typical, it may be concluded that the main factors adopted as the bases for the design of impervious elements are the following: general characteristics, interpretation, and purposeful evaluation of the engineeringhydrogeologic conditions. The main type of investigation for this purpose is the hydraulic verification of the wells, which makes it possible to disclose the zonal distribution, and sometimes the value of the permeability, of saturated rock, and to evaluate the conditions and need for grouting the saturated rock. as well as the unsaturated rock in the aeration zone.Impervious curtains can be divided into two types: a) foundation curtains, located within the boundaries the river-valley portion limited in the vertical direction by the normal water level, and b) bank curtains, between the normal water level and the bank rock masses. The main hydrogeologic characteristics determining the parameters of foundation curtains are: a) presence and depth of practically impervious or very weakly pervious layers into which the curtain may be closed, thus making it complete, and b) presence or absence of a regular decrease of the permeability as the depth increases, associated with a decrease of the jointing or karat characteristics of the rock. These two factors almost always determine the depth of the curtains, with the exception of some relatively infrequent cases in which the curtain has a purely constructional significance; that is, when it is designed as an incomplete curtain ensuring only the required reduction of the uplift pressure. The required depth of these curtains is nsually determined by modeling (electrohydrodynamic analogy method) and is verified by rough analyses based on approximate schemes. The most difficult step is the establishment of the upper boundary of the zone which, from the standpoint of regularity of decrease of the water conductivity through the joints or the karat formations as the depth increases, is considered to be sufficiently impervious, that is, adequate as support for the curtain. Examples of the construction of curtains on the basis of this principle are the curtains at the Pavlovsk. Cbarvaksk. and Ingursk plants, and, abroad, at the Grou. and Saint Croix dams. among others. The number of complete...

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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From The Editors. A. G. Lykoshin's article raises serious questions vith regard to reducing the costs and curtailing the lengths of time required for engineering-geologic surveys, which comprise the principal and most labor-consuming part of such surveys. Therefore, these questions are extremely urgent now and require wide discussion. The editors request builders, designers and planners, surveyors, as well as workers in scientific-research institutes and institutions of higher learning to comment on the essential points of the questions raised in this article.Improving the quality and reducing the costs of engineering-geologic investigative surveys depend, for the most part, upon perfecting methods of carrying out these operations. All the other elements of technical progress (utilizing new equipment, raising the level of mechanization of labor-consuming production processes, and so forth) play a secondary role. In our opinion, we must adhere to two basic principles in perfecting the methods of engineering-geologic investigative surveys. The first of these is a differentiated approach to determining the composition and scope of operations, depending on the degree of importance of the facilities under construction, with a subdivision into the following two categories: principal structures of hydro-complexes and auxiliary facilities (settlements, roadways, transmission lines' etc.). The second is a distinction to be made at the facilities of the primary degree of importance between the main and the secondary engineering-geologic factors. The main ones, moreover, should be thoroughly studied in the maximum possible detail, whereas the secondary ones could be studied in a less detailed manner, allowing for a calculated engineering risk. The degree of the latter should be determined by the characteristics of the natural situation and the technical potential for eliminating unexpected complications during construction with sufficient speed and without undesirable consequences.Complications appear most frequently as a result of the disclosure after construction pits have been opened up of sources of local water flow, karst hollows (sink holes), zones of tectonic fracturing, etc. Such unexpected factors may require an intensified pumping, sealing with concrete or cementing rocks, on-site utilization of anchor bolts, and so forth.In carrying out investigative surveys at major facilities, principal attention should be concentrated on the most exact possible exposition of the principal engineering-geologic factors, determining the most important planning decisions. It is important, moreover, to establish the principle that in opening up a construction pit the complications mentioned above might manifest themselves and, accordingly, direct the planners to work out design or construction measures the implementation of which might be required during the course of construction. We should not economize on detailed surveys in those instances where an insufficiently precise knowledge of the facility's foundation might bring about ...