INTERNATIONAL SOCIETY FOR SOIL MECHANICS AND GEOTECHNICAL ENGINEERING This paper was downloaded from the Online Library of the International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE). The library is available here: https://www.issmge.org/publications/online-library This is an open-access database that archives thousands of papers published under the Auspices of the ISSMGE and maintained by the Innovation and Development Committee of ISSMGE. * 9 * Geological aspects of geotechnical engineering Aspects geologiques de genie geotechnique G. TER-STEPANIAN, Prof., DrSc. (Eng.), Corr.Mem.Armen.Ac.Sc., Yerevan, Armenia, USSR SYNOPSIS Analytical methods used in soil mechanics are based on considerable simplifica­ tion of geological structure. The influence of geological conditions on geotechnical engineering is discussed. The inverse - influence of Man's activity on geological conditions - has become evident at present. Therefore, the knowledge of engineering geology and some other geological disciplines is important for geotechnical engineers. Geotechnical engineering should be separated from civil engineering and be engaged in foundation, fill, dam, and subsurface problems. Geomechanics is one of the bases of geotechnical engineering; it is concerned with studying the mechanisms of geological processes. Use of back analyses for integral evaluation of earthen masses, the observational method, and monitoring for decreasing the time and costs of construction are discussed. Combating geological hazards is one of the important geotechnical problems in the near future. Discussion topics are commented upon. INTRODUCTION be of prime importance in the turn of the century. It is a great honor for me to deliver this Theme Lecture before the International We live in a very dynamic, difficult, and Conference on Soil Mechanics and Foundation interesting time. The duration of this century Engineering - the highest forum in our field is negligible compared with the lifetime of of science. Two circumstances make my task humanity. Nevertheless, enormous man-induced more responsible. changes in nature, planned and unforeseen, reasonable and unreasonable, occurred during Firstly, this is the jubilee conference when the present century. Similar environmental we sum up the results of the enormous progress changes would need many milleniums and even in the field of soil mechanics and foundation millions of years in normal natural conditions; engineering during half a century all over they take place nowadays during the lifetime the world. I am among a few of this audience of one generation. These changes are concerned who presented papers to the First International directly with this lecture. Conference in 1936 and, thereby, I can rank myself among the participants of the heroic Our present is not like our past, and the stage of soil mechanics history. future will not be as the present. We apply to history just to understand better our present An immense road almost fifty years long from state and to conceive the forthcoming problems. Harvard to San Francisco passed through many capitals and cities of the world - Rotterdam, The beginning and the end of the last 50-year Zurich, London, Paris, Toronto, Mexico, Moscow, period were important turning points in soil Tokyo, and Stockholm. Many important events mechanics thinking; they deserve to be analyzed. and great changes took place during this time, many prominent scientists astonished us with Terzaghi's brilliant discovery of soil their discoveries, and the need of our knowledge mechanics, marked by publication of grew everywhere. Our science developed in "Erdbaumechanik auf bodenphysikalischer front of the elder generation of soil mechanics Grundlage" and "Principles of Soil Mechanics" experts and became now one of the leading in 1925, gave a great impulse to civil engineers sciences of the civil engineering profile. dealing in foundations and earth structures. They obtained, lastly, a new tool enabling Secondly, the Theme Lectures of this Conference them to calculate the mysterious earth; true, should have a new, particular feature; they as a material with intricate properties that are not meant to be State-of-the-Art or General change depending on stress state and time. reports but more the type of papers presented as Rankine or Terzaghi lectures. I understand The idea that earth may be treated as an this requirement as the wish of the Organizing ordinary building material like concrete or Committee of the Conference to deal not so steel was attractive. Thus, soil mechanics much with the past or the present as to look became a kind of strength of materials applied forward, to think about the future, about to soils. In early investigations soils were the ways of further development of our science. considered exactly as a material, their These ways must be adequate to problems standing structure being of no importance. This is before the human society even now; they will confirmed by methods of soil preparation for 377 testing; they were dried, ground, sifted, of excavated earth structures (cuts, tunnels, and mixed with water. large underground openings, etc.), and foundations of engineering structures, dams, However, soil mechanics, even at the earliest etc., the work is carried out in an environment stage of its development, was never like soil formed during a long history of geological science, dealing with soil properties only; development. Its result depends essentially problems pertaining to soil masses were on disposition, mode of occurrence, and considered as well, such as stability of slopes, properties of soil bodies. It is certainly pile foundations, retaining walls, flow nets, possible to improve the soil properties by etc. It should be particularly emphasized means of dewatering, grouting, piling, etc., that homogeneous soil and the simplest in accordance with information obtained as geological structure were meant in all these a result of site exploration. However, such problems. improvements fail in efficiency in a number of cases owing to insufficient knowledge of It could not be otherwise in that stage of geological conditions and their substantial study; our . aim is not to criticize but to simplification on boring results interpretation, understand the state of the problem. Creation due to the unrevealed role of minor geologic of a science on the strength of such material details and inevitable uncertainties associated as soil was a great progress. We all remember with performance forecast at given sites and, the triumphant road of soil mechanics. It finally, with difficulties of execution control. associates in our memory with names of such The misuse of soil mechanics is the well known prominent scientists as Bishop, Bjerrum, result of disregarding the physical side of Casagrande, De Beer, Florin, Gersevanov, the process and of overestimating the Goldstein, Kerisel, Lambe, Leonards, Mitchell, mathematical methods. Such performance may Murayama, Peck, Roscoe, Schultze, Seed, be likened to a case of construction using Skempton, Suklje, Taylor, Terzaghi, the existent complicated structures, when Tschebotarioff, Tystovich, Whitman, and many the type and the elemental properties of these others. However, knowledge of strength of structures are known insufficiently and when materials enables the calculation of compara­ only a little poorly calculable and control­ tively simple elements of structures or machines lable strengthening may be effected. but not the structures or machines themselves. Sciences of subsequent level such as structural Attention is deserved by the fact that soil mechanics or science of machines serve this mechanics in its initial stage of development purpose. produced better results in northern regions laid down by young Quaternary deposits than Unfortunately, the situation regarding earthen in southern areas of the northern hemisphere, structures and foundations was otherwise. composed by overconsolidated Tertiary clays. Soil mechanics and conclusions drawn through Later on, understanding of the nature of consideration of simple soil models were applied overconsolidated clays became possible based to complicated natural conditions. The on concepts of stress history and geological available mathematical machinery was used pressure. They led to important conclusions and numerous design methods were proposed on recoverable strain energy locked in the which have rapidly and extensively spread. clay shales by diagenetic bonds (Bjerrum, These two circumstances are interrelated since 1967). Study of the lithified overconsolidated difficulties of the mathematical analysis clays and clay shales is also of great paleogeo- required accepting a number of assumptions, graphical significance for reconstructing one of which was simplifying the geological the formation conditions of these rocks and setting. the distribution of vertical and horizontal stresses acting in the past. GEOLOGICAL IMPACT ON GEOTECHNICS The tendency towards misuse in soil mechanics, existing undoubtedly even in our days, is Euphoria caused by the possibility to use stimulated by a tradition to publish results freely engineering methods in calculation of successful use of soil mechanics and to and design of foundations and earth structures gloss over the failures. Only the cases of was not long-lasting. Considerable schemati- serious failures and collapse of large zation of geological structure was needed structures gain notoriety, especially when for applying soil mechanics solutions,