Papper

ENGINEERING GEOLOGY ON THE JOB AND IN THE CLASSROOM
By Karl Terzaghi
In this paper the term “engineering geology” is applied exclusively to small fraction of the sum total of geological knowledge which the civil engineer engaged in design and construction of subsurface structures such as foundations and tunnels must posses in order to practice his profession competently. Until a few decades agothe civil engineer knew enough about geology of he was thoroughly familiar with the meaning of the terms which are used by professional geologists in their reports on the results of their site explorations. At that stage every elementary course in general geology served this purpose, although at some institutions the course was given the name “engineering geology.” At the present time a course inengineering geology also has the important function of focusing the attention of the engineer on the nature and importance of the uncertainties involved in the design of foundations and tunnel supports in the basis of test results and computation. This new requirement grew out the development of soil mechanic and calls for increased emphasis on the engineering properties of sediments and theengineering significance of patterns of stratification. The need for such emphasis in not yet recognized by many teachers of the subject and the consequences become apparent in what the writer has called misuse of soil mechanics. The statements contained in this paper are based in the writer’s personal experience covering a period of more than half a century. His experience record includes thepractice of engineering geology in four continents and the teaching of engineering geology at four different institutions of higher learning in Europe an the United States. These activities have given him manifold opportunities to become acquainted with the essential requirements to be satisfied by the geological training of candidates for subsurface engineering and with the consequences of thedeficiencies of current methods of teaching engineering geology.

“THE MISSING LINK” IN THE INGINEERING GEOLOGY
At the turn of the century design of foundations and earthworks was based almost entirely on empirical rules and equations. The metrical values in the empirical equations contained constants which depended only on the type of material underlying the site. On routine jobs the classification onthe materials was performed by the engineer or the boring foreman, and the important projects the services of a professional geologist were retained. After graduation in 1906 the writer joined a contracting firm in the capacity of a junior engineer. During the following five years he had unusual opportunities to find out that empirical rules then in use in the field of subsurface engineering wereappallingly unreliable. Detrimental settlements and the failure of foundations though common always came as a surprise and no rational explanations were available. Since the performance of a foundation obviously depends on the properties of the materials supporting the foundation, the writer arrived at what appeared to be the logical conclusion that our incapacity to predict the performance offoundations grows out of inarlequate knowledge of the relationship between the data furnished by the geologist and the subsequent performance. Therefore, starting in 1912, he concentrated for several years on an attempt to discover these relationships by correlating observed unsatisfactory with the data contained in the geological reports describing the site. Some of these reports were as complete asone could wish. Yet no relationships of general validity could be discovered.

Not until 1018 did the writer begin to realize that his quest was doomed to failure, because the materials encountered at the investigated sites were designated by both geologist and engineers by terms which, from an engineering point of view. Have no well-defined meaning. For instance, sand was described in both...