Karl Terzaghi's Legacy in Geotechnical Engineering

This article was published in the October 2002, GEO-STRATA magazine of the ASCE and was writen by Professor Richard Goodman. We have considered that the article was very interesting and should be read by all geotechs and we requested to host the article in the Geoengineer website. Permission for its use was granted by ASCE on November 19th. For more information about the publications of the ASCE you can click here and for information about the GEOINSTITUTE click here

Karl Terzaghi's legacy in Geotechnical Engineering

By Richard E. Goodman*

Karl Terzaghi (1883-1963) was the first to elaborate a comprehensive mechanics of soils with his publication of Erdbaumechanik in 1925. His recognition and formulation of the effective stress principle and its influence on settlement analysis, strength, permeability and erosion of soils was his most prodigious contribution. But Terzaghi also pioneered a great range of methods and procedures for investigation, analysis, testing, instrumentation, and practice that defined much of the field we currently know as geotechnical engineering.

Among Terzaghi’s publications, reports and lectures, one finds seminal contributions across a wide terrain, including: classification methods for soils and rocks; capillary phenomena in soils; the theory and documentation of consolidation and settlement; piping and its prevention; design and construction of earth, rock and concrete dams on all kinds of foundations; anchorages for suspension bridges in soils; field and laboratory measurement of pore pressures and soil properties; use of flow nets in two and three dimensions; design of drainage wells and tunnels; design to avoid scour of river and waterfront structures; earth pressure variations on walls and bulkheads; engineering in terrain underlain by permafrost; pile foundations; soil improvement by compaction, pile-driving, grouting and incorporation of geotextiles; soil and rock tunneling; engineering geology; sinkhole formation and collapse; regional subsidence due to oil-field operations; and landslides.

He was the great professor of geotechnical engineering of his day, with regular appointments first in Istanbul, then at MIT, Vienna, and Harvard, as well as courses of lectures in Berlin, Texas and Illinois. Through hisvoluminous correspondence with engineers and scientists, his lifelong devotion to publishing both research findings and practical experiences, his numerous public lectures, and his authorship of clear and complete procedures in many engineering reports, Terzaghi disseminated advances in soils engineering that influenced the entire civil engineering world.

Ironically, although he was a great educator, Terzaghi grew to entertain a suspicion of formal education, which he thought had the capacity to obscure observation of new phenomena. He reserved his greater admiration for “self-
made men” who learned from their open eyes and minds.

TERZAGHI’S PERSONALITY AND INTERESTS

In reviewing the range of accomplishments and his domination of the field, it is interesting to examine Terzaghi’s background and interests as well as his philosophy and methods of working. His upbringing and education combined Austrian rigor and military training and a passion for observation of natural science and the contemplative beauty of nature. His attractions ranged widely: construction, geology, mathematics, philosophy and ethics, architecture, flowers, swimming, conversation, travel, literature, music, art, women, men and writing.

He was certainly a remarkable listener as well as a reader and an observer. He was also an exceptionally faithful diarist and prolific correspondent, and through his correspondence he revealed a penchant for classifying almost everything in his experience; people, ideas, objects and of course, rocks and soils. Terzaghi could be a severe critic, especially of those who tended to be blinded by their own theories, or worse, those utterly devoid of theories. He accused some of hiding inarticulately, behind a pensive exterior.

Terzaghi’s goals, which were set like sails to drive his life, changed dramatically at about age 43 (1926). As a younger man he had striven t formulate a rational analytical or empirical methodology, properly embracing geological constraints, for designing works founded on soils (and, to a lesser extent, rocks). But as a mature man, having achieved his first target, he pursued the practice of engineering passionately to test and temper the emerging methods by physical realities.

In this he became increasingly concerned wit the difficulty or knowing enough of a site’s morphology and properties to determine a design solution before construction had started. This worry committed him ever further to the observation of soil and structural response throughout the construction period in order to inform a constant updating of the designs, transforming him into a proponent and practitioner (with coworker Ralph Peck) of the "observational method". Thus, despite Terzaghi’s considerable achievement in advancing the theory of soil mechanics, he repeatedly counseled the profession to stay connected with the behavior of the actual soil in engineering practice.

TERZAGHI’S PRAGMATIC PHILOSOPHY AND METHOD

As his own method of accomplishment became formed, Karl Terzaghi expressed his personal beliefs about the practice of engineering to others. The key components included the following points:

• Take on only what one’s own competence allows him or her to handle personally. Terzaghi had such confidence in his own core resources as to seek out the most challenging (some would say “adventurous”) projects.
• Assume the worst configuration of properties and boundary conditions consistent with data from site investigations.
• Follow through on every angle and every subtask.
• Don’t oversimplify the site model, its properties, or its response.
• Take responsibility as an engineer, even beyond the specifics of one’s own specific assignment.
• Learn continuously from experience, personal and vicarious, and publish meaningful experiences for the betterment of the profession.

These items from Terzaghi’s personal creed colored his attitude as an engineering consultant, the methods he adopted in working with others to solve engineering problems, and the way he wrote his own engineering reports. The following describes some key facets of his system.

1. He reported relevant case histories, from his own experience or about which he had learned from conversations with engineers, or reading, both of which he pursued diligently.
2. In the beginning, and throughout the course of a job, Terzaghi demanded a great deal of data and was usually persistent in obtaining most of the specifics he needed. He often questioned the results of prior soil investigations, sometimes rejecting their conclusions outright and beginning a new.
3. He generally tried to unravel a site’s geological history, then used it to develop a list of questions that the investigations should attempt to address. He applied this history, and geological logic, to infer a foundation’s geometric and material properties.
4. In sleuthing failures, he tried to obtain old records, photos, and eyewitness accounts and worked to identify and resolve inconsistencies among these data.
5. In writing his reports, he chose his words so as t make his thought process visible, being careful to expose the logic that led to certain simplifications and/or correlations observations.
6. His calculations were tempered by judgments concerning imperfections in sampling and testing and variability in the morphology and properties of different layers.
7. He tried to develop and explain simplified procedures or apparatus that the client could adopt to carry out the recommendations without undue inconvenience.
8. When criticizing previous work, he was courteous and careful to explain the nature of his disagreement, yet firm in his resolve.
9. He reviewed any specific design with a checklist of possible defects related to the interaction of geological and engineering factors and then meticulously examined each, point by point. He then computed or judged the capacity of the design to overcome the specific obstacles and, if warranted, suggested refinements or reworkings in the design, which were accompanied by detailed sketches and drawings as well as pertinent case histories.
10. In completing a study he tried to cover all the essential bases – engineering geology, geotechnical engineering, structural engineering, sometimes even hydraulics – so as not to leave the client hanging by overspecialization.
11. He used hydrologic measurements from weirs to piezometers, together with analysis to compare the response of homogeneous materials with that of the actual site. Anomalies thus identified focused the investigations on critical locations.
12. He attached as much interest to the construction procedures as to the design itself, with full expectation that the design would be appropriately modified during construction, as the true conditions were unveiled through observations and measurements.
13. He insisted on obtaining, and often helped recruit, highly qualified people to conduct the sensitive construction jobs, whether engineering measurement, excavation supervision, or tunnel foreman, and he argued for the employment of engineering geologists.
14. He invariably required measurements to be made on the site, with sufficient lead time to establish behavior before, during and after construction. He warned of the implications of not making the required measurements.
15. He provided very definite and explicit recommendations in a way that was immediately useful to his clients. He stated his recommendations convincingly, sometimes almost threateningly, warning the reader, in the sternest, absolute terms, that the difference between success and failure, safety and catastrophe, resided in absolute adherence to his word.
16. He was always conscious of the need to be efficient, if not optimal, in approach to excavation and design of any work within the constraints of assured safety. He often recommended staged design, awaiting the results of measurements, in order to avoid overdesign.
17. He was entirely committed to sticking with a project to its completion, even in the face of changes in management such that he no longer had a client to fund his involvement.
18. He was consistently aware of his ethical responsibility as an engineer and did not hesitate to indicate problems in a part of a job even if it lay outside his specific charge.

Karl Terzaghi was a remarkable mad and an impassioned engineer. As he put it himself, “All the modest achievements which I have to my credit can be described by a simple formula… Guided by common sense and casual observations, I recognized weak points in traditional procedures and tried to make them less weak. Sometimes I failed, but usually I succeeded.”

*Richard Goodman, M.ASCE, a member of the National Academy of Engineering, is Cahill Professor Emeritus in Geotechnical Engineering at the University ofCalifornia, Berkeley, and a regular visiting Professor in the Technical University of Graz, Austria. His research in applied rock mechanics led to development of the joint element for finite element analysis (with Robert Taylor), introduction of the base friction model test, and the development of block theory (with Gen hua Shi). He is the author of five books, including Karl Terzaghi, the Engineer as Artist available through ASCE. He can be reached at [email protected]. 

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