Manuel Melis Maynar

Catedrático de Geotecnia

Catedrático de Ferrocarriles

ESTAS PÁGINAS ESTÁN DEDICADAS EXCLUSIVAMENTE A LOS ALUMNOS DE 6º CURSO DE FERROCARRILES DE LA ETS DE CAMINOS DE MADRID.

ESTÁN PROTEGIDAS POR LA CONSTITUCIÓN ESPAÑOLA, ARTÍCULO 20.c "Libertad de Cátedra".

LA UNIVERSIDAD ES APRENDER A PENSAR, ESPÍRITU DE TRABAJO  Y ESPÍRITU CRÍTICO AL MÁXIMO NIVEL.

El Prof. KARL TERZAGHI, creador de la Geotecnia o Mecánica del Suelo, cambió por completo la Ingeniería Civil. Su influencia es probablemente la mayor que ha tenido ningún hombre sobre ninguna ciencia o disciplina.

Incluyo aquí el artículo que el Prof. A. Casagrande, uno de sus primeros discípulos, escribió como homenaje tras su muerte en 1963.

KARL TERZAGHI 1883-1963

by  ARTHUR CASAGRANDE, Professor oí Soil Mechanics and Foundation Engineering, Harvard University, Cambridge, Mass.

With the death of Karl Terzaghi, the creator of soil mechanics, on October 25, 1963, the engineering profession lost one of its most eminent and colourful personalities. Even as a young man he had the vision to recognize the great need for a rational approach to foundation engineering. The importance of this need challenged his imagination and led him to develop this new interdisciplinary science which revolutionized design and construction practice in foundation and earthwork engineering.

In the preface to the anniversary volume ("From Theory to Practice in Soil Mechanics", john Wiley & Sons, 1960. To this volume I have contributed a chapter entitled Karl Terzaghi-His Life and Achievements which contains other biographical details) which was compiled by my colleagues, L. Bjerrum (Norway), A. W. Skempton (Great Britain), R. B. Peck (U.S.A.) and myself, we expressed this view : "Few men in a lifetime have exerted an influence on their profession to compare with that of Karl Terzaghi on civil engineering and engineering geology. Yet his writings and practice are so diverse, have covered so long a period, and have stemmed from so many countries that the full scope of his career remains unrealized by even his closest associates."

I find it a difficult task to write about a man so soon after his passing, in whom I mourn not only the brilliant master, but a fatherly friend to whom I was deeply devoted. Yet it is my task because I had the good fortune to be closely associated with Karl Terzaghi from 1926 until his death, probably longer than any other member of the profession.

Karl Terzaghi was born October 2, 1883, in Prague, Austria, where his father, Anton von Terzaghi, was temporarily stationed as an army officer. Young Karl was expected to follow the military career of his ancestors. When he discovered, at the age of 14, that a slight defect in his vision would prevent him from joining the Austrian navy, he decided against such a career. He studied mechanical engineering at the Technical University in Graz and graduated in 1904. As a student he devoted more time to attending courses in geology, astronomy, and philosophy, than to his essential subjects. He had already started a search for something that would satisfy his intense curiosity and desire to explore beyond the limits of man's knowledge. But the student years were stormy years of his life. Without a star to guide him and without someone to hold the rudder firmly he was close to being shipwrecked. True, there were some members of the faculty who recognized in him a gifted and potentially creative mind. One of these was F. Wittenbauer, Professor of Mechanics, who was also a poet and a playwright. It is reported that he defended Terzaghi when the Faculty was about to expel him for excessive indulgence in "academic freedom ". On this occasion Professor Wittenbauer reminded his colleagues that the three students who had been expelled from the Technische Hochschule in Graz had become eminently successful men -one was Nicola Tesla.

After Terzaghi received the engineering degree, he served one year in the army. In his ample free time he translated A. Geikie's "Outline of Field Geology" into German. That was his first professional publication of a list that today numbers in the hundreds. A bibliography complete to 1960 is included in the above-mentioned anniversary volume.

As a student he had already become aware that mechanical engineering was not to his liking. Therefore, after completing his essential year in the army, he returned to his alma mater for another year of study, concentrating chiefly on geology. Then he worked for 3 years with an Austrian civil engineering and contracting firm on a variety of projects on which he learned the practical side of civil engineering. He then eagerly accepted an opportunity to take charge of a geological and hydrographical survey for a hydro-electric project in the Karst mountains of Croatia. He enjoyed the extensive field investigations and, after completing this assignment in 2 years, he wrote a comprehensive Paper on the landforrns and groundwater conditions in the Karst region where this project was located. This Paper is still considered an up-to-date discussion of the geology of karst phenomena. (A revision of it was published in recent years in English and is also reprinted in the anniversary volume.) While he was preparing this Paper, a friend informed him of difficulties which had arisen in constructing the foundations for a large building in St Petersburg (now Leningrad). Terzaghi offered to take charge of this project: his offer was accepted and he succeeded in controlling a dangerous condition. On this project the highly unsatisfactory state of the art of foundation engineering became clearly apparent to him. This challenge to his imagination was so intense that he decided to sacrifice his savings and time to collect and correlate all available knowledge on this subject, in the hope that it would lead to a rational approach for predicting the performance of soils in earthwork and foundation engineering. For a short period he continued practising in Russia, in an atmosphere which professionally, socially, and financially was very attractive. Stimulated by the problems which he encountered in Russia, he made significant contributions to reinforced concrete design which he published later in several Papers and in a small book co-authored by T. Poschl. Also, he used some of this original work as a basis for a doctoral thesis; in January 1912 he received the degree of doctor of technical sciences from Graz Technical University. A few weeks later he was on his way to the United States.

Terzaghi had gained the impression that earthwork engineering was most advanced in the United States and that the U.S. Reclamation Service was the principal pioneer. Therefore, he called first on F. H. Newell of Washington, who was at that time Director of the Reclamation Service, and asked his advice about locations where difficult problems in earthwork engineering are encountered. Terzaghi remained in Washington, D.C., long enough to study the geology of those regions described in the publications of the U .S. Geological Survey: he then proceeded to visit one site after another. To supplement his meagre funds he accepted any kind of work -as engineer, boring foreman, time-keeper, even as driller. In this manner he became acquainted with the soft alluvial clays of the Mississippi delta, with the soils of the semi-arid regions of the south-west and west, and with the clays in Oregon and Washington which there cause instability of slopes. He also observed with interest novel earth work construction procedures. At the end of 1913 he returned to Austria, quite discouraged because he had failed in his self-imposed task. While he was digesting the relatively small amount of useful material he had collected, the First World War broke out.

After briefly participating in the fighting on the Serbian front, he asked for transfer to the Austrian air force which was then being organized. He spent 2 years as Commanding Officer of the aeronautical testing station at Aspern (near Vienna) where he was associated with Theodor von Karman and Richard von Mises. All three were to meet again in the United States many years later.

At that time, Professor Philip Forchheimer, who had been one of Terzaghi's teachers at the Graz Technical University, was assisting the Turkish Government to reorganize engineering education in Turkey. He needed a capable and energetic man, and, without even consulting Terzaghi, he arranged in 1916 for his transfer to Turkey as Professor of Foundation Engineering at the Imperial School of Engineering, Constantinople (later Istanbul). Thus, at the age of 33, Terzaghi began his 10-year sojourn in Turkey during which the subject of soil mechanics was conceived and born.

In his spare time he began a systematic digest of all German, French, and English literature on earthwork and foundation engineering for the period 1860-1917, resorting chiefly to libraries in Vienna during visits to that city. As a result of this effort and of his experience in the United States, he concluded that there was no hope of condensing empirical knowledge into a useful system without methods describing clearly and measuring quantitatively the engineering properties of the vast spectrum of soils. Because such methods did not exist, he concluded that it was a hopeless task to find any relationships between the records of the subsoil conditions and the performance of the structures. Once this conclusion was clearly established in his mind, he wasted no more time on trying to find the key by studying available empirical knowledge. Instead he began a systematic experimentation with soils, starting with sands. Using cigar boxes and odds and ends, and with borrowed measuring devices, he built an apparatus with which he quickly obtained significant results on earth pressure.

At the end of the First World War, members of the teaching staff from the defeated nations were dismissed. Terzaghi accepted a lectureship at the American Robert College, Istanbul, which he had visited from time to time. Despite a heavy teaching load (chiefiy thermodynamics and mechanical engineering subjects) he immediately began to establish a soils laboratory. Many parts for building his apparatus he salvaged from the college dump. Lacking funds for a precision extensometer, he invented one based on the spacing of Newtonian rings that form when water is trapped between glass plates. Sources for clay he found along the Bosporus. Night after night he worked with his primitive equipment and thus discovered the mechanism of consolidation of clay and other important principles which form the basis of modern soil mechanics. In 1923 he published the fundamental differential equation for the consolidation processes which also established the mathematical analogy with heat transfer. Although this Paper received little attention, it represented a milestone which he reached at the halfway mark of his life. In his own words: "The results of my efforts exceeded my expectations". From then on he saw clearly the outlines of his future mission in life, which he pursued with remarkable consistency for forty years until his death.

In 1924 he read a Paper on his theory of consolidation of clays (for which he also used the name theory of hydrodynamic stresses) at the First International Conference on Applied Mechanics in Delft, Holland. The audience responded enthusiastically, and "after the meeting Forchheimer shook Terzagbi's hand and said to him: "This was the day of your birth into the scientific world". The following year his first major book appeared in print, a classic in soil mechanics literature, entitled " Erdbaumechanik auf bodenphysikalischer Grundlage". The publication of this book (in 1925) is now generally considered to be the birth of Soil Mechanics. It attracted the attention of John R. Freeman of Rhode Island, a well-known specialist in hydraulics who was then engaged in disseminating knowledge of European hydraulic laboratories in the United States. Mr. Freeman suggested to the late Professor Charles M. Spofford, then the head of the civil engineering department at the Massachusetts Institute of Technology, that he should invite Terzaghi as visiting lecturer. Since at that time the large and continuing settlements of the new M.I. T. buildings had become a matter of concern, the ensuing invitation from M.I.T. was not motivated only by a desire to promote the teaching of this new subject.

Terzaghi arrived there in the autumn of 1925, to start his second period in the United States which ended in the autumn of 1929. It was the period of steepest ascent in his professional career and of vital importance for the acceptance of soil mechanics by the profession. In his small office at M.I.T. he immediately began to assemble equipment for soil testing; and there a few months later in May 1926 (when by luck I met him for the first time), he showed me with great pride a miniature consolidation apparatus that his machinist had just completed.

He explained to his young countryman how this miniature device would permit measurement of all consolidation properties of clays within one hour. Actually it soon became apparent that this device was of little use for testing clays; but it vas eminently successful in demonstrating that the phenomenon of the swelling of gels was essentially a physical phenomenon which was described accurately by his theory of consolidation and swelling of clays. He presented these results at the Colloid Symposium which was held at M.I.T. in the same year, 1926, and a few years later he was asked to contribute a chapter on this topic to volume 3 of "Colloid Chemistry".

During the summer of 1926 I worked for Terzaghi in Washington as a private assistant, and -starting in December of that year - as research assistant assigned to him under a cooperative agreement between the U .S. Bureau of Public Roads and M.I.T. Soon I was deeply involved in research, in addition to a variety of unexpected duties. With a minimum of guidance by him I had to find new ways to tackle the problems handed to me. When the results were unsatisfactory, more often than not the only comment I got was: "Find out why!" It was the method of learning to swim by being thrown into the water, and it worked well. Even my typing skill, with which I am writing these lines, I owe to Terzaghi who never typed a word himself. Since his typist at M.I.T. could not handle his German letters and manuscripts, one day he gave me a pile of handwritten material to type. "But, Professor, I don't know how to type." "Then learn !", was his simple reply; and I did.

There was a curious difference between the almost complete freedom which he allowed his staff and students in their research efforts, and the tight control he exercised on his consulting projects where he prescribed in great detail, in writing, the exploratory, testing, or observational programmes. His representative on a job was usually required to mail him weekly reports. In addition, Terzaghi made frequent visits to the site, to examine personally all new evidence and to keep in close contact with all developments.

Long working days usually ended late in the evening when I would accompany him across the Harvard Bridge to his home on Beacon Street. One of the topics of conversation on these walks was the unfavourable, even resentful, reaction to his theories and efforts. In a short time he had become a well-known but controversial personality among American civil engineers. Once he remarked that probably an entire new generation of civil engineers would have to grow up before soil mechanics would be generally accepted. Indeed, some of the concepts which Terzaghi introduced into civil engineering were so strange that at first they created widespread scepticism; and these ideas certainly did not sell themselves. They began to be accepted and to spread under their own momentum only after years of tireless efforts and almost missionary zeal with which he disseminated his knowledge by lecturing and writing in three languages and in many countries. He demonstrated the validity of these new concepts by their practical application in his consulting practice.

Perhaps I should give some examples of the unfavourable reactions that Terzaghi faced in those years. Many engineers were unable to comprehend how tensile stresses larger than one atmosphere could possibly develop in the pore-water. In the discussion after a lecture someone emphasized the "well-known fact that one cannot create more than one atmosphere tension in water". In his reply Terzaghi related how in medieval times in a remote part of Asia this method of torture was practised: The victim was tied and wrapped in a thick layer of plastic clay, then laid in the sun. As the clay dried, the victim was crushed by the capillary forces.

Some of Terzaghi's written replies were so salty that they were refused for publication; others appeared only after thorough "editorial changes."

In those days any foundation engineer who had doubts about the foundation conditions followed the rule: “In case of doubt drive piles". And if, in spite of the piles excessive settlements developed, it was concluded that the piles were overloaded and that more piles should have been used. Imagine the engineers' surprise when Terzaghi told them to omit the piles. In a city underlain by heavily overconsolidated clay, where all buildings were founded on piles driven part way into this clay stratum, he recommended the use of a mat without piles for a new and unusually heavy building. He was subjected to pressure from many sides that he should withdraw this recommendation. A prominent engineer with whom he was well acquainted, sincerely believed that Terzaghi was risking his reputation, and that this venture could end only in disaster. It was the only time when I observed Terzaghi disconcerted; he did not want to offend a professional friend for whom he had a high regard. But he remained true to himself and the design engineer for the owner had full confidence in Terzaghi. The building was constructed without piles and performed well, as Terzaghi had predicted.

As his reputation as a consultant grew, requests for his advice carne from many States. In addition, he sought out problems in Central America, because he wanted to get acquainted with tropical soils.

His two-semester course in soil mechanics at M.I.T. attracted many students, and it set a pattern for teaching of soil mechanics which was gradually adopted by other schools.

Invaluable as his period at M.I.T. was for his professional development, I doubt if at that time he considered making the United States his permanent borne. When a chair in civil engineering at the Technische Hochschule, Vienna, was offered to him, he was delighted about the prospect of returning to his borne country. Besides, this invitation represented an outstanding recognition of his achievements and professional stature. He suggested to me that I should take a half-year's leave and accompany him to Vienna for the purpose of organizing a soil mechanics laboratory and training his new assistants. We crossed the ocean together early in October 1929, and while Terzaghi went on to Russia where he had been invited to carry out an investigation of the foundations for the locks of the Don-Volga Canal, I proceeded with my assignment in Vienna.

He started teaching in Vienna in 1930. Soon his courses and research activities in his laboratory began to attract students and practising engineers from many countries, and his department became a renowned centre of soil mechanics. He was also much in demand as a lecturer and as a consultant on important projects all over Europe, North Africa, and in the Soviet Union. Wherever he went, he aroused such great interest that local engineering groups felt motivated to promote soil mechanics. In 1935, he was a guest lecturer for 3 months at the Technische Hochschule, Berlin.

Harvard invited Terzaghi as visiting lecturer for the 1936 spring semester. Immediately thereafter he served as President of the First International Conference on Soil Mechanics and Foundation Engineering which met in Pierce Hall. On that occasion the International Society of Soil Mechanics and Foundation Engineering was founded and Terzaghi was elected its first President, a position he continued to hold until the Fourth International Conference in 1957 in London.

In the spring of 1938, after Hitler occupied Austria, Terzaghi and his family settled temporarily in France which was convenient for his consulting activities. He and his wife considered settling permanently in the United States, and he informed me that he would be interested in a part-time teaching position which would leave him ample time for his other activities. I persuaded Dean Westergaard that he should invite Terzaghi as visiting lecturer, and during the autumn semester 1938/9 he taught Engineering Geology for the first time at the Harvard Graduate School of Engineering. During the spring of 1939 he fulfilled a promise to give a series of lectures at the Imperial College, London. Also, he presented the James Forrest Lecture at the Institution of Civil Engineers, the second non-British engineer (the first was Marconi) to be so honoured since 1890 when the lecture was endowed. His lectures in London helped greatly to stimulate of the rapid growth of soil mechanics in England.

At Harvard University Terzagbi found an intellectual atmosphere that was very much to his liking. He enjoyed his contacts with his colleagues in our faculty, to mention only those who have departed beíore him: Harold M. Westergaard, whom he had known in the late '20s in Washington, D.C., when both served as consultants to the Bureau of Public Roads; his countryman Richard von Mises; Lionel Marks; and Percy Bridgman in Physics. At his desk in his office on the third floor of Pierce Hall (which he occupied from 1938 until1960 when his physical condition forced him to work at home), he did more writing than in any other office he occupied: two major books, over 100 papers, and countless reports in connexion with his consulting activities. The Gordon McKay Líbrary, almost next door to his office, he found most convenient, and he appreciated the efficient service of the librarians, including their skill in procuring books from other libraries. He usually found sufficient help among my staff and students to satisfy his high standards. He learned to derive increasing enjoyment from teaching his courses. Although only on a quarter-time appointment, he added a second course, entitled “Applied Soil Mechanics," in which he adopted the case method, making liberal use of his consulting experiences. He continued his custom of presenting lectures at other universities and before professional societies in many of the countries where he was engaged on consulting work. He also accepted an assignment as visiting lecturer and research consultant on a more permanent basis at the University of Illinois, and later also at M.I.T.

In 1946 Harvard gave him the title, Professor of the Practice of Civil Engineering. He retired in 1956 with the title emeritus, but he continued to lecture in engineering geology for several additional years. His courses at Harvard, and his other activities which were centered in his office at Pierce Hall, has added greatly to the splendid reputation which civil engineering at Harvard enjoyed during that period.

His consulting activities spread into many parts of the globe. He was careful to select only assignments which promised to yield valuable information. The list of these projects includes important earth dams, stabilization of landslides, foundations for buildings and bridges, dry docks, waterfront problems, airports, highways, foundation problems in permafrost, a variety of special problems arising from construction difficulties or accidents, tunnels in hard rock and in soft ground, subways, and foundation problems with ore docks. In 1954 he was appointed chairman of the Board of Consultants for the proposed High Aswan Dam in Egypt. However, he resigned from this Board in 1959 when the Soviet Union took over the design and construction, and the design was changed from that developed under his guidance.

Terzaghi's accomplishments were the product of many outstanding personal characteristics. With his bold vision, brilliant analytical mind, and insatiable curiosity of the type that makes a great physicist, he combined a gift and love for patient and thorough observation of nature that is a prerequisite for a successful geologist. He had a most unusual capacity for mental activity, long hours of work never seemingly tiring him. This combined with an enviable power of concentration and a great skill to push aside demands on his time that interfered with his primary interests (yet in such a gracious manner that it hardly ever engendered ill feelings), accounts for the enormous volume of work he produced during his life. His splendid memory was a great asset in digesting and retaining a large volume of geological and other observational data which invariably accumulate prior to and during construction of any difficult earthwork or foundation project; and he had a capacity to recognize quickly the essentials in the maze of data.

With his highly developed literary talent, writing was for him an easy and pleasant task. When someone once sympathized with him, upon conclusion of a long-drawn-out and complicated investigation, that he "now faced the hardest task," namely writing a comprehensive report, he replied: Ah, but that is the best part!" The picture that is indelibly impressed upon my mind, because I saw it innumerable times, is Terzaghi sitting at his desk, writing steadily by the hour, with only occasional pauses in which he organized his thoughts and with the help of a good cigar replenished the consistency of the smoke screen that surrounded him. He also had an artistic talent for drawing. which he used to great advantage in preparing and lettering the many illustrations for his reports and publications.

Until late in life he was favoured by rugged health and physical stamina. Young geologists accustomed to field work could hardly keep up with his pace in the mountains when he was 70. Until past his 75th birthday he maintained a work and travel schedule that would have worn out much younger men.

He was endowed with a warm and resonant speaking voice which carried well into the farthest reaches of a large lecture hall. Until late in lile he would present lectures lasting well over an hour, without resorting to any notes. His lectures, oral discussions, and conversation were enlivened with a refreshing humour, and sometimes a biting wit. He could keep an audience fascinated even when describing tedious details. His magnetic personality and sparkling conversation quickly made him the centre of attention at any social affair.

As a young man one of his desires was to become an explorer. This desire was always latent. In his extensive travels he would often use the opportunity íor travel beyond the immediate scope of the project on which he was engaged: e.g. side trips into the jungles of Guatemala and Panama, the Mato Grosso of Brazil, the Maya ruins in Yucatan, and mountaineering in the Garibaldi Mountains oí British Columbia. Such excursions would also provide him with material which he used íor his much appreciated non-professional talks illustrated with his own colour slides.

Essential for his great success as a consulting engineer were other personal qualities, particularly his readiness to assume responsibility, his authority, his courage to pioneer with novel solutions, and a remarkable ability to diagnose hidden causes and relationships. The latter was based not only on his excellent judgement and intuition, but also on a careful analysis of every bit of information. Often seemingly unimportant details gave him vital clues which he then pursued further by preparing a well-considered programme for additional explorations or observations.

In the biography in the anniversary volume, I briefly described his most significant contributions up to his 75th birthday. During the last 5 years of his life he was concerned particularly with the following three groups of topics which are reflected in his recent publications:

(1) The first group deals with a detailed description of the soil mechanics problems and their solution in connexion with important earth dam projects on which he served as principal consultant. These Papers document his belief that most of the existing gaps in soil mechanics, as well as in rock mechanics, can be closed only on the basis of patient and thorough field investigations and observations, rather than by theoretical or laboratory research.

(2) The second group contains Papers concerned with "soil mechanics in action". In his extensive experience with the application of soil mechanics, Terzaghi had ample opportunity to observe the many pitfalls which face a soil mechanics consultant; the most common one lies in the fact that he is not given opportunity to check his design assumptions by observing first-hand the soil conditions as they are being exposed during construction. He emphasized that a consultant “will find himself in the forefront oí scapegoats ...," even if the designers have completely ignored his recommendations. Another cause for trouble is reliance on soil mechanics theory without adequate practical experience. Terzaghi acquired his aversion to theory uncontaminated by practical experience early in his career. I recall his prediction made in the late '20s, that the worst enemies of soil mechanics would not be those who were at that time trying to deny the validity of its basic principles, because those men would die out; but that the worst harm would be done when pure theoreticians discovered soil mechanics, because the efforts of such men could undermine its very purpose.

(3) The third group of Papers is concerned with rock mechanics. (Readers of Géotechnique are familiar with Terzaghi's recent papers on this topic.) To visitors in recent years, he expressed concern that too much attention to theory and too little attention to reality based on field observations, might also seriously retard the development of rock mechanics.

Thus, in the last years of his life, Terzaghi used his energy and vision trying to protect the young generation of soils engineers from pitfalls and to guide them wisely. He certainly did not try, as some believe, to discourage them from the use of theory or from efforts to expand our theoretical tools, and he certainly did not try to discourage the young engineer from practising, as some have interpreted his views. He who created soil mechanics and retained undisputed leadership in this field to the end of his life was trying to share his wisdom with those willing to listen.

Terzaghi's eminent achievements were reflected by nine honorary doctors degrees (Trinity College, Dublin, 1949; Turkish Technical University, Istanbul, 1950; National Universityoí Mexico, 1951; Eidgen. Politechnische Hochschule, Zürich, 1953; Lehigh University, 1954; Technical University oí West Berlin, 1958; Norges Tekniske Hogskole. Trondheim, 1960; Technische Hochschule in Graz, Austria, 1962; Ohio States University, 1963), and by many awards and prizes from engineering and scientific societies. He was the only man to receive the Norman Medal four times, the highest award of the American Society of Civil Engineers -in 1930, 1943, 1946, and 1955. He was also awarded honorary membership by the American Society of Civil Engineers, as well as by other professional societies in many countries. In 1960 A.S.C.E. announced the creation of the Karl Terzaghi Award and Lectureship, with an initial fund of over $20,000 contributed by members of the Society; a memorial truly worthy of this great man.  In appreciation of Terzaghi's international activities, this Award will also be presented from time to time to engineers from other countries who are not members of A.S.C.E., just as Terzaghi was the first non-member of the Institution of Civil Engineers to be invited to give the James Forrest Lecture. He deeply appreciated all the honours and he enjoyed the great number of messages from all over the world which he received on his 80th birthday. But to him the greatest satisfaction of all was to be able to experience the full and enthusiastic measure of professional recognition which soil mechanics achieved during his life time.

This biographical memoir would not be complete without mentioning the vital contributions to his life and work by his second wife, the former Ruth Doggett whom he met in 1928 while she was engaged in research for her doctorate at the Harvard Faculty of Arts and Sciences. They were married in 1930 after she received her doctor's degree. In Ruth (who has survived him) he found a charming and gifted wife who provided him with a happy family life, and who not only shared his interest in geology but became a highly competent associate in his work, which included teaching his courses. Their son, Eric, is engaged in doctoral research in molecular biology at the University of Oregon. Their daughter, Margaret, is a senior at Boston University, in a premedical programme. Since Terzaghi's serious operation late in 1960, and his subsequent loss of a leg, it was not only his iron willpower, but the remarkable qualities of his wife, and the undiminished cheerfulness with which she accepted the additional heavy burdens, that made it possible for him to continue his work effectively. The invaluable contributions which he produced during that period were in no small measure due to the strength of her own spirit with which she sustained him, particularly during the last few months when he suffered increasing physical pain.

The cruelties with which fate tested him toward the end of his life succeeded in creating a frame in which the strength of his spirit and the clarity of his thoughts stood out with such brilliance that every time I visited him I was deeply moved with admiration. And when we talked by telephone, his voice still sounded so strong and beautiful that I would forget how his fraíl body suffered, barely clinging to life.

As I review the pattern of Terzaghi's life, I find it is similar to that of many great men who left a mark on their century, including Goethe who described it in symbolic terms in his drama, Faust. As a young man Terzaghi passed through a turbulent and rather unhappy period, often tormented by the question concerning the meaning of life. Spells of dissipation alternated with remorse and despondency. This period is pathetically reflected by the contents of his unpublished essays that he wrote in those years, and his diaries. After completion of his university studies, he enjoyed his first assignments in civil engineering which he frequently combined with geological investigations. But restlessly he kept looking for more challenging tasks. Then he found himself confronted with an enormous gap in engineering science that challenged his imagination. His first efforts to explore this uncharted area consisted of years of travel and literature search, all ending apparently in failure. Unknown to him those efforts formed a necessary preliminary approach to the discovery of the right path. Then there were 6 years of strenuous pioneer work and personal sacrifices during which he developed the principals of modern soil mechanics. When he reached the half-way mark of his life, at the age of 40, he realized that he had succeeded. His frequent inner conflicts were eliminated, and the second half of his life burst forth in prodigious activity. He maintained an amazing productivity until the last days of his life. Thanks to his genius, his energy and tireless eftorts, soil mechanics today forms a vital part of every civil engineering curriculum, and no important foundation or earthwork project is designed without making substantial use of the science he created.

To identify the principal driving force in his life, let Terzaghi speak for himself. This is what he wrote in the introductory paragraph of an incomplete autobiographical sketch which carne to my attention after his death (translated from German) : When I compare the importance of the various driving forces that have controlled my inner development, a passionate dislike of any lack of clarity in my thinking overshadows all the others. The satisfaction which I have derived from a clear, orderly perception of relationships has always been so great that I valued material success only as a means of preserving my independence and my freedom to act in accordance with my own inner needs. The erratic and frequent changes which have characterized my life are rooted in this attitude. Before I recognized my mission an oppressive sense of dissatisfaction drove me from one extreme to another, and I never hesitated to abandon a field of activity if another environment promised broader stimulation and greater opportunities for growth".

I consider it fitting to close this memoir by quoting in Terzaghi's own words something about his philosophy of life that he had gradually acquired. In 1956, in a letter to his son Eric he wrote this about the meaning of life, a question which had troubled him so much as a young man: "The meaning of life is life itself. However, there is no short cut to realizing this fact, and if you have inherited some of my disposition, you will have a long road to travel. But don't worry. Sooner or later you will see the light -your light- and from then on sailing will be smoother". From his after-dinner speech to a small circle of friends on his 75th birthday, I quote: "Our achievements are -or should be- the result of a natural process of sprouting, growing, and maturing in accordance with a predestined pattern. The meaning of the pattern, and the function of our existence in the resplendent and awesome world into which we were born are far beyond the microscopic range of our comprehension. The best we can do is to live and act in tune  with our pattern and without wasting our time trying to answer unanswerable questions."