Review of Modern Conceptions Concerning Foundation Engineering (Terzaghi, 1925)
By Michael Bennett, P.E. , M.ASCE (A.G.E.S., Inc. – King of Prussia, PA)
“People spend their first 40 years trying to conquer the world,” an old saying goes, “and spend their next 40 realizing that the world won’t be conquered by their likes.” Like every aphorism, this one contains a kernel of wisdom, but remains open to debate. To some extent, its commentary on the hubris of youth and the wisdom of age rings true. Yet history is replete with stories of people who have accomplished their most impactful achievements in the second halves of their lives. A clear example is geotechnical pioneer Karl Terzaghi, whose life spanned from October 2, 1883, to October 25, 1963 – almost precisely eight decades (Goodman 1999).
Richard Goodman, Professor Emeritus of Geosystems Engineering at UC Berkeley, masterfully relates Terzaghi’s personal and professional development in his biography, Karl Terzaghi: The Engineer as Artist. Goodman’s well-researched narrative of Terzaghi’s life is so colorful and entertaining that it often beggars belief. Terzaghi grew up in the town of Graz, Austria-Hungary, and attended military boarding school. He next had an excellent, if not entirely sober, university career, and graduated in 1906 with a degree in mechanical engineering. Terzaghi then spent several years working for the Viennese contracting firm Adolf Baron Pittel and supervising construction projects across eastern Europe. During that span, Terzaghi drew upon his experiences with several of these projects to compose a manuscript on aspects of reinforced concrete design. Engineers at the time were just starting to understand the material behavior of reinforced concrete, and Terzaghi successfully parlayed his write-up into a doctorate early in 1912 (Goodman 1999, Gromicko and Shepard 2011).
In his spare time, Terzaghi nurtured his passion for geology, most notably when he took an extended sojourn through the United States from early 1912 to late 1913. Terzaghi spent his American adventure exploring the country’s geologic wonders, toiling with contracting crews through long and hazardous shifts of rock-blasting work, and even consulting the latest in US engineering literature at the library of the American Society of Civil Engineers in New York City. Terzaghi hoped to use these experiences to help bridge the yawning chasm between engineering and geology which he had seen firsthand on both sides of the Atlantic. Foundation failures were all too common at the time; as Terzaghi later noted, “for every recorded instance of flagrant contradiction between what [foundation] engineers anticipated and what they experienced afterwards, ten others could be named which were hushed up.” Alas, Terzaghi concluded only that, until then, subsurface conditions had been described almost exclusively in qualitative, broad-brush geologic terms. As he returned to Europe, Terzaghi still could not decipher how to turn these descriptions into quantitative, strictly defined engineering properties. He had to put his conundrum on hold shortly after his arrival home, though, when World War I broke out in the summer of 1914. In short order, Terzaghi found himself mustered into the Austro-Hungarian Army, commissioned as a lieutenant, and stationed first on the Eastern Front and then at an airfield (Terzaghi 1944, Goodman 1999).
Fortunately for posterity, Austria-Hungary eventually decided to better utilize Lt. Terzaghi’s technical expertise. In 1916, the Army reassigned him to bolster ties with a fellow Central Power, the Ottoman Empire, by teaching civil engineering in the Ottoman capital of Constantinople at the Royal Ottoman College. Terzaghi took advantage of his new duties to revisit his quest to frame soil and geological conditions in engineering terms. He began by reviewing everything he could find from 1850 onward in English, German, or French on the engineering behavior of soils and foundations. Terzaghi soon established that almost all the works he reviewed on the topic, which he termed soil mechanics, took one of two approaches. Some authors, such as university professors like William Rankine, had examined problems of soil mechanics using solutions derived entirely through mathematical theory. Others, who had adopted outlooks more like those of Terzaghi’s former colleagues at Pittel, had relied entirely upon field experience to reach judgments about soil mechanics. Works in both camps were redolent of what Terzaghi later called “the time-honored antagonism between theory and practice” (Goodman 1999, Terzaghi 1936).
Initially, Terzaghi felt disheartened that he had turned up little technical information of value in his review. Upon reflecting, however, Terzaghi saw that the feuding theory- and practice-driven camps working on problems of soil mechanics had a common basis for their mutual antipathy – limitations on their respective views. In his view, the former group failed to recognize that extant “dogmatic theory” on soil mechanics was insufficiently grounded in a sound understanding of field conditions. Similarly, Terzaghi felt that the latter group overlooked how relying purely on “inadequate experience” did not permit a complete understanding of the material behavior of soil; “theory,” he noted a few years later, “is the language by means of which lessons of experience can be clearly expressed.” Terzaghi decided that the two perspectives, while not without merit on their own, were most powerful when combined. Soil mechanics, he realized, would be most effective if civil engineers used field data and well-grounded theories to generate rational, quantifiable designs which they could then check and, as needed, revise based on observations during construction. Terzaghi concluded that bringing this vision to fruition would first require performing an extensive program of laboratory testing to develop such theories (Goodman 1999, Terzaghi 1936).
Before he could even begin his research, he had to build equipment for it using both purchased items, such as a vintage balance, and scavenged materials, such as cigar boxes and kitchenware.
Terzaghi spent the next seven-plus years in Constantinople making his dream a reality. Before he could even begin his research, he had to build equipment for it using both purchased items, such as a vintage balance, and scavenged materials, such as cigar boxes and kitchenware. Following this laborious process, Terzaghi got to work on his experiments. He first explored the behavior of sands by examining their at-rest, active, and passive lateral earth pressures, as well as their internal erosion, or piping, by subsurface water flows. Terzaghi then turned his attention to clays by describing the process of consolidation and – in early October 1923, exactly 100 years ago – formulating it based on an analogous equation in thermodynamics. In turn, his work on clay proved critical as he developed and articulated the principle of effective stress. Terzaghi’s pioneering work played out against a background of political tumult in Turkey, as the end of World War I in 1918 brought about the collapse of both the Ottoman and Austro-Hungarian Empires. Yet he quickly found new employment at Robert College, now Boğaziçi University, and continued his work in Constantinople. Terzaghi summarized his blockbuster geotechnical breakthroughs in a book he wrote in German, Erdbaumechanik auf Bodenphysikalischer Grundlage, which translates roughly as Earthwork Mechanics Based on Soil Physics. He sent the manuscript to his publishing house in the spring of 1924, just months after turning 40 (Goodman 1999).
News of Terzaghi’s findings steadily spread as practicing civil engineers realized how valuable his work could prove to the profession. Engineering organizations began inviting him to share his conclusions from progressively larger platforms. Terzaghi published his first article on his work in 1919 in an Austrian technical journal, and the US magazine Engineering News-Record a year later. The steady drip of opportunities coming his way became a torrent once Erdbaumechanik went to press early in 1925. The book soon began receiving enthusiastically positive reviews from prominent civil engineers across Europe and the US. An editor at ENR asked Terzaghi to write a series of additional articles on the main points of Erdbaumechanik for an English-speaking audience. He readily accepted, and the series appeared in the American magazine that autumn (Goodman 1999).
By the fall of 1925, Terzaghi himself had also returned to the USA. No longer was he the highly educated vagabond who had quietly toured the nation a dozen years earlier. Now, Terzaghi had achieved wide renown as the triumphant pioneer of a new field in civil engineering. He had also accepted an invitation from Dr. Charles Spofford, the Chairman of the Department of Civil and Sanitary Engineering at the Massachusetts Institute of Technology, to teach and research at MIT for a year. Once Terzaghi found his bearings in Cambridge, the prestigious Boston Society of Civil Engineers added another honor to his lengthening list by inviting him to speak at a BSCE meeting. Thus, on Wednesday, November 18th, Karl Terzaghi – his first name anglicized to “Charles” – stepped up to a lectern before the BSCE to address its members on his work. Clearly, 1925 was turning out to be quite a wonderful year, or annus mirabilis in Latin, for Terzaghi and the nascent field of soil mechanics. In fairness, he was not alone in his good fortunes in greater Boston that year, or even that week. Two days later, on Friday, November 20th, banker Joseph Kennedy and his wife, Rose, welcomed their seventh baby, a star-crossed boy named Robert Francis (BSCE 1940, Goodman 1999, JFKPLM 2023).
Terzaghi began his remarks that evening by contrasting the increasing accuracy and sophistication of structural engineering over the previous one hundred years with the limited advances which had, prior to his work, taken place in soil mechanics during the same period. He declared that this needed to be fixed “by careful study of all those physical factors which cause the difference between the soils the engineer has to deal with and the ideal material invented by the authors of our classical earth-pressure theories.” Terzaghi noted that the theories of Coulomb and Rankine could not accurately describe the behavior of fine-grained soils because they failed to account for influences such as forces between both soil molecules and their adsorbed water molecules. (He omitted the theory of equivalent fluid pressures, which was well-known to civil engineers by 1925; perhaps he deemed it not established rigorously enough for his liking.) Terzaghi then briefly discussed flocculent and dispersed clay structures and noted how much a soil’s properties depended on its confining pressure (Terzaghi 1925).
Terzaghi then rolled out one of the crown jewels of his research for his audience by reviewing the flow of water through a soil. He noted that this could only occur if an external pressure were applied to the soil, producing a hydraulic gradient within it. Terzaghi then carefully explained how the settlement of a soil under loading depended on the flow of water through it, which in turn depended on its grain size distribution. He noted that this settlement occurred rapidly in coarse-grained, free-draining soils such as sands but could occur only far more slowly in fine-grained, poorly draining soils such as clays. Terzaghi then introduced a governing equation to explain the flow of water through loaded soils of any grain size. Nearly a century later, his review of the theory of consolidation still stands as a simple yet elegant explanation of one of the most fundamental of all geotechnical principles. To be sure, people employed in almost every field will likely find it powerful to read one of the first articulations of a core tenet in their field. Given the relatively recent nature of Terzaghi’s address to the BSCE, though – plenty of geotechnical practitioners either know or have known people who were alive in 1925 – reading this passage from the speech might leave even the most experienced geo-professional momentarily speechless (Terzaghi 1925).
Next, Terzaghi moved onto a discussion of how to assess the capacity of driven piles. “For more than a century[,] desperate efforts have been displayed to derive a pile-driving formula,” he explained; “judging from the intensity of these mental efforts one could believe that such a formula represents the Philosopher’s Stone.” Terzaghi then elaborated on his sarcastic reference to the mythical rock, which Renaissance alchemists believed could turn base metals into silver or gold, by comparing the results of pile loading and extraction tests to pile load capacities predicted by dynamic formulas. He observed that results from static load tests in the field, unlike pile formulas, suggested a linear increase in pile capacity with increasing length. Terzaghi also pointed out that the dynamic driving resistance of piles was not necessarily equivalent to their static bearing capacity, meaning that “no pile-driving formula of universal validity [could] possibly be obtained.” A century later, systems such as Pile Driving Analyzer, used in conjunction with programs such as CAPWAP and GRLWEAP, represent a rapid, reliable, and affordable method for predicting pile capacity. However, the myth of accurate pile dynamic formulas persists, and occasionally their use must still be discouraged (Terzaghi 1925).
Finally, Terzaghi discussed the foundations of weirs on permeable ground. This time, he coupled his equations for describing the flow of water through porous media with a graphical representation of the phenomenon. This illustrative technique, now known as the flow net, had been developed by Terzaghi’s former professor, Philipp Forchheimer, and remains widely used in modern geotechnical practice. Terzaghi supplemented these established contributions with a discussion of his research on hydrodynamic forces beneath embankments, internal erosion/piping, and preventative filters for dams. Having traversed considerable ground in his lecture, Terzaghi then opened the floor for discussion (Terzaghi 1925).
The five attendees whose observations on Terzaghi’s lecture that evening have been preserved were all titans of US civil engineering in the early 20th century. Dr. Spofford led off by briefly providing background on how Terzaghi had joined the MIT community. The next commenter was Lazarus White, president of the New York City foundation engineering firm Spencer, White and Prentis. Terzaghi had met and befriended White, who had also co-authored a 1917 book on underpinning foundations, shortly after arriving in the US. White, to Terzaghi’s amusement, had remarked – tongue firmly in cheek – that Spencer, White, and Prentis ought to buy every copy of Erdbaumechanik and dump them all into the Hudson River to avoid telling the competition too much! White was earnest, though, when he declared after Terzaghi’s BSCE address that “this lecture appealed to me so much that I think if a second one were to be given in Constantinople I should go there to hear it.” White noted that Terzaghi, through his address and his ENR articles (then in print), was helping make sense of “results we [foundation engineers] have seen and have not been able to explain.” White also showed the audience several film slides to illustrate how Terzaghi’s theories matched field observations made by engineers with Spencer, White and Prentis (Goodman 1999, Terzaghi 1925).
White was followed by Allen Hazen, who had created the coefficient of uniformity, Cu, for grain size distributions of soils and had been among the first to attempt to correlate soil grain size and permeability. Hazen remarked that several rules of thumb which he had developed from working on various hydraulic fill dam projects matched up well to the principles of soil mechanics as articulated that evening and praised Terzaghi for his efforts. The next speaker, Manhattan consulting engineer George Paaswell, was similarly laudatory in his comments. Paaswell, one of the earliest and most vocal American champions of Erdbaumechanik, had written a 1920 book on designing retaining walls, and – perhaps more importantly to Terzaghi – had helped him find whiskey upon arriving in the US to circumvent the onerous burden of Prohibition. Paaswell also cautioned Terzaghi, though, that his work on soil mechanics would be most fruitful and manageable once additional civil engineers joined him in shouldering the load. Paaswell’s sentiments were seconded by the final commenter, Frederic Fay, who was a partner with Dr. Spofford in the prominent Boston civil engineering firm of Fay, Spofford, and Thorndike. Fay elaborated on Paaswell’s suggestion by proposing that Terzaghi outline a program for gathering data on, and performing research in, soil mechanics (Terzaghi 1925).
Author’s Note: No image of George Paaswell could readily be procured.
Terzaghi wrapped up the meeting with an enlightening closing discussion. He started by thanking the commenters, especially Lazarus White. Terzaghi then devoted most of his concluding remarks to addressing Frederic Fay’s question regarding next steps for the foundation engineering profession. He recommended, given the scarcity of literature in English at the time, that anglophone practitioners in the field focus instead on collecting field data, just as White had, on various topics in soil mechanics. The construction of pile foundations was among the data collection topics about which Terzaghi spoke at the greatest length. Per his meticulous, practical nature, Terzaghi suggested that the audience members and their subordinates keep careful records on each pile driven, such as hammer size, pile dimensions, and penetration per blow. Nearly a century later, engineers inspecting the driving of piles continue to diligently record all these details (Terzaghi 1925).
Terzaghi’s BSCE audience so appreciated his presentation that, for his efforts, they conferred on him their Clemens Herschel Award in 1926. The BSCE – which later became the BSCE Section of ASCE – awards the prize, usually on an annual basis, to authors of “papers which have been particularly useful and commendable.” In 1940, the BSCE honored Terzaghi’s landmark address once more by including it in a commemorative volume of the most important early works the group had published on soil mechanics. By then, Terzaghi – now a lecturer at Harvard, a husband to Dr. Ruth Doggett (herself a geologist), and a father – was well-established on the Boston civil engineering scene, and he remained involved with the BSCE for decades. In fact, over the decade following the commemorative publication, the Terzaghi household was graced with two more Herschel Awards. In 1943, the group again recognized Karl Terzaghi with the Award for his paper on shield tunneling work for the Chicago subway system. Then, in 1950, Ruth Terzaghi completed the family hat trick when the BSCE bestowed the honor on her for her study of the corrosive effects of carbonic acid on concrete (BSCE 1940, BSCES 2023, Goodman 1999, Hives and Wodarczak 2020, Peck 1993).
Karl Terzaghi’s three major professional achievements in 1925 – the publication of Erdbaumechanik, the appearance of his series of ENR articles, and his address to the BSCE – truly mark that year as the debut of modern geotechnical engineering. Collectively, his accomplishments represented the culmination of years of hard work and careful study. As Terzaghi loosed his ideas upon the world of civil engineering that year, he broke the deadlock between the theory- and practice-driven approaches to problems of soil mechanics and foundations by combining the strengths of each method. In doing so, Terzaghi reached the vast, untapped seam of subsurface engineering knowledge that geo-professionals have been mining ever since. From the 1920s until his passing in 1963, he would continue illuminating ever-broader swaths of the geotechnical field. Thus, in 1925, Terzaghi – who turned 42 that October – was also about to turn the old aphorism about the two 40-year sections of a person’s life on its head. He had spent his first 40 years in search of a new world to conquer, and he would spend his remaining 40 years conquering much of it (Goodman 1999).
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CAAF (Century Association Archives Foundation). 2023. “Allen Hazen, civil engineer.” CAAF. Accessed Oct. 1, 2023. https://centuryarchives.org/caba/bio.php?PersonID=1335
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Gromicko, N., and K. Shepard. 2011. “The history of concrete.” International Association of Certified Home Inspectors. Accessed Oct. 1, 2023. https://www.nachi.org/history-of-concrete.htm
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Terzaghi, K. 1925. “Modern conceptions concerning foundation engineering (with Discussion and Closure).” J. Boston Soc. Civ. Eng., 12 (10), 397-439. Reprinted in BSCE (1940), 1-43.
. 1936. “Presidential address: Relationship between soil mechanics and foundation engineering.” In Proc., Int. Conf. Soil Mech. Found. Eng., Cambridge, MA, USA: ISSMFE, Vol. 1, 13-18.
. 1944. “Ends and means in soil mechanics.” Eng. J., 27, 608-615.
The author’s colleague, Sebastian Lobo-Guerrero, PhD, PE, BC.GE, M.ASCE (A.G.E.S., Inc. – Canonsburg, PA), reviewed the technical content of the entry. The author’s Virginia Tech classmate, Thomas Kennedy (Geopier –Davidson, NC), co-wrote a previous version of this entry posted on an independent webpage in 2021.