Review of Foundations, abutments and footings (Hool and Kinne, Eds., 1923), Section 4:
Spread footings, featuring the Tunkhannock Viaduct as a case study

By Michael Bennett, P.E., M.ASCE (Gannett Fleming TranSystems: Audubon, PA)

 

US railroads truly brought the nation into the modern age. The completion of the Transcontinental Railroad in 1869 heralded a boom in railroad construction, and new tracks crept across the nation like vines over the ensuing decades. Four other routes from the Mississippi River to the Pacific Ocean joined the original by 1900, and these lines connected with a much denser network of eastern railroads to unite the nation’s producers and consumers. Railroads also helped nurture the Industrial Revolution, as the legs of the “iron triangle” of coal, steel, and railroads reinforced each other’s growth and that of related industries. Collectively, the rail boom fueled the US’s transformation into an economic and international superpower.  By 1916, the country boasted over 250,000 miles of trackage, enough to reach the Moon – and still construct four tracks from New York to San Francisco (AAR 2024).

As railroads created the modern US, their employees helped create modern civil engineering. Yet their innovations were as unevenly distributed across the profession as their employers’ tracks were across the country. Structural engineering was fairly well-covered. The Cooper E-load series for railroad bridge design, which debuted in the Transactions of ASCE in 1894, was among the first universal design codes in American civil engineering practice and remains in use today. By contrast, early geotechnical studies from US railroad civil engineers were more scattershot and consisted mainly of case histories of tunnels, landslides, and bridges. Civil engineers elsewhere took different approaches. From 1914 to 1922, the Geotechnical Commission of the Swedish State Railways performed the first in-depth geotechnical study (and coined the term “geotechnical”) following a series of lethal slide-induced derailments. In the US, though, geotechnical questions in civil engineering generally received less methodical consideration than structural ones, and railroads were no exception (SJGK 1922).

 

 

 

Section 4 of Foundations, abutments and footings, which covered spread footings, plainly reflected the gap in US civil engineering in 1923 between increasingly sophisticated structural analyses and geotechnical designs that were still primitive. The listed author of the section was Albert Wolf, cited as president of the civil engineering and architectural firm of Wolf, Sexton, Harper, and Treaux; however, he had died in 1921. Plenty of books have been published posthumously, so it remains unclear whether Wolf himself authored Section 4 or whether editors George Hool and William Kinne compiled it from his previous writings. In any event, Wolf was ably qualified for the assignment. He had studied civil engineering at universities in Strasbourg and Berlin before returning home to the US, where he had practiced for over 30 years (Hool and Kinne 1923, Marquis 1917, Marquis 1926).

Wolf included some geotechnical material in Section 4. At one point, he noted that a soil’s bearing capacity can be increased by improving its drainage. This insight makes sense a century later when viewed through the lens of pore pressures, effective stresses, and shear strengths. Wolf also observed that “any table of bearing values for various soils should be used with a great deal of discretion and modified to correspond with what experience has taught to be safe,” showing an awareness not all civil engineers then shared (see entry for Section 1). Later, Wolf wrote that “plain concrete footings should be used” for structures founded on bedrock “rather than reinforced concrete since owing to the unyielding character of the foundation the reinforced concrete footing could not act as designed.” Clearly, he recognized that structural and geotechnical considerations were interdependent (Wolf 1923).

Despite Wolf’s (or the editors’) awareness on these counts, though, Section 4 consisted predominantly of structural calculations. Wolf used worked examples to show readers how to determine the loads on footings, proportion their areas and depths, size their rebars as needed, and check their shear and moment capacities. Some examples showcased recent key developments in structural engineering. Wolf discussed at length the research Arthur Talbot did on reinforced concrete footings at the University of Illinois in the early 1910s; the work demonstrated the need for clear cover of rebar and for considerations of its delamination. Other examples of Wolf’s illustrate what remained to be standardized in the field. The advent of universal LRFD-based structural codes has rendered moot his discussions on how multiplication or reduction factors for live loads varied across municipalities (Wolf 1923).

 

 

Current geo-professionals reading Section 4 may be most struck by its most fundamental assumption. Wolf grasped that structural engineering needed to include geotechnical considerations, but Section 4 also indicates that he and editors Hool and Kinne felt the growing intricacy of structural design was more than enough to compensate for any subsurface hiccups. This assumption was brave at best and risky at worst. Karl Terzaghi later estimated that every reported foundation failure in the early 1900s was accompanied by at least 10 unreported ones (see entry for Terzaghi (1925)). However, the perspective Wolf, Hool, and Kinne held predominated among civil engineers 100 years ago. Practitioners saw subsurface conditions as problems to be worked out during construction, not constraints to be incorporated into design. A case history Wolf had penned a few years earlier for a book on reinforced concrete construction, one also edited by George Hool, reflected this viewpoint even more clearly than Section 4. The case study was on one of the US’s biggest, boldest railroad civil engineering projects of the early 20th century – the Delaware, Lackawanna, and Western Railroad’s Tunkhannock Viaduct, 16 miles northwest of Scranton, Pennsylvania (Wolf 1916, Wolf 1923).

 

 

The Lackawanna Railroad, as everyone called it, was an industry powerhouse as the 20th century began. Founded in Scranton 50 years earlier, it had grown quickly as the region’s iron and anthracite coal deposits were rapidly developed after the Civil War. The Lackawanna and its civil engineers soon designed and built a line from Hoboken (and, by ferry, Manhattan) to Buffalo, connecting Atlantic Ocean ports with their Great Lakes counterparts, and heavy coal and steel traffic followed. Scranton became the heart of the Lackawanna system, serving as home to the railroad’s headquarters, locomotive shops, and a major freight yard. The Lackawanna also took advantage of its proximity to northeast Pennsylvania’s vast deposits of anthracite coal by having its engines built to burn it. Anthracite is harder and ignites at higher temperatures than the bituminous coal most railroads used to power their locomotives, but it also emits less soot in combustion. Beginning in the early 1900s, the Lackawanna touted its cleaner-burning fuel with ads featuring a character named Phoebe Snow. An archetypal Gibson girl, she waxed eloquent in clever poems about how spotless her white linens stayed aboard the “Road of Anthracite” (Flanagan 1984, Steamtown NHS).

 

 

Meanwhile, Phoebe’s corporate overlords puzzled over how to navigate an increasingly restrictive business environment. The Gilded Age had been good for railroads, if not for their employees and customers. The Lackawanna Railroad owned many of the mines from which it hauled anthracite coal, giving it a vertical monopoly on the commodity, and it was hardly unique in this regard. Like its peers, the Lackawanna also set its own rates for shipping freight, and chagrined companies had little choice but to pay these oft-exorbitant fees. In 1887, the US government had begun regulating rates for passenger and freight service to keep railroads from holding their clients over a barrel. The nation’s carriers could no longer reap the heady rewards of unbridled capitalism, and they had to change course to maintain profitability. William Truesdale, who became the Lackawanna’s president in 1899, decided to do so by undertaking massive infrastructural improvements (Flanagan 1984, Steamtown NHS).

 

 

Truesdale and his civil engineers soon kicked off three major projects. The first involved building the railroad a modern headquarters which would double as its Scranton train station. The structure was finished in 1908 at a cost of $500,000, or $16.8 million in 2024. Arriving travelers stepped into a two story-high marbled waiting room featuring a Tiffany glass ceiling and tiles depicting scenes along the Lackawanna’s Hoboken-Buffalo main line. The three floors (another was added later) above them housed the railroad’s finance, engineering, construction, legal, freight, and real estate departments. Next, the Lackawanna built the Slateford Cutoff, a 30-mile stretch of track across western New Jersey that shaved 12 miles off its main line. The cutoff featured additional tracks, long straightaways, easy curves, dramatic viaducts, and grade-separated crossings; it also used reinforced concrete extensively at a time when it was not yet in vogue for railroad construction. The Slateford Cutoff was completed in 1911 at a cost of $11 million, or $365 million in 2024 (Flanagan 1984, NAL 1976, Steamtown NHS, Webster 2024).

 

 

In the early 1910s, William Truesdale and his civil engineers buckled down to work on the third, and in many ways most daunting, of his planned major infrastructure projects. The Lackawanna’s main line between Clarks Summit, a few miles northwest of Scranton, and Hallstead, a hamlet on the Susquehanna River near the New York state line, dated back to the 1850s. Like most early railroads, it had been built economically to follow the surrounding terrain – in its case, Pennsylvania’s rugged Endless Mountains. Yet this section had scarcely been improved since then and now featured some of the steepest grades and sharpest curves on the entire Hoboken-Buffalo route. Truesdale and his civil engineering team determined that building a cutoff to Hallstead would be the most economical option for straightening and flattening this section of the Lackawanna’s main line (NAL 1976).

 

 The route Truesdale and his civil engineers selected for the Hallstead Cutoff would trim only 3.6 miles off the Hoboken-Buffalo trip, but it would save the Lackawanna Railroad far more than distance alone could indicate. The cutoff would feature a maximum grade 40 percent gentler than the existing route (0.68% versus 1.23%) and a maximum curve half as sharp (3.0° versus 6.4°). It would also feature six fewer circles worth of total curvature (1,570° versus 3,970°) than the extant Lackawanna route and would be 30 feet lower at Clarks Summit, easing the tough climb from Scranton into the Endless Mountains. Ultimately, the cutoff would save freight trains an hour between Scranton and Binghamton, New York, and would save passenger trains 20 minutes. The cutoff would be a formidable civil engineering challenge involving massive cuts, huge fills, and a 3,630-foot tunnel. Its linchpin, though, would be a mammoth viaduct over Tunkhannock Creek in the borough of Nicholson. A large fill with culverts might have been cheaper to build, but Lackawanna civil engineers chose a viaduct after observing the raging creek during a spring flood (ASCE 1914, ASCE 2024, NAL 1976).

 

 

Two Lackawanna designers – civil engineer Abraham Cohen, still in his 20s, and seasoned architect William Botsford – worked hand in glove to make the Tunkhannock Viaduct both beautiful and functional. They modeled their final design on the Pont du Gard aqueduct of the Roman Empire. It would be 2,375 feet long, have 12 arches, and soar 240 feet above the creek and 180 feet above the Lackawanna’s existing main line. (Tragically, after Botsford visited Europe in early 1912 to study historic architecture there, he attempted to return home – and perished – on the Titanic.) The viaduct would be a marvel of advanced structural design. Albert Wolf rightfully noted that “this bridge is indicative of the high state of development of the concrete designing practice of the D.L.&W. R.R. and in addition reflects great credit upon the status of concrete bridge design and construction in America” as he elaborated on its structural details. The viaduct’s geotechnical design also reflected the state of US practice, albeit in a less flattering light. Cohen and Botsford prudently decided to found the structure on bedrock, and the Lackawanna determined the depth to rock at the site using borings; its mining subsidiaries already used the practice to locate economical coal seams. Still, the designers left the question of how exactly footings would be excavated to bedrock for C.W. Simpson, the Lackawanna’s construction engineer for the viaduct, to figure out (Baker 2015, Simpson 1916, Wolf 1916).

 

 

 

Construction of the Hallstead Cutoff began in May 1912. The 200 skilled craftsmen and 300 laborers under C.W. Simpson’s command started work on the Tunkhannock Viaduct by building railroad sidings on the Lackawanna Railroad’s extant main line and constructing temporary narrow-gauge tracks around the site for moving construction supplies and excavated soil and rock. One of the first obstacles the Lackawanna faced was getting dynamite to the site for construction. The railroad, mindful of all the coal it carried, strictly forbade trains on its lines from hauling explosives. Instead, the dynamite had to travel through another railroad’s depot 11 miles away, from which horse-drawn wagons brought it to Nicholson. By July, the crews were ready to excavate the foundations of the bridge’s 11 piers (NAL 1976, NHA 2024, Wolf 1916).

 

 

Abraham Cohen had designed the Tunkhannock Viaduct to hold the heaviest steam locomotive of the day – the 300-ton Mallet – and loaded cars weighing 3 tons per foot on both its tracks. These massive loads translated into piers measuring 43.5 feet by 36.5 feet at their footings; those of the deepest piers were enlarged to 46 feet by 40 feet. Crews working for Flickwir & Bush, the Lackawanna’s contractor for the viaduct, started excavations for the pier footings by laying out steel sheet piling measuring 52 feet by 46 feet around each pier location. Once the sheet piles were partially driven using a steam hammer, excavation began. As it progressed, the sheet piling was gradually driven deeper; meanwhile, the excavated material was used to level the site for construction of work buildings and temporary tracks. When the piling at each pier had been driven to its full height of 30 feet, a second steel sheet pile cofferdam measuring 65 feet by 59 feet was driven around the first and the material between the cofferdams was excavated. Sheet pile driving and excavation then continued within the first cofferdam. Plentiful timber bracing was used to support the excavations as they progressed (Wolf 1916).

 

 

Bedrock at the Tunkhannock Viaduct site consists primarily of sandstone, siltstone, and shale and is usually a sound bearing stratum provided it is excavated to intact material and kept dry. The steam shovels and clamshell buckets used by Flickwir & Bush crews ensured that excavation proceeded to sound material; the crews carefully dug out the corners of the cofferdams by hand and, occasionally, broke up boulders with dynamite. Simultaneously, the pumps they deployed within the cofferdams largely kept their excavations dry. However, their luck ran out at Piers 4 and 5, where excavation was significantly affected by running sands. At Pier 4, which is next to Tunkhannock Creek, the issue was encountered 40 feet below grade and quickly grew so severe that the cofferdam shifted 15 inches, its timber bracing warped, and the surrounding ground settled as much as 10 feet. C.W. Simpson got his crews to swiftly and correctly reposition the cofferdam using jacks and additional excavation, but a new strategy for excavation to bedrock was clearly necessary. He hit upon the brilliantly simple idea of using timber sheet piling to divide the interior of the Pier 4 cofferdam into three sections and sequentially excavate each to sound bedrock and pour concrete into it. He also bolstered the dewatering system within the Pier 4 cofferdam so that up to 200,000 gallons of water per hour could be pumped from it. Simpson’s scheme worked, and construction of Pier 4 proceeded smoothly from there (Geyer and Wilshusen 1982, PaGEODE 2024, Wolf 1916).

 

 

 

The Pier 4 boondoggle gave Simpson and the Flickwir & Bush crews a better idea of what to expect as excavation progressed at Pier 5, just north of Pier 4, and subsurface conditions there were indeed similar. However, Simpson’s plan to reuse his timber sheet piling technique failed due to a key geotechnical detail. Northeast Pennsylvania was heavily glaciated during the last ice age, and the retreating glaciers left behind extensive boulder deposits. Flickwir & Bush crews attempting to drive timber sheet piles in the Pier 5 cofferdam roughly 75 feet below grade found that these boulders, which had not been problematic at Pier 4, were everywhere at Pier 5. The timber sheet piles were soon badly damaged by impacts on boulders, and excavation stalled while a change of plan was worked out. The troubles at Piers 4 and 5 were by then significantly delaying completion of the Tunkhannock Viaduct, and Lackawanna Railroad president Truesdale was no doubt deeply frustrated by the mounting construction expenses and profits lost due to the holdup. The Lackawanna hosted an ASCE excursion train tour of the Hallstead Cutoff in January 1914, but its civil engineers probably downplayed that the excavation issues were threatening to delay its planned completion date of July 1, 1915 (ASCE 1914, Simpson 1916, Wolf 1916).

 

 

 

At length, however, C.W. Simpson and Flickwir & Bush worked out a solution at Pier 5. Pneumatic caissons, or chambers filled with forced air in which excavation proceeds manually, were on their way out in construction by 1914 but represented one of the few viable alternatives left at the project team’s disposal. Furthermore, the threat of decompression sickness which had formerly plagued caisson workers had by then been effectively addressed using airlocks. Flickwir & Bush brought an airlock-equipped caisson to the Pier 5 site in December 1914 and promptly resumed excavation. The caisson steadily inched downward as its crew dug material out from beneath it, and laborers outside the caisson accelerated its descent by pouring concrete atop it. When the Pier 5 caisson reached sound bedrock in February 1915, Flickwir & Bush backfilled it with concrete, and Pier 5 swiftly began rising toward its comrades. From there, the structural construction of using steel falsework trusses to erect the Tunkhannock Viaduct’s 12 arches (two are buried within the viaduct’s approaches) and pouring the concrete arches using a cable system proceeded rapidly. Simpson had twice surmounted serious subsurface issues with his quick improvisation, but the geotechnical headaches he had been forced to tackle slowly and painfully stood in stark contrast to the neat efficiency with which structural work on the viaduct proceeded (NAL 1976, Simpson 1916, Wolf 1916).

 

 

The Tunkhannock Viaduct’s foundation problems were the main reason the Lackawanna Railroad and its contractors completed the Hallstead Cutoff 4 months behind schedule in November 1915. Still, the feat was nothing short of astounding. The project had cost $12 million, or $378 million in 2024. It had involved excavating 5.5 million cubic yards of soil and 7.6 million cubic yards of rock, and it had used 300,000 cubic yards of concrete and 2,360 tons of rebar. The Tunkhannock Viaduct alone had cost $1.4 million, or $44.1 million in 2024, and had used roughly half of the cutoff’s total concrete and rebar. Its 11 piers had required excavations ranging in depth from 60 to 103 feet, and bedrock at the deepest pier lay 309 feet below the double-tracked bridge deck. So exacting were the Lackawanna’s construction standards that each pier, some of which were over 200 feet high, was within a quarter inch of plumb. Sadly, some numbers from the project were far more sobering; 30 workers had died building the viaduct. Still, the fact remained that the Lackawanna had built the largest concrete bridge, if not structure, in the world (ASCE 1914, ASCE 2024, Baker 2015, NAL 1976, NHA 2024, Simpson 1916, Webster 2024, Wolf 1916).

 

The Lackawanna Railroad commemorated the Hallstead Cutoff with a grand opening ceremony for it on November 7, 1915. Fittingly, the ceremony was held at the Tunkhannock Viaduct. Dignitaries included the governor of Pennsylvania and a 50-year Lackawanna employee who had ridden one of the railroad’s first passenger trains in 1851. Predictably, the keynote speaker was William Truesdale, who vowed that his railroad would continue to strive for constant improvement in its infrastructure and service. With a shout of “All aboard!” from a Lackawanna conductor, the first passenger train then chugged across the viaduct to raucous cheering. It appeared that Phoebe Snow’s travels on the Road of Anthracite would be swifter and more pleasant for a long time to come (Baker 1915, Scranton Times 1915, Wolf 1916).

 

“Railroading is changing very rapidly,” Truesdale noted in his dedicatory remarks, “and no prophet who is wise will venture a prediction as to what the next development will be.” Unbeknownst to him, the next development was already there that day, as dozens of locals drove their automobiles to the opening ceremony. In hindsight, the Lackawanna Railroad’s completion of the viaduct marked high noon for US railroads as well as any event could. Further ambitious projects on the scale of the Hallstead Cutoff were initially shelved when the country entered World War I in 1917. (To save anthracite for the war effort, the US government ordered all railroads to burn bituminous coal during the conflict, prompting the Lackawanna to retire Phoebe Snow.) A short but painful recession followed the war, and the Supreme Court further curtailed railroad spending by forcing lines to divest their vertical monopolies, such as the Lackawanna’s coal companies. As the 1920s got roaring, the shift toward cars became even more noticeable. It was research for highway, not railroad, construction that led to many early advances in geotechnical engineering as the discipline came into its own at that time. The Great Depression and World War II temporarily halted further paradigm shifts in US transportation – rail passenger miles traveled hit its peak in 1944 – but the automotive age shifted into high gear as peacetime returned (Steamtown NHS).

 

During the 1950s, the economic tide turned harshly against American railroads. The US government invested its transportation resources in alternative modes of infrastructure, including airports, pipelines, canals such as the St. Lawrence Seaway, and – most notably – the interstate highway system. The cross-country freeway network was an undeniable positive but created a market distortion that subsidized the automobile, trucking, and oil industries and made it tough for railroads to compete. A 1959 geotechnical report for Interstate 81 near Scranton noted that its planned alignment extended across a bridge “over […] the Delaware, Lackawanna, and Western Railroad.” The symbolic, if inadvertent, juxtaposition of the interstate soaring high above the railroad track was powerful. Meanwhile, the federal regulatory structure designed to keep Gilded Age railroads from holding competitors and clients over a barrel now held those railroads over one by restricting their abilities to set competitive and goods-specific freight shipping rates and to discontinue money-losing passenger services. Consumers switched to the cheaper, more flexible alternatives of car travel and long-haul trucking, and American railroads’ retreat soon turned into a rout (AAR 2024, GFCC 1959, Steamtown NHS).

 

 

 

The Lackawanna Railroad struggled gamely to keep going. It replaced its anthracite-powered steam locomotives with diesel engines that were easier to run and maintain and, with an eye on nostalgia, even renamed its marquee passenger train the Phoebe Snow. (It was from this train that an aspiring musician took her stage name en route to pop stardom.) However, the triple blow of the rise of the interstates, extensive infrastructure damage from Hurricane Diane in 1955, and the precipitous postwar decline of the Pennsylvania anthracite industry meant that the Lackawanna’s strenuous efforts merely bought it time. Next, it followed many of its floundering US peers in merging with an old rival to try to stay afloat; in 1960, the Lackawanna threw in its lot with the Erie Railroad. The new company remained solvent for 12 more years, a respectable performance compared to how quickly most of the panicked, ill-advised rail mergers of the era tanked.  In the end, though, the Erie Lackawanna was done in by economic forces beyond its control. The Phoebe Snow left Scranton for the final time in 1966, and the immense track damage done by Hurricane Agnes in June 1972 pushed the Erie Lackawanna into bankruptcy (Holden 2011, STT 2022, Steamtown NHS).

 

 

 

By then, the US government was finally acting on the crisis gripping American railroads.  The 1970 failure of the Penn Central – another poorly planned merger, but this one between two of the country’s most powerful carriers – represented the largest bankruptcy in US history until then and spurred Washington to act. First, Congress nationalized passenger rail service by creating Amtrak; the move saved US railroads roughly $200 million annually, or $1.6 billion in 2024. Next, the government created Conrail to take over and consolidate the operations of bankrupt freight railroads in the northeast US, including the Erie Lackawanna. Finally, Washington passed bipartisan deregulation to modernize federal oversight of railroads, which helped stabilize the health of remaining US freight lines. Conrail soon began turning a profit and was privatized; it has since been purchased by its competitors. US passenger rail has also undergone a renaissance over the past decade. Amtrak now stands on the verge of turning its first profit and recently released a 15-year plan to extend service to destinations where passengers have not disembarked in decades, including Scranton. Regional lawmakers are currently securing funds for the infrastructural improvements necessary to bring passenger rail back to the city, which most Americans now know not from its industrial roots but from the sitcom The Office (AAR 2024, Schaffer 2024, Steamtown NHS).

 

Remnants of the Lackawanna Railroad still dot the landscape in and around Scranton. The Steamtown National Historic Site is housed in the line’s former downtown freight yard and ably tells the story of the US’s railroading heritage. Blocks away, the railroad’s former station and office building now serves as a hotel that combines its historic charms with modern travel conveniences. However, the clearest reminder of the Lackawanna stands in Nicholson, where several freight trains trundle over the Tunkhannock Viaduct every day. The throbbing diesel engines pulling double-stacked trailer containers still look miniscule atop the massive structure with its clear, if worn, marking (added decades after construction) of “LACKAWANNA RR.” The graceful behemoth is now a National Historic Civil Engineering Landmark and sits on the National Register of Historic Places, ensuring its preservation for future generations. Part of the structure’s historic significance in civil engineering arises from its being the world’s largest concrete bridge upon its completion; another comes from its construction, which reflected an era when the complexity of structural design far outpaced that of geotechnical design. However, its deeper historic significance in the profession may be how it reflects the brilliance of American railroads’ civil engineers. It was the ingenuity and innovation of people such as Abraham Cohen and C.W. Simpson that made possible structures such as the Tunkhannock Viaduct and rail routes such as the Road of Anthracite (Flanagan 1984, NHA 2024, Steamtown NHS).

 

 

Acknowledgments

Sebastian Lobo-Guerrero, Ph.D., P.E., BC.GE, F.ASCE (A.G.E.S., Inc.: Canonsburg, PA), the author’s former colleague, reviewed the entry’s geotechnical content. Thomas Kennedy (Geopier: Davidson, NC), the author’s Virginia Tech classmate, co-authored a 2021 version of the entry posted on an independent webpage.

 

 

References

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Anthracite Heritage Museum. Scranton, PA: Pennsylvania Historical & Museum Commission. Visited Apr. 14, 2024.

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