Review of Foundations, Abutments, and Footings (Hool and Kinne, Eds., 1923)
By Michael Bennett, P.E., M.ASCE (A.G.E.S., Inc., King of Prussia, PA)
Section 2: Excavation, featuring the Lincoln Memorial as a Case Study
The second section of the 1923 book Foundations, Abutments, and Footings covered topics in excavation. Its author, Allen McDaniel, was a leading authority on the topic. After earning his S.B. in Architectural Engineering from M.I.T. in 1901, McDaniel cut his professional teeth as a field engineer on the construction of the East River Tunnels in New York City, used today by the Long Island Railroad. He then spent the 1910s teaching civil engineering at several US universities, although he took a sabbatical during the World War (as it was then known) to serve as a civilian engineering consultant to the US Army. Finally, once peacetime returned, McDaniel became the civilian head of the Army’s Construction Division. There, he oversaw a portfolio of capital improvements across all 48 states, as well as the US territories of Hawaii, the Philippines, and the Panama Canal Zone, worth $100 million annually, or $1.8 billion in 2023 dollars. Somehow, he also found time throughout the decade to pen three books on excavation. By 1923, McDaniel had moved into a role on the Civilian Advisory Board of the US Department of War, which allowed the Army to continue tapping his expertise on excavation best practices while giving him more leeway to pursue independent consulting opportunities. Thus, McDaniel’s chapter within Foundations, Abutments, and Footings truly represented the apex of excavation practice in 1923 (Marquis 1922, Webster 2023).
McDaniel made his 60-page chapter both well-written and, for his time, comprehensive. He first reviewed methods for smaller-scale excavations, including hand tools and horse-drawn equipment. McDaniel next discussed methods for completing larger-scale earthwork projects. He devoted some space to excavators, or “shovels,” powered by electric and gasoline motors but focused primarily on the steam-powered machines which dominated the market in 1923. (Later, these would be immortalized in the classic children’s book Mike Mulligan and His Steam Shovel). McDaniel then turned his attention to manual and mechanized methods of rock excavation and blasting. Finally, he summarized techniques both of excavating underwater and of dewatering sands back on land (McDaniel 1923).
McDaniel’s chapter captures a bygone era in earthwork construction on which technological innovation was about to draw the curtain. To be sure, contractors back then had plenty of ingenuity. Indeed, McDaniel reviewed several clear examples of their creativity in completing projects requiring heavy excavation within constrained access, such as by mounting steam shovels on railroad flatcars and by pulling mammoth buckets along steel draglines. Over the following decades, though, the impacts of such ingenuity were far surpassed as monumental advances in mechanical and electrical engineering led to hugely improved construction equipment. Contractors soon realized that trucks, bulldozers, and excavators, among other machines, which ran on four-cylinder power could complete excavation and earthwork more efficiently, more quickly, and more cheaply than those running on four-legged power. The economic effects were dramatic. In 1914, American contractors finishing the Panama Canal spent about $24.25, adjusted for inflation, excavating one cubic yard of soil and rock. By contrast, excavation on a typical current project costs just $5 to $6.50 per cubic yard. Plenty of other fields were also transitioning from horse power to horsepower by 1923. The leaders and civil servants in the War Department headquarters in Washington, DC, who were translating Allen McDaniel’s excavation guidance into policies for the US Army had front-row seats to one such change. Most units in the District’s Fire Department had already switched to automotive fire engines by then, and the Department would retire its final active horses just two years later (Coduto et al. 2011, Kelly 2009, LOC 2023, Webster 2023).
The phasing out by the Washington, DC Fire Department of its horses epitomized the many ways in which the nation’s capital was modernizing in the Roaring Twenties. (Sadly, this trend was not universal, as evidenced by the District’s segregated schools, pools, and parks.) Another had arrived in 1922 when the Lincoln Memorial had opened after strenuous efforts of excavation, earthwork, and foundation engineering. The building of a monument to honor President Lincoln, first suggested a few years after his assassination, gained traction in the early 1900s once the bitter divisions of the US Civil War had partially cooled. Congress, the White House, and various artistic commissions then spent a decade jousting over both where to build the structure and how it should look. Sites considered in the District included Meridian Hill Park in the Columbia Heights neighborhood, the grounds of Union Station (then under construction), and the swampy flats of the Potomac River about a mile from the Washington Monument. The debate over designing the structure was just as fierce. Advocates of a monument with a Classical or Egyptian style clashed with those who viewed such shrine-like proposals as sacrilegious. Ultimately, the Potomac Flats site won out early in 1913, as did a design which architect Henry Bacon had based on the Parthenon. Within the building, a 10-foot statue of Lincoln crafted by sculptor Daniel Chester French would overlook the expanse slowly becoming the National Mall (Chesterwood 2023, Mandel 2008, McQuirter 2003).
Congress tasked the US Army Corps of Engineers with constructing the Lincoln Memorial once its location had been settled. The Corps immediately faced the problem of building an adequate foundation. The Potomac Flats had been a wharf during Lincoln’s presidency, and only during the Gilded Age had earlier Corps engineers raised the flats by dumping river-bottom soil atop them while dredging the Potomac. Now, the Army Corps would have to construct the Memorial upon this layer of dredge spoils. Thus, in 1913, the Corpsmen drilled 20 borings along the Flats within the planned footprint of the structure. They found that the project site consisted of four relatively horizontal soil layers. On top lay 16 feet of dredge spoils, which the Corps engineers described as sandy river-bottom loam; under the USCS, this material would most likely be classified as a silty sand, SM. Below that lay: buried surface mud and organic matter from the former marsh, averaging 2 feet thick; native alluvium, consisting of blue clay and averaging 30 feet thick; and highly weathered gneiss, averaging 2 feet thick. Competent gneiss bedrock lay beneath these layers at approximately 50 feet below grade (Darton 1950, Garcia-Gaines and Frankenstein 2015, Mandel 2008, O’Connor 1916).
Static load tests conducted by Army Corps engineers revealed that both the river-bottom loam/silty sand and the blue clay were stronger than expected. The loam/sand did not settle under a pressure of 4 tons per square foot, and neither did the alluvial clay under a test load of 1 ton per square foot. Yet the immense weight of the Lincoln Memorial, later pegged at 38,000 tons, led the Corps to decide to build the structure upon deep foundations extending 2 feet into competent gneiss bedrock. The engineers also felt secure that such foundations could safely support the vertical and lateral loads from the estimated one million cubic yards of soil which would be used to construct a series of stair-connected terraces, totaling over 30 feet high, around the Memorial. (Architect Bacon subtly honored Lincoln’s most famous speech by giving each staircase to the Memorial exactly 87 – i.e., “four score and seven” – steps.) The Corps engineers assumed in their design that the deep foundation elements would behave as unbraced columns, knowing that lateral support from the surrounding soil would make this decision conservative. Accordingly, they opted to use rectangular concrete piers for these elements instead of comparatively slender piles (NPS 2015, NPS 2021 C, O’Connor 1916).
Most contractors that submitted bids for the foundation of the Lincoln Memorial in the fall of 1913 based their pricing on the rectangular concrete piers called for by the Army Corps. However, one bidder, M.F. Comer & Co. of Toledo, Ohio, won the contract by proposing a replacement for the concrete piers. Comer’s low bid of $215,000, or about $6.65 million in modern dollars, called for sinking large-diameter steel pipe piles to bedrock, excavating out the soil within each, and filling them with reinforced concrete. The final step was state-of-the-art for 1913 given that civil engineers – including George Hool, who would co-edit Foundations, Abutments, and Footings a decade later – were then just beginning to understand the behavior of reinforced concrete. Comer’s foundation plan included 122 pipe piles ranging from 42 to 50 inches in outside diameter. The Corps engineers performed detailed calculations to confirm the structural integrity of the piles both individually and as a group before approving Comer’s plan. Their calculations, preserved for history, remind modern readers both of how advanced structural engineering was just before World War I and, in stark contrast, of how unsophisticated foundation design was at the time (Gromicko and Shepard 2011, O’Connor 1916, USACE 2022).
Within weeks after the groundbreaking ceremony for the Lincoln Memorial in February 1914, M.F. Comer & Co. began constructing its foundation. Comer laborers first drove each pipe pile to bedrock in three sections. As they drove the first section of a pile, they used temporary wooden cribbing reaching 7 feet below grade to keep it plumb. Then, once the section had been driven, they excavated the material within it. The loam and clay proved too stiff for machinery to excavate, and workers ended up completing the work with manual shovels; however, the open-air construction of the pipe piles removed any risk of decompression sickness. The laborers then repeated the process twice for each pile as they brought it up to its full length by bolting on two additional sections. As work progressed at each pipe pile, crews kept the driving process moving both by mounting water jets along the pile perimeter and by placing concrete blocks weighing 5,000 pounds atop the pile. Finally, once a pile had been driven to bedrock, the crew used small-scale blasting to complete the 2-foot rock socket. The laborers then placed rebar and poured concrete within each pile (O’Connor 1916).
The Army Corps engineers and M.F. Comer crews building the foundation of the Lincoln Memorial did encounter some difficulties. Water from the high-pressure jets continually seeped into the steel cylinders during driving and had to be removed using labor-intensive pumps and crane buckets. Buried piles from old shipping docks along the Potomac Flats also caused headaches. Laborers digging out several pipe piles found that the pipes had somehow been driven precisely around old dock piles. Another dock pile forced a pipe pile so far out of plumb that the pipe had to be jacked out of the ground and redriven. On the whole, though, these obstacles proved fairly straightforward to overcome. The pipe piles were all dewatered, and the uncovered dock piles were all removed. As some Comer crews finished the last pipe piles, other laborers began constructing caps atop the completed piles. They then joined the caps using reinforced concrete grade beams, built a 45-foot-high concrete column atop each cap, and constructed a 1-foot-thick concrete retaining wall around the perimeter of the column configuration. The Comer crews completed their work in March 1915 (O’Connor 1916).
Over the next two years, building contractors completed the Classical superstructure of the Lincoln Memorial under the conscientious supervision of Army Corps engineers. Their addition of the floor of the Memorial atop the concrete columns and retaining wall created a large, empty chamber known as an undercroft beneath the structure. From there, they began vertical construction. As the project progressed, the design team made several adjustments. For instance, Daniel Chester French realized immediately when he visited the site in the winter of 1917 that the immense Memorial building would overwhelm a 10-foot sculpture of Lincoln, and he quickly opted to roughly double its dimensions. Meanwhile, the Army Corps was busy designing additional foundation work immediately east of the Memorial on the National Mall. Nearly two decades earlier, urban planners for the District had recommended situating a pond on the site to further beautify the Washington Monument. The impoundment, originally called “the lagoon,” was soon christened the Reflecting Pool, while a second, smaller pond at its eastern end was named the Rainbow Pool (Chesterwood 2023, O’Connor 1916, Peters 1923, USACE 2022).
Early in 1917, Army Corps engineers conducted an 11-boring program of subsurface exploration within the planned sites of the Reflecting and Rainbow Pools and determined that soil conditions at the sites were identical to those beneath the Lincoln Memorial. Corps engineers recognized that, while the Pools would be just 3.5 feet deep, their combined volume of 7.5 million gallons of water would weigh approximately 31,300 tons, or nearly as much as the Memorial. They therefore decided that the perimeters of the Pools would bear on piles driven to bedrock to prevent differential settlement. The Corps also designed the floors of the Pools to rest on-grade in hopes of avoiding expensive cracks and leakage by allowing minimal differential settlement. US entry into World War I in April 1917 delayed construction of the Pools and slowed work at the Memorial, but the project plodded on through both the conflict and the deadly 1918 influenza pandemic. The signing of the Armistice in November 1918 ended the War and allowed work on the Memorial and Pools to resume at full speed (Peters 1923).
Contractors began excavating the Reflecting and Rainbow Pools early in 1919. The excavations soon proved convenient in constructing the terraces around the Lincoln Memorial. The crews using an army of steam shovels to dig out the 160-foot-wide footprints of the 2,200 foot-long Reflecting Pool and the 150-foot-long Rainbow Pool eventually removed 135,000 cubic yards of soil fit for use on the terraces. As they excavated the soil, they used their shovels to load it into gondola cars on temporary narrow-gauge railroad tracks. Finally, miniature steam locomotives hauled the soil-filled cars to the crews building the Memorial terraces (Peters 1923).
The laborers excavating the Reflecting and Rainbow Pools encountered groundwater within both structures’ footprints soon after beginning work. The high water table resulted in fluidized or “running” sands pouring into the excavations, which complicated construction. Army Corps engineers quickly had the laborers install extensive support systems for the excavations along with dewatering pumps to keep excavation moving. The crews also installed a drainage system beneath and around the Pool footprints consisting of vitrified clay pipes placed in beds of compacted gravel. The crews connected these to an outfall pipe which would drain excess water from the Pools into the adjacent Tidal Basin. Equally importantly, they also constructed intake pipes for filling the Pools and connected them to the new Washington, DC municipal water system (Peters 1923).
Over the next three years, the Army Corps engineers and the civilian construction crews pressed steadily forward in building the Lincoln Memorial and the Reflecting and Rainbow Pools. Within the Memorial, laborers assembled the statue of President Lincoln from late 1919 to early 1920. Per the revisions by French, the figure measured 19 feet in height and width. Outside the Memorial, foundation contractors drove 336 piles to refusal along the perimeters of the Pools once excavation had been finished. Laborers then formed those perimeters by pouring concrete caps and connecting grade beams atop the piles and placing granite coping stones above the caps and beams. Finally, other crews placed a waterproof membrane of wool impregnated with asbestos along the bottom of each Pool excavation, then covered the membrane with slate tiles slathered in tar. As the laborers finished their toils, the Army Corps tabulated the total cost of the Memorial and its grounds to be roughly $3 million, or about $55.7 million in modern dollars. The price tag, when adjusted for inflation, matched closely with the $2 million figure projected for the work in 1913 (NPS 2021 A, Peters 1923, Progress 2023, Webster 2023).
The US government opened the Lincoln Memorial and the Reflecting and Rainbow Pools in a grand ceremony on May 30, 1922. The date marked the federal holiday of Decoration Day, later to become Memorial Day. Chief Justice of the US Supreme Court, and former US President, William Howard Taft opened the event, while Dr. Robert Moton, President of the Tuskegee Institute, delivered the keynote address; incumbent President Warren Harding gave closing remarks. The crowd included many US Civil War veterans, both Union and Confederate, in their late 70s and early 80s. However, one gray-bearded Union Army Captain may have been the most distinguished veteran at the ceremony. The 78-year-old man, who had witnessed Lee’s surrender at Appomattox before going on to serve the US as both Secretary of War and Minister to the United Kingdom, was Robert Todd Lincoln – the former President’s lone surviving son. In his youth, Secretary Lincoln had watched his father endure the scorn and ridicule which Americans have always directed at their sitting President. Now, sixty years later, he had a front-row seat as the dedication of the Memorial confirmed his father’s place in the pantheon of American heroes (Laban 2022, NPS 2022).
Army Corps engineers spent the rest of the 1920s supervising minor improvements in and around the Lincoln Memorial and the Reflecting and Rainbow Pools, including landscaping the vicinity and enhancing the lighting around the statue of President Lincoln. However, a far more dramatic change at the site played out over the following decades as the popular meaning of the Memorial slowly changed. The speakers at the 1922 dedication ceremony emphasized that Lincoln’s greatness came mainly from his role in reunifying the USA. The perspective was more politically palatable than one focused on emancipation during a decade when segregation was an abhorrent fact of American life. Gradually, though, the tides of US public opinion shifted, and more and more Americans came to believe that their government should protect the civil rights of all its citizens regardless of race. The Memorial itself served as a backdrop for two key events in this transformation. In April 1939, Black contralto Marian Anderson – denied the chance to perform at a segregated venue – instead sang on the steps of the Memorial for 75,000 dazzled spectators. A quarter-century later, 250,000 supporters of civil rights attended the August 1963 March on Washington and finished their demonstration at the Memorial. There, they cheered as Rev. Dr. Martin Luther King, Jr., delivered one of the most stirring declarations of American ideals ever in his “I Have a Dream” address. Almost 50 years later, in 2011, the National Park Service would honor King with his own memorial on the National Mall, just a few hundred yards from the Lincoln Memorial. By then, almost all Americans across all backgrounds and political stripes had come to view Lincoln’s greatness as the product of his successful work to abolish US slavery (Dunlap 2023, Gormley 2022, Laban 2022, NPS 2021 A, NPS 2022, Stamberg 2014).
Unfortunately, albeit unsurprisingly, the passage of time took its toll on the Lincoln Memorial site, especially at the Reflecting and Rainbow Pools. By the start of the 21st century, the bottom of the Reflecting Pool had settled as much as one foot, and the 6.75 million-gallon Pool was leaking its volume in water every three months. Wheels began turning, though, after the 9/11 attacks made federal officials keen to renovate the Memorial area both to preserve it and to harden it against terrorism. Contractors working for the National Park Service had already begun rebuilding and reconfiguring the Rainbow Pool into the National World War II Memorial, which opened in 2004. Five years later, the 2009 American Recovery and Reinvestment Act, also known as “the stimulus” at the time, provided funding to reconstruct the Reflecting Pool as well. The rebuild’s total cost came to about $45.5 million in modern dollars, which was in line with the stimulus funding provided for the job (ENR 2013, NPS 2021 C, Ruane 2012, USACE 2022, Webster 2023).
Starting in 2010, contractors worked for two years to restore the Reflecting Pool to its former splendor. Laborers first cataloged the nearly 600 granite coping stones around the Pool and removed them for restoration. Demolition crews working alongside PPE-clad environmental specialists then carefully removed the bottom of the Pool along with the 335,000 square feet of asbestos-laden waterproofing below it. Next, foundation contractors drove over 2,100 timber piles 50 feet to bedrock to support the rebuilt Pool. Crews then connected the piles using concrete pile caps and grade beams, just as previous crews had done 90 years earlier at the original Pool. Afterward, contractors constructed a rebar cage above the caps and beams proper rebar Pool slab and poured custom dark gray concrete over the cage to form the bottom and sides of the new Pool. The refurbished coping stones were then reset in their original locations around the Pool (EIG 2011, ENR 2013, Monjar 2013, Progress 2023, Ruane 2012).
IMAGE 14: Crews drive timber piles for the rebuilding of the Reflecting Pool, 2011. Source: ENR (2013).
Meanwhile, other contractors completed equally top-notch work on other facets of the project. Most notably, they equipped the new Pool with a water treatment plant near the Tidal Basin. The plant includes two pumps which can draw Basin water through the plant and into the Pool, improving its sustainability. The multi-directional pumps are also used to recirculate and clean the Pool water throughout the year, and, every spring, to empty the Pool for its annual cleaning. The plant is outfitted with both traditional sand filtration tanks and a state-of-the-art ozone disinfecting machine to purify Pool water during either intake or recirculation. Further upgrades included accessible paved walkways around the Pool, converting the road between the Pool and the Memorial into a pedestrian and bike path, and adding bollards and granite-faced concrete barriers around the Memorial to strengthen security. In August 2012, the National Park Service reopened the rejuvenated Pool. Only the sharpest-eyed visitors will readily observe that the revamped Pool, with a volume of about 4 million gallons, holds roughly 40 percent less water than the original (ENR 2013, Monjar 2013, Ruane 2012).
Surprisingly, given the rudimentary state of foundation design in the early 1900s, the Lincoln Memorial itself has held up remarkably well over time. Its durability over its first 100 years has meant that most contracting work done there to date has been routine maintenance and attests to the hard work of the engineers and laborers who constructed it. As the Memorial enters its second century, though, it is receiving a major improvement which will highlight the geotechnical feats required to build it. This past spring, the National Park Service initiated the construction of a 15,000-square-foot museum within the long-vacant undercroft of the Memorial. The $69 million space will share the history of the construction and continuing use of the Memorial and is slated to open in 2026 to help celebrate the 250th birthday of the United States. Geo-professionals visiting the museum will, perhaps, be most intrigued by an observation room from which tourists will have a clear view of the yawning, unfinished undercroft. One can only wonder what the Army Corps engineers and M.F. Comer laborers who created the Memorial undercroft would think of their handiwork returning to public view after being out of sight since its completion in 1915. Hopefully, they – not to mention Allen McDaniel and the contemporary readers of his chapter on excavation – would be quite pleased by the news. It seems fitting, and almost poetic, that the laborers’ toils in digging out the steel pipe piles beneath the Lincoln Memorial will at last be excavated from the dusty annals of history (Kuta 2023, NPS 2023).
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The author’s cousin, Michael A. Bennett (W.S. Cumby Construction: Springfield, PA), shared select data on contemporary earthwork costs. The author’s colleague, Sebastian Lobo-Guerrero, PhD, PE, D.GE (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-authored a previous version of this entry posted on an independent webpage in 2021.