Editing Hoover Dam (section)

== Construction ==

=== Labor force ===

[[File:HooverDamJumboRig.jpg|thumb|Workers on a "Jumbo Rig"; used for drilling the Hoover Dam's tunnels]]

[[File:"Apache Indians employed as high-scalers on the construction of Hoover Dam." - NARA - 293746.tif|thumb|"Apache Indians employed as high-scalers on the construction of Hoover Dam." – NARA]]

Soon after the dam was authorized, increasing numbers of unemployed people converged on southern Nevada. Las Vegas, then a small city of some 5,000, saw between 10,000 and 20,000 unemployed descend on it.{{sfn|Dunar|McBride|2001|p=28}} A government camp was established for surveyors and other personnel near the dam site; this soon became surrounded by a squatters' camp. Known as McKeeversville, the camp was home to men hoping for work on the project, together with their families.{{sfn|Dunar|McBride|2001|p=32}} Another camp, on the flats along the Colorado River, was officially called Williamsville, but was known to its inhabitants as "Ragtown".{{sfn|Stevens|1988|pp=53–54}} When construction began, Six Companies hired large numbers of workers, with more than 3,000 on the payroll by 1932{{sfn|Hiltzik|2010|p=194}} and with employment peaking at 5,251 in July 1934.{{sfn|Hiltzik|2010|p=317}} "Mongolian" (Chinese) labor was prevented by the construction contract,{{sfn|Hiltzik|2010|p=317}} while the number of black people employed by Six Companies never exceeded thirty, mostly lowest-pay-scale laborers in a segregated crew, who were issued separate water buckets.{{sfn|Hiltzik|2010|p=315}}

As part of the contract, Six Companies, Inc. was to build Boulder City to house the workers. The original timetable called for Boulder City to be built before the dam project began, but President Hoover ordered work on the dam to begin in March 1931 rather than in October.{{sfn|Stevens|1988|p=65}} The company built bunkhouses, attached to the canyon wall, to house 480&nbsp;single men at what became known as River Camp. Workers with families were left to provide their own accommodations until Boulder City could be completed,{{sfn|Stevens|1988|p=56}} and many lived in Ragtown.{{sfn|Dunar|McBride|2001|p=40}} The site of Hoover Dam endures extremely hot weather, and the summer of 1931 was especially torrid, with the daytime high averaging {{convert|abbr=on|119.9|°F |°C}}.{{sfn|Hiltzik|2010|pp=219–220}} Sixteen workers and other riverbank residents died of [[heat prostration]] between June 25 and July 26, 1931.{{sfn|Hiltzik|2010|p=223}}

[[File:FrankCrowe.jpg|thumb|left|General Superintendent [[Frank Crowe]] ''(right)'' with Bureau of Reclamation engineer Walker Young in 1935]]

The [[Industrial Workers of the World]] (IWW or "Wobblies"), though much-reduced from their heyday as militant labor organizers in the early years of the century, hoped to unionize the Six Companies workers by capitalizing on their discontent. They sent eleven organizers,{{sfn|Hiltzik|2010|pp=226–228}} several of whom were arrested by Las Vegas police.{{sfn|Hiltzik|2010|p=230}} On August 7, 1931, the company cut wages for all tunnel workers. Although the workers sent the organizers away, not wanting to be associated with the "Wobblies", they formed a committee to represent them with the company. The committee drew up a list of demands that evening and presented them to Crowe the following morning. He was noncommittal. The workers hoped that Crowe, the general superintendent of the job, would be sympathetic; instead, he gave a scathing interview to a newspaper, describing the workers as "malcontents".{{sfn|Hiltzik|2010|pp=234–237}}

On the morning of the 9th, Crowe met with the committee and told them that management refused their demands, was stopping all work, and was laying off the entire work force, except for a few office workers and carpenters. The workers were given until 5&nbsp;p.m. to vacate the premises. Concerned that a violent confrontation was imminent, most workers took their paychecks and left for Las Vegas to await developments.{{sfn|Stevens|1988|pp=70–73}} Two days later, the remainder were talked into leaving by law enforcement. On August 13, the company began hiring workers again, and two days later, the strike was called off.{{sfn|Stevens|1988|pp=73–78}} While the workers received none of their demands, the company guaranteed there would be no further reductions in wages. Living conditions began to improve as the first residents moved into Boulder City in late 1931.{{sfn|Stevens|1988|p=78}}

A second labor action took place in July 1935, as construction on the dam wound down. When a Six Companies manager altered working times to force workers to take lunch on their own time, workers responded with a strike. Emboldened by Crowe's reversal of the lunch decree, workers raised their demands to include a $1-per-day raise. The company agreed to ask the Federal government to supplement the pay, but no money was forthcoming from Washington. The strike ended.{{sfn|Hiltzik|2010|pp=362–365}}

=== River diversion ===
[[File:Hoover-summary-map.jpg|thumb|Overview of dam mechanisms; diversion tunnels shown]]
Before the dam could be built, the [[Colorado River]] needed to be diverted away from the construction site. To accomplish this, four diversion tunnels were driven through the canyon walls, two on the [[Nevada]] side and two on the [[Arizona]] side. These tunnels were {{convert|abbr=on|56|ft|m}} in diameter.<ref name="usbrfaq" /> Their combined length was nearly 16,000&nbsp;ft, or more than {{convert|3|mi|km|0}}.<ref name="hovtun" /> The contract required these tunnels to be completed by October 1, 1933, with a $3,000-per-day fine to be assessed for any delay. To meet the deadline, Six Companies had to complete work by early 1933, since only in late fall and winter was the water level in the river low enough to safely divert.{{sfn|Stevens|1988|p=84}}

Tunneling began at the lower portals of the Nevada tunnels in May 1931. Shortly afterward, work began on two similar tunnels in the Arizona canyon wall. In March 1932, work began on lining the tunnels with concrete. First the base, or invert, was poured. [[Gantry crane]]s, running on rails through the entire length of each tunnel were used to place the concrete. The sidewalls were poured next. Movable sections of steel forms were used for the sidewalls. Finally, using pneumatic guns, the overheads were filled in. The concrete lining is {{convert|3|ft|m|0}} thick, reducing the finished tunnel diameter to {{convert|abbr=on|50|ft}}.<ref name="hovtun" /> The river was diverted into the two Arizona tunnels on November 13, 1932; the Nevada tunnels were kept in reserve for high water. This was done by exploding a temporary [[cofferdam]] protecting the Arizona tunnels while at the same time dumping rubble into the river until its natural course was blocked.{{sfn|Hiltzik|2010|pp=305–306}}

Following the completion of the dam, the entrances to the two outer diversion tunnels were sealed at the opening and halfway through the tunnels with large concrete plugs. The downstream halves of the tunnels following the inner plugs are now the main bodies of the spillway tunnels.<ref name="hovtun" /> The inner diversion tunnels were plugged at approximately one-third of their length, beyond which they now carry steel pipes connecting the intake towers to the power plant and outlet works.<ref name="usbrfaq" /> The inner tunnels' outlets are equipped with gates that can be closed to drain the tunnels for maintenance.<ref name="usbrfaq" />

=== Groundworks, rock clearance and grout curtain ===
To protect the construction site from the Colorado River and to facilitate the river's diversion, two [[cofferdam]]s were constructed. Work on the upper cofferdam began in September 1932, even though the river had not yet been diverted.<ref name="USBR, Cofferdams" /> The cofferdams were designed to protect against the possibility of the river's flooding a site at which two thousand men might be at work, and their specifications were covered in the bid documents in nearly as much detail as the dam itself. The upper cofferdam was {{convert|abbr=on|96|ft}} high, and {{convert|750|ft}} thick at its base, thicker than the dam itself. It contained {{convert|650,000|cuyd}} of material.{{sfn|Hiltzik|2010|pp=318–319}}

[[File:HooverDamHighScaler.jpg|left|thumb|Looking down at "high scalers" above the Colorado River]]

When the cofferdams were in place and the construction site was drained of water, excavation for the dam foundation began. For the dam to rest on solid rock, it was necessary to remove [[Fluvial|accumulated erosion soils]] and other loose materials in the riverbed until sound bedrock was reached. Work on the foundation excavations was completed in June 1933. During this excavation, approximately {{convert|abbr=on|1,500,000 |cuyd}} of material was removed. Since the dam was an arch-gravity type, the side-walls of the canyon would bear the force of the impounded lake. Therefore, the side-walls were also excavated to reach virgin rock, as weathered rock might provide pathways for water seepage.<ref name="USBR, Cofferdams" /> Shovels for the excavation came from the [[Marion Power Shovel Company]].<ref>Olberhelman, Olberhelman, and Lampe. Quail Lakes & Coal: Energy for Wildlife ... and the World, 2013, page 60</ref>

The men who removed this rock were called "high scalers". While suspended from the top of the canyon with ropes, the high-scalers climbed down the canyon walls and removed the loose rock with [[jackhammers]] and [[dynamite]]. Falling objects were the most common cause of death on the dam site; the high scalers' work thus helped ensure worker safety.<ref name="USBR, High Scalers" /> One high scaler was able to save a life in a more direct manner: when a government inspector lost his grip on a safety line and began tumbling down a slope towards almost certain death, a high scaler was able to intercept him and pull him into the air. The construction site had become a magnet for tourists. The high scalers were prime attractions and showed off for the watchers. The high scalers received considerable media attention, with one worker dubbed the "Human Pendulum" for swinging co-workers (and, at other times, cases of dynamite) across the canyon.{{sfn|Hiltzik|2010|pp=308–309}} To protect themselves against falling objects, some high scalers dipped cloth hats in tar and allowed them to harden. When workers wearing such headgear were struck hard enough to inflict broken jaws, they sustained no skull damage. Six Companies ordered thousands of what initially were called "hard boiled hats" (later "[[hard hat]]s") and strongly encouraged their use.{{sfn|Stevens|1988|p=104}}

The cleared, underlying rock foundation of the dam site was reinforced with [[grout]], forming a [[grout curtain]]. Holes were driven into the walls and base of the canyon, as deep as {{convert|150|ft}} into the rock, and any cavities encountered were to be filled with grout. This was done to stabilize the rock, to prevent water from seeping past the dam through the canyon rock, and to limit "uplift"—upward pressure from water seeping under the dam. The workers were under severe time constraints due to the beginning of the concrete pour. When they encountered hot springs or cavities too large to readily fill, they moved on without resolving the problem. A total of 58 of the 393 holes were incompletely filled.{{sfn|Hiltzik|2010|pp=331–332}} After the dam was completed and the lake began to fill, large numbers of significant leaks caused the Bureau of Reclamation to examine the situation. It found that the work had been incompletely done, and was based on less than a full understanding of the canyon's geology. New holes were drilled from inspection galleries inside the dam into the surrounding bedrock.{{sfn|Hiltzik|2010|pp=387–390}} It took nine years (1938–47) under relative secrecy to complete the supplemental grout curtain.<ref name="Rogers 2005" />

=== Concrete ===

[[File:Damforms.jpg|thumb|Columns of Hoover Dam being filled with concrete, February 1934 ''(looking upstream from the Nevada rim)'']]

The first concrete was poured into the dam on June 6, 1933, 18&nbsp;months ahead of schedule.{{sfn|Hiltzik|2010|pp=323–324}} Since concrete [[Thermal expansion|heats and contracts]] as it cures, the potential for uneven cooling and contraction of the concrete posed a serious problem. Bureau of Reclamation engineers calculated that if the dam were to be built in a single continuous pour, the concrete would take 125 years to cool, and the resulting stresses would cause the dam to crack and crumble. Instead, the ground where the dam would rise was marked with rectangles, and concrete blocks in columns were poured, some as large as {{convert|abbr=on|50|ft|m |adj=mid|square}} and {{convert|5|ft}} high.{{sfn|Hiltzik|2010|pp=325–326}} Each five-foot form contained a set of {{convert|1|in|adj=on}} steel pipes; cool river water would be poured through the pipes, followed by ice-cold water from a [[refrigeration]] plant. When an individual block had cured and had stopped contracting, the pipes were filled with [[grout]]. Grout was also used to fill the hairline spaces between columns, which were grooved to increase the strength of the joints.{{sfn|Stevens|1988|pp=193–194}}

The concrete was delivered in huge steel buckets {{convert|7|ft|m|disp=x| high (|)}} and almost 7&nbsp;feet in diameter; Crowe was awarded two patents for their design. These buckets, which weighed {{convert|20|ST|t LT|1}} when full, were filled at two massive concrete plants on the Nevada side, and were delivered to the site in special [[Railroad car#Freight cars|railcars]]. The buckets were then suspended from aerial [[cableway]]s which were used to deliver the bucket to a specific column. As the required grade of [[Construction aggregate|aggregate]] in the concrete differed depending on placement in the dam (from pea-sized gravel to {{convert|9|in|disp=sqbr}} stones), it was vital that the bucket be maneuvered to the proper column. When the bottom of the bucket opened up, disgorging {{convert|abbr=on|8|cuyd}} of concrete, a team of men worked it throughout the form. Although there are myths that men were caught in the pour and are entombed in the dam to this day, each bucket deepened the concrete in a form by only {{convert|1|in}}, and Six Companies engineers would not have permitted a flaw caused by the presence of a human body.{{sfn|Hiltzik|2010|pp=327–330}}

A total of {{convert|3250000|cuyd|abbr=off|sp=us}} of concrete was used in the dam before concrete pouring ceased on May 29, 1935. In addition, {{convert|abbr=on|1,110,000|cuyd}} were used in the power plant and other works. More than {{convert|582|mi}} of cooling pipes were placed within the concrete. Overall, there is enough concrete in the dam to pave a two-lane highway from San Francisco to New York.<ref name="usbrfaq" /> Concrete cores were removed from the dam for testing in 1995; they showed that "Hoover Dam's concrete has continued to slowly gain strength" and the dam is composed of a "durable concrete having a compressive strength exceeding the range typically found in normal mass concrete".{{sfn|Bartojay|Joy|2010}} Hoover Dam concrete is not subject to [[alkali–silica reaction]] (ASR), as the Hoover Dam builders happened to use nonreactive aggregate, unlike that at downstream [[Parker Dam]], where ASR has caused measurable deterioration.{{sfn|Bartojay|Joy|2010}}

=== Dedication and completion ===

[[File:Damupstream.jpg|thumb|left|The upstream face of Hoover Dam slowly disappears as Lake Mead fills, May 1935 ''(looking downstream from the Arizona rim)'']]

With most work finished on the dam itself (the powerhouse remained uncompleted), a formal dedication ceremony was arranged for September 30, 1935, to coincide with a western tour being made by President [[Franklin D. Roosevelt]]. The morning of the dedication, it was moved forward three hours from 2&nbsp;p.m. Pacific time to 11&nbsp;a.m.; this was done because [[United States Secretary of the Interior|Secretary of the Interior]] [[Harold L. Ickes]] had reserved a radio slot for the President for 2&nbsp;p.m. but officials did not realize until the day of the ceremony that the slot was for 2&nbsp;p.m. Eastern Time.{{sfn|Hiltzik|2010|pp=366–369}} Despite the change in the ceremony time, and temperatures of {{convert|abbr=on|102|°F|°C}}, 10,000&nbsp;people were present for the President's speech, in which he avoided mentioning the name of former President Hoover,{{sfn|Hiltzik|2010|p=373}} who was not invited to the ceremony.{{sfn|Hiltzik|2010|p=304}} To mark the occasion, a three-cent stamp was issued by the [[United States Post Office Department]]—bearing the name "Boulder Dam", the official name of the dam between 1933 and 1947.{{sfn|Hiltzik|2010|p=372}} After the ceremony, Roosevelt made the first visit by any American president to Las Vegas.{{sfn|Hiltzik|2010|p=373}}

Most work had been completed by the dedication, and Six Companies negotiated with the government through late 1935 and early 1936 to settle all claims and arrange for the formal transfer of the dam to the Federal Government. The parties came to an agreement and on March 1, 1936, Secretary Ickes formally accepted the dam on behalf of the government. Six Companies was not required to complete work on one item, a concrete plug for one of the bypass tunnels, as the tunnel had to be used to take in irrigation water until the powerhouse went into operation.{{sfn|Stevens|1988|pp=250–252}}

=== Construction deaths ===
[[File:HansenHooverMemorial.jpg|thumb|[[Oskar J. W. Hansen]]'s memorial at the dam which reads in part "They died to make the desert bloom."<ref name="USBR, Hover Artwork" />]]

There were 112 deaths reported as associated with the construction of the dam.<ref name="blf1" /> The first was Bureau of Reclamation employee Harold Connelly who died on May 15, 1921, after falling from a barge while surveying the [[Colorado River]] for an ideal spot for the dam.<ref name="blf1" /> Surveyor John Gregory ("J.G.") Tierney, who drowned on December 20, 1922, in a flash flood while looking for an ideal spot for the dam was the second person.<ref name="blf1" /> The official list's final death occurred on December 20, 1935, when Patrick Tierney, electrician's helper and the son of J.G. Tierney, fell from one of the two Arizona-side intake towers. Included in the fatality list are three workers who took their own lives on site, one in 1932 and two in 1933.<ref>{{cite book| last = DuTemple| first = Lesley| year = 2003| title = The Hoover Dam| publisher = Twenty-First Century Books| page = [https://archive.org/details/hooverdam00dute/page/82 82]| isbn = 0822546914| url = https://archive.org/details/hooverdam00dute/page/82}}</ref><ref>{{cite web| title = Fatalities at Hoover Dam| work = Desert Gazette| url = http://digital-desert.com/hoover-dam/fatalities.html| access-date = December 7, 2016| archive-url = https://web.archive.org/web/20161220112832/http://digital-desert.com/hoover-dam/fatalities.html| archive-date = December 20, 2016| url-status = live}}</ref><ref>{{cite web| date = March 12, 2015| title = Hoover Dam: 1935 Fatalities| work = United States Bureau of Reclamation| url = http://www.usbr.gov/lc/hooverdam/history/essays/fat1935.html| access-date = December 7, 2016| url-status = dead| archive-url = https://web.archive.org/web/20161230171345/https://www.usbr.gov/lc/hooverdam/history/essays/fat1935.html| archive-date = December 30, 2016}}</ref> Of the 112 fatalities, 91 were Six Companies employees, three were Bureau of Reclamation employees, and one was a visitor to the site; the remainder were employees of various contractors not part of Six Companies.{{sfn|Stevens|1988|p=320}}

Ninety-six of the deaths occurred during construction at the site.<ref name="blf1" /> Not included in the official number of fatalities were deaths that were recorded as [[pneumonia]]. Workers alleged that this diagnosis was a cover for death from [[carbon monoxide]] poisoning (brought on by the use of gasoline-fueled vehicles in the diversion tunnels), and a classification used by Six Companies to avoid paying compensation claims.{{sfn|Hiltzik|2010|pp=284–286}} The site's diversion tunnels frequently reached {{convert|abbr=on|140|F|C}}, enveloped in thick plumes of vehicle exhaust gases.<ref name="I&amp;T-2010.V25.2" /> A total of 42 workers were recorded as having died from pneumonia and were not included in the above total; none were listed as having died from carbon monoxide poisoning. No deaths of non-workers from pneumonia were recorded in Boulder City during the construction period.{{sfn|Hiltzik|2010|pp=284–286}}

=== Architectural style ===
The initial plans for the facade of the dam, the power plant, the outlet tunnels and ornaments clashed with the modern look of an arch dam. The Bureau of Reclamation, more concerned with the dam's functionality, adorned it with a [[Gothic architecture|Gothic]]-inspired [[baluster|balustrade]] and eagle statues. This initial design was criticized by many as being too plain and unremarkable for a project of such immense scale, so Los Angeles-based architect [[Gordon Kaufmann|Gordon B. Kaufmann]], then the supervising architect to the Bureau of Reclamation, was brought in to redesign the exteriors.{{sfn|True|Kirby|2009|p=341}} Kaufmann greatly streamlined the design and applied an elegant [[Art Deco]] style to the entire project. He designed sculpted turrets rising seamlessly from the dam face and clock faces on the intake towers set for the time in Nevada and Arizona—both states are in different time zones, but since Arizona does not observe [[daylight saving time]], the clocks display the same time for more than half the year.<ref name="Rhinehart 2004" />

[[File:HooverDamTrueDesign.jpg|thumb|right|Tile floor designed by [[Allen Tupper True]]]]
[[File:HansenBasReliefHooverDam.jpg|thumb|upright|left|Hansen's bas-relief on the Nevada elevator]]

At Kaufmann's request, Denver artist [[Allen Tupper True]]{{sfn|True|Kirby|2009|p=341}} was hired to handle the design and decoration of the walls and floors of the new dam. True's design scheme incorporated motifs of the [[Navajo people|Navajo]] and [[Pueblo]] tribes of the region.{{sfn|True|Kirby|2009|pp=342–343}} Although some were initially opposed to these designs, True was given the go-ahead and was officially appointed consulting artist.{{sfn|True|Kirby|2009|p=346}} With the assistance of the National Laboratory of Anthropology, True researched authentic decorative motifs from Indian sand paintings, textiles, baskets and ceramics.{{sfn|True|Kirby|2009|p=343}} The images and colors are based on Native American visions of rain, lightning, water, clouds, and local animals—lizards, serpents, birds—and on the Southwestern landscape of stepped mesas.{{sfn|True|Kirby|2009|pp=342–343}} In these works, which are integrated into the walkways and interior halls of the dam, True also reflected on the machinery of the operation, making the symbolic patterns appear both ancient and modern.{{sfn|True|Kirby|2009|p=358}}

With the agreement of Kaufmann and the engineers, True also devised for the pipes and machinery an innovative color-coding which was implemented throughout all BOR projects.{{sfn|True|Kirby|2009|pp=354–356}} True's consulting artist job lasted through 1942; it was extended so he could complete design work for the [[Parker Dam|Parker]], [[Shasta Dam|Shasta]] and [[Grand Coulee Dam|Grand Coulee]] dams and power plants. True's work on the Hoover Dam was humorously referred to in a poem published in ''[[The New Yorker]]'', part of which read, "lose the spark, and justify the dream; but also worthy of remark will be the color scheme".{{sfn|True|Kirby|2009|pp=361–362}}

Complementing Kaufmann and True's work, sculptor [[Oskar J. W. Hansen]] designed many of the sculptures on and around the dam. His works include the monument of dedication plaza, a plaque to memorialize the workers killed and the [[Relief|bas-reliefs]] on the elevator towers. In his words, Hansen wanted his work to express "the immutable calm of intellectual resolution, and the enormous power of trained physical strength, equally enthroned in placid triumph of scientific accomplishment", because "[t]he building of Hoover Dam belongs to the sagas of the daring."<ref name="USBR, Hover Artwork" /> Hansen's dedication plaza, on the Nevada abutment, contains a sculpture of two winged figures flanking a flagpole.

[[File:Hoover Dam star map floor center.jpg|thumb|Hoover Dam memorial star map floor, center area]]
Surrounding the base of the monument is a [[terrazzo]] floor embedded with a "star map". The map depicts the Northern Hemisphere sky at the moment of President Roosevelt's dedication of the dam. This is intended to help future astronomers, if necessary, calculate the exact date of dedication.<ref name="USBR, Hover Artwork" />{{sfn|Hiltzik|2010|pp=379–380}} The {{convert|30|ft |m|adj=mid|-high}} bronze figures, dubbed ''[[Winged Figures of the Republic]]'', were both formed in a continuous pour. To put such large bronzes into place without marring the highly polished bronze surface, they were placed on ice and guided into position as the ice melted.{{sfn|Bureau of Reclamation|2006|p=43}} Hansen's bas-relief on the Nevada elevator tower depicts the benefits of the dam: flood control, navigation, irrigation, water storage, and power. The bas-relief on the Arizona elevator depicts, in his words, "the visages of those Indian tribes who have inhabited mountains and plains from ages distant."<ref name="USBR, Hover Artwork" />