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For the first time ever, I am thrilled to say we have an official sponsor for the Dirt Talk podcast, and that's Ariat. I've worn Ariat boots on every job site I visited over the years, traveling in them across five continents. More importantly, I have yet to find a single project where working folks, unlike me, are not wearing Ariat boots and workwear in every condition imaginable. And there's really good reason for that, and that's because it's phenomenal stuff. And the more I've learned about Ariat and the company, the more I've loved their brand. So with this, Ariat is offering any dirt talk listener 10% off their next Ariat order at ariat.com dirttalk that's 10% off boots, jeans and workwear@arianat.com dirttalk or at the link in this episode's description. With that, let's get to the show. Hello, everybody. Welcome back. Dirt Talk Podcast Monday edition. We are going to review another famous project today, this time being one of the most famous construction projects probably in the world, and that is the Hoover Dam. It is an engineering marvel. I have loved learning about the structure and I figured I would come on here and use some research from the incredible online free Wikipedia, free encyclopedia that is Wikipedia. It's a great resource. There's a bunch of other stuff on the Hoover Dam with how well known it is, so I've compiled some information and we're gonna talk all about it today. So with that, just some big picture here. Hoover Dam is a concrete arch gravity dam in the Black Canyon of the Colorado river on the border between the states of Nevada and Arizona. It was constructed between 1931 and 1936 during the Great Depression, and it was dedicated on September 30, 1935 by President Franklin D. Roosevelt. Its construction was the result of a massive effort involving thousands of workers and cost over 100 lives. Bills passed by Congress during its construction referred to it as the Hoover Dam, after President Herbert Hoover, but the Roosevelt administration then named it the Boulder dam. However, in 1947, Congress restored the name to the Hoover Dam, which is how we know of it today. Since about 1900, the Black Canyon and nearby Boulder Canyon had been investigated for their potential to support a dam that would control floods, provide irrigation water and produce hydroelectric power. In 1928, Congress authorized the project. The winning bid to build the dam was submitted by a consortium named Six Companies Incorporated, which began construction in early 1931. Such a large concrete structure had never been built before, and some of the techniques used were unproven. The torrid summer weather and lack of facilities near the site also presented difficulties. Nevertheless, the six companies turned the dam over to the federal government on March 1, 1936, more than two years ahead of schedule. As America developed the Southwest, the Colorado river was seen as a potential source of irrigation. An initial attempt at diverting the river for irrigation purposes occurred in the late 1890s, when land speculator William Beatty built the Alamo Canal just north of the Mexican border. The canal dipped into Mexico before running to a desolate area Beatty named the Imperial Valley. Though water from the Alamo Canal allowed for the widespread settlement of the valley, the canal proved expensive to operate. After a catastrophic breach that caused the Colorado river to fill the Salton Sea, the Southern Pacific Railroad spent $3 million in 1906 to stabilize the waterway, an amount it hoped in vain that it would be reimbursed for by the federal government. Even after the waterway was stabilized, it proved unsatisfactory because of constant disputes with landowners on Mexican side of the border. As the technology for electric power transmission improved, the Lower Colorado was considered for its hydroelectric power potential. In 1902, the Edison Electric Company of Los Angeles surveyed the river in the hope of building a 40 foot rock dam that could generate 10,000 horsepower or 7,500 kilowatts. However, at the time, the limit of transmission of electric power was about 80 miles, and there were very few customers within that limit. Edison allowed land options it held on the river to lapse, including an option for what became the site of the Hoover Dam. In the following years, the Bureau of Reclamation, known as Reclamation Service at the time, also considered the Lower Colorado as the site for a dam. They proposed using dynamite to collapse the walls of Boulder Canyon, 20 miles north of the eventual dam site, into the river. The river would carry off the smaller pieces of debris, and a dam would be built incorporating the remaining rubble. In 1922, after considering it for several years, the Reclamation Service finally rejected the proposal, citing doubts about the unproven technique and questions as to whether it would, in fact, save money. Go figure. In 1922, the Reclamation Service presented a report calling for the development of a dam on the Colorado river for flood control and electric power generation. With a little guidance on water allocation from the Supreme Court. Proponents of the dam feared endless litigation. Delph Carpenter, a Colorado attorney, proposed that the seven states which fell within the river's basin, which were California, Nevada, Arizona, Utah, New Mexico, Colorado, and Wyoming, form an interstate compact with the approval from Congress. Such compacts were authorized by Article 1 of the United States Constitution, but had never been concluded among more than two states. In 1922, representatives of seven states met with then Secretary of Commerce Herbert Hoover. Initial talks produced no result, but when the Supreme Court handed down the Wyoming vs Colorado decision undermining the claims of the upstream states, they became anxious to reach an agreement. The resulting Colorado River Compact was signed on November 24, 1922. Legislation then to authorize the dam was introduced repeatedly by two California Republicans. But representatives from other parts of the country considered the project as hugely expensive and one that would mostly benefit California. The 1927 Mississippi flood made Midwestern and southern congressmen and senators more sympathetic toward the dam project. On March 12, 1928, then, the failure of the St. Francis Dam, constructed by the city of Los Angeles, caused a disastrous flood that killed up to 600 people. As that dam was a gravity curve type similar in design to the arch gravity as was proposed for the Black Canyon damage, opponents claimed that the Black Canyon Dam's safety could not be guaranteed. Congress authorized a board of engineers to review plans for the proposed dam. The Colorado River Board found the project feasible, but warned that should the dam fail, every downstream Colorado river community would be destroyed and that the river might change course and empty into the Salton Sea. The board cautioned to avoid such possibilities, the proposed dam should be constructed on conservative, if not ultra conservative lines. Then, In December of 1928, President Coolidge signed the bill authorizing the dam. The Boulder Canyon Project act appropriated $165 million for the project along with the downstream Imperial Dam and All American Canal, a replacement for Beatty's canal entirely on the US Side of the border. It also permitted the compact to go into effect when at least six of the seven states approved it. This occurred on March 6, 1929, with Utah's ratification, and Arizona did not approve it until 1944. Even before Congress approved the Boulder Canyon Project, the Bureau of Reclamation was considering what kind of dam should be used. Officials eventually decided on a massive concrete arch gravity dam, the design of which was overseen by the Bureau's chief design engineer, John Savage. The monolithic dam would be thick at the bottom and thin near the top and would present a convex face toward the water above the dam. The curving arch of the dam would transmit the water's force into the abutments, in this case the rock walls of the canyon. The wedge shaped dam would be 660ft thick at the bottom, narrowing to only 45ft thick at the top, leaving room for a highway connecting Nevada and Arizona. On January 10, 1931, the Bureau made the bid documents available to interested parties at $5 a copy. The government was to provide the materials, and the contractor was to prepare the site and build the dam. The dam was described in minute detail, covering 100 pages of text and 76 drawings. Now a Target parking lot gets more than that. A $2 million bid bond was to accompany each bid. The winner then would have to post a $5 million performance bond. The contractor had seven years to build the dam or liquidated. Damages would ensue. The Wattis brothers, heads of the Utah Construction Company, were interested in bidding on the project but lacked the money for the performance bond. They lacked sufficient resources, even in combination with their longtime partners, Morrison Knudsen, which employed the nation's leading dam builder, Frank Crow. They formed a joint venture to bid for the project with Pacific Bridge Company of Portland, Oregon, Henry Kaiser and W.A. bechtel Company of San Francisco, McDonald & Khan Limited of Los Angeles, and the J.F. shea Company of Portland, Oregon. The joint venture was called Six Companies, Inc. As Bechtel and Kaiser were considered one company for purposes of six in the name, there were three valid bids with the Six Companies. Bid of $48,890,000 was the lowest within $24,000 of the confidential government estimate of what the dam would cost to build and $5 million less than the next lowest bid. Soon after the dam was authorized, increasing numbers of unemployed people converged on southern Nevada. Because this was peak of the Great Depression, Las Vegas, then a small city of some 5,000, saw between 10 and 20,000 unemployed people descend upon it. 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 to work on the project together with their families. Another camp on the flats along the Colorado river was officially called Williamsville, but was known to its inhabitants as Ragtown. When construction began, six companies hired large numbers of workers with more than 3,000 on the payroll by 1932 and with employment peaking at 5,251 in July of 1934. Before the dam could be built, the Colorado river needed to be diverted away from the construction site. To do this, four diversion tunnels were driven through the canyon walls. Two on the Nevada side and two on the Arizona side. These tunnels were 56ft in diameter. Their combined length was nearly 16,000ft or more than three miles. 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 the late fall and winter was the water level in the river low enough to safely divert. 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 cranes running on rails through the entire length of each tunnel were used to place the concrete. The side walls were poured. Next, movable sections of steel forms were used for the side walls. Finally, using pneumatic guns, the overheads were filled in. The concrete lining is 3ft thick, reducing the finished tunnel diameter to about 50ft. The river was diverted into the two Arizona tunnels on November 13, 1932, and the Nevada tunnels were kept in reserve for high water. This was done by exploding a temporary cofferdam protecting the Arizona tunnels while simultaneously dumping rubble into the river until its natural course was blocked. To protect the construction site from the Colorado river and to facilitate the river's diversion, two cofferdams were constructed. Work on the upper Coffer dam began in September 1932. Even though the river had not yet been diverted. The cofferdams were designed to protect against the possibility of the river's flooding. A site at which 2,000 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 96ft high and 750ft thick at its base. Thicker than the Hoover Dam itself, it contained about 650,000 cubic yards of earth. When the coffer dams were in place, the construction site was drained of water. Excavation for the dam foundation finally began. For the dam to rest on rock, it was necessary to remove the soils and other loose materials in the riverbed until sound bedrock was reached. Work on the foundation excavations was completed in June of 1933. During this excavation, approximately 1,500 cubic yards of earth was removed. Since the dam was an arch gravity type, the sidewalls of the canyon would bear the force of the impounded lake. Therefore, the sidewalls were also excavated to reach virgin rock at as weathered rock might provide pathways for water seepage. Shovels for the excavation came from the Marion Power Shovel Company. Love Me some Old Marians 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. Like looney tunes style, falling objects were the most common cause of death on the dam site. The high scalers work thus helped ensure worker safety. 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 toward 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 coworkers and at other times, cases of dynamite across the canyon. To protect themselves against falling objects, some high skillers 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 known as hard hats. The underlying rock foundation of the dam site was reinforced with grout, forming a grout curtain. Holes were driven into the walls and the base of the canyon as deep as 150ft into the rock, and any cavities encountered were to be filled. This was done to stabilize the rock, to prevent water from seeping past the dam through the canyon, to prevent water from seeping past the dam through the canyon rock, and to limit uplift or 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 fill, they moved on without resolving the problems. A total of 58 of the 398 fill holes were incompletely filled. 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. When it found that the work had been incompletely done. New holes were drilled for inspection galleries inside the dam into the surrounding bedrock. It took then nine years under secrecy to complete the supplemental grout curtain. And now for the concrete. The first concrete was poured into the dam on June 6, 1933, 18 months ahead of schedule. Since concrete 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 50ft square and 5ft high. Each 5 foot form contained a set of 1 inch steel pipes. Cool river water would be poured through the pipes, following 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 the columns which were grooved to increase the strength of the joints. Very cool engineering. The concrete was delivered in huge steel buckets 7ft high and almost 7ft in diameter. Crow was awarded two patents for their design. These buckets, which weighed about 20 short tons when full, were filled at two massive concrete plants on the Nevada side and were delivered to the site in special rail cars. The buckets were then suspended from aerial cableways which were then used to deliver the bucket to a specific column. As the required grade of aggregate in the concrete differed depending on placement in the dam from pea size to 9 inch stone, it was vital that the bucket be maneuvered to the proper column. When the bottom of the bucket opened up, disgorging 8 cubic yards of concrete, a team of men worked it throughout the form. Although there are myths about men caught in the poor and that were entombed in the dam to this day, each bucket deepened the concrete form by only about one inch and six company engineers would not have permitted a flaw caused by the presence of a human body. That's definitely what they would say. It's definitely what corporate would say. A total of 3,250,000 cubic yards of concrete were used in the dam before concrete pouring ceased in May of 1935. Additionally, 1.1 million cubic yards was used in the power plant and other works. More than 582 miles of cooling pipes were placed within the concrete. Overall, there's enough concrete in the dam to pave a two lane highway from San Francisco to New York City. Concrete cores were removed from the dam for testing in 1995 and 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. With most of the work finished on the dam itself, but the powerhouse remaining incomplete. A formal dedication ceremony was arranged for September 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 2:00pm Pacific Time to 11:00am because the Secretary of the Interior had reserved a radio slot for the president for 2pm but officials did not realize until the day of the ceremony that the slot was for 2pm Eastern time. Silly, silly. I make that mistake all the time. Despite the change in time and temperatures exceeding 100 degrees, about 10,000 people were present for the President's speech in which he avoided mentioning the name of former President Hoover who was not invited to the ceremony. Man, they did him dirty talking about fatalities since that's a common talking point with the Hoover dam. Of the 112 fatalities, 91 were six companies employees, three were Bureau Reclamation employees and one was a visitor. The remainder were employees of various contractors. 96 of the deaths occurred during construction at the site, not included in the official number of fatalities or deaths that were recorded as pneumonia. Workers alleged that this diagnosis was to cover for death from carbon monoxide poisoning brought on by the use of gasoline powered vehicles in the diversion tunnels and classification used by six companies to avoid paying compensation claims. The site's diversion tunnels frequently reached 140 degrees Fahrenheit, enveloped in thick plumes of vehicle exhaust gases. A total of 42 workers were recorded having died from pneumonia and were not included in the above total. None were listed as having died from carbon monoxide poisoning. When it comes to the power plant, excavation for the powerhouse was carried out simultaneously with the excavation for the dam foundation and abutments. The excavation of this U shaped structure located at the downstream toe of the dam was completed in 1933 with the first concrete placed in November of 1933. Filling of Lake Mead began in February of 1935 even before the last of the concrete was poured that May. The powerhouse was one of the projects uncompleted at the time of the formal dedication. A crew of 500 men remained to finish it and the other structures to make the powerhouse roof bomb proof. It was constructed of layers of concrete, rock and steel with a total thickness of about three and a half feet, topped with layers of sand and tar. In the latter half of 1936, water levels in Lake Mead were high enough to permit power generation and the first three generators, all on the Nevada side, began operating. In March of 1937, one more Nevada generator went online and the first Arizona generator by August. By September of 1939, four more generators were operating and the dam's power plant became the largest hydroelectricity facility in the world. The final generator was not placed in service until 1961, bringing the maximum generating capacity to 1,345 megawatts. Original plans called for 16 generators, eight on each side. But two smaller generators were installed instead of one large one on the Arizona side, for a total of 17. Before water from Lake Mead reaches the turbines, it enters the intake towers and then four gradually narrowing penstocks which funnel the water down toward the powerhouse. The intakes provide a maximum hydraulic head of 590ft. As the water reaches a speed of about 85 miles per hour. The entire flow of the Colorado river usually passes through the turbines. The spillways and the outlet works are rarely used. The jet flow gates, located in the concrete structures 180ft above the river and also at the outlets of the inner diversion tunnels at river level, may be used to divert water around the dam in emergency or flood conditions, but they've never been used and in practice are used only to drain water from the penstocks for maintenance. The amount of electricity generated by Hoover Dam has been decreasing along with the falling water level in Lake Mead due to the prolonged drought since the year 2000 and high demand for the Colorado River's water. By 2014, its generating capacity was downrated by 23% to 1,592 megawatts and was providing power only during periods of peak demand. Lake Mead fell to a new record low elevation of 1,071ft on July 2016 before beginning to rebound. Under its original design, the dam would no longer generate power once the water level fell below 1,050ft, which might have occurred in 2017 had water restrictions not been enforced to lower the minimum power pool elevation from 1,050 to 950ft. Five wide head turbines designed to work efficiently with less flow, were installed. Water levels were maintained at over 1,075ft in 2018 and 2019, but then fell to a new record low in 2021. Control of water was the primary concern in building the dam. Power generation has allowed the dam project to be self sustaining. Proceeds from the sale of power repaid the 50 year construction loan, and those revenues also financed the multimillion dollar yearly maintenance budget. Power is generated in step with and only with the release of water in response to downstream water demands. Lake Mead and downstream releases from the dam also provide water for both municipal and irrigation use. Water released from the Hoover Dam eventually reaches several canals. The Colorado River Aqueduct and the Central Arizona Project branch off Lake Havasu, while the All American Canal is supplied by the Imperial Dam. In total, water from Lake Mead serves 18 million people in Arizona, Nevada and California and supplies the irrigation of over 1 million acres of land. Absolutely spectacular. Big, big, big time. So that is the Hoover Dam in a nutshell. It's a spectacular piece of engineering. This was a very high level explanation. I looked at other articles. Most of this was from Wikipedia because they have the nicest, cleanest summaries. But you can go way down the rabbit hole on this project. There is so much literature online and I have enjoyed reading much of it. If you want to learn more, just search Hoover Dam on the Internet and you will be amazed at what you can find. So hopefully you enjoyed learning more about the good old Hoover Dam. If you have other ideas as far as projects I should look into and should feature on this podcast, reach out to us@dirt talkillwith.com and with that we will see you on the next one. Stay dirty everybody.