Engineering the Hoover Dam

“To be sure, there [are] a lot of lessons to be learned from civil engineering history,” said Kiewit’s Paul Giroux, explaining the purpose of his presentation “Building Hoover Dam: Men, Machines, and Methods.” Giroux offered a brief, behind-the-scenes history of the Hoover Dam, as he explained the engineering innovations and processes that enabled the project.

“Because of the speed of technological change in the early twentieth century, it’s safe to say that Hoover Dam could not have been built more efficiently or to the standards achieved even a decade earlier,” asserted Giroux. The rapid construction of Hoover Dam was enabled by a variety of factors, including technological advancements, well-qualified personnel, and politics. The Bureau of Reclamation, a major proponent and funder of the project, was founded in 1902 and quickly established itself as a formidable organization in the following years. The Arrowrock Dam, constructed from 1911-1915, served as a training grounds for the engineers of Hoover Dam. Local floods and a large dam break in the 1920s left the public clamoring for safe dams of the Colorado River and with the 1929 Stock Market Crash there already existed a ready supply of willing labor.

The Hoover Dam required several different, difficult components. The first main challenge was the river diversion project. According to Giroux, this “consisted of installing upstream and downstream coffer dams and installing four concrete-lined fifty foot diameter tunnels, each approximately 4000 feet in length.” Other components of the dam included “a u-shaped hydroelectric powerhouse; twin, open line concrete spillways; the intake towers that channeled water to the powerhouse; and finally the twin outlet works,” he said. The most noticeable portion of the system was certainly the 726 foot high arch gravity dam composed of 3,250,000 cubic yards of concrete. 

A coalition of six different companies, dubbed Six Companies, Inc., submitted a bid March 4, 1931, with an estimate cost of $48.9 million. Their bid was accepted, and the companies began work on the project soon after. Before any of the actual dam structures could be constructed, however, the remote site needed to have extensive infrastructure added. “Like the dam, the scope of the temporary construction works required to build Hoover Dam were unprecedented,” commented Giroux. Railroad lines, roads, electrical lines, water lines, and telephone lines had to be added. An entire town had to be constructed. 

The first component of the actual dam to actually be built was the river diversion works. These consisted of four fifty-six foot diameter, 4000 foot long tunnels requiring1,563,000 cubic yards of concrete. They were crucial to further construction, as the river was piped through them while the rest of the dam was constructed. First, the tunnels had to be painstakingly excavated in temperatures up to 130 degrees and oxygen levels so low the workers were literally gasping for air. Then, the concrete had to be laid at an average daily production of 2000 cubic yards, or eighty linear feet, per day. Original plans required the tunnels to be completed by October 1, 1933, but through diligent hard work and extensive use of new technologies, the diversion tunnels were completed November 12, 1932.

While the diversion tasks were being completed, dam excavation and aggregate production were also occurring. The dam required the construction and use of two concrete plants and an aggregate processing plant, which mixed together the extremely large volume of ingredients required for the huge quantities of concrete in the dam and diversion tunnels. In preparation for the actual dam structure, approximately 22,000 cubic yards of debris and fractured rock were removed per day. This required high-scalers, workers conducting probably the most dangerous job on the project, who hung from the canyon walls and blasted away bits of loose rock. They made $5.60 per day, as opposed to the average worker’s $4.00.

Once the debris was removed and the river diverted, the first bucket of concrete was dropped for the actual dam structure on June 6, 1933.  “Concrete was placed block by block in five foot high lifts in hundreds of interlocking concrete blocks, which ranged in size from about twenty-five to sixty foot squares,” explained Giroux. And although crews had placed only 25,000 cubic yards of concrete by the end of June 1933, this number would skyrocket to over 250,000 cubic yards per month in the spring of 1934. During peak employment, the Hoover Dam project employed 5,000 workers working in three shifts, making safety crucial. Concrete was poured out of eight-cubic-yard bins as fast as possible and then held in a frame for approximately twenty-four hours before the frame was moved up to the next level. Simultaneously, pipes were laid in the dam to prevent dangerous shrinkage as the concrete continued to cool. Concrete pouring was completed in May, 1935, and grouting was then pumped into the holes of the dam.

Another important component of the Hoover Dam project was the 650 foot long u-shaped hydroelectric powerhouse. It was constructed by Six Companies, Inc., but all of the internal components were contributed by the Bureau of Reclamation. The powerhouse is capable of housing seventeen turbine generators and became fully operational on October 26, 1936. As Giroux explained, “Dwarfed by the dam, the 250,000 cubic yard power house also tends to be overshadowed in public accounts of Hoover Dam’s construction, yet the drawings indicate a complex structure [requiring as much attention as the dam].”

In a time dominated by innovation and technology, Giroux reminded his audience that the “Hoover Dam was completed seventy-five years ago in the age of the propeller aircraft, but its design, construction, and lessons have endured well into the jet age.”

Picture Caption: Paul Giroux explains the story and the legacy of Hoover Dam.