On it’s completed in 1936 this was the largest concrete structure ever built.
The incredible feat of engineering played a critical role in the development of the
American Southwest during the early 20th century,
providing flood management, hydro-electric power
and securing a reliable source of water for millions.
This is how the Hoover Dam was built.
With plans around since 1900 to harness the power from the mighty Colorado River,
it wasn't until 1928, that the United States Congress authorised the project and
initial surveying began.
With the onset of the great depression just a year later, the project was seen as a way
for the government to provide much-needed jobs in the American southwest, which had
been experiencing a population boom prior to the stock market crash.
Located 26 miles southwest of Las Vegas, on the Nevada-Arizona border, the project required
a vast number of workers and their families to relocate - and an entire new town was established.
Owned and run by the government, Boulder City was to be a model for the rest of the country
to follow in the dark times of the depression.
To drive the project’s progress, President Hoover ordered construction of the dam to
start in May 1931 - before the necessary infrastructure at Boulder City was in place - and many workers
lived in temporary tents in what became dubbed Ragtown.
To escape the harsh living conditions, many workers began to frequent the then small outpost
of Las Vegas, driving significant growth and earning it a reputation for gambling and adult entertainment.
Though living conditions were poor, work began on diverting the Colorado river so that the
dam could be constructed on the dry riverbed.
To divert the waterflow, four 56 foot, 17 metre wide diversion tunnels (two on each
side of the river) were bored through the canyon using nothing more than dynamite followed
by workers using pneumatic jackhammers.
Excavated rock was then dumped into the Colorado River, creating a cofferdam that forced water
to flow through the newly constructed tunnels.
A second cofferdam downstream prevented water flowing back into the construction site
and formed an area that could be pumped dry, exposing the river bed.
The Hoover Dam employs a gravity-arch design and is held in place by the weight of its
concrete together with the pressure of the water it holds forcing it into the canyon
floor and walls.
Such a principle required the canyon surfaces to be smoothed as one of the first activities,
to prevent leaks.
It was during this phase of the project that the first hard hats began to be used.
Workers dipped their hats in tar and let it harden, protecting them (at least to some extent)
from falling debris.
Seeing their success, the project’s leaders quickly ordered thousands
of these hats and mandated their use by the workers.
In 1933 - some 18 months ahead of schedule - the first concrete pours began on the dam.
As concrete gives off heat and contracts as it cures, a project on the scale of the Hoover
Dam would have taken more than 125 years to harden if poured in a single continuous pour
and structural weaknesses would have caused the dam to crack under its own weight.
Instead, the site was divided into a series of rectangle moulds, some as large as 50 square
feet (or 15 square metres) in size.
These moulds were fitted with a series of steel pipes that carried river water through
them, allowing the concrete to cool and harden much faster than if it was left to do so alone
in the heat of the desert.
Once the concrete had hardened and stopped contracting the pipes and hairline cracks between
neighbouring blocks were filled in with grout and a new layer of moulds was placed on top.
This process was repeated time and again to build the dam walls.
As the dam steadily rose, getting the concrete to where it had to go before it began to harden
started to pose a significant challenge.
To overcome this, an ingenious system of overhead cables that carried buckets of concrete from
specially built concrete plants on the Nevada side of the dam to the required location on
the construction site was used.
In total, 87.5 million cubic feet of concrete and
some 582 miles of cooling pipes were used in the construction of the dam.
By 1935 - two years ahead of schedule - the 726 foot high dam was complete and the river
diversion tunnels were sealed shut, allowing the Colorado to begin flooding the canyon
behind the structure and creating the reservoir that we know today as Lake Mead.
Fit out of the adjacent power plant and its associated infrastructure took place in parallel
with construction of the main structure - and the dam began generating electricity at the
end of 1936.
Today, this remarkable infrastructure project has an average output of 4.2 billion kilowatt
hours and provides water and electricity to millions across the southwestern United States.
An economic catalyst to an entire region of North America and a powerful example of the
impact that our industry can have.
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