I remember standing at the base of Hoover Dam the mist rising from the Colorado River. You look up, but can't just raise your head, you have to arch your back and lean backwards to see to the top of this massive structure, 726 feet in height. The concrete arch curves across the canyon in a smooth graceful form. It is hard to appreciate that Lake Mead, the largest reservoir in the United States by volume (when it is full) is sitting calmly behind the dam, waiting patiently to pass through the dam and meander downstream on its way through Mexico and into the Gulf of California. It’s not a small job, there are 3,250,000 cubic yards of concrete sitting there in the valley.
Lake Mead at Hoover Dam
Standing in Hoover Dam, to my left, was the powerhouse sending electricity to Las Vegas about an hour’s drive away. The bright lights fire up from the turbines spinning using the water’s head downstream. The turbines on the Nevada side and the Arizona side combine for an installed capacity of 2080 MW generating 4.2 trillion watt hours of electricity annually. It’s hot up on the abutments but in the valley along the river, the mist cools you as it rises from the turbine outflows.
Arizona side of Hoover Dam
and the Nevada side of Hoover Dam
There are many sources of information regarding Hoover Dam (see the links below) but here are some fun facts. Hoover Dam was built from 1931 to 1936, and at the peak of construction 5,251 workers were employed at the dam. The 1931 cost was budgeted for $49 million and Lake Mead covers 247 square miles.
I am a concrete guy and here are some concrete facts. Concrete generates heat and then contracts as it cures, the potential for contraction and cracks caused by the tension of contracting needed careful consideration. Hoover Dam and most large concrete dams are built in blocks. For Hoover Dam, some of the blocks were as large as 50 square feet and 5 feet high with steel pipes to provide flowing cool river water. Ice cold water was supplied from a refrigeration plant for the final cooling. After curing, pipes were filled with grout, and grout filled any spaces between columns. The Hoover Dam concrete mix is referred to as mass concrete, having large rocks in the mix to help build up the volume and reduce the need for cement. All concrete mix designs have aggregate, sand, cement and water, but formerly referred to mass concrete (concrete with very large diameter aggregate) creates specialized material properties and requires specialized considerations in review and analysis of the aged structures.
Hoover Dam on the Arizona-Nevada border where the hydroelectric power is generated
Hoover Dam is considered as the 8th Wonder of the World. It is interesting to read facts about the dam, it is inspiring to be there, and it was an honor to be on the United States Bureau of Reclamation (USBR) engineering staff to study this iconic structure. To evaluate a dam it is important to know the current properties of the dam. As Chief of Materials Engineering and Research Laboratory for USBR, I oversaw the drilling of concrete cores resulting in long cylinders of concrete which were then boxed and shipped to the lab for testing.
The boxes were laid out on exam tables in the order of depth. The core was shiny when misted with a spray of water and rocks the size of footballs could be seen. We searched for any small cracks or joints as these needed to be tested to determine the concrete strength in shear. Some joints were intact and required careful investigation with a magnifying glass to even be found. Other planes could be found across the diameter of the core including the breakoff point when obtaining the core, cracks caused by spinning during drilling, or they could just be open or weak areas. The remaining intact cores became the samples for testing.
The purpose of the cores was to determine the condition of the dam this many years after construction. Properties such as compression strength, the stress at failure, failure strains, and the normalized deflection at failure were found using laboratory tests. These properties were compared with computer analysis of the dam under current conditions and with projected extreme conditions such as an earthquake. This was critical considering the dam’s age and that the loading conditions actually experienced may be substantially different than those expected years ago when the dam was originally designed.
After 9/11, I helped set up the security procedures and evaluations for USBR’s more than 350 dams. For Hoover Dam, I wish I could tell you more, but I can tell you the dam stands tall and strong after more than 75 years. Hoover Dam is a true credit to Civil Engineers even today.
As an American Society of Civil Engineers (ASCE) Fellow of the Structural Engineering Institute (SEI) I am proud to have worked on this massive and magnificent structure representing the Civil Engineering profession. For younger students, come join us in an interesting and rewarding profession. We need your creativity to solve the problems of today for a better tomorrow.
One of the Winged Figures of the Republic sculptures seen at the Nevada end of Hoover Dam
REFERENCES:
1. 'Hoover Dam.' Wikipedia. Accessed September 25, 2020. https://en.wikipedia.org/wiki/Hoover_Dam
2. Koch, E., ‘Eighth Wonder of the World.’ Las Vegas Sun., May 15, 2008. https://lasvegassun.com/news/2008/may/15/what-dam-project/
Links for more information: Historical Information & Photographs (From United States Bureau of Reclamation Hoover Dam Website)
The Story of Hoover Dam - A series of articles that explain the history and some of the technical aspects of Hoover Dam. These articles offer a more in-depth explanation than the FAQ statements.
Hoover Dam Historical Collection - A collection of museum items, historic photographs, and news clippings related to Hoover Dam.
Photograph Gallery - Historic and modern photographs of Hoover Dam.
Hoover Dam 75th Anniversary - Photographs, a video, and media coverage of the September 30, 2010 event at Hoover Dam.
Images taken by Lara Barker of Integral Engineering Co.
