Hoover Dam

[walkinghorse]

The Hoover Dam is sturdy enough to last 10,000 years without any maintenance!
Ripley's Believe It or Not Comic Strip
on GoComics.com

Wonder if changing water levels affect that?

 

[cougar14]

My guess, like a Roman arch on it's side, is that since the amount of water behind it is limited by the height of the dam, the design cannot be overcome just by water weight. Don't know what earthquake parameters or any other phenomenon were considered.

 

[reddogge]

It's an impressive thing to see in person, especially down in the bowels.

 

[daniel lawecki]

If I remember right the cement is still setting it is still not hard as it could be.

 

[rburg]

It's an impressive thing to see in person, especially down in the bowels.

There was a cute little waitress that served us a while back. I wouldn't mind examining her bowels. I'm not big on damn bowels.

 

[Big Cholla]

The Hoover Dam design is called a "Gravity Arch". The water against the face pushes the abutments of the arch into the rock walls of the canyon with a force directly proportional to the depth of the water. The weight of the concrete is sufficient to prevent the water pressure from pushing under and lifting it out of position. The vast majority of the concrete poured was designed to achieve 2500 lbs per sq. inch (psi) crush rating in 30 days after emplacement. In certain higher requirement areas smaller quantities of concrete were poured with an initial 4000 lbs. rating. It is true that em-placed concrete will continue to develop more crush strength over many years. The maximum strength achievable is dependent on many factors, time being only one. The 2500 psi concrete will or has achieved around 4000 lbs and the 4000 psi concrete will or has achieved 6000 to 7000 psi by this time. If the original design values were the absolute maximum achievable, those values would have been sufficient for all design purposes.

The Hoover Dam Project is called "The Boulder Canyon Project". It was not sited in Boulder Canyon because the geologists found a significant earthquake fault across the proposed dam site. Boulder Canyon is the next big narrow canyon up stream. Hoover Dam is sited in Black Canyon which is earthquake fault free. Concrete structures are relatively elastic and therefore have a lot of 'give' before failure, therefore the Dam is very very earthquake resistant. The English and USA Armed Services during WW II found out just how hard it is to cause even a small concrete dam to fail.

As a Construction Engineer, I was privileged to work on the installation of the last generator Nevada (N) 8. Later in life I came to be awed by the engineering abilities of the designers, the sheer brain power and planning abilities of the contractors and the durability of the workmen. They designed and built that dam using No. 2 pencils, slide-rules, and yellow pads of paper. Compare that to the CAD/CAM and computer power available today. They did have a rudimentary phone system, but darn few of them. My father started work as a carpenter on July 6th, 1933. He said that the workmen survived the brutal summer heat down in the canyon by drinking from 3 to 5 gallons of ice water each per shift. He said some of the bigger guys drank twice that. I have literally been every place that a human can explore in the dam. I am still awed by the project.

 

[DWalt]

About the only events which could seriously damage the dam would be a massive earthquake or a nuclear blast.

 

[Big Cholla]

ISIS wishes you were right, but the size of the earthquake required would mean that we humans have a much bigger problem than the failure of Hoover Dam. A direct air blast of EMP from a significant atomic bomb would shut down the production of electricity for a long time but the basic structure would stand, damaged but basically intact. The right design of an atomic warhead set off upstream at near the base of the dam just might have fatal consequences. That would most certainly take out the intake towers and their ability to control water flow. So, the lake would drop to their base level. Still , I wouldn't count against the basic dam structures. ..... Remember, I moved from dam construction to the Nevada Test Site and the testing of atomic bombs.

One last bon mot; Take a look at the pictures of Hiroshima and Nagasaki post atomic bomb explosion. The only structures left standing even at ground zero were simple steel reinforced concrete buildings. ........... I rest my case. .....

 

[Big Cholla]

Oh, I missed answering the OP's question about the effect of changing water levels on the long term durability of the Dam structure. Again, concrete structures are relatively elastic in physical nature. Therefore, when the water lever rises the Dam arch is compressed into the side walls of the canyon. The degree of movement is measurable, but not noticeable. The number of those high pressure to low pressure cycles is very low and done at a very slow pace. This change in pressure cycle is never going to come close to the maximum number of pressure cycles that would cause failure of the Dam's concrete archway. Now on the other hand, our jet airliners must be inspected regularly during their design lifetime for structural failure to exactly that sort of pressure cycle consequences. And, they are taken out of service and scrapped when that life cycle limit is reached. They will never have to take Hoover Dam out of service because the water level has raised and fallen too many times. .....

 

[Chuck24]

About the only events which could seriously damage the dam would be a massive earthquake or a nuclear blast.

Or Clark Griswold !

 

[muddocktor]

ISIS wishes you were right, but the size of the earthquake required would mean that we humans have a much bigger problem than the failure of Hoover Dam. A direct air blast from a significant atomic bomb would shut down the production of electricity for along time but the basic structure would stand, damaged but basically intact. The right design of an atomic warhead set off upstream at near the base of the dam just might have fatal consequences. That would most certainly take out the intake towers and their ability to control water flow. So, the lake would drop to their base level. Still , I wouldn't count against the basic dam structures. ..... Remember, I moved from dam construction to the Nevada Test Site and the testing of atomic bombs.

One last bon mot; Take a look at the pictures of Hiroshima and Nagasaki post atomic bomb explosion. The only structures left standing even at ground zero were simple steel reinforced concrete buildings. ........... I rest my case. .....

Big Cholla, I don't doubt what you posted here and I'm certainly not a structural engineer, but what if the dam was hit with a few of those "bunker buster" type bombs that they developed for Desert Storm that were made out of old 8" naval cannon barrels and penetrated 100 feet or so into the ground before exploding. It would seem to me that these would do significant or even fatal damage to the dam if used to penetrate the dam or one of the abutments.

 

[Big Cholla]

The lower face of the dam is near vertical with the lower 1/2 swelled out downstream some. The upstream face starts in a parabolic curve getting significantly thicker towards the base. Penetrating earth or a few layers of 1 to 3 ft. thick concrete slabs with a bunker buster is one thing, but penetrating really hard steel reinforced solid concrete block structure is something else. The powerhouse wings and main control room structures could all be penetrated by the blockbuster, but there are much cheaper and more sure ways to deliver a knockout block to any electrical producing plant. Just overload the wiring and transformers with a huge blast of EMF (EMP).

I'm not a structural engineer either. I am also not an electrical engineer. But, I read a lot of various essays written by learned people that are not on ego trips, but are just delivering some very bad news from the viewpoint of their special educational niche. IMHO, the design of our nations's power grid is our weakest point for remaining in production during war or terrorist attacks. Most all of us are aware of the potential for disaster caused by an atomic bomb air burst of the correct design aimed at hitting our power grid systems and telecommunication systems and making them fail. The ultimate fix would be to move all power generation systems well under ground along with the transmission lines and switching stations. It would probably be cheaper to just build a state of the art anti-missile system and ring the USA and Canada with it.

But getting back to Hoover Dam. The generation of electricity there is much less important today than it was back in the late '30s. Lose the KWHs from Hoover Dam and the solution would be to just slightly crank up the production from a couple of Nuke Plants in the West. Hoover Dam is just idling along right now because of the extreme low water level of Lake Mead. Most of the electrical transmission lines that were so important for So. Cali. and So. Arizona in the '40's thru the year 2000 are now more important just because they connect switch stations in the overall grid system of the West.

And, speaking very plainly, the total destruction of the Dam would cause an huge loss of life and destruction of property downstream all the way to Mexico, but in the big picture of things those losses wouldn't affect the USA'a ability to fight WW III very much at all. Las Vegas would slow up for a spell because of the loss of water from Lake Mead, but it would very cheap and fairly quick to be done to just blast the canyon wall into the void where the Dam was and create an earth/rock fill dam that would back up the river and recreate Lake Mead in short order. In fact if the West hadn't of needed the electrical production of Hoover Dam, that would have been the cheapest solution to controlling the flooding of the Colorado River. ......

 

[Onomea]

Interesting explanations for us laymen, Big Cholla. Thanks!

 

[Big Cholla]

And to add to my post No. 12, due to the Great Depression, the country and Pres. Roosevelt needed a huge shot in the arm economically and the building of Hoover Dam was selected as one of those "shots in the arm". An unintended consequence was providing the vast amount of electricity to So. California just in time to be ready for all those defense plants to be built to aid in winning WW II. One WW II defense plant was built right here in Henderson, NV because of the availability of vast amounts of electrical power and the close availability of the metal ore required. ....

 

[rwsmith]

Don't forget how......

Don't forget how incredibly THICK the dam is. The concrete pours were so massive that they had to install cooling pipes in the concrete to relieve the heat given off by the chemical reaction of hardening.

The structural part of the dam alone has 3.25 million cubic yards of concrete. If you include all of the concrete structures you can add another million cubic yards.

 

[DWalt]

There were stories about workers being entombed in concrete during its construction, but in fact none were. The concrete was poured in relatively thin layers, not much more than several feet deep. Most worker deaths were the result of falls. As I remember, one odd fact is that the first construction project death and the last were a father and his son.

 

[rwsmith]

Boy was I glad.....

....

As a Construction Engineer, I was privileged to work on the installation of the last generator Nevada (N) 8. Later in life I came to be awed by the engineering abilities of the designers, the sheer brain power and planning abilities of the contractors and the durability of the workmen. They designed and built that dam using No. 2 pencils, slide-rules, and yellow pads of paper. Compare that to the CAD/CAM and computer power available today. They did have a rudimentary phone system, but darn few of them. My father started work as a carpenter on July 6th, 1933. He said that the workmen survived the brutal summer heat down in the canyon by drinking from 3 to 5 gallons of ice water each per shift. He said some of the bigger guys drank twice that. I have literally been every place that a human can explore in the dam. I am still awed by the project.

CAD/CAM was used by Aerospace and a few other select fields like automotive, where the volume justified the investment. In fact, the system that I (finally) got on (Cadam) was first used at Lockheed then was sold (for use on mainframes) until PCs finally got powerful enough to handle it. Our company had used mainframe Cadam, and I trained on it, but adopt the (very weak) PC version. By the time I retired in 2002 (early) Computers were fast as blazes and the software much better.

Anyway, nuclear submarines, all aircraft and ships, the Pentagon, Empire State Building, bridges and early spacecraft were all done on the drawing board. Everything. And it was amazing what could be accomplished with a lot of sweat and brains. When I worked as a Naval Contractor the roll of drawings for one signal exploitation (read 'spy') space on a ship was 6" in diameter on mylar. I can attest that working on a drawing board was a real bitch and after I acquired CAD you couldn't drag me back to a drawing table. I wasn't that hot of a draftsman but I could turn and burn with CAD. Though it looked much more plain Jane than Autocad, the interface was very fast and accurate and blew Autocad out of the water in competitions.

PS Funny story about that big roll of Mylar drawings. I was carrying that roll to the blue line machine at the other end of the complex on a crisp, cold day across a carpeted floor. As I walked the roll (think of all that surface area) acted like a big capacitor for static electricity. I must have built up quite a charge because when I walked by a metal typewriter stand a thick spark jumped to my leg and the mylar roll lit up like a failing fluorescent tube. I almost dropped to the floor That HURT.

 

[Big Cholla]

A Slight Correction

There were stories about workers being entombed in concrete during its construction, but in fact none were. The concrete was poured in relatively thin layers, not much more than several feet deep. Most worker deaths were the result of falls. As I remember, one odd fact is that the first construction project death and the last were a father and his son.

The official death toll was from accidents and even the definition of accident was narrowly defined to keep that death toll total low as possible for political purposes. Sound familiar? You are absolutely correct in that there are no bodies buried in the concrete. The USBR Inspectors were death on even a cigarette butt being tossed in a pour.

But, the real death toll should have included workmen's deaths from heat related complications. It is estimated that upwards to 250 more men died in the hospitals or at home from heat prostration complications. Still, all in all, it was a fairly safe place to work at least for a project at that time, in that sort of place and one that was working three shifts in all sorts of weather. .......

 

[DWalt]

Back in my earlier days as an engineer, all we had to use was the drafting table and the slide rule. There were some mechanical calculators for multiplication and division, but that was pretty much it. The very first thing I ever used having any similarity to a computer was in the late 1960s, basically a fairly crude programmable calculator. Of course, there were mainframe computers around long before that, but mere mortals weren't allowed to go anywhere near those.

 

[Big Cholla]

I started with a slide rule, and a mechanical Marchant (spelling?) adding machine. The first electrical calculator I ever saw in person would add, subtract, multiply and divide out to about 6 places. It had to be plugged into 110v. current and it cost $750. I was in my own construction firm by that time and I gladly paid the price. Recently the Bank I deal with gave me free of charge a calculator that is on the cutting edge of being called a computer. In fact it can be connected to a computer. I imagine that on the retail market it would bring $60 tops.

I remember how great the feeling it was on my first construction management job to have a telephone on the project. Then came the electrical calculators. Then came the fax machine. I thought that it just couldn't get any better. Then the computers started showing up. Then CAD/CAM and I was almost overwhelmed. When cell phones were available I thought nothing could surpass what the average Construction Engineer now had to work with. Then here came the laptop computer and the smart phone. I'm glad I'm as old as I am. The next innovation would probable make my brain explode. ...

I still have my first serious Surveyor's Transit. It is a German made Lietz. It is totally mechanical and optical. I'm sure that today's graduate civil engineer wouldn't know how to use it and get any good results. I don't know what I'm going to do with it. Perhaps a museum would like to have it. I still use it around my little building projects here at home. It can be used as a Surveyor's Level and that is about all I use it for. But, I still know how to turn an angle and to layout super elevations for a roadbed curve. ..... Oh, and I got it out last night to look at the super moon.......