1930s Aerial Tramways

During the construction of the Hover Dam in the 1930s, 10 aerial tramways were built in order to move material from the canyon sides down to the construction side 700' below. The five 20-ton tramways operated at a horizontal speed of 1,200 ft/minute and could lower at 300 ft/minute.

In addition, a single 150-ton aerial tramway was built, which still survives although it does not appear to be serviceable:

Nevada tower:
🔗Hoover-Dam-Tunnel-User-Album-Image-028[linkphoto]Hoover-Dam-Tunnel-User-Album-Image-028[/linkphoto][/link]
🔗Hoover-Dam-Tunnel-User-Album-Image-027[linkphoto]Hoover-Dam-Tunnel-User-Album-Image-027[/linkphoto][/link]

The track is made up of six 3.5" steel cables spaced 18.5" apart horizontally and supported by a tower on the Nevada side and by a steel and concrete saddle on the Arizona side, set into a tunnel bored into the rockface.

Detail of cables:
🔗Hoover-Dam-Tunnel-User-Album-Image-029[linkphoto]Hoover-Dam-Tunnel-User-Album-Image-029[/linkphoto][/link]

The 150-ton tramway operated at 240 ft/minute with a travel of 1,050' of a total 1,200' span. Maximum load speed (for hoisting and lowering) was 120 ft/min for loads up to 40 tons and 30 ft/min for loads between 40 tons and 150tons.

In order to operate the tramway, five control stations were established: the main one on a lookout projecting 20' from the canyon wall and the remaining four at the portals of the construction adits leading to the penstock header tunnels.

The machinery was located inshore of the tower on the Nevada side, with each drum of the hoisting and conveying system driven by its own motor. In something of an advanced used of technology for the 1930s, the retardation of lowering loads was regenerative, although dynamic brakes were also provided to stop the descent and hold loads. As an aside, the emergency brakes utilised a Ferodo lining.

The three driving motors were rated at 400hp and the hoist motors at 175hp (there seems to be a lack of information on how many of these there were).

The anchorages at both ends consisted of 6.5' x 9' tunnels driven into the rock of the canyon sides, opening into chambers of 18'x18'x10' - these chambers and at least 50' of the tunnel were subsequently filled with concrete, with six 'bar-and-pin' units connected to a 13'x13' structural steelwork in the chamber itself. The cables were tensioned by 60 ton hydraulic jacks located between the Nevada tower and the anchor.

Arizona side anchor:
🔗Hoover-Dam-Tunnel-User-Album-Image-024[linkphoto]Hoover-Dam-Tunnel-User-Album-Image-024[/linkphoto][/link]

When operating with a full 150 ton load, the pull on the Arizona side would have been 2,058,000 pounds and 2,100,000 pounds on the Nevada side: the breaking strain of the six cables was set at around 3x this, at 1,070,00 pounds each, or 6,420,000 pounds in total.

The track carriage used 48 rollers, 8 on each cable. These were of 24" diameter whilst the hoist sheaves were of 35" diameter.

Close-up of Nevada tower:
🔗Hoover-Dam-Tunnel-User-Album-Image-026[linkphoto]Hoover-Dam-Tunnel-User-Album-Image-026[/linkphoto][/link]
🔗Hoover-Dam-Tunnel-User-Album-Image-025[linkphoto]Hoover-Dam-Tunnel-User-Album-Image-025[/linkphoto][/link]

The main purpose of the 150 ton tramway was to lower the steel sections of the penstock tunnels: these are of 30 diameter and due to their size had to be cast on site. It also seems likely that the tramway was used to lower the turbine components.

The smaller 20 ton tramways were mainly used to lower concrete to the construction site, although they could also be used in pairs to move larger items of machinery.

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2006 aerial tramways

In an echo of the 1930s work, a new (temporary) aerial tramway has been installed in order to permit the construction of a new bridge, just downstream of the Hoover dam.

This is a twin-track tramway, supported on a pair of towers located at either side of the canyon. It can handle up to 50 tons of materials and is located 890' (270m) above the Colorado River and spanning 2,300' (700m).

New tramway:
🔗Hoover-Dam-Tunnel-User-Album-Image-033[linkphoto]Hoover-Dam-Tunnel-User-Album-Image-033[/linkphoto][/link]

The original aerial tramway (a refurbished 42-year old system!) suffered a considerable setback on September 15th 2006, when strong winds gusts caused the collapse of the four supporting cranes, causing a two-year delay to construction.

The new system was provided by Italian company Agudio http://www.agudio.com/en/products/cablecranes.php , who interestingly refer to them as 'Blondins'!

Close-ups of man baskets:
🔗Hoover-Dam-Tunnel-User-Album-Image-032[linkphoto]Hoover-Dam-Tunnel-User-Album-Image-032[/linkphoto][/link]
🔗Hoover-Dam-Tunnel-User-Album-Image-031[linkphoto]Hoover-Dam-Tunnel-User-Album-Image-031[/linkphoto][/link]

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Great album Vanoord. I see what you mean now about being several leagues over the sea. There was a doc. on TV some time ago on the building of the original dam that was very interesting. It was a very hairy business for the workers. I believe over 200 were killed or died.

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Cheers Carnkie :)

I'll put up a thread about the dam itself in the next couple of days - the scale is hard to comprehend, for example the four diversion tunnels that had a diameter of 50' and were a total of 3 miles in length! Mind you, I'd still say that a 150 ton aerial tramway is very impressive...

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Great album Vanoord. I see what you mean now about being several leagues over the sea. There was a doc. on TV some time ago on the building of the original dam that was very interesting. It was a very hairy business for the workers. I believe over 200 were killed or died.

Aa I saw that program, it was a great series, there was another one I think about The Panama Canal.
Great Album by the way Vannoord, when did you visit the dam?

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Fascinating and very impressive indeed.
Thank you, Vanoord.
I seem to recall (from the TV documentary?) that the underground workers suffered from sub-lethal, carbon monoxide poisoning but it was dismissed as pneumonia/flu.

Ah yes, something else about a man falling into the setting concerete and being trapped... 😢

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There is a pretty impressive aerial shot of the dam in Wiki.

http://upload.wikimedia.org/wikipedia/commons/9/94/HooverDam.jpg 

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Ah yes, something else about a man falling into the setting concerete and being trapped... 😢

Nope: no bodies in the concrete, the guide assured us. Said they were not structurally sound... 😉

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The concrete pours averaged 6" in depth, little room to bury a body!

As I recall from the documentary, the dam was poured in 6' cubes with cooling water pipes run through them (I *think* it was quoted that it would take 100 years or so for the whole lot to cure). Yes many of the tunnelers did suffer from CO poisioning. Along with the non unionisation of the whole project (If you didn't like the condidtions there were may more willing to take your place.) In someways it was a very brutal (in human terms) project, but, it did provide massive employment at a time of recession.

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There are quite a number of sites with interesting historical photos of the dam construction. The main one (with links to others) is :
http://www.usbr.gov/lc/hooverdam/index.html 

And this one:

http://www.ecommcode.com/hoover/hooveronline/hoover_dam/splash.html 

The original "blondins" were constructed by Lidgerwoods - a company which still exists after many mergers.

I'll wax lyrical on the subject of the development of the "american" blondin another time.


Grahami

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I bought a book when I was there which was, in fact, copies of about 20 articles published at the time the dam was being built in something called Compressed Air Magazine .

I'll transcribe some of the tunneling-related bits of the articles later on - the methods were rather interesting, although I can't quite get my head round all of it at the moment...

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