While building an igloo for kids the other day I thought how stable the whole thing becomes when you stack the final blocks, and the arched shape is complete. Then thought about masonry. It occurred to me that a standalone arch should hold up pretty well, even without the surrounding dome. Something like this:
http://en.wikipedia.org/wiki/File:CatenaryKilnConstruction06025.JPG
but made of snow:
https://lh5.googleusercontent.com/-KbVotGTvyj8/URvnKm3Do6I/AAAAAAAAAXs/_dyeaBGZOi0/w323-h241-n-k/IMAG0324.jpg
The test arch is just two feet tall, snow is sticky stuff at 32F and plastic support salvaged from trash is really flimsy. But it was promising. The arc stood fine after removing the plastic and it was dead easy to build it. So next one to one scale tests.

My idea is to shovel and stomp a pile of snow, let it harden for a while and then cut lots of blocks (that's how the igloo was constructed, along guidelines of BPL article by Tad Englund). Then stack one arch, move the support a bit, stack a new arch, move the support ... and thus start forming a snow tunnel.
I hope it would be very fast and easy to build. While igloo is quite limited in size and shape this method would also allow long tunnels, curved tunnels, tunnel crossings etc.

Weather is going to be wet for few days and snow will be way heavier than ideal for this so I'm going to have a week to come up with a good design for the support. Any suggestions about:
- size?
- materials?
- packability?
- else?

Alpo, this is a novel concept. Please do some testing on the thing and let us know how it goes.
The arch will need to have some length to give it some torsional strength kind of like a tunnel.

The only limit to size (length) would be the location and the amount of snow available. It might take a lot of time to get the size needed to be a workable/livable structure and for a large length structure you would want more then one support to speed up the process, but it might work just fine.

Let us know,
Tad

edited: you will need a 12.56 ft piece to make an arch equivalent to the interior of the igloo I build. That would give you an 8 ft floor. Of course you could make it smaller and the arch in more like a parabola than a half circle

Edited by bestbuilder on 02/13/2013 13:51:34 MST.

I like the idea!

Concerning packability, I'm not sure that any material conducive to rolling-up will have enough strength to support the blocks, but it sounds like your plan is to only rest the blocks on the frame rather than trying to create them in place by packing snow.

If so you may be able to use a more skeletal structure (e.g. a pair of tent poles with something to maintain their spacing and tension).

OTOH, if you go with a single sheet of stiffer plastic, you should be able to halve the length by hinging it at the midpoint.

Someone needs to design and sell a lightweight inflatable form that could be supported by trekking/ski poles for additional strength that you blow up, pack around with snow to make your igloo, and then deflate and remove.

If you followed Tad's igloo-building techniques and the majority of the weight of the snow remained on the walls rather than the inflatable this seems to me it would work.

I found this at Amazon.


It's too small for adults, but it does include a hole in the roof that would be used to finish the igloo from the inside.

More masonry:


And finished shape:

This time support was three sections of 5/16" tent pole bent in shape with thin cord. Snow blocks took care of the torsional rigidity. Still wet and heavy snow here. 1m high & wide shape would probably be still ok with this pole diameter if the snow was drier and lighter. But blocks of drier snow probably need a wider support.

I was thinking on how you might easily combine adjacent arches, and realized that using this method you'll end up with all the vertical joints lined up rather than staggered. Hmm...

Bicycle wheel is a very strong structure in respect to it's weight, right?



11 feet 'rim' made of same 5/16 tent poles in a sleeve. Holds heavy wet blocks to three feet height before bending. I'll tension the spokes a bit and wait for drier snow conditions. Collapsible just like tents, but if you'd just stuff it into your backpack - well you know what happened in Gordion.

Tensioning it like a bicycle wheel is a brilliant idea. Potentially the pole(s) are the same as for your back-up tent (you know, the one you bring in case the snow-cave-building conditions aren't right).

Alternately, I'm thinking of a 2-beam or 3-beam truss using 2 or 3 tent poles which pass through plastic or metal spacers. By fixing the distance between the otherwise flexible tent poles, they become much, much stronger and stiffer as an assembly.

Look at smaller radio towers - a triangular configuration of three main vertical members, trussed with many, small spacers which triangulate many points along the three long members.

In my caving days, I imagined such a contraption, compact until assembled, for pushing vertical leads where one couldn't rock climb up a face.

That is nice from you as it does look pretty awesome, you made better effort.

Finally got some drier cold snow and I had to give up the abovementioned 'bicycle wheel' construction. At least one made of odinary 5/16" diameter tent pole. Construction weighted total 350grams which is a bit ambitious. Three last blocks were always too much. Lessons learned:
- Snow knife as seen in classic film of Douglas Wilkinson is a very useful tool. In absence of one I used a mineral wool knife.
- First blocks need a solid base.
- Use the knife as in the film to get the blocks stick to each other.
- Few last blocks are the toughest bit.
- When the first arch is ready the next one with sideways support from the first arc is a piece of cake (tried with smaller sized shapes)

Finally got something useful done. With some leftovers of kitchen renovation I built a sturdier support. Snow is already pretty hopeless sugary powder for construction purposes and night temperatures are just few degrees below freezing. Trampled some snow and let it cure overnight and voila:

Also stacking second arch was easy (very easy), but didn't have enough firm snow so it collapsed right away.

Materials are 1/2 inch OSB board and 2mm plastic. Pretty suitable materials for building a toboggan, so maybe there is a chance to use this also for hiking.