Compacting Snow with a Jumping Jack or Plate Compactor
Well, you’re going to like this. It’s an interesting challenge involving preparing a base for a building on snow. The building is on piers like you would see in houses down the shore. Instead of being driven into the ground like pilings, they rest on 5’x5′ footers, which are then buried in the snow. The cool part is that the piers can be adjusted to raise the building periodically in order to prevent it from being completely buried by snow drift. To do this we install a temporary “house jack” type system that supports the building independently of the piers. The piers can than be raised up and the area where the footers sat can be back-filled to a new higher elevation. The footers are then re-installed and the building can be lifted to accommodate the new elevation.
So the dilemma is how to compact the back-filled snow where the footers will land. When this process was done previously, the footer pads were compacted by hand. This resulted in some sensible, but not significant settling. We had been advised to use a jumping-jack to compact the snow and had tested the theory when back-filling a trench. The results were…horrendous. It took 3 of us to keep the jumping jack from burying itself in the snow. I’m not sure if they did a core sample to see if it had any impact on the density, but in the top 6 inches or so, it seemed to fluff the snow rather than compact.
The way that snow behaves is very much dependent on the temperature. When it’s warmer, the snow is wetter, and behaves more like a cohesive soil. When it’s colder, the snow behaves more like a loose sand. So, I’m looking at a vibratory plate compactor as one possible solution. The other is to use a roofing torch to sinter each lift. Another idea was to somehow use the footer itself or something of similar area and load and unload the footer after each lift to compact.
Regardless of the exact method of compaction, we’re intending to do a number of small lifts using a massive snow blower type puppy called a snow beast.
The building is 100k lbs and there are 8 footers each having a 5’x5′ area ( 25 sq.ft.). So, we’re looking for the snow to be loaded at about 3.5 psi. I think minimally, we’ll want to compact the snow to support 10 psi.
What are your wild and crazy ideas?
Replies
As you understand, snow is not soil.
Tools developed for soil compaction will have issues with the snow.
You might see better results with a modified compaction tool, one with either more surface area or a modified vibration profile. (or both)
It also might make a difference to fill with snow located at some distance below the surface, rather than surface snow. the density of snow at the surface is likely less, and dryer in most conditions, while the snow at depth may be higher in density. your compacted fill will end up interacting with snow at depth in any case
Liquid or spray water may help modify the fill and help with compaction.
Thinner layers also may help this process.
All these modifications take energy, which I assume comes with a high cost to transport into the area.
Using the pylons to compact the snow might be more effective if you concentrate the force on a subset of the area. (example would be to lift the 5 foot pad, install a layer of fill, press with the pad, raise the pad, place something under the pad, (like 5 foot long 6x6 timbers spaced 6 inches from each other), Press, lift, remove timbers, fill between, replace timbers shifted for the new fill, press, repeat....
Not sure how the dynamics of this will impact your other pads or the building as a whole.
Thanks for that thoughtful reply. Gives me a couple of ideas for field tests.
We actually did build a larger foot for the jumping jack, which did not produce the results we were after. It dug itself into a slightly bigger hole. I'm under the impression that the jumping jack is not the right tool for the job at all and looking more towards vibratory plate compactors. What were you thinking about in terms of a modified vibration profile?
I had considered using essentially a garden sprayer to introduce moisture to the area but the struggle is with keeping the nozzle from freezing as well as volume of water used. We make our water in a snow melter. I think it's a good option, it will just take some figuring to make it viable.
Thanks for your feedback. I'll let you know how things turn out.
One other thing to consider is making suitable fill snow from water and compressed air. This takes lots of energy, however, but there are a few places who have spent much time making snow for the ski industry. The "snow" made is very different than the stuff that falls from the sky, but I do not have any feel as to how it would compare with the stuff you can dig up onsite.
I bet you could get a suitable fill with some experimentation that would not require compacting (or much compacting)
Somewhere there is a person who learned how to make snow concrete while trying to make powder.
Ask an old Inuit.
If you're looking for 10PSI compaction, that's 20 sq in of bearing area for a 200 lb person. Sounds like Japanese geisha clogs to me, Kinda low tech, but no fossil fuels involved and the old Inuit could probably show you how to make them.
Would a sod roller do the trick? The nice thing there is you get lots of contact with fluffy snow>> low compaction, but as you get more compaction, you get less contact area>> higher compaction. Stop when your 200 lb geisha doesn't sink in. Only problem is keeping the expansion of freezing water from popping the roller.
If my sources are credible, plate compactors range from 7 to17 PSI, (listed compaction force divided by plate area) so they should be usable as is. I'd consider misting the snow for better cohesion. Good luck finding one rated for Arctic service.
These are not bad ideas. We have access to spent food grade glycol we could use in place of water for a sod roller. Be a little heavier/ volume too.
I'm particularly tickled by the clogs idea. I'm imagining being in the pit with my crew decked in homemade clogs stomping to the Tarantella like Lucille Ball in a vat of grapes.
When faced with many options, I always opt for the italianest.
Can you make the footers bigger or continuous?
The footers are pre-built steel plates with various webbing and supports. So, short answer, no.
I think you are supposed to wait 6 hours? between lifts. Not sure on the timing but that is an important part. Maybe a pentometer would give you an idea of how you are doing?
Tagging along the Inuit suggestion, you could have your crew put on skis and compact the area. This is what I was taught (long ago) for backcountry ski shelters, we would cut the compacted snow into blocks for igloos.
Tim,
I'm surprised that compacting with skis led to a cohered material that could be cut into blocks and stacked. One back-country ski would be at least 1.5x"72" ~= 100 sq in ~= 2psi for my 200 lb geisha and I wouldn't expect the compacted layer to be more than a few inches thick.
Ref Uncle Mike's vibration profile suggestion, I believe there are pile drivers that consist of rotating eccentric weights, somehow tuned to the natural period of the piles, hopefully adaptively, since I'd expect the resonant frequency to change as the pile gets buried. Each "stroke" only gives a small fraction of an inch, but even 100 RPM would add up fast.
I'm getting curious about the purpose and location of this building. My current hypothesis is long term shelter in Antarctica. U55 has definitely gotta let us know how it all comes out.
Yes Im curious as well. My guess is Greenland.
Well when you have a dozen 19 years olds on skis in really good conditions on a well-compacted base it is possible. You leave the area to consolidate overnight into a cuttable medium. You don't get perfect blocks of styrofoam, but it worked well enough. We were up in the mountains of Wyoming.
Jumping jack is a bad idea for this) Maybe you should try paving machine and make some substance from snow with adding water in it? I've heard in some cold countries they even do roads from it.
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