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My 12x20' outdoor bedroom has a sinkhole below it. The land is lava rock and here, the lava rock was bulldozed, so it was all broken up and indeed, there are lava tubes around these parts. The one below the bedroom has opened up several times and has been filled as much as possible with rocks of varying sizes and cinder.

I am thinking about using that expandable foam now. Any thoughts out there on that?

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Are you asking how to fill the sinkhole? It's not quite clear from your question. –  Chris Cudmore May 1 '13 at 20:16
    
It'd be nice to know what's actually down there: groundpenetratingradar.com/hawaii.html also google.com/… –  Wayfaring Stranger May 1 '13 at 20:34
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This is really a localized problem. Unless we have some users who are native to volcanically active regions, no one here will be able to answer. I'd look for local advice. People who have dealt with similar problems. –  Chris Cudmore May 1 '13 at 21:42
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Fixing the earth's crust doesn't seem like a DIY project. –  DA01 May 2 '13 at 3:42
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4 Answers 4

Foam sounds like a bad idea to me for a sinkhole. I've seen them cover old wells with large quantities of foam followed by earth, but your situation is a never ending geological process caused by water flow. Have you read this about the Guatemala sink hole? The article suggests the right way would be to layer rocks. Very large at the bottom and smaller as you go up so that the water can flow through that area but doesn't take the soil with it causing another sink hole. I'd go that route if it was me.

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Dow does make GREAT STUFF™ Big Gap Filler. Though I'm not sure if a sinkhole would be considered a big gap, a huge gap, or even a gap at all.

Since you mention the sinkhole might be a lava tube, you may want to try GREAT STUFF™ Fireblock. However, according to the GREAT STUFF™ Consumer Safety Information, GREAT STUFF™ will combust at 240°F (116°C). Since lava tends to be 1,292 to 2,192 °F (700 to 1,200 °C), GREAT STUFF™ probably won't hold up if the tube fills with lava.

I'm not sure how well polyurethane foam would hold up in/underground, but I'm guessing it's probably not a recommended use. Your best bet would probably be to fill the hole with large rocks instead.

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Large rocks are also known to melt when exposed to lava. –  BMitch May 2 '13 at 11:53
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Dow GREAT STUFF™ Sink Hole Filler is pretty good. The catch is that it comes via railroad tanker cars and it's a real chore shaking it before every use. –  DA01 May 2 '13 at 16:50
    
@DA01 - The shaking is no problem, as long as you arrange for an earthquake. Does Dow make a LAVABLOCK product? –  user558 May 28 '13 at 13:39
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You need a ramp that hits level ground.

Then you need a large bin of rock and dirt that is higher than the ramp (maybe much higher). The rock and dirt will slide down the ramp until the hole is full. This may take some testing.

So as the sinkhole opens you will be giving rock and dirt to it. And once it has enough it should wait on the ramp for the next opening.

An optional suggestion would be a raking system at the top that would be triggered when items come off of the ramp. This would evenly distribute the sediment across the hole.

And an optional optional suggestion would be a sprinkler system that would trigger for a certain amount of time after the raking. This would add weight to your sinkhole so that it compacts in the hole. This may trigger more dirt and rock to be used but I take sinkhole filling seriously.

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My answer is based on opinion and since I live on the big island I know some things about the land here. There are lava tubes everywhere on this island, the longest one I know about is 77 miles from volcano to Kaloli pt. Filling in could be a futile project since your tube could be really big and rain is plentiful. You did not specify your location, my land is in mt view hilo side. If you really can't or want to move your house, I would fill as much as possible with large substantial rock and find the biggest piece of 3/4 or thicker steel metal to go overlapped on solid rock over your opening. However without knowing the geology of what's under there exactly it could be questionable to be sleeping over it. Thanks for posting this, I found it because I was seeking knowledge as how to prep after bulldozing seems a little unstable

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