How to fill in a sinkhole?

[Squirrel Girl]

OK, as cavers, we all know not to build over sinkholes. Rah to Cindy for her work to keep the WalMart off the cave in Alachua!

BUT! Take your average US homeowner (e.g. MY SISTER) who lives in a karst area and who has had a sinkhole open NEXT TO HER HOUSE. She keeps filling it, it keeps opening back up.

Yes, my reaction is DUH! But I'm a geologist, not a geotechnical engineer. What can she do that is practical? I think she just threw in cinderblocks and rocks for her next try.

FYI - we're talking Bloomington, IN. She claims the sinkhole is big enough to stuff a small body into (HAH! I guess that means not hers nor mine! )

[JackW]

OK, as cavers, we all know not to build over sinkholes. Rah to Cindy for her work to keep the WalMart off the cave in Alachua!

BUT! Take your average US homeowner (e.g. MY SISTER) who lives in a karst area and who has had a sinkhole open NEXT TO HER HOUSE. She keeps filling it, it keeps opening back up.

Yes, my reaction is DUH! But I'm a geologist, not a geotechnical engineer. What can she do that is practical? I think she just threw in cinderblocks and rocks for her next try.

FYI - we're talking Bloomington, IN. She claims the sinkhole is big enough to stuff a small body into (HAH! I guess that means not hers nor mine! )

Oh, can I come check it out before she tries to fill it in again?

I also have a card that says I'm certified safe in unstable rock zones (I made it myself - but don't tell anyone )

On a serious note, I can get her in touch with people from the city of Bloomington that can likely help her.

There is a PM on its way to you!

[Squirrel Girl]

Hi JackW,

Thanks for the info. They won't condemn my sister's house will they? Could be it better for her to just keep filling away (after you've checked for the cave????)

[George Dasher]

The State of WV has guidelines for filling in sinkholes.

I'll email them to you if you want them.

[Squirrel Girl]

The State of WV has guidelines for filling in sinkholes.

I'll email them to you if you want them.

That'd be great. I'm sure you've got my email address. I'll have my sister contact JackW before she actually does any more work, though. It'd be a bummer to have her fill in an honest to goodness cave entrance.

And, of course, I suppose that if her house is going to collapse into an underground void, that maybe she ought to know that instead of just pouring rocks in the hole.

Thanks

[hewhocaves]

And, of course, I suppose that if her house is going to collapse into an underground void, that maybe she ought to know that instead of just pouring rocks in the hole.

Thanks

that would be a very sisterly thing to do.... not laughing afterwards would be another. :)

In NJ, we 'fixed' a cave entrance at the bottom of a sink by extending the passage up to the surface using concrete sewer pipe (the landower, coincidentlaly, made septic systems, so we used his spoils). We cemented the first segment directly to the rock face, then extended it up till it reached the surface (slightly higher, actually). Once we felt we had a 'good seal' we backfilled around it. We had to do that a couple of times to account for simple compression, but afterwards it was remarkably stable.

Because he made septic tanks, one of the segments was the tank itself. This actually provided a nice room to finish getting ready in (in a pinch you could change completely in it). We also noticed that bats liked to be in that room as well.

one of the things we wished we did was place rebar on the upper inside part of the tube as ladder rungs (the tube was at about a 60 degree angle). We had one or two on the bottom and it stops an otherwise enjoyable slide.

Point is, we tried to locate the passage where all the fill is going to, isolate it and move it right up to the surface. then fill around it. It's great if it's heading towards cave.

john

[bigalpha]

hey John,

that's how I've always seen it around here. occassionally, you'll see a big piece of pipe sticking up out of the ground, filled in around by rip rap.

[JackW]

Hey, what ever happen with this?

[Squirrel Girl]

Hey, what ever happen with this?

I dunno. I passed on the info to my sister. I haven't heard that she's actually done anything. Perhaps her previous "fix" has lasted long enough that she hasn't implemented anyone's suggestions.

[Amemeba]

OK, as cavers, we all know not to build over sinkholes. Rah to Cindy for her work to keep the WalMart off the cave in Alachua!

BUT! Take your average US homeowner (e.g. MY SISTER) who lives in a karst area and who has had a sinkhole open NEXT TO HER HOUSE. She keeps filling it, it keeps opening back up.

Say Squirrel Girl, back in the early sixties the easily accessible crawlway leading to an attractive limestone cave was blocked by US Steel by stuffing rolled-up newspapers in the entrance and then back filling with rubble.

Well, here it is 2006 and after much effort and digging over the years we still use the tricky upper drop to enter the cave.

When wet the rolled up newspapers swelled up and they became impenetrable.

[Squirrel Girl]

Wow, amemeba, that's kinda weird. I would have thought eventually they would have rotted. But I'm sure you've heard of the weird things they've found in landfills that HAVEN'T rotted. So I guess you never know.

[Larry E. Matthews]

We get that question occasionally here where I work (Tennessee Department of Environment and Conservation. If it appears to be threatening a house, we recommend:

1. Plug the bottom of the hole with the biggest rocks practical.

2. Then add smaller rocks, bricks, etc.

3. Keep adding smaller material to fill up the voids.

4. Do this up to about one foot from the surface, then cover with an impermeable layer, like thick plastic.

5. Top off with soil and plant grass.

6. Call and make sure your home owner's insurance covers you if it collapses into a sinkhole. If not, get a rider immediately !!!!!

The idea is to try to PLUG the hole, to prevent water from continuing to enlarge it.

On second thought, do # 6 FIRST, then do # 1 - 5.

Larry E. Matthews
Professional Geologist

[George Dasher]

The trouble is, the water has to go somewhere.

So you can't plug all the sinkholes.

And the ones you don't plug are more in danger of collapsing, because now they have to handle more water.

We try to stablize the sinkhole but still let the water enter.

[hewhocaves]

The trouble is, the water has to go somewhere.

So you can't plug all the sinkholes.

And the ones you don't plug are more in danger of collapsing, because now they have to handle more water.

We try to stablize the sinkhole but still let the water enter.

agreed. too often sinkholes are simply viewed as a problem with a *automatic solution*. But George is right. Plug that crack up sufficiently well and the water will find another, easier place to eat away at (or you'll get a swamp, lol).
I would argue that sinkholes are a blessing - when they open up we now know where the water wants to go. Our goal should be to allow that water to take its natural course while leaving as small a footprint as possible. So this may mean everything from shoring up the sides of the sinkhole to landscaping around it with good, soil retaining bushes to possibly building a platform over it so that the space is still usable even though the sink is still there (make sure to leave an access point to check on it, though.)

On the road to Lost World Caverns in Lewisburg someone had the right idea... they built a gazeebo across the top of the sink and lined it with shrubbery. Eyesore gone!

john

[Larry E. Matthews]

I was referring to small, new sinkholes close to people's homes. Usually, these holes are only 1 to 3 feet across, when we go look at them.

I was not referring to large, previously existing sinkholes that provide significant drainage.

I think the question was addressing new openings that threaten existing houses.

Larry E. Matthews
Professional Geologist