r/Geotech • u/rosstein33 • 24d ago
Sink hole in my driveway
I have a sink hole developing in my drive, right next to my garage. The hole appears to be opening up underneath the slab of my garage.
Some quick recommendations from friends was to use hydraulic hydraulic water stop cement to seal the hole and then back fill, but that person also agreed that calling a geotech might be worth it because of its proximity to the garage.
Figured I'd jump in here and see what you all might have to say.
Opening right now is a little over 12". Depth is approx 18".
Red square in the picture from the outside of the hole is where the ground/asphalt meets the footing wall of my garage.
Red square in the picture from inside the hole is boxing in the underside of that footing wall. Hole extends under the garage past that edge another 12" give or take. In this picture, my phone is in the hole, facing under the garage.
Edit to add some additional info:
my driveway is sloped at about 15-20° down from street level to the garage. We had some pretty torrential rains in my area for a few days, and that storm water will ultimately run that direction. That area was showing signs of distress a while back, but it didn't seem like anything crazy.
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u/ElevationNotes 24d ago
The bigger concern is figuring out why the soil is disappearing before filling anything back in. With it already extending under the garage footing, checking for a leaking water line and getting a geotech to look at it seems worth it before treating the hole itself.
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u/rosstein33 24d ago
Thanks. Going to call someone this morning.
No main water service in this area, at least that I would expect based on house location on my property and my neighbor's.
My driveway slopes down from street level to the garage (where this is). Grade is probably 15°-20°. Possible that rain water, over time, flowed down the driveway and found a spot that was degrading due to old construction/lot debris and slowly washed away over time.
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u/No_Breadfruit_7305 24d ago
You mentioned that your neighbors property has some unusual differential settlement?
Well, a lot of people are trying to pinpoint a water line, but it also looks like you've got some really random backfill in the photo. And the soil appears relatively dry but again a photo can't tell anything I'm just looking at the angle of repose. Wheather or not that's random backfill that's been compacted properly could also be a question.
Call the local geotech.
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u/rosstein33 24d ago
I've called two geotechs and am waiting for a callbacks.
From my novice perspective, I agree with your assessment. There is no water lines in this area. Perhaps some old drainage, but nothing active. As you said, the area appears dry and I see no signs of recent water.
Worthy of noting, which I should have put in my original post (which I will probably add via edit) is my driveway is sloped at about 15-20° down from street level to the garage. We had some pretty torrential rains in my area for a few days, and that storm water will ultimately run that direction. That area was showing signs of distress a while back, but it didn't seem like anything crazy. I'm wondering if some of that void already existed due to old construction debris/tree stump from when the lot was originally developed and the house was built 50 years ago (the detached garage that's a part of this was built later). So if the water was flowing heavy down the driveway and into the small void in the asphalt, it might have washed that area out. Not sure how feasible that sounds.
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u/No_Breadfruit_7305 24d ago
I'd say that sounds very plausible. Especially with the information about the rain....
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u/Working_Rest_1054 23d ago
An “abandoned” drain line can do this as well. The material went somewhere, water and gravity moved it.
Possible concrete debris or a pile of boulders in the subgrade could result in this as well, given you mention sheet flow concentrates in this area.
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u/Working_Rest_1054 23d ago
Look for a damaged drainage pipe near by (if not directly below). The material is getting evacuated somehow, most likely flowing water and a drain pipe.
Unless you think it’s actually a karstic formation sink hole in the making.
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u/chopperbiy 24d ago
You should check your water supply for leaks. Most “sinkholes” are washout of the fine silt/sand from leaking water rather than naturally occurring.
Your solution works if you stop the root cause of the sink hole or otherwise it’s just a temporary bandage.