There's a hole in the driveway, dear Lisa, dear Lisa...
September 10, 2012 8:21 AM   Subscribe

Who should I be contacting to fix this sinkhole?

This summer, I discovered a smallish sinkhole that developed right at the corner where my driveway meets the garage and the front sidewalk. Pictures here, here and here.

As far as I can tell, the hole is about 2 feet deep - the foundation of the garage prevents it from going too far back under the garage itself. It doesn't appear to have grown since I discovered it, but it has been very dry here the last couple of months.

I will be correcting what I believe to be the source of the hole by installing gutters on the house - I'm pretty sure there was excess water pooling around and wrapping in front of the small garden seen in the first pic which was the source of this washout.

The question is, I'm not sure who I should be calling to fix this? Or could I even fix it myself? The driveway needs to be repaired in this spot but driveway repair guys don't deal much with structural foundations, and vice versa. Any advice would he helpful, bonus points for specific recommendations in the northern Twin Cities suburbs. I want to get this fixed before winter. Other recommendations or ideas on what to do, how it happened, and how to prevent more are also welcome.

Potentially relevant details:

- House was new 10 years ago in a new neighborhood that was previously cropland. I'm the original owner and have not noticed any other issues, only the usual small basement and garage floor cracks. (This is normal as the new house settles, right?)
- Soil content here is mostly slightly sandy clay.
- We are not too far from, but definitely above, the water table. There is a pond 200 feet behind the house with a maximum elevation of maybe 20 feet below the house.
- We do have a sump pump that runs only when it rains hard (presumably due to the lack of gutters).

Thanks in advance!
posted by SquidLips to Home & Garden (5 answers total) 1 user marked this as a favorite
 
It's odd and could be the result of critters burrowing under your garage. You may check with the pest control people first. If it seems to get bigger after rain events then there is probably a failing underground drain line there. Its hard to tell in the last picture if that is what is down there. Without knowing the topography of your yard, it is hard to determine if there is a water issue causing the sinkhole.

The other question is how has it developed over time? Did it suddenly appear or has it slowly appeared over those ten years? Does the rainy season cause it to increase in size? If it is a slowly appearing hole and there is no underground drain there then you could have a mudjacker come in and fill it with grout.
posted by JJ86 at 8:42 AM on September 10, 2012


I would say this is a drainage problem. The pavement around the hole is kinda swelled up and cracking in a fairly classic subgrade failure. The subgrade is the actual dirt the structure is built on. Subgrade failure is almost always the result of water infiltration, either from ground water or from a improperly sealed surface. My guess is the construction joint between the pavement and the garage slab was not installed or done improperly and with the standing water from the lack of gutters you got infiltration and the subgrade wasn't compacted enough and with the load from the structure on it and the water it has know compacted/washed away and you have a sinkhole.

The first thing to do is fix the drainage so NO water pools here or runs across this area. If the driveway slopes so water runs to this area or the gutter discharges here or anything that directs water here nothing you do will fix this problem for more than a short time. If you keep the water away a cheap DIY fix might solve all your problems, so address drainage first.

As to the cracking, small random direction hairline cracks are fine. If you have a set of radial/bullseye cracks around this point you have a foundation issue and you need to fix that ASAP by a professional. If you aren't sure, get a pro out to look at it and give you advice. Maybe pay a structural engineer a couple of hundred to come look at it and give you on the spot advice about both the cracking and the drainage issue/subgrade failure. On site visits from a pro are usually worth it.

The right way to fix this is to sawcut the pavement back a few inches beyond the cracking/heaving then jackhammer out the pavement between the sawcut and the concrete slab. This will expose the failure and let you know better the extent of the damage. Then get a product called controlled density fill (or non shrink grout) which is just a really runny concrete without aggregate (small rocks) pumped in to fill the hole. After this hardens (usually about a day) you then install the proper construction joint and repave with asphalt or better yet concrete. This will be pretty pricey but you will end up with a final product better than the initial construction.

For the DIY approach you can just dump home mixed non shrink grout (you can mix it just like any other kind of mortar in bucket at home) and pour it in the hole until it stops accepting any more than try to pry out the cracked pavement areas as much as you can until you hit solid pavement( you can actually do the pry out first) and put in a cold patch asphalt material and compact it good (do not skip this-rent the right equipment from you local construction rental business) or if you have any talent with concrete finishing use a bag or two of quikcrete (properly mixed-water content is critical) to patch the top of the hole. This will hold for a while (years) as long as you fix the drainage issues so water doesn't pool here or get much rainfall.
posted by bartonlong at 9:37 AM on September 10, 2012 [1 favorite]


Thanks for the answers so far.

It's very possible the hole itself has existed for some time, and only recently did the asphalt over it weaken enough to start falling in. I did notice over the last year or two this exact spot having kind of a sunken quality that, at the time, I attributed simply to settling, and figured some new asphalt overlay and a little mudjacking on the sidewalk would bring things back to level. I would guess it was about two weeks to go from from 'the corner there looks really sunken today' to looking like it looks now, 2-3 months later, and this was during a particularly wet period earlier in the summer, so I'm pretty certain this is a drainage issue (hence the gutters I'll be installing).

From overseeing the construction, I'm remembering the water and sewer lines being more off to one side of the house. Additionally, given the construction I would expect those lines to be located a good 8-10 feet beneath this surface point. Which isn't to say they're not the issue, I just would have thought such a problem would have manifested itself in a much larger way, and it doesn't seem to be growing in the absence of rain around here lately.

I would guess it was about two weeks to go from from 'the corner there looks really sunken today' to looking like it looks now, and this was during a particularly wet period earlier in the summer, so I'm pretty certain this is a drainage issue (hence the gutters I'll be installing).

The critter theory is interesting; our neighbors did have a gopher problem this spring that started to spill into our lawn, but all of the gopher holes were on a different side of the house, the nearest being a good 30-40 feet from this spot.

Would a driveway firm be able to accomplish all of this work? I need work done anyway on other areas - due for sealcoat, and the guy who quoted my gutter work recommended I consider replacing the first foot or two of the driveway next to the house with a concrete apron - and it would be great if this could all be done at once.
posted by SquidLips at 2:59 PM on September 10, 2012


Call Digger or Julie or whoever does utility locates and make sure there are no buried utilities near there. It would be a whole different problem if the hole was caused by a leak in something like that.

Who I would call would be one of those basement sealer places. They are skilled at digging up around foundations, fixing shit, and then filling it back in correctly. Even though it looks minor, you'd hate to just fill it in with Sackrete and later find out the whole corner of your garage is cantilevered over an empty hole.

Or look for companies who do mud jacking. This is where they drill a hole in the floor, jam a hose into it and pump a mud/grout sort of mixture into the ground, to raise and level concrete slabs. They probably have some kind of inspection process to see whether there are any voids under the slab or the sidewalk.
posted by gjc at 8:07 PM on September 10, 2012


That section of your asphalt driveway doesn't get driven over or walked on so it is likely that it was an older problem that finally became visible.

Asphalt driveway people may or may not be able to handle filling the hole. Although you could fill it yourself as bartonlong suggests, I would actually opt for putting grout in the hole under pressure so that it can fill more extensive cavities, if required. Mudjacking companies can do this easily and quickly. Gophers will be quickly encased in grout for future generations to enjoy if they are the culprit.

Before you do that, make damn sure that there isn't an issue with your sewer lateral or you will have very expensive problems. You can hire a plumber to do a sewer lateral inspection by video if the laterals run nearby. They aren't cheap but will be cheaper than having to dig up a lateral full of grout. Laterals do fail, especially if they were put in poorly. If it is more than ten feet away from this corner of the garage then it probably isn't likely that it is an issue.
posted by JJ86 at 8:33 AM on September 11, 2012


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