Filling void under asphalt driveway

Question

We recently moved into a new to us house. There are a couple of depressions in the asphalt driveway that I thought I should try to level with some bagged asphalt patch.

Maybe unsurprisingly, when I swept the dirt and loose debris out of one of them, I found that there was a hole straight through the asphalt and into a void in the soil below. I am thinking this is an animal burrow, since I have found another void just under the soil surface nearby which I was able to confirm is a burrow.

My thought is that I could break away an opening in the asphalt large enough to gain greater access, fill the cavity to the best of my ability with crushed stone and then cover with and tamp the patch material.

I realize of course that if there is a burrow that close to the surface, it may manifest in other locations over time which I'll have to address too.

Otherwise, does this seem like an okay plan? Or should I be looking to do something else? (Short of tearing up the driveway, re-grading and repaving..)

Answer 1

Possible causes: (not all of them equally likely)

• Burrowing.
• Poor compacting prior to paving.
• Wood e.g roots, logs, garbage left under the gravel now decomposing.
• Could be water erosion, perhaps a burst pipe. That would probably be obvious though.

I'd make a small effort to determine what's causing it, but at this stage I wouldn't make too much effort at that, and jump quickly to exactly what you are planning to do. If the situation returns I'd then dig it up and figure out what's causing it.

I wouldn't assume it's burrowing just because there is burrowing somewhere else. It's a clue. I have chipmunks, rabbits, groundhogs, voles, and hornets digging up my lawn constantly but I've never seen any of them burrow all the way under a paved driveway for no reason. Might be a question of Outdoors SE.

Answer 2

I hope you weren't planning to dump some patch into the hole and forget about it.

The proper way to patch a hole is to cut out a clean square, add substrate if needed, and then apply the patch.

So if you do this properly then the cause of the issue will reveal itself at some point.

Here is a video which shows a very similar situation: How to Repair an Asphalt Pothole | Ask This Old House

Answer 3

So here is what I ended up doing.

Tools used:

• Masonry Chisel & small sledge
• Pinch Point Bar
• Shovel
• Trowel

Materials used:

• 3 bags paver base sand
• 2 bags crushed (drainage) rock
• 2 bags cold asphalt patch

First, I used the chisel to lightly mark a perimeter outside the depression.

Then using the chisel & pinch point bar, I was able to open up the area and achieve fairly vertical walls. I wouldn't call them smooth, so certainly not as good as using a saw.

I dug down, clearing asphalt debris, base rock and some of the underlying stone & clay. Doing so I could follow the void (loosely filled with debris) down maybe 18" until it went underneath a small buried boulder. I'm now more than ever fairly certain it was a burrow. By this point I had removed 4 (or 5?) five-gallon buckets worth of material (asphalt, crushed rock, clay soil / stone).

Photo looking into the burrow under the boulder.

I forgot to take pictures at this stage, but I filled the burrow with crushed stone, packing using the pinch point bar.

I then added & tamped down the paver sand.

Followed by crushed stone, up to a level just below the existing asphalt.

I then added 1 bag at a time of the cold patch, tamping flat between bags (I actually didn't need the whole second bag and used the rest elsewhere.

Looking at it now, I probably should have removed a bit more of the asphalt, widening the hole. I say this because although it wasn't noticeably depressed (on the right side of the final picture) there is still a crack visible in the asphalt. So I guess I'll see if it stands the test of time...