“My asphalt driveway is sinking, along with the yard next to it. The sunken area is a car-length wide and two car-lengths long. I repaired it with two tons of asphalt, and since then it has sunk 6” to 8” more. Can you please give repair advice?”
Asphalt driveways should be poured over a base of crushed stone, which is placed either on undisturbed grade, or on fill soil that has been mechanically compacted. When driveways sink, it’s most often because the underlying dirt was not properly compacted, or because the fill dirt contains debris (such as tree stumps) that are decomposing and collapsing underground. However, there can be some other causes:
- Erosion and undermining of the soil bed due to improper rainwater drainage.
- Underground collapse or erosion due to a broken buried pipe or underground stream.
- Environmental factors specific to your region and building site, such as sinkholes, unstable marshland, expansive soil, volcanic or seismic activity, or hillside erosion.
You’ve described some pretty significant sinking, more than I’d expect from normal soil settling. I’d take these steps:
- If your home is fairly new, contact your builder. Improper compaction of the driveway subsoil is an issue that should be covered under your home’s warranty.
- Contact your utility company, or dial 811 for a free identification of buried lines and cables. Not only is this a good safety measure, but it could also tell you if a broken buried line or pipe could be contributing to your problem.
- Examine your downspouts and rainwater drainage. Make sure water isn’t running toward your driveway, pooling or eroding the soil underneath it.
- Contact a soil engineer, to determine exactly what’s going on underground – particularly to diagnose regional geologic conditions. You don’t want to keep on patching your driveway if it’s going to keep on sinking, and you really need to make sure there’s not an underlying problem that could grow worse or even affect your nearby home’s foundation.
Based on the soil engineer’s report, your repair may be as simple as another patch, or it may involve taking up the existing driveway and making extensive repairs to the subsoil. The repair may or may not be a DIY job, but you could really use a professional opinion (or more than one) for diagnosis and recommendations.