Why Is My Driveway Sinking?

Short answer: Most Oklahoma City driveways sink for one of four reasons. Shrink-swell clay pulls away from the slab in dry weather. Loose backfill beside the foundation or over utility trenches settles. Water from downspouts or slopes washes the base out. Or a leaking pipe erodes soil from below. Where it sinks, and when, tells you which.

OKC Driveway Repair Co. repairs sinking driveways across Oklahoma City, and the cause decides the fix. Why is my driveway sinking? In this part of Oklahoma the answer is almost always one of four things, and the place the slab is sinking is the best clue to which one.

1. Shrink-swell clay

Much of the metro sits on red Permian clays. The USDA describes the Kirkland series as formed in clayey sediments over Permian shale, and the Oklahoma County soil survey rates it high for shrink-swell; the related Renfrow series formed in the same Wellington, Garber and Hennessey formations. Clay like this swells when it is wet and shrinks when it dries. In a dry Oklahoma summer it pulls away from the underside of the slab, leaving gaps. In a wet spring it swells back, but not always evenly.

The clue: panels dropping a little at a time across the drive, often worst at the joints and edges, with no single obvious source of water. Hot, dry summers make it worse. Oklahoma City has seen as many as 63 days over 100°F in a single year.

2. Loose backfill

When a house is built, the soil next to the foundation is dug out and refilled after the footing is poured. Utility trenches for water, sewer and gas are dug and refilled too. That fill is often not compacted as well as the undisturbed ground around it, and it keeps settling for years.

The clue: sinking in a specific strip. Right at the garage joint (see driveway sinking at garage), or in a line across the drive near the street where a utility runs, or at the apron.

3. Water washing out the base

Downspouts aimed at the drive, slopes that send runoff along its edge, and flat lots where water stands against the slab all carry soil away or keep the base soaked. This is erosion, not settling.

The clue: sinking along one edge or at a corner, a hollow you can see or reach under the slab, soil washed onto the street, and changes right after heavy rain. That’s a washout.

4. A leaking pipe

A broken water or sewer line under or beside the drive can wash out soil from below with no surface water at all.

The clue: sinking in one spot that keeps getting worse, a wet area that doesn’t dry, an unexplained jump in the water bill, or a sewer smell. Call a plumber or the utility before any slab work.

What it means for the repair

• Clay and settled backfill: driveway leveling lifts intact panels; joint sealing and drainage keep them up.
• Backfill still moving or panel broken: cut out, dig out the soft fill, replace with compacted stone and re-pour.
• Washout: fill the void with something that won’t erode and redirect the water.
• Leak: fix the pipe first.

If you’re not sure the sinking is safe to leave, read is a sinking driveway dangerous?

Bottom line

Clay, loose backfill, water and leaks sink almost every driveway in the metro. Where the slab is sinking tells you which. Fix the cause along with the slab, or it will sink again. For an on-site look at yours, call (405) 442-4044.