Why is my concrete driveway sinking on one side?

Almost always because the ground under that side moved while the rest held. The usual causes are a base that was never compacted properly, fill that washed out when water funneled under the slab, or a section sitting over softer ground like an old trench or tree-root zone. The slab is just following the dirt below it. Sinking on one side is common and often fixable by lifting, as long as the concrete itself hasn't broken up.

Is a sinking slab dangerous or just ugly?

It depends on the slab. A slab that has settled as one solid piece is mostly a trip hazard and a drainage problem, and it can usually be lifted back to grade. A slab that has cracked into separate pieces that rock or sit at different heights has lost its structure, and that's the kind that gets worse every winter. The way to know for sure is to have it looked at before the freeze widens it.

Can a sunken slab be raised instead of replaced?

Yes, if the slab is still in one sound piece. Lifting works by filling the void underneath and floating the slab back up to level, which is faster and less invasive than tearing it out. It's the right call when the concrete is good and only the base settled. When the slab is cracked apart or the ground under it is gone, lifting has nothing solid to push against, and removal with a fresh pour is the better spend.

What makes concrete sink in the first place?

Movement in the ground underneath. Water is the biggest driver: it washes out fill, erodes the base, and saturates the soil so it can't hold weight. Southern Ontario's clay also shrinks in dry spells and swells when wet, which heaves and drops slabs over the years. Frost, tree roots, and a base that was never compacted right round out the list. Concrete doesn't sink on its own, the dirt below it does.

Should I wait and see if my driveway keeps sinking?

Waiting usually costs more. A small dip lets water pool and run toward the low spot, which feeds the same erosion that caused it, and every freeze-thaw cycle pries the crack a little wider. Catching it while the slab is still sound often means a lift instead of a tear-out. The assessment is free, so there's little reason to let another winter work on it.

Why Your Driveway or Slab Is Sinking, and What to Do

A driveway or slab almost never sinks because of bad concrete. It sinks because the ground underneath it moved, and the slab just went along for the ride. Figuring out why the ground moved is the whole game, because it tells you whether you can lift the slab back to level or whether it’s time to take it out and start over. Here’s how to read it.

What’s actually making it sink

Concrete is heavy and stiff, so when you see it dip, settle, or pull away from a step, the cause is almost always below it. The common ones in Southern Ontario:

A base that was never compacted. If the gravel under the slab wasn’t packed down before the pour, it keeps settling for years. This is the most common reason a newer driveway starts to dip.
Washed-out or eroded fill. Water moving under the slab carries the base material away a little at a time, and the concrete drops into the empty space it leaves behind.
Clay that shrinks and swells. Our clay soils expand when they’re wet and pull back when they dry out. Over enough seasons that movement heaves slabs up and drops them again, often unevenly.
Poor drainage funneling water under the slab. Grading that slopes toward the concrete, or downspouts dumping right beside it, sends water exactly where it does the most damage to the base.
Tree roots. Roots growing under a slab lift it, and roots that later die and rot leave a void that the slab settles into.
Frost. Water in the ground freezes and expands, pushing slabs around through the winter, then leaves gaps as it thaws.

Notice that water shows up in most of those. That’s not a coincidence. Keep water away from a slab and you take away the main thing that makes the ground under it move.

How to tell cosmetic from structural

This is the part that decides everything, and you can do a rough read yourself before anyone looks at it.

A problem is mostly cosmetic when the slab has settled as one solid piece. It might sit lower than it used to, or tilt toward one corner, but it’s still whole. You don’t have chunks rocking against each other. That slab still has its strength, it just isn’t sitting where it should.

A problem is structural when the slab has broken into separate pieces. Tell-tale signs: cracks wide enough to slip a coin into, sections that sit at clearly different heights, pieces that move or rock when you step across them, or crumbling along the crack edges. Once a slab is in pieces, it can’t carry load as one unit anymore, and each piece keeps moving on its own.

Quick gut check while you’re out there. A driveway that dips smoothly toward the road but stays in one piece is usually a lifting candidate. A driveway that looks like a broken-up puzzle is usually a removal job. The assessment confirms it, but that read gets you in the right ballpark.

Fix one: lifting a sound slab

When the concrete is still good and only the base settled, the fix is to raise the slab back to grade rather than tear it out. It works by filling the empty space under the slab and floating it back up to level. Faster than replacement, far less mess, and you keep the slab you already have.

There are two common ways to do it, and the right one depends on the slab and the void underneath:

Mudjacking pumps a cement-and-soil slurry under the slab to fill the gap and push it up. It’s a proven method and well suited to larger slabs.
Polyjacking injects an expanding foam that does the same job with a lighter material and smaller access holes.

We make that call after seeing the slab, the size of the void, and what the soil is doing. The point either way is the same: if the concrete is sound, lifting it is usually the smarter spend than replacing it. You can read more on the method on our concrete repair and resurfacing page.

One honest caveat. Lifting fixes the height. It does not fix the reason the ground moved. If a downspout or bad grade caused the washout, that has to be corrected too, or the slab will settle again. A real assessment looks at the drainage, not just the dip.

Fix two: removal and a fresh pour

Sometimes the slab is too far gone to save, and forcing a lift on it is throwing good money after bad. Removal and re-pour is the right answer when:

The slab has cracked into multiple pieces that move independently.
The surface is crumbling, spalling, or breaking up across a wide area.
The base under it is so eroded or soft there’s nothing solid to lift against.
The slab has been lifted before and keeps failing.

The advantage of starting over is that the base gets fixed properly. The old concrete comes out, the ground gets graded and compacted the way it should have been the first time, and the new slab is poured on a base built to hold it. That’s why a fresh pour done right outlasts a patch on a failing slab. Our concrete removal and demolition page covers how the tear-out works, and a new concrete driveway goes back over a corrected base.

It costs more up front than a lift. But on a slab that’s already in pieces, it’s the only fix that actually lasts, and an honest contractor will tell you which camp your slab is in instead of selling you the cheaper option on a job it won’t hold.

What to do right now

You don’t have to fix anything today, but a few simple moves stop it from getting worse before someone can look at it:

Keep water away from it. Make sure downspouts discharge well away from the slab, and clear any spot where water pools against it or runs toward the dip. Cutting off the water slows the erosion that’s feeding the problem.
Mark the trip hazards. A raised edge or a sudden drop is easy to catch a toe or a stroller wheel on. Note the worst spots so nobody goes down on them, especially in the dark or under snow.
Get it looked at before winter. This is the one that saves money. Every freeze-thaw cycle widens a crack and works the slab a little further out of place. A small dip caught in the fall is often a lift. The same slab after a hard winter can be a tear-out.

The longer a settled slab sits, the more the ground keeps moving under it, and the more your options narrow toward the expensive end.

Get it assessed before it widens

The honest truth is that you can’t tell from the curb whether your slab needs a lift or a full replacement, and guessing wrong in either direction costs you. We come out, look at the slab, the base, and the drainage, and tell you plainly which fix it needs and why.

The written assessment is free. Reach out, describe what you’re seeing, and book a look before the next freeze gets to work on it. You’ll get a clear answer on whether you’re lifting a good slab or replacing a failed one, before you spend a dollar on the wrong fix.