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Sunken Concrete Sidewalk Panels
in Ann Arbor, MI
Sunken sidewalk panels are one of the most common problems we see around Ann Arbor, especially on older tree-lined streets where tree roots have disturbed the soil underneath the concrete. Homes built before 1970 in areas like the Old Fourth Ward often have sidewalk slabs that have been settling for decades. A sunken panel creates a lip that people trip on, and it only gets worse as water follows gravity into the low spot.
Quick Answer
Sunken sidewalk panels in Ann Arbor usually mean the soil underneath has washed away or compacted unevenly under the slab. The most common fix is foam lifting, where expanding foam is injected under the slab to raise it back to grade. If the slab is broken badly it needs to be replaced. A raised edge over half an inch is a real trip hazard and should be addressed soon.
Telltale Signs
Warning Signs to Watch For
- One slab panel is visibly lower than the one next to it
- A lip or ledge of half an inch or more at a slab joint
- Water pools on the sidewalk in one spot after rain
- You can see a gap or void under the edge of the slab
- The slab rocks or flexes when you walk across it
Root Causes
What Causes Sunken Concrete Sidewalk Panels?
Soil washout beneath slab
Water running along the edge of the sidewalk slowly washes fine soil particles out from under the concrete. Over time a void forms, and the slab drops into it. This happens quickly on properties with grading that directs water toward the walk.
The Fix
Polyurethane Foam Slab Lifting
Small holes are drilled through the slab, foam is injected to fill the void and expand under the concrete, and the panel rises back to level. The holes are patched and the walk is usable within an hour.
Tree root soil disturbance
Large tree roots near older sidewalks on streets like Olivia Avenue push panels up at first, then when the root dies or is cut, the soil collapses and the panel sinks. The Ann Arbor urban tree canopy is dense enough that this is extremely common.
The Fix
Slab Replacement with Root Barrier
The broken or sunken panel is removed and the soil is regraded and compacted. A root barrier is placed if a tree is still nearby, and a new panel is poured. This is necessary when the slab is too cracked to lift intact.
Self-Diagnosis
Which Cause Applies to You?
Check the signs you're observing to narrow down the likely root cause before your inspection.
| What You're Seeing | Soil washout beneath slab | Tree root soil disturbance |
|---|---|---|
| Large tree root visible near the sunken slab | ||
| Void visible under slab edge when you look with a flashlight | ||
| Slab sunk but surface is still in one piece | ||
| Panel is cracked into multiple pieces as well as sunken | ||
| Water comes out from under slab when you step on it |
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