Leaning and Tilting
A retaining wall should sit plumb or lean slightly back into the slope it is holding. If your wall is leaning outward, even a little, that is the clearest sign that something is wrong. In Abbotsford, wall lean is almost always caused by hydrostatic pressure from water building up behind the wall in our clay soil. Without adequate drainage, the water saturated clay pushes against the back of the wall like a hydraulic press.
We have seen walls in the Fraser Valley that tilt a quarter inch per year and then suddenly shift several inches during a heavy November rainstorm. If you notice any outward lean, do not wait. The forces behind the wall are increasing every time it rains, and the longer you wait, the more likely the wall will need full replacement instead of repair.
Cracking and Separation Between Blocks
Cracks in a retaining wall are a symptom, not the problem itself. Vertical cracks usually indicate uneven settling in the base, often caused by poor compaction during original construction or erosion undermining the footing. Horizontal cracks or separation between courses suggest the wall is being pushed outward by soil pressure.
In Abbotsford's freeze thaw climate, water gets into small cracks, freezes, expands, and widens them over each cycle. A hairline crack in October can become a significant gap by March. Check your wall in early spring after the winter freeze thaw cycles have done their work. That is when new damage reveals itself.
Bulging and Bowing
A bulge in the middle of a retaining wall usually means the base is holding but the mid section is taking more pressure than it can handle. This is common in walls that lack geogrid reinforcement or have drainage that has clogged over time. The bulge creates a weak point, and if the pressure is not relieved, that section can blow out suddenly.
Bowing along the length of the wall, where a section curves outward compared to the rest, often points to a localized drainage failure. A downspout dumping water behind one section, a blocked drain pipe, or a broken irrigation line can all create concentrated pressure that pushes the wall out in one area while the rest looks fine.
What Causes Retaining Wall Failure
The overwhelming majority of retaining wall failures we see in Abbotsford come down to three causes: inadequate drainage, poor base preparation, and lack of geogrid in walls that needed it. Our clay soil makes drainage the number one issue. A wall built without gravel backfill and a perforated drain pipe behind it is fighting a losing battle against hydrostatic pressure every time it rains.
Poor base preparation, meaning insufficient excavation depth, wrong base material, or inadequate compaction, causes settling and tilting. And walls over three to four feet that lack geogrid reinforcement simply do not have the structural capacity to resist the soil loads behind them long term. If your wall was built by an unlicensed contractor without engineering input, these three problems are almost always present.
| Symptom | Likely cause | Urgency | Typical fix |
|---|---|---|---|
| Outward lean (any amount) | Hydrostatic pressure from failed drainage | High — call immediately | Tiebacks or full rebuild with drainage |
| Vertical cracks | Uneven base settling or erosion | Medium — monitor seasonally | Targeted base repair or section rebuild |
| Horizontal cracks / course separation | Outward soil pressure, missing geogrid | High | Rebuild with geogrid reinforcement |
| Bulging mid-wall | Clogged drainage or missing geogrid | High — blowout risk | Full rebuild with proper drainage |
| Localized bowing in one section | Concentrated water (downspout, leak) | Medium to high | Fix water source, rebuild affected section |
Sources & References
- NCMA Design Manual for Segmental Retaining Walls — National Concrete Masonry Association
- Allan Block Engineering — Failure Analysis and Drainage — Allan Block Corporation
- Engineers and Geoscientists BC — Retaining Wall Guidance — Engineers and Geoscientists British Columbia