When a Retaining Wall Starts to Fail, Drainage Is Usually the Reason

A leaning, bulging, or cracked retaining wall looks like a wall problem. Most of the time it is a water problem wearing a wall's clothes.

It is a reasonable thing to get wrong. The wall is what you see moving, so the wall is what seems broken. But a retaining wall holds back more than soil. After a wet stretch it is holding back saturated ground, and saturated ground is heavy and pushes hard.

Water is what actually pushes the wall over

Soil behind a wall soaks up rain and holds it, especially the heavier clay soils common around here. Water that cannot drain builds up behind the wall as pressure. Through a Pacific Northwest winter, that pressure works on the wall day after day. Add a hard freeze that expands the wet ground, and even a solid looking wall starts to lean, bow in the middle, or crack along a line.

Building the wall heavier or stacking it higher does not fix that. If the water still has nowhere to go, it will push on a stronger wall too.

A retaining wall is a drainage system with a face on it

A wall that holds is built to let water out from behind it. That means a few things working together: a compacted base below frost depth, so the wall is not sitting on ground that heaves; clean gravel backfill directly behind the wall, giving water a path down instead of soaking the soil against the face; a perforated drain pipe at the base of that gravel, run to daylight or a drain so the water actually leaves. I often put a swale above the retaining wall, if possible. Retaining wall 4ft or less generally don’t need a engineer aslong as its not holding up a commercial lot or major building 

When a wall fails, the fix is almost always back there, not on the face. We dig behind it, correct the base, put in the gravel and the drain the wall never had, and rebuild it to shed water. On taller walls, the ones tall enough to need an engineer's design, we coordinate with the engineer rather than guess at it, because a wall holding back that much ground is not the place to cut corners.

Catch it early

A wall that is just starting to lean is a smaller job than a wall that has come apart. If yours is bulging, tilting, or opening up cracks after one of our wet winters, it is worth looking at before the next one arrives.

We build and fix retaining walls and rock walls across Cowlitz County.

Call us at (360) 957-8847 and we will find out what the water is doing before we touch the wall.