Most wall failures give warnings first
A retaining wall does not usually collapse without warning. The structural distress that leads to failure shows up in visible signs weeks, months, or sometimes years before the wall actually lets go. Knowing what to look for means you can get ahead of a problem instead of dealing with a failed wall after the damage is done.
In San Diego, the wet season from December through March is when failing walls are most likely to worsen quickly. Heavy rain saturates the soil behind the wall, adds weight and hydrostatic pressure, and accelerates the forces acting on a structure that is already compromised. If a wall has been showing signs of distress heading into a wet season, it deserves attention before the rain arrives.
Leaning or outward bowing
The most obvious sign of wall failure is a wall that is no longer vertical or that has developed a visible bow outward from the slope. On a block wall, you may see this as a gradual curve across the face of the wall. On a poured concrete wall, it may appear as a tilt in the upper portion.
A wall leans because the lateral force pressing against it has exceeded what it can resist. This can happen because the wall was originally undersized for the retained height, because drainage was inadequate and hydrostatic pressure built up over time, because soil conditions were worse than anticipated, or because the soil above the wall has been loaded with additional weight such as a new structure, a driveway, or accumulated fill.
A wall that is leaning is a wall that is actively failing. The lean rarely stops on its own. Get it assessed before it progresses.
Cracking in the wall face
Cracks in retaining walls are common, but not all cracks mean the same thing.
Vertical cracks that run from top to bottom of a concrete or block wall often indicate differential settling. The wall is settling at different rates across its length, which stresses the middle. Vertical cracks are worth watching but are not always a sign of imminent failure.
Horizontal cracks on a concrete wall, or horizontal displacement of a block wall where a course has pushed out relative to the one above or below, are more serious. Horizontal cracking indicates bending failure, where the wall is flexing under load. This type of failure can progress quickly.
Stair-step cracking following mortar joints on a mortared block or brick wall indicates the wall is racking under lateral load. The mortar joints are the weak point and they crack in a diagonal pattern as the wall deforms.
Any crack that is widening over time, particularly after rain or during wet season, is a warning sign. Photograph cracks and compare photos over several weeks to see if they are growing.
Separation between the wall and adjacent structures
If the retaining wall meets a house foundation, driveway, patio, or stairs, watch the joint between them. Separation at that joint means the wall has moved relative to the structure. Movement of even an inch or two indicates the wall has shifted under load.
In hillside neighborhoods like La Mesa, Lemon Grove, and the elevated neighborhoods in East San Diego, retaining walls often support or are connected to stairs that run from street level to a downslope house. Gaps opening at the top of the wall where stairs meet, or stairs that have tilted relative to their original position, are signs of wall movement.
Bulging or erosion at the wall base
At the base of the wall, look for soil that has mounded outward from the wall face, or gravel and drain material that appears to be pushing through the wall. This is called piping or base failure and indicates the wall is being pushed forward at the bottom.
Also look for erosion channels at the base of the wall. Water flowing out from under a wall is carrying material with it, which undermines the base and reduces the wall’s stability over time.
Water staining and efflorescence
Heavy white mineral deposits on the face of a concrete or block wall indicate water is moving through the wall material. This is called efflorescence and forms when water dissolves minerals in the concrete and deposits them on the surface as it evaporates.
Efflorescence is not a structural emergency by itself, but it signals that water is getting behind the wall and finding its way through rather than draining out properly. Heavy or widespread efflorescence on an older wall often means the drainage system is not functioning correctly.
What to do if you see these signs
If your retaining wall shows one or more of these signs, a site visit from an experienced contractor is the right first step. They can assess whether the problem is cosmetic, whether it can be addressed with targeted repairs, or whether the wall has progressed to a point where replacement is the correct answer.
On a leaning wall or a wall with horizontal cracking, do not wait through another wet season. These are conditions that can worsen rapidly under load from saturated soil.
Document what you see with photos. Note whether the distress appears to be getting worse over time, and whether you have had any significant grading, loading, or construction above the wall since it was built.
Wall Pro SD connects San Diego homeowners with insured local contractors who can evaluate retaining wall distress and recommend the right course of action. Call (858) 925-5546 for a site assessment.
For a professional assessment, see our retaining wall inspection and emergency retaining wall repair service pages.