Retaining Walls Fail for Reasons That Are Usually Identifiable
Seattle has a great deal of sloped residential ground, and a corresponding number of retaining walls holding it. Many were built decades ago, some without engineering, and a good proportion without the drainage that keeps a wall within the loads it was designed for.
A retaining wall resists lateral earth pressure. When the soil behind it becomes saturated, that pressure increases substantially, water adds its own hydrostatic component and the soil itself becomes heavier. A wall that performed adequately for thirty years can start moving in a single unusually wet winter, not because the wall changed but because the load did.
Three failure modes account for most of what we assess: the wall slides forward at its base, the wall rotates outward about its toe, or the wall bulges as individual courses displace, common on CMU block walls where a mortar joint gives before the units do. We assess them with the same measured approach we bring to Seattle foundation repair. Each looks different and each points at a different combination of drainage failure, surcharge, and design capacity.
Drainage Is Usually the Story
Look behind a failing residential retaining wall and you will frequently find one of these.
Weep holes blocked. Soil, roots, or landscape fabric installed later has sealed the path water was meant to take through the wall.
No drainage envelope. The wall was backfilled with the native soil that came out of the excavation rather than with free-draining aggregate wrapped in geotextile. Water arriving behind the wall has nowhere to go.
A failed drain line. There was a perforated pipe behind the wall, and it has silted up, been crushed, or lost its outlet.
Surface water directed at the wall. Grading above the wall, or a downspout discharging into the retained soil, delivering water directly into the zone that should stay drained.
Restoring drainage is frequently the largest and most valuable part of a retaining wall repair, because it removes the load that caused the failure rather than just resisting it harder. The retaining wall movement guide covers the symptoms in detail.
Surcharge Loads
A retaining wall designed for the soil behind it can be overwhelmed by something added later.
A driveway extended to the top of a wall. A vehicle habitually parked near the edge. A shed, a deck footing, or an addition built within the zone that loads the wall. Even a substantial change in the height of the retained soil from years of fill and landscaping.
We identify surcharge during the assessment because it changes both the diagnosis and the repair. A wall failing under a load it was never designed for may need a different answer than a wall failing because its drainage stopped working.
Wall Movement Versus Slope Movement
This distinction matters more than anything else on this page.
If a wall is failing on its own, it is a defined problem with a defined repair. If a wall is being displaced because the ground it sits in is moving, then repairing the wall accomplishes nothing. You would be stabilising an object that is riding on the actual problem.
Signs that point beyond the wall include cracked or displaced hardscape well away from it, fence posts and trees leaning in a consistent direction, ground fissures on the slope, and movement in nearby structures. Where we see that pattern, the question belongs with a geotechnical engineer and we refer it. We will not sell a wall repair into a slope problem.
What We Repair, and What We Refer
Within scope: restoring drainage behind a wall, clearing and reinstating weep holes, rebuilding failed sections of modest walls, installing helical tiebacks where the design permits, and correcting surface water routing above the wall.
Referred: walls whose height or loading requires engineered design, walls in mapped critical areas where review demands it, walls whose failure would affect a neighbouring property, and any situation where slope stability is the underlying question.
This is a smaller list than some contractors advertise. It is the list we can stand behind. A retaining wall that fails after a repair does not fail quietly, and taking on work that should have gone to an engineer is not a service to anyone.
Waterfront Bulkheads and Seawalls
Shoreline structures are a distinct category. Tidal action and wave energy work at the toe of a structure continuously, and hydrostatic voids form behind bulkheads as water moves in and out with the tide, carrying backfill fines with it.
Shoreline work also commonly triggers permitting beyond a standard building permit, with additional review reflecting the environment it sits in. We identify that before quoting rather than after, and we take on shoreline work only where it genuinely falls within what we offer. The seawall and bulkhead stabilisation guide explains the considerations in more detail.
