Safeguarding Against Three Common Failures

Retaining walls usually fail slowly. Common problems can often be fixed if you act quickly. You can also protect a new wall in the building process by safeguarding it against the three most common failures:

Blowout Failure
What happens: A load is added within 3 feet of the top of the wall. The wall leans out at the top and eventually tips over
What to do: Tell your landscape architect or engineer if a car or shed will be placed near the wall. The pro should then beef up the footer and increase the number of tiebacks or deadmen to add strength. Adding retrofit tiebacks is expensive and requires excavation, partial dismantling, and reengineering the wall

Wet-Soil Failure
What happens: Soil behind the wall gets saturated, causing hydrostatic water pressure and weight to topple the wall.
What to do: Replace native soil behind the wall with 3/4-minus or bank-run gravel for 2 feet. Line the inside base of the wall with 4-inch perforated tile drain on a gravel bed that slopes 1 inch for every 4 feet of run to carry water to daylight or a dry well. Topsoil should take up only the top 6 inches behind the wall.

Frost-Heave Failure
What happens: Retaining wall lacks proper drainage or a footer. Soil becomes saturated and freezes, heaving upward and breaking the wall apart.
What to do: Walls should rest on 3/4-minus or bank-run gravel, with the footer or wall base buried beneath the frost line (6 to 48 inches, depending on region). For deep frost, use concrete block rather than retaining wall to ground level, then build the retaining wall on that. Well-drained gravel behind and beneath the wall can substantially diminish frost heaving.

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