Reasons for wall failure

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:

COMMON FAILURE	WHAT HAPPENS	WHAT TO DO
Blowout Failure	A load is added within 3 ft. of the top of the wall. The wall leans out at the top and eventually tips over.	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	Soil behind the wall gets saturated, causing hydrostatic water pressure and weight to topple the wall.	Replace native soil behind the wall with 3/4-minus or bank-run gravel for 2 ft. Line the inside base of the wall with 4-in. perforated tile drain on a gravel bed that slopes 1 in. for every 4 ft. of run to carry water to daylight or a dry well. Topsoil should take up only the top 6 in. behind the wall.
Frost-Heave Failure	Retaining wall lacks proper drainage or a footer. Soil becomes saturated and freezes, heaving upward and breaking the wall apart.	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 in., 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.