What causes retaining wall failure?

Retaining wall failure is driven primarily by hydrostatic pressure. When soil behind the wall becomes saturated, water pressure builds against the wall face. The wall was designed to hold dry or partially saturated soil at a known weight. Saturated soil is significantly heavier and exerts lateral pressure that exceeds the wall's original design load. Freeze-thaw cycling compounds this by expanding water in the wall material itself, widening cracks each winter until the wall begins to displace outward.