Why retaining walls fail — hydrostatic pressure without drainage

Trapped water is the #1 reason retaining walls fail: it builds hydrostatic pressure that tips the wall. Back the wall with gravel, filter fabric, and a perforated pipe so the water drains out and never loads the wall.

Two retaining walls compared. On the left, with no drainage, rain saturates the soil behind the wall and the water builds hydrostatic pressure that pushes the wall outward until it tips over — the single most common cause of retaining-wall failure. On the right, a chimney of free-draining gravel with filter fabric and a perforated pipe at the base lets the water run down and out, so no water pressure ever loads the wall and it stays plumb. — Source: NCMA SRW design manual §5.1 (drainage)

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Two retaining walls compared. On the left, with no drainage, rain saturates the soil behind the wall and the water builds hydrostatic pressure that pushes the wall outward until it tips over — the single most common cause of retaining-wall failure. On the right, a chimney of free-draining gravel with filter fabric and a perforated pipe at the base lets the water run down and out, so no water pressure ever loads the wall and it stays plumb.

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