Why Retaining Walls Fail (and How to Avoid It)

Retaining walls rarely fail from one big mistake, it's usually a missing detail. The big four:

1. No drainage (the #1 cause)

Water builds up behind the wall, adds hydrostatic pressure and saturates the soil. Fix: drain rock, perforated pipe to daylight, filter fabric. Always.

2. A bad base

A thin or unlevel leveling pad lets the wall settle and lean. Fix: 6 inches of compacted crushed stone, dead level, with the first course buried.

3. Too narrow / too tall for gravity

A gravity wall without enough base width overturns or slides; built too tall without geogrid, it bulges. Fix: size the base to FS ≥ 2.0 overturning and 1.5 sliding, and reinforce when the checks fail.

4. Ignored surcharge

A driveway or slope above the wall that wasn't in the design overloads it. Fix: include the surcharge, it often means an engineer and a permit.

The calculator addresses all four: it sizes the base, includes drainage, checks the factors of safety, and accounts for surcharge and slope. Above 4 ft, still hire an engineer.