Retaining Wall Engineering Basics: The Three Checks

Every retaining wall has to pass three classical checks. Here's what each one means.

1. Overturning

The soil tries to tip the wall forward about its toe. You compare the wall's righting moment (its weight × the distance to the toe) with the soil's tipping moment. The ratio is the factor of safety; the standard minimum is 2.0.

2. Sliding

The soil tries to push the whole wall outward. You compare the friction under the base (weight × a friction coefficient) with the horizontal push. The standard minimum factor of safety is 1.5.

3. Bearing

The wall's weight, offset by the soil push, concentrates pressure under the toe. That peak pressure must stay below the soil's allowable bearing (IBC Table 1806.2), and ideally the resultant stays in the middle third of the base so the heel doesn't lift.

The earth pressure that drives them

The push itself comes from IBC Table 1610.1 (or Rankine theory): an equivalent-fluid pressure that grows with the square of the height. Surcharge, slope and water all add to it.

Our calculator computes all three factors of safety for your wall and solves for the base width that passes them. Above 4 ft, an engineer must run these for your specific site.