How to use the retaining wall stability calculator
A cantilever retaining wall is checked three ways: sliding, overturning, and bearing pressure. Lateral load comes from Rankine active pressure with Ka = tan²(45 − φ/2). The backfill contributes 0.5·Ka·γ·H² acting at H/3 above the base, and a uniform surcharge adds Ka·q·H acting at H/2. Wall friction and passive resistance at the toe are ignored, which is the conservative assumption used for preliminary sizing.
On the resisting side the tool sums the base slab, the stem, the soil over the heel, and the surcharge over the heel, each with its own moment arm measured from the toe. Sliding safety factor is μ·ΣW divided by the horizontal thrust, and overturning safety factor is the resisting moment divided by the overturning moment. The resultant eccentricity is compared with B/6: beyond that the base slab develops tension and the pressure diagram is no longer trapezoidal, so the base needs to be widened.
Blocked drainage is the most common cause of retaining wall failure, because full hydrostatic pressure can more than double the design thrust, so a drainage layer and weep holes behind the wall are essential. Seismic load cases, cohesive backfill, sloping backfill, and walls on slopes all need a separate analysis. Use this as a screening calculation and have a licensed structural or geotechnical engineer confirm the final design.
Frequently Asked Questions
IBC 1807.2.3 sets a minimum safety factor of 1.5 against both sliding and overturning. Most geotechnical and DOT practice is stricter on overturning and uses 2.0, which is the value checked here, so a wall between 1.5 and 2.0 meets the code minimum but not common practice.
Widen the base to add dead weight, add a shear key under the base slab, deepen the embedment so passive pressure at the toe can help, or replace the backfill with a free-draining granular material that has a higher friction angle.