Gravity Retaining Wall Design Explained

A gravity retaining wall resists lateral soil pressure using only its own weight — no reinforcement, no steel, no anchors. The categories include segmental block (SRW), stacked stone, mass concrete, and boulders.

The key principle

Gravity keeps the wall stable in two ways: 1. Overturning: the wall's weight × the distance to the toe creates a righting moment. The soil's horizontal push × the wall height creates a tipping moment. For safety, the righting moment must be at least 2× the tipping moment (factor of safety ≥ 2.0). 2. Sliding: friction between the base and soil resists forward movement. The friction force (weight × friction coefficient) must be at least 1.5× the horizontal push (FS ≥ 1.5).

What drives the base width

To pass both checks, the base must be wide enough that the wall is heavy enough. The rule of thumb is 0.5–0.7 × wall height, but the actual number depends on: - The soil's equivalent-fluid pressure (30–60 pcf depending on soil type) - Any surcharge above the wall - The wall's own density (concrete block vs stone) - The foundation soil's bearing capacity

When gravity fails

Past roughly 4 ft (or any height with a surcharge), the base width needed for a pure gravity wall becomes impractically large. That's when you switch to reinforced segmental walls (geogrid extending into the backfill) or engineered cantilever walls (rebar in a poured-concrete T or L shape). The calculator flags this crossover and shows the minimum base width at each wall height.