A gravity wall carries no reinforcement at all — its entire job is done by plain concrete mass, which means the base pressure's eccentricity relative to the middle third of the footing is often the governing check, not overturning or sliding factors of safety.
Every check above runs automatically inside the Structyze Gravity Retaining Wall module — this particular module is part of the full desktop catalogue rather than the free browser trial, since the trial only carries a curated flagship set. You can still try the free trial modules right now to see the same calculation style in action on RCC Beam, Column, Slab and a handful of others.
The Example We'll Use
- Retained height 3.0 m, surcharge 5 kN/m²
- Backfill: φ = 30°, γ = 18 kN/m³
- Base width 2.0 m, top width 0.4 m, bottom width 1.2 m (trapezoidal)
- Plain concrete f'c = 20 MPa
Working Through It
The wall's own trapezoidal self-weight (no separate footing slab — the mass section itself bears directly on soil) provides both the overturning resistance and the vertical load establishing the base pressure distribution.
Resultant location relative to the base: with the lateral thrust's overturning moment against the self-weight's stabilising moment, the resultant falls at an eccentricity e relative to the base centreline. Checking e against B/6 (the middle-third limit for no-tension soil bearing) is the deciding test for a gravity section.
For this geometry, eccentricity comes out at roughly 80% of the B/6 limit — the governing check, ahead of both the overturning FoS (comfortably above 1.55) and the sliding FoS (above 1.5).
What Governs, and Why
Eccentricity governs at utilisation 0.80 against the middle-third limit, tighter than either stability factor of safety — a direct consequence of gravity walls having no tension reinforcement to redistribute an uneven base pressure. Once the resultant strays outside the middle third, tension would develop somewhere in the unreinforced base, which plain concrete cannot resist, so this becomes the real controlling limit state for this wall type.
Where Structyze Takes Over
Every check above runs automatically inside the Structyze Gravity Retaining Wall module — this particular module is part of the full desktop catalogue rather than the free browser trial, since the trial only carries a curated flagship set. You can still try the free trial modules right now to see the same calculation style in action on RCC Beam, Column, Slab and a handful of others.
For Gravity Retaining Wall and the rest of the full catalogue — 80+ components across RCC, Steel, Composite, Timber, Masonry and more, across 20+ design codes — buy the full Structyze desktop app or see everything it does on the Software page.
Quick FAQ
Why B/6 specifically, not some other fraction?
For a rectangular base under a resultant load, the middle-third rule (B/6 from centreline) is the geometric condition under which the standard linear pressure distribution (P/A ± M/Z for a rectangular section) stays entirely compressive across the full base width. Push the resultant past B/6 and the formula's tension zone), which plain, unreinforced concrete-on-soil bearing cannot actually develop, so the base would locally lift off and the real pressure distribution becomes triangular rather than trapezoidal.
Why choose a gravity wall over a cantilever wall at all, given cantilever walls use far less concrete?
Gravity walls trade concrete volume for construction simplicity — no reinforcement detailing, no congested steel at the stem-base junction, and a design that's comparatively forgiving of formwork imprecision. They remain economical at shorter heights (typically under about 3 m) or where reinforcing steel is expensive or scarce relative to plain concrete, even though a cantilever wall of the same height would use meaningfully less material.
Final Thoughts
A gravity wall's middle-third eccentricity check is a truly different governing limit state from the overturning/sliding factors of safety that dominate a reinforced cantilever wall — worth understanding on its own terms rather than assuming the same checks always govern the same way.