Retaining Wall Stability Check
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Enter the wall height and base width with the backfill properties, and get the factor of safety against overturning and sliding — a first-pass check for a gravity wall against a level backfill.
Retaining Wall Stability Check
Rankine active pressure · overturning & sliding factor of safety about the toe
Gravity wall + backfill
Ka 0.333 · Pa 48 kN · W 192 kN
tanδ ≈ 0.5
Concrete 24, masonry 20
Overturning factor of safety
3
sliding FoS 2 · stable ✓
Overturning FoS
3
Sliding FoS
2
Active thrust Pa
48 kN
Wall weight W
192 kN
How it resolves
Ka (active)
0.333
Overturning moment
64 kN·m
Resisting moment
192 kN·m
Thrust arm
1.33 m
Keep overturning ≥ 2 and sliding ≥ 1.5. This treats the wall as a solid rectangular gravity block against a level backfill with no water — add a drainage layer and weep holes so pore pressure never builds behind it, and check the base pressure against the soil's bearing capacity.
How it works (Rankine)
- Active pressure coefficient Ka = tan²(45 − φ/2).
- Active thrust Pa = ½ · Ka · γ · H², acting at H/3 above the base.
- Overturning FoS = resisting moment ÷ overturning moment about the toe (keep ≥ 2).
- Sliding FoS = μ · W ÷ Pa, where W is the wall weight and μ the base friction (keep ≥ 1.5).
Worked example
A 4 m high, 2 m wide gravity wall, backfill γ = 18 kN/m³, φ = 30°, μ = 0.5, concrete 24 kN/m³:
- Ka = tan²(30°) = 0.333; Pa = ½ × 0.333 × 18 × 4² = 48 kN; W = 2 × 4 × 24 = 192 kN
- Overturning FoS = 192 ÷ 64 = 3.0 (≥ 2 ✓)
- Sliding FoS = 0.5 × 192 ÷ 48 = 2.0 (≥ 1.5 ✓)
Frequently asked questions
How do I check a retaining wall for stability? Compare the resisting moment (the wall's weight × its lever arm) to the overturning moment (the earth thrust × H/3), and the friction under the base to the horizontal thrust. Keep overturning ≥ 2 and sliding ≥ 1.5.
What is the active earth pressure coefficient? Ka = tan²(45 − φ/2). For φ = 30° it is 0.333 — the fraction of the vertical soil weight that pushes horizontally on the wall.
How wide should the base of a retaining wall be? A common starting point is 0.5–0.6 × the height for a gravity wall; increase it until both factors of safety are met. The 4 m wall above needs about a 2 m base.
Why add drainage behind a retaining wall? Water trapped behind the wall adds hydrostatic pressure that can more than double the thrust. Weep holes and a granular drainage layer keep the pressure to the soil-only case checked here.
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CivilSite Editorial Team✓ Engineer reviewed
Written and reviewed by practising civil engineers with 10+ years of Indian residential construction experience.