Calculate active and passive lateral earth pressure distributions and overturning moments on retaining walls using Rankine and Coulomb geotechnical equations.
Formula and method
Rankine active earth pressure estimates the lateral soil thrust on a vertical retaining face and the overturning moment about the toe.
Compute active earth pressure coefficient Ka from soil friction angle φ (and optional backfill slope).
Lateral thrust Pa = ½ · Ka · γ · H² acting at H/3 above the base.
Overturning moment about the toe = Pa · (H/3).
Frequently asked questions
What is the Rankine active earth pressure theory?
Rankine theory assumes a vertical retaining wall with horizontal backfill. The active earth pressure coefficient Ka = (1-sinφ)/(1+sinφ), where φ is the soil friction angle. The total lateral thrust is Pa = 0.5·Ka·γ·H².
How is overturning moment calculated?
The lateral thrust Pa acts at a height of H/3 above the base of the wall for triangular pressure distribution. The overturning moment about the toe is Mo = Pa × (H/3).
Can I specify sloping backfill?
Yes. If the backfill surface is sloping at an angle β from horizontal, the calculator adjusts the Ka coefficient using the appropriate Rankine equation for sloping backfill.
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Calculations are preliminary estimates for planning and education.
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