Formula
Ka = tan²(45° − φ/2) — Rankine active coefficient
Pa = 0.5 × Ka × γ × H² + Ka × q × H
H=3m, γ=18, φ=30°, q=0:
Ka=0.333 | Pa=0.5×0.333×18×9 = 27 kN/m
Frequently Asked Questions
Rankine assumes soil is in active failure, giving minimum lateral pressure. Ka = tan²(45°−φ/2). Used for gravity and cantilever retaining walls.
Minimum FOS against overturning = 2.0, against sliding = 1.5. For important structures, use 2.5–3.0.