Active Thrust on a Retaining Wall
Hardretaining wallactive pressure
A rigid retaining wall 5 m high retains cohesionless backfill with unit weight 18 kN/m³ and friction angle 30°. The backfill is level and drained. The total active thrust per metre of wall is most nearly:
- A45 kN/m
- B75 kN/m
- C135 kN/m
- D225 kN/m
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Answer: B. 75 kN/m
The Rankine active coefficient is Ka = (1 − sinφ)/(1 + sinφ) = 0.333. The thrust is the area of the triangular pressure diagram: Pa = ½KaγH² = ½(0.333)(18)(5)² = 75 kN/m, acting at H/3 above the base. Omitting the factor of ½ gives 150 kN/m and treats the triangular distribution as if it were uniform.
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