The active earth pressure coefficient (Ka) for a cohesionless soil with an internal friction angle (phi) of 30° is:
A0.333 (1/3)
B0.500
C1.000
D3.000
Explanation
Rankine’s active earth pressure coefficient Ka = (1 – sin(phi)) / (1 + sin(phi)). For phi = 30°, Ka = (1 – 0.5) / (1 + 0.5) = 0.5 / 1.5 = 1/3 = 0.333.

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