Civil Engineering MCQJE Level Civil Engineering
Rankine''s active earth pressure coefficient Ka for a cohesionless soil with friction angle φ is:
Soil MechanicsSoil MechanicsMEDIUM
Choose the correct answer
A
Ka = tan²(45° + φ/2)
B
Ka = tan²(45° − φ/2)
C
Ka = 1 + sinφ
D
Ka = 1/(1 − sinφ)
Correct Answer
B. Ka = tan²(45° − φ/2)
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Ka = tan²(45° − φ/2) = (1 − sinφ)/(1 + sinφ). This gives the minimum earth pressure (active case) when wall moves away from soil (failure by forward movement). Active pressure pa = Ka·γ·z − 2c√Ka. For φ = 30°: Ka = tan²30° = 0.333.
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