Subtopic: Controlled and modified atmosphere storage
Question Statement:
For a mass of grain stored in a bin, the angle of internal friction of the grain is 30°. The ratio of normal pressure to the applied pressure within the bin is
Options:
(A) 0.25
(B) 0.33
(C) 0.50
(D) 1.00
Official Answer Key:
B
Step-by-Step Solution & Explanation
The ratio of lateral (normal, wall) pressure to vertical (applied/overburden) pressure in a granular mass follows the Rankine active-pressure coefficient: K = (1 − sinφ)/(1 + sinφ), where φ is the angle of internal friction. With φ = 30°, sinφ = 0.5: K = (1−0.5)/(1+0.5) = 0.5/1.5 = 0.333, matching option (B). This is the standard Janssen/Rankine relation used for grain-bin lateral-pressure design.
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