Question

Compute the active pressure intensity when the backfill has unit weight of 18 KN/m^3 and height of wall is 6 m. The angle of internal friction is 30°.

(a) 45 KN/m^2

(b) 36 KN/m^3

(c) 87 KN/m^2

(d) 27 KN/m^2

This question was posed to me during an interview for a job.

Origin of the question is Earth Pressure Problems topic in section Failure Envelopes & Earth Pressure of Geotechnical Engineering II

Answer 1

Right answer is (b) 36 KN/m^3

Explanation: Given,

γ= 18 kN/m^3

H=6m

Φ=30°

Therefore  \(K_a=\frac{1-sin⁡φ}{1+sin⁡φ}=\frac{1+sin⁡30}{1+sin⁡30}=\frac{1}{3}\)

Pp= KaγH = \((\frac{1}{3})\)×18×6 = 36 kN/m^2.