Question

The relation between Kp and Ka  is _____________

(a) Kp=Ka

(b) Kp=1+Ka

(c) Kp=1-Ka

(d) Kp=1/Ka

This question was posed to me during an interview.

This intriguing question comes from Passive Earth Pressure: Rankine’s Theory topic in chapter Failure Envelopes & Earth Pressure of Geotechnical Engineering II

Answer 1

Correct answer is (d) Kp=1/Ka

For explanation: The coefficient of passive earth pressure is,

Kp= tan^2 α,

the coefficient of active earth pressure is,

\(K_a=\frac{1}{tan^2(45°+\frac{φ}{2})},\)

∴ Kp=1/Ka.