Question

For finding out the active earth pressure for a backfill with sloping surface, the Rankine’s theory makes as additional assumption of ________

(a) vertical and lateral stresses are normal to surcharge

(b) vertical and lateral stresses are tangential to surcharge

(c) vertical and lateral stresses are conjugate

(d) vertical and lateral stresses are negligible

This question was posed to me in an interview for job.

This key question is from Active Earth Pressure: Rankine’s Theory topic in chapter Failure Envelopes & Earth Pressure of Geotechnical Engineering II

Answer 1

Correct answer is (c) vertical and lateral stresses are conjugate

Easy explanation: The additional assumption of vertical and lateral stresses are conjugate is made as, it can be shown that stresses on a given plane at a given point is parallel to another plane, the stresses on the latter plane at the same point must be parallel to the first plane.