Question

For the same value of φ, the backfill is partly submerged to height H2 and the backfill is moist to a depth H1. Find the lateral pressure intensity at the base of wall.

(a) pa=Ka γH1-Ka γ’ H2+γw H2

(b) pa=Ka γH1+Ka γ’ H2+γw H2

(c) pa=Ka γH1+γw H2

(d) pa=Ka γH1+Ka γ’ H2

I have been asked this question during an internship interview.

My question is taken from Active Earth Pressure: Rankine’s Theory topic in division Failure Envelopes & Earth Pressure of Geotechnical Engineering II

Answer 1

Right option is (b) pa=Ka γH1+Ka γ’ H2+γw H2

The explanation is: When the backfill is partly submerged to height H2 and the backfill is moist to a depth H1, lateral pressure intensity is due to:

lateral pressure due to moist weight of backfill

 lateral pressure due to saturated weight of backfill

 lateral pressure due to water

∴ pa=Ka γH1+Ka γ’ H2+γw H2.