Question

For the different 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 for φ1>φ2.

(a) pa=Ka2 γH1-Ka2 γ’ H2+γw H2

(b) pa=Ka2 γH1+Ka2 γ’ H2+γw H2

(c) pa=Ka2 γH1+γw H2

(d) pa=Ka2 γH1+Ka2 γ’ H2

I had been asked this question in my homework.

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

Answer 1

Right option is (b) pa=Ka2 γH1+Ka2 γ’ H2+γw H2

To elaborate: For the different value of φ, the coefficient of active earth pressure is different. Since, the 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=Ka2 γH1+Ka2 γ’ H2+γw H2. We have to consider Ka2 over Ka1 as the φ1>φ2.