Question

The tension at the top level of retaining wall reduces to zero at a depth ___________

(a) \(z_0=\frac{q-2c cot⁡α}{γ} \)

(b) \(z_0=\frac{2c tan⁡α}{γ} \)

(c) \(z_0=\frac{2 cot⁡α}{γ} \)

(d) \(z_0=\frac{cot⁡α}{γ} \)

I got this question in exam.

My question is based upon Active Earth Pressure of Cohesive Soils in portion Failure Envelopes & Earth Pressure of Geotechnical Engineering II

Answer 1

Right choice is (b) \(z_0=\frac{2c tan⁡α}{γ} \)

Easy explanation: Since the Belli equation of lateral pressure of cohesive soil is given by,

pa=γzcot^2 α-2c cot⁡α,

When  pa=0,

∴ \(z_0=\frac{2c tan⁡α}{γ} \)