Question

If σ’ is the effective overburden pressure, then the effective penetration resistance is given by _____________

(a) Ne=\(N \frac{50}{1.42σ^{‘}}\)

(b) Ne=\(N \frac{50}{σ^{‘}+10}\)

(c) Ne=\(N \frac{1}{1.42σ^{‘}+10}\)

(d) Ne=\(N \frac{50}{1.42σ^{‘}+10}\)

The question was posed to me during an interview for a job.

Enquiry is from Geophysical Methods in chapter Stabilisation of Soils, Site Investigation and Sub – Soil Exploration of Geotechnical Engineering II

Answer 1

The correct choice is (d) Ne=\(N \frac{50}{1.42σ^{‘}+10}\)

The best I can explain: Gibbs and Holtz have experimentally studied the effect of overburden on values of N.

Ne=\(N \frac{50}{1.42σ^{‘}+10}\), where, Ne=corrected value for overburden effect

N=actual value of blows

σ’ =effective overburden pressure.