Question

If the soil sample has porosity of 30% and specific gravity of solids G=2.7, then its dry unit weight will be ______

(a) 18.350 kN/m^3

(b) 18.535 kN/m^3

(c) 18.640 kN/m^3

(d) 18.545 kN/m^3

The question was asked during an internship interview.

My question is taken from Functional Relationships in chapter Preliminary Definitions and Relationships of Geotechnical Engineering I

Answer 1

The correct answer is (b) 18.535 kN/m^3

To explain: Given,

Porosity n=30%=0.3

Specific gravity G=2.7

Voids ratio e = n / (1-n)

e=0.3/(1-0.3)=0.429

Dry unit weight γd = Gγw/(1-e)

γd=(2.7*9.81)/(11+0.429)

γd=18.535 kN/m^3.