Question

For a soil sample, the ratio of saturated unit weight to dry unit weight is equal to 1.2 and specific gravity of solids G is 2.65, then its void ratio will be _____

(a) 0.58

(b) 0.66

(c) 0.53

(d) 0.94

The question was asked in a national level competition.

My doubt is from Void Ratio, Porosity and Degree of Saturation in portion Preliminary Definitions and Relationships of Geotechnical Engineering I

Answer 1

Right choice is (b) 0.66

To explain I would say: Given,

The ratio of saturated unit weight to dry unit weight is equal to 1.2

γsat/γd= 1.2

Specific gravity of solids G is 2.65

γsat = \(\frac{(G+e)}{1+e} \gamma_w \,and\, \gamma_d = \frac{G}{1+e}\gamma_w\)

→ γsat/γd= \(\frac{(G+e)}{1+e} \gamma_w /\frac{G}{1+e}\gamma_w\)

γsat/γd = (G+e) / e

→(G+e) / e = 1.2

e = 1.2*G – G

e = 1.2*2.65 – 2.65

e = 0.53.