Determine the degree of saturation of the soil if...?

Question

This is a soil mechanics problem.

A soil has known water content of 18% and specific gravity of 2.68. Determine the degree of saturation if it has a moist unit weight of 17.30 kN/m³.

Answer 1

First, calculate the void ratio, e,  from the unit weight equation:

gamma = [ (Gs)(gamma_w)(1+w) ] / (1+e)

e = [[ (Gs)(gamma_w)(1+w) ] / gamma]  - 1

e = [[(2.68)(9.81 kN/m3)(1 + 0.18)] / (17.30 kN/m3)] - 1 = 0.79

Now, insert void ratio into the following phase relationship equation and solve for degree of saturation: (S)(e) = (Gs)(w)

S = (Gs)(w) / e

   = (2.68)(0.18) / (0.79) = 0.61

S = 61%