Soil volume and density relationships

by Helmut Schmidhofer

Soil definitions and gravimetric-volumetric relationships are presented with online calculations. The four input values are obtained from laboratory tests of a soil sample.
The formulas are based on Foundation Analysis and Design, 5th Edition by Joseph E. Bowles (permission granted).

You should do at least one calculation manually, for two reasons:
1. to check the spreadsheet so you can have confidence in its results; and
2. to appreciate how much time the spreadsheet saves.

Please support the ongoing maintenance of this site. For just $7 I shall send you the Excel spreadsheet so you can satisfy yourself that the program uses the equations correctly.

Soil volume and density relationships
Given:
sample total volume, Vt				cm3
sample mass, Wt				g
moisture content, w				%
specific gravity of soil particles, Gs
Then:
wet unit mass, rho-wet				g/cm3	=Wt/Vt
wet unit weight, gam-wet				kN/m3	=rho-wet*9.807
dry unit weight, gam-dry				kN/m3	=gam-wet/(1+w/100)
unit mass of solids, Ws				g/cm3	=rho-wet/(1+w/100)
volume of solids, Vs				cm3	=Ws/Gs
volume of voids, Vv				cm3	=1-Vs
void ratio, e					=Vv/Vs
porosity, n					=Vv/1
unit mass of water, Ww				g/cm3	=rho-wet - Ws
degree of saturation, S				%	=100*Ww/Vv
unit weight of water, gam-w				g/cm3
dry bulk specific gracity, Gb					=gam-dry/gam-w