Soil Properties and Relation Between Them

Three-Phase System of Soil

  • A Soil mass is a three-phase system consisting of solid particles (called soil grains) with water and air filling the void spaces between the soil grains. The void spaces are sometimes filled partly with air and water. But in the case of a dry soil mass, the voids are completely filled with air only and in the case of a saturated soil mass, the voids are completely filled with water.

  • The properties of the soil mass which is a blend of the three constituents together forming a complex material depend on the relative percentages of these constituents, their arrangement and a variety of other factors.

Fig 2.1 Soil as a Three-Phase System

  • Terms And Symbols (Denoted By): Table-2.1

V = Total Volume of the Soil Mass

W = Total Weight of the Soil Mass

Vs = Volume of Solids

Wd = Weight of Solids

Vv =Volume of Voids

Wv = Weight of Voids

Va = Volume of Air

Wa = Weight of Air

Vw = Volume of Water

Ww = Weight of Water


a) V=Vs+Vv                  

b) Vv=Va+Vw

  1.  In case of dry soil mass: 

  Vv=Va as Vw=0

  1. In case of saturated soil mass: Vv=Vw as Va=0


a) W=Wd+Wv

b) Wv=Ww  as  Wa=0

  • Table-2.2

M = Total Soil Mass

W = Total Weight of Soil Mass

Mw = Mass of Water

Ww = Weight of water 

Md = Mass Soil Solids

Wd = Weight of Soil Solids

(Md)sub = Mass of Submerged Soil Solids 

(Wd)sub= Weight of Submerged Soil Solids

ρw = Density of Water ( 1000 kg/m3 )

γw = Unit Weight of Water ( 9.81 kN/m3 )

Inter-conversion between ρ and γ :

1 γ (kN/m3)  = 9.81 ρ (g/cm3)

γd,max = Maximum dry density from compaction test

g = 9.81 m/s2

emax = Voids ratio, in the loosest state.

1N = 0.10197 kg

emin = Voids ratio, in the densest state.

1 kg = 9.81 N

e = Natural voice ratio of the deposit.

1m = 100cm = 1000mm