Soil Mechanics, Index Properties, Densities & Specific Gravities related to Soil

Soil Mechanics

“Soil Mechanics is the application of laws of mechanics to the Engineering Problems deals with soils e.g sediments or other unconsolidated accumulation of soil particles produce by the mechanical & chemical disintegration of rocks”

Since Soil is generally a three phase material consists of Soil Solids, Water & Air. So that’s why it exhibits different properties and behave differently under same load conditions. So the following is some of the basics properties and parameters that involves while studying Soil Mechanics and Geotechnical Engineering.

General Parameters

  1. Va=Volume of Air
  2. V=Total Volume of soil mass
  3. Vw=Volume of Water
  4. Vs=Volume of Solids
  5. Vv=Volume of voids
  6. W=Weight of Soil Mass
  7. Ww=Weight of Water content
  8. Ws=Weight of Solids
  9. Weight of Soil Mass=W=Ws+Ww,(Air weight neglected)
  10. Volume of Voids=Vv=Va+Vw
  11. Wsat=Weight of fully Saturated Soil
  12. (Ws)sub=Submerged Weight or Buoyant weight of soil below water surface or under ground water table.

Index Properties of Soil

  1. Water Content(W)=Ww / Ws
  2. Void Ratio(e)=Vv / Vs
  3. Porosity (n )=Vv / V
  4. Degree of Saturation(Sr)=Vw / Vv
  5. Air Content(ac)=Va / Vv
  6. Percentage of Air Void( a)=Va / V


Definition: It is the Weight of any material per unit Volume of that material and Units of measurement is SI is Kg/m3 or g/cm3 .

  1. Bulk Density or Bulk Unit Weight of Soil mass (r)=W / V
  2. Dry Density or Dry Unit Weight of Soil(rd)=Ws / V
  3. Desity of Soilds (rs)=Ws / Vs
  4. Saturated Density of Soil Mass(rsat)=Wsat / V
  5. Submerged Density of Soil Mass(rsub)=(Ws)sub / V

Specific Gravities

Definition: It is the ratio of density of any material to the density of water and since it is the ratio, so this is the unitless quantity .

  1. Specific gravity of Soil Solids(G)=rs / rw
  2. Bulk or mass Specific gravity of Soil Solids(Gm)=r / rw

Watch the Video, these parameters have been discussed briefly.

========Thank Y0u=======

Author: Engineer-Nisar

Civil Engineer

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