A soil mass consists of solid particles which form a porous structure. The voids in the soil mass may be filled with air, water or partly with water and partly with water. Soil is a three phase system in general.
- Void Ratio
- BULK UNIT WEIGHT (γ)= W/V
- DRY UNIT WEIGHT (γd) = Ws/V
- SATURATED UNIT WEIGHT (γsat) = Wsat/V
- SUBMERGED UNIT WEIGHT (γsub or γ’) = Wsub/V
- UNIT WEIGHT OF SOIL SOLIDS (γs) = Ws/Vs
Void ratio is the volume of voids to the volume of solids. It is denoted by ‘e’
It is expressed as a decimal.
It is defined as the ratio of volume of voids to the total volume. It is denoted by ‘n’
It is generally expressed as a percentage
1/n= 1+ (1/e) = (1+e)/e
n=e/ (1+e) (a)
1/e= (1/n)-1= (1-n)/n
e=n/ (1-n) (b)
In equations (a) and (b), the porosity should be expressed as a ratio and not percentage.
Degree of saturation
The degree of saturation is the ratio of the volume of water to the volume of voids. It is denoted by ‘S’.
The degree of saturation generally expressed as a percentage. It is equal to zero when the soil is absolutely dry and 100% when the soil is fully saturated.
Percentage air voids
It is the ratio of volume of air to the total volume.
It is also expressed as a percentage.
Air content is defined as the ratio of the volume of air to the volume of voids
The water content (w) is defined as the ratio of the mass of water to the mass of soilids
It is also known as the moisture content (m). It is expressed as a percentage but used as a decimal in computation.
1. BULK MASS DENSITY
The bulk mass density (ρ) is defined as the total mass (M) per unit volume (V)
2. DRY MASS DENSITY
The dry mass density (ρd) is defined as the mass of solids per unit total volume
3. SATURATED MASS DENSITY
The saturated mass density (ρsat) is the bulk density of the soil when it is fully saturated
4. SUBMERGED MASS DENSITY
When the soil exists below water, it is in a submerged condition. The submerged mass density (ρ’) of the soil is defined as the submerged mass per unit total volume.
5. MASS DENSITY OF SOLIDS
The mass density of solids (ρs) is equal to the ratio of the mass of solids to the volume of solids
SPECIFIC GRAVITY OF SOLIDS
The specific gravity of soil particles (G) is defined as the ratio of the mass of a given volume of solids to the mass of an equal volume of water at 4° C.
G = ρs/ρw
The mass density of water ρw at 4°C is 1gm/ml, 1000 kg/m3 or 1 Mg/m3
|Sl No||Relationship in mass density||Relationship in unit weight|
|1||n = e/(1+e)||n = e/(1+e)|
|2||e = n/(1-n)||e = n/(1-n)|
|3||na = n ac||na = n ac|
|4||ρ= (G+Se)ρw/(1+e)||γ= (G+Se) γ w/(1+e)|
|5||ρd = Gρw/(1+e)||γd = G γ w/(1+e)|
|6||ρsat = (G+e)ρw/(1+e)||γsat = (G+e) γ w/(1+e)|
|7||ρ’ = (G-1)ρw/(1+e)||γ’ = (G-1) γ w/(1+e)|
|8||e = wG/s||e = wG/s|
|9||ρd = ρ/(1+w)||γd = γ/(1+w)|
|10||ρd = (1-na)G ρw/(1+wG)||γd = (1-na)G γ w/(1+wG)|