# Density of Soil

It is defined as “Mass of soil per unit volume of soil”

**Mathematically**

Density of Soil= (Mass of Soil /Volume of soil)

It is denoted by Greek word ? (Rho)

It is expressed in or

# Unit Weight of Soil

It is defined as “the weight of soil per unit volume of soil”

**Mathematically**

Unit Weight of Soil= (Weight of Soil /Volume of Soil)

It is denoted by “”

It is expressed in

# Bulk Unit Weight of Soil

It is sometimes called Unit Weight only. It is the ratio of the total weight of soil to the total volume of soil

**Mathematically**

Bulk Unit Weight of Soil= (Weight of Soil/ Total Volume of Soil)

It is also called Moist Unit Weight

# Dry Unit Weight of Soil

It is defined as “ the weight of soil solids per unit total volume of sample”

**Mathematically**

Dry Unit Weight of Soil=( Weight of Soil Solids/Total Volume of Soil)

Since

W = Wa + Ww + Ws = 0 + 0 + Ws = Ws = Wd ,therefore,

When all the voids of soil are filled with air it is called Dry Soil and Unit Weight as Dry Unit Weight e.g. Oven Dried Soil in Laboratory

# Unit Weight of Soil Solids

It is defined as “the weight of soil solid per unit total volume of soil solid”

**Mathematically**

Unit Weight of Soil Solid=( Weight of Soil Solids/Volume of Soil)

# Saturated Unit Weight

It is defined as “the total weight of saturated soil sample per units its total volume”

**Mathematically**

When all the voids of soil are filled with water it is called Saturated Soil and its weight as Saturated Unit Weight

# Submerged Unit Weight

It is defined as “the submerge weight of soil per unit its total volume”

**Mathematically**

Submerged Unit Weight = (Submerged Weight of Soil/ Total Volume of Soil)

According to the Archimedes’ Principle;

An object immersed in water will experience a buoyant force in upward direction causing reduction in weight

Thus soil submerged in water will thus have a unit weight

# Three Phase System of Soil

A soil mass is a three phase system consisting of solid particles (soil grains), water and air. Thus four cases arises

**Soil Particles**with**NO AIR**and**NO WATER**in voids (i.e.*Ideal Case*)*100% Compacted Soil***Soil Particles**with**ONLY AIR**in voids ()*Dry Soil***Soil Particles**with**ONLY WATER**in voids ()*Saturated Soil***Soil Particles**with**BOTH AIR**and**WATER**in voids ()*Partially Saturated Soil*

# Specific Gravity

It is defined as “the ratio of the unit weight of soil sample to the unit weight of water at standard temperature and pressure i.e. and 1atm or 101.325kPa

OR

It is defined as “the ratio of the density of soil sample to the density of water at standard temperature and pressure i.e. and 1atm or 101.325kPa

**Mathematically**

Specific Gravity =(Unit weight of Soil/Unit Weight of Water)

It is denoted by G or S.G.

# Water Content

It is defined as “The ratio of the weight of water to the weight of solids”

**Mathematically**

Water Content =(Weight of Water /Weight of Solids)

It is denoted by w

**Void Ratio**

It is defined as “The ratio of the volume of voids to the volume of soil solid”. It is denoted by “e”

**Mathematically**

Void ratio = (Volume of Voids/Volume of Soil Solids)

**Porosity**

It is defined as “The ratio of the volume of voids to the total volume of soil sample”. It is denoted by “n”

**Mathematically**

Porosity = (Volume of Voids/Volume of Soil Sample)

# Degree of Saturation

It is the ratio of the Volume of Water to the Volume of Voids. It is denoted by “S”

**Mathematically**

Degree of Saturation= (Volume of Water / Volume Voids)

Vw = Vv

Hence S = 1 or 100%

S = 0

# Air Content

It is the ratio of Volume of Air to the Volume of Voids present in the given soil sample

**Mathematically**

Air Content = (Volume of Air/Volume of Voids)

Void Ratio, Porosity, Degree of Saturation and Air Content are **Volume Ratios**