## Terms and Definitions in Soil Engineering

Various definitions of terms used in Geotechnical Soil Engineering are presented.

## 1. Void Ratio

Void ratio is the volume of voids to the volume of solids. It is denoted by ‘e’.

e=Vv/Vs

It is expressed as a decimal.

## 2. Porosity

It is defined as the ratio of volume of voids to the total volume. It is denoted by ‘n’.

n=Vv/V

It is generally expressed as a percentage

1/n=V/Vv= (Vv+vs)/Vv

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.

## 3. 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’.

S=Vw/Vv

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.

## 4. Percentage air voids

It is the ratio of volume of air to the total volume.

na= Va/V

It is also expressed as a percentage.

## 5. Air content

Air content is defined as the ratio of the volume of air to the volume of voids

ac= Va/Vv

Also,

na=n ac

## 6. Water content

The water content (w) is defined as the ratio of the mass of water to the mass of solids

w= Mw/Ms

It is also known as the moisture content (m). It is expressed as a percentage but used as a decimal in computation.

## 7. Bulk Mass Density of Soil

The bulk mass density (?) is defined as the total mass (M) per unit volume (V)

?=M/V

## 8. Dry Mass Density

The dry mass density (?d) is defined as the mass of solids per unit total volume

?d= Ms/V

## 9. Saturated Mass Density

The saturated mass density (?sat) is the bulk density of the soil when it is fully saturated

?sat= Msat/V

## 10. Submerged Mass Density

When the soil exists below water, it is in a submerged condition. The submerged mass density (?’) of the soil is defined as the submerged mass per unit total volume.

?’= Msub/V

## 11. Mass Density of Solids

The mass density of solids (?s) is equal to the ratio of the mass of solids to the volume of solids

?s=Ms/Vs

## Volume-Weight Relationships of Soils

1. BULK UNIT WEIGHT (?)= W/V
2. DRY UNIT WEIGHT (?d) = Ws/V
3. SATURATED UNIT WEIGHT (?sat) = Wsat/V
4. SUBMERGED UNIT WEIGHT (?sub or ?’) = Wsub/V
5. UNIT WEIGHT OF SOIL SOLIDS (?s) = Ws/Vs

## 12. 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 = ?s/?w

The mass density of water ?w at 4°C is 1gm/ml, 1000 kg/m3 or 1 Mg/m3

## Basic Soil Relationships

 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 ?= (G+Se)?w/(1+e) ?= (G+Se) ? w/(1+e) 5 ?d = G?w/(1+e) ?d = G ? w/(1+e) 6 ?sat = (G+e)?w/(1+e) ?sat = (G+e) ? w/(1+e) 7 ?’ = (G-1)?w/(1+e) ?’ = (G-1) ? w/(1+e) 8 e = wG/s e = wG/s 9 ?d = ?/(1+w) ?d = ?/(1+w) 10 ?d = (1-na)G ?w/(1+wG) ?d = (1-na)G ? w/(1+wG)