**Terms and Definitions in Soil Engineering**

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

**Volumetric Relationships of Soil**

**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.

**n _{a}= 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

**a _{c}= Va/Vv**

Also,

**n _{a}=n a_{c}**

**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.

**Volume Mass Relationship of Soils**

**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**

- BULK UNIT WEIGHT (?)= W/V
- DRY UNIT WEIGHT (?
_{d) }= Ws/V - SATURATED UNIT WEIGHT (?
_{sat}) = Wsat/V - SUBMERGED UNIT WEIGHT (?
_{sub}or ?’) = Wsub/V - 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/m^{3 }or 1 Mg/m^{3 }

**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 | n_{a} = n a_{c} | n_{a} = n a_{c} |

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) |