COMPOSITION OF SOILS - SOIL MECHANICS (StudyCivilEngg.com)

COMPOSITION OF SOILS

SUBJECT : SOIL MECHANICS

Soil is a complex physical system consisting of different phases. The term phase which is derived from a Greek word phasis, means any homogeneous part of the system different from other parts of the system and separated from them by abrupt transition. In other words, each physically or chemically different, homogeneous and mechanically separable part of a system constitutes a distinct phase. A system consisting of more than one phase is said to be hetrogeneous.

A mass of soil includes accumulated solid particles or soil grains and the void spaces existing between the particles. The void spaces may be partially or completely filled with water or some other liquid, and those not occupied by water or any other liquid are filled with air or some other gas. Since a soil mass as it exists in nature has generally three constituents viz., solid particles or soil grains, water and air, i.e., it has materials in all the three states of matter viz., solid, liquid and gas, soil is, in general, considered to be a “three-phase system”. The three constituents of a soil mass do not occupy separate spaces but are blended together forming a complex material as shown in below figure

Actual Soil Mass

However, for the purposes of analysis it is convenient to represent the soil mass by a block diagram called ‘phase-diagram’ as shown below, in which the three constituents of the soil mass are shown to occupy separate spaces. 

Representation of Soil mass - Three Phase Diagram

When the soil voids are completely filled with water, the gaseous phase being absent, the soil is said to be ‘fully saturated’ or merely ‘saturated’. When there is no water at all in the voids, the voids will be full of air, the liquid phase being absent, the soil is said to be dry. In both these cases the soil system reduces to a Two-phase system as shown in below figures

Two Phase Diagram - Saturated Soils

Two Phase Diagram - Dry Soil

It may be noted that the separation of solids from voids is only imaginary. However, the phase-diagram provides a convenient means of developing the weight-volume relationships for a soils which will be discussed in further posts of Soil Mechanics.

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RELATED POSTS

• RESIDUAL AND TRANSPORTED SOILS
• INTRODUCTION & BASIC DEFINITIONS IN SOIL MECHANICS
• SOIL GROUPS IN INDIA
• FORMATION OF SOILS
• DIFFERENT TYPES OF SOILS

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