Why Study Soil Mechanics in Civil Engg?

Definition of Soil:

Soil is a natural agglomerate used as a construction as well as supporting material and is composed of particles of broken rocks which keep on changing in their texture, structure, consistency, color, chemical, biological and other characteristics from their parent material (rock) by chemical and mechanical processes like disintegration erosion, freezing and thawing.

Definition of Mechanics:

Mechanics is the branch of science dealing with the behavior or response of bodies at rest or with negligible velocity subjected to forces, pressures or displacements.

Soil Mechanics

Soil Mechanics is the branch of civil engineering that is concerned with behavior of soil at rest under different conditions of direct (Structural Loads) and indirect (Thermal Stresses) loading.

According to Terzaghi

Soil Mechanics is the application of the laws of mechanics and hydraulics to engineering problems dealing with sediments and other unconsolidated accumulations of solid particles produced by chemical and mechanical disintegration of rocks regardless of whether or not they contain an admixture of organic constituents.

Why do we Study Soil Mechanics?

• Every man made structure rests on earth and thus need a foundation to transfer the ultimate load without failure. To determine the behavior of soil and to resist these ultimate loads we need to study its mechanics.
• To make new researches in the relevant field
• To replace the old (unscientific) methods of construction with the new and advanced ones

Uses of Soil in Civil Engineering

In civil engineering the soil can be used in different ways. The uses of soil can be divided into three categories:

1) As a Supporting Material

Soil is used as a supporting material to bear the load of structures e.g.

• Bridges,
• Roads
• Buildings

2) As a Raw Material (Unprocessed Material)

In natural form soil can be used for the following purposes:

• Flood Control Embankments
• Road Embankments
• Earth-Filled Dam

3) As a Processed Material

Passed through some process to get

• Burnt Bricks
• Concrete Mixes

Formation of Soil

• The formation of soil starts with the parent material and continues for a very long period of time taking 1000 years or more.
• As the parent material is weathered and / or transported, deposited and precipitated it is transformed into a soil.
• The parent material may be in the form of bedrock, glacial deposits, and loose deposits under water or material moving down sloping land.

Factors Affecting Formation of Soil

Soil formation process is influenced by the following factors:

• Composition of Parent Material
• Climate
• Topography
• Organisms
• Time

Bare rocks exposed to warm climate, frequent and heavy annual rainfalls causes faster development of soil.