Introduction to Soil Mechanics


The term “soil” can have different meanings, depending upon the field in which it is considered.

To a geologist, it is the material in the relative thin zone of the Earth’s surface within which roots occur, and which are formed as the products of past surface processes. The rest of the crust is grouped under the term “rock”.

To a pedologist, it is the substance existing on the surface, which supports plant life.

To an engineer, it is a material that can be:

  • built on: foundations of buildings, bridges
  • built in: basements, culverts, tunnels
  • built with: embankments, roads, dams
  • supported: retaining walls

Soil Mechanics is a discipline of Civil Engineering involving the study of soil, its behavior and application as an engineering material.

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

Soil consists of a multi-phase aggregation of solid particles, water, and air. This fundamental composition gives rise to unique engineering properties, and the description of its mechanical behavior requires some of the most classic principles of engineering mechanics.

Engineers are concerned with soil’s mechanical properties: permeability, stiffness, and strength. These depend primarily on the nature of the soil grains, the current stress, the water content and unit weight.

Formation of Soils

In the Earth's surface, rocks extend up to as much as 20 km depth. Types …Read More..

Soil Types

Soils as they are found in different regions can be classified into two broad categories: (1) …Read More..

Phase Relations of Soils

Soil is not a coherent solid material like steel and concrete, but is a particulate …Read More..

Three-phase System of Soils

Soils can be partially saturated (with both air and water present), or be fully saturated …Read More..

Volume Relations for Soil

As the amounts of both water and air are variable, the volume of solids is …Read More..

Weight Relations of Soil

Density is a measure of the quantity of mass in a unit volume of material. …Read More..

Interrelations between soil weights

It is important to quantify the state of a soil immediately after receiving in the …Read More..

Soil Weight Worked Examples

Example 1: A soil has void ratio = 0.72, moisture content = 12% and Gs= 2.72. …Read More..

Soil Classification

It is necessary to adopt a formal system of soil description and classification in order …Read More..

Soil Particle Size Distribution

For measuring the distribution of particle sizes in a soil sample, it is necessary to …Read More..

Soil Grain Size Distribution Curve

The size distribution curves, as obtained from coarse and fine grained portions, can be combined …Read More..