Soil mechanics and foundations- Introduction

  • Soil mechanics is the application of laws of mechanics and hydraulics to engineering problems dealing with sediments and other unconsolidated accumulation of soil particles produced by the mechanical and chemical disintegration of rocks ,regardless of whether or not they contain and admixture of organic constituents.
  • Dr.Karl Terzaghi – Father of soil mechanics.

Definitions of soil:-

1) for engineering purpose:- soil is defined as a natural aggregate of mineral grains, loose or moderately cohesive, inorganic or organic in nature.

2) According to a geologist:-soil is defined as a disintegrated rock.

3) According to agriculturist:-soil is the loose mantle at the surface of the Earth which favours the growth of plant.

The soil is produced by the mechanical or chemical weathering of the solid rocks which may be igneous rock, sedimentary rock or metamorphic rock.

Mechanical weathering is caused by- 1) periodical temperature changes 2) impact and spilting action of flowing water, ice and wind. 3) splitting action of ice, plants and animals.

Chemical weathering is caused by-1) oxidation 2) hydration 3) carbonation 4) leaching by organic acids and water.

Types of soil:-

Residual soil-formed by weathering of rocks, but located at the place of origin. Sand ,silt and clay are residual soils.

Transported soils- soils which are carried away by the force of wind, ice, water and gravity.

Aeolian soil- transported by wind (loess)

Alluvial soil- transported by running water

Lacustrine soil- deposited at the bottom of the lakes.

Colluvial soil- transported by gravitational force (talus)

Glacier soil- transported by glaciers by ice or by water issuing from melting of glaciers.( Drift)

Cumulose soils- the accumulation of decaying and chemically deposited vegetable matter under conditions of excessive moisture results. (Peat and muck)