Introduction
Soil (L. solium = upper layer of the earth that may be dug or plowed) is a naturally occurring loose or soft deposit which is also a part of the earth's crust and produced as a result of weathering, disintegration or deposition of rocks and decay of vegetation.
Soil is defined as the uncemented aggregate of mineral grains and decayed organic matter (solid particles) with liquid and gas in the empty spaces between the solid particles.
SOIL MECHANICS is the branch of civil engineering involving application of laws of hydraulics and mechanics in order to solve engineering problems related to soil.
Soil Mechanics is the branch of science that deals with the study of the physical properties of soil and the behaviour of soil masses subjected to various types of forces.
The term "Soil Mechanics" was coined by Dr. Karl Terzaghi in 1925. According to him, "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 the mechanical and chemical disintegration of rock, regardless of whether or not they contain an admixture of organic constituents."
Soil (L. solium = upper layer of the earth that may be dug or plowed) is a naturally occurring loose or soft deposit which is also a part of the earth's crust and produced as a result of weathering, disintegration or deposition of rocks and decay of vegetation.
Soil is defined as the uncemented aggregate of mineral grains and decayed organic matter (solid particles) with liquid and gas in the empty spaces between the solid particles.
SOIL MECHANICS is the branch of civil engineering involving application of laws of hydraulics and mechanics in order to solve engineering problems related to soil.
Soil Mechanics is the branch of science that deals with the study of the physical properties of soil and the behaviour of soil masses subjected to various types of forces.
The term "Soil Mechanics" was coined by Dr. Karl Terzaghi in 1925. According to him, "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 the mechanical and chemical disintegration of rock, regardless of whether or not they contain an admixture of organic constituents."
Why does a civil engineer need to study Soil Mechanics?
All branches of civil engineering namely Structural, Transportation, Environmental and Hydraulics require an understanding of soil and how it behaves.
All branches of civil engineering namely Structural, Transportation, Environmental and Hydraulics require an understanding of soil and how it behaves.
- Virtually, all civil engineering structures come into contact with soil via their foundations. Knowledge of soil mechanics is essential to assure that the structures are properly supported. This can avert: (i) structural damage and failure, (ii) loss of life, (iii) financial loss, etc.
- Road beds are often built of soil, and the roadways themselves can often pass through mountains, cuts, fills, etc. Understanding soil mechanics can preclude problems with pavement potholing and cracking, as well as embankment failure, slope failures that can wipe out entire roadways.
- (i) Liquid toxins or pollutants are often spilled or released inadvertently onto or into the soil. (ii) Land filling of solid wastes. As a result, important questions that need to be addressed are: (i) Will the pollutants remain in place, or possibly be transmitted through soil? If so, on what rate? (ii) Can anything be done to clean up the pollution?
- The design of earthen flow retention structures such as dams, levees, dikes, storage ponds, etc. require a knowledge of how water is transported through soil.
Formation of Soil
(1) Physical Factors:
i. Thermal changes (due to different coefficients of thermal expansion of the mineral constituents)
ii. Abrasion due to water, wind or glacier
iii. Wedging action of ice (expansion and subsequent disintegration)
iv. Spreading of roots (creation of cracks and fissures in the rock)
(2) Chemical Factors:
i. Oxidation: Combination of oxygen ions with minerals in rocks.
ii. Carbonation: Carbon dioxide of air combines with water to form carbonic acid.
iii. Hydrolysis: Water dissociates into hydrogen and hydroxide ions. Hydrogen cations replace the metallic ions in the constituent minerals of the rocks.
iv. Hydration: Water combines with the rock minerals resulting into the formation of new compounds.
v. Leaching/Solution: Formation of solution when certain rock minerals combine with water.
(3) Biological Factors: Decay of vegetation.
(1) Physical Factors:
i. Thermal changes (due to different coefficients of thermal expansion of the mineral constituents)
ii. Abrasion due to water, wind or glacier
iii. Wedging action of ice (expansion and subsequent disintegration)
iv. Spreading of roots (creation of cracks and fissures in the rock)
(2) Chemical Factors:
i. Oxidation: Combination of oxygen ions with minerals in rocks.
ii. Carbonation: Carbon dioxide of air combines with water to form carbonic acid.
iii. Hydrolysis: Water dissociates into hydrogen and hydroxide ions. Hydrogen cations replace the metallic ions in the constituent minerals of the rocks.
iv. Hydration: Water combines with the rock minerals resulting into the formation of new compounds.
v. Leaching/Solution: Formation of solution when certain rock minerals combine with water.
(3) Biological Factors: Decay of vegetation.
Origin
Parent Material (Rock) ----------> Soil (Basis of Classification:- Deposition) ---------->
I. Residual Soil:- If the soil is deposited at the place of origin, it is known as residual soil.
II. Transported Soil:- Transported soil refers to that soil which has been transported and deposited away from the origin. Various factors are responsible for the transportation of soil from its place of origin and accordingly, transported soil can be classified:
i. Alluvial - river
ii. Colluvial - gravity
iii. Aeolian - air
iv. Glacial - glacier
v. Lacustrine - lake
vi. Marine - sea
Parent Material (Rock) ----------> Soil (Basis of Classification:- Deposition) ---------->
I. Residual Soil:- If the soil is deposited at the place of origin, it is known as residual soil.
II. Transported Soil:- Transported soil refers to that soil which has been transported and deposited away from the origin. Various factors are responsible for the transportation of soil from its place of origin and accordingly, transported soil can be classified:
i. Alluvial - river
ii. Colluvial - gravity
iii. Aeolian - air
iv. Glacial - glacier
v. Lacustrine - lake
vi. Marine - sea