January 28, 2021

Introduction to soil and its formation

Definition of Soil : The terminology Soil is define as an unconsolidated material composed of solid particles which produce by disintegration of rock.

Soil formation and soil types :

1.On the basis Of geological origin soil may organic or inorganic types
2.Organic soils are extremely compressible und their use a foundation material is avoided.
3.Peat muck and humus are organic soils. Organic oil also known as cumulose soil.
4.Inorganic soils are formed by weathering Of rocks due to mechanical disintegration or chemical decomposition.
5.Physical disintegration or mechanical weathering occurs due to the effects temperature changes. wedging action of ice, spreading of roots of plants and abrasion.
6.Due to physical disintegration. there is no change in chemical composition
7.Coarse grained soils, such IS gravel and sand are formed by the process of physical disintegration.
8.Chemical decomposition or chemical weathering of rocks occurs due to hydration, carbonation, Oxidation, solution and hydrolysis.
9.Due to chemical decomposition, original materials are transformed into new minerals by chemical reactions
10.Chemical decomposition of rocks results in formation of clay minerals
11.Soils are obtained geologic cycle. which goes On continuously in nature
12.the geological cycle consists of corrosion. Transportation, deposition and upheaval of soil.
Commonly used soil designation

Bentonite : Decomposed volcanic ash containing a high % of clay mineral ex. Montmorillonite 

Black Cotton soil : It contain the mineral montmorillonite and contain large swelling and shrinkage.

Loam : It is a mixture of sand, silt and clay size particles in equal ratio.

Moorum : It is gravel mixed with red clay.

Varved clay : It is clay and slit of glacial origin usually a lacustrine deposited.

1.Gravitational forces are predominant in gravels and sand
2.Surface forces, electrical forces, chemical forced are predominant in clays.
Soil Structure :

1.Geometric arrangement of soil particles with respect to one another is known as soil structure.
2.Depending upon the particle size and mode of formation the various types were found such as Single grained structure, Honey comb structure, Flocculated structure, Dispersed structures & composite structures.

Single Grained Structure:

1.Found in coarse grained soils like gravel and sand.
2.The major cause for formation is gravitational force, here the surface forces are negligible.
3.Under the influence of gravitational forces, the grained will assume a particle to particle contact referred to as single grained structure.
4.Single grained structures may be loose or dense as shown below.
Honey Comb Structure :

1.It is possible for fine sand or silts.
2.Both gravitational forces and surface forces are responsible.
3.Such a structure can support loads, only under static conditions.
4.Under vibrations and shocks, the structures collapse and large deformation takes place.

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