1 - Definition of Soil

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What is Soil?

The term SOIL has several meanings

depending on the general field it is being

considered.Generally,

Soil

is the surface layer of the

earth, composed of fine rock material

disintegrated by geological processes;

and humus, the organic remains of

decomposed vegetation.

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In Soil Science: Soil is the substance

existing on the earth’s surface, which

grows and develops plant life.

In Geology: Soil is the material in the

relative thin surface zone within which

roots occur and all the rest of the crust is

grouped under the term ROCK,

irrespective of its hardness.

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In Engineering: Soil is the un

-

aggregated or

un

-

cemented deposits of mineral and/or

organic particles or fragments covering

large portion of the earth’s crust.

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FUNCTIONS OF SOIL IN THE

ECOSYSTEM:1.

As a medium for plant growth

-

 provides anchor to the root system of the

 plant to prevent it from toppling-

soil pores hold rainwater for plant uptake

-

soil moderates temperature fluctuations

that supports development of root

system

-

a medium that supplies inorganic, mineral

nutrients in the form of dissolved ions.

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2. As a system for water supply and

purification-every drop of water in our rivers, lakes,

estuaries, and aquifers has either traveled

through the soil or flowed over its surface-the nature and management of soils in a

watershed will have a major influence on

the purity and amount of water finding itsway to the aquatic system as a waterresource

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3. As a recycling system for nutrients

and organic wastes-soils have the capacity to assimilate great

quantities of organic waste, turning it into

 beneficial humus, converting the mineralnutrients in the wastes to forms that can be utilized by plants and animals, andreturning the carbon to the atmosphere ascarbon dioxide, where it again will

 become a part of living organismsthrough plant photosynthesis

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4. As a Habitat for Soil Organisms

- Soil harbor much of the earth’s genetic

diversity: water in soil pores may be

filled with swimming organisms such asroundworms, diatoms, tiny insects and

mites may be crawling in larger pores

with moist air.

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5. As an Engineering Medium

- Soil is thought of as a firm and solid base

for road construction and vertical

structures-The nature and properties of soil will

dictate sustainability as roadbeds or

 building formation

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Soil Engineering and Soil Mechanics

-Soil Engineering is the application of the

 properties of Soil Mechanics to practical

 problems.-Soil Mechanics is the branch of science

that deals with the study of the physical

 properties of soil and the behavior of soilmasses subjected to various types of

forces.

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According to Terzaghi (1948), Soil

Mechanics is the application of laws ofmechanics and hydraulics to engineering

 problems dealing with sediments and

other unconsolidated accumulations ofsolid particles produced by the

mechanical and chemical disintegration

of rocks regardless of whether or not theycontain an admixture of organic

constituent.

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Karl Terzaghi is the undisputed father of

Soil Mechanics. His publication

“Erdbaumechanik” 1925 laid the

foundation of Soil Mechanics. It brought

recognition to importance of soils iin

engineering.

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Other names for Soil Mechanics

- Geotechnique

- Geotechnics

- Geomechanics- Geotechnical Engineering

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