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There are three properties of soil:

i. Cohesive soil

ii. Non-cohesive soiliii. Organic soil

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Cohesive soil is formed from flaky fine particles

with high cohesive force.

In moist condition, the soil particles stick to each

other due to this cohesive force.

Has low permeability.

Has the ability to return water for a longer time.

In dry condition, the cohesive soil form hard solidparticles.

Examples: clay and silt.

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Formed from cohesive soil particles withsize less than 0.002mm.

Prismatic in shape with smooth and oilysurface.

Clay swells when it is wet.

In wet condition, when the water content

reaches a certain limit, clay starts tobehave like plastic.

It is easy to mould the soil.

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In dry condition, it becomes very high

particles and does not leave any strain

when being rub onto fingers.The extremely fine clay particles cause it

to have very low permeability and

seepage.

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Consists of soil particles between 0.002mm to0.06mm.

Silt particles are larger than clay particles and

are almost rounded.Has low plasticity if compared to clay.

In dry state, silt becomes very brittle and stainfingers when rubbed on it.

Has low cohesion, high permeability and doesnot retain water because of its coarser soilparticles and weaker bond between particles.

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Has particles which are rounded, angular

or prismatic.

The texture of the soil is hard and rough.The bond between particles is loose.

Its stability depends on the friction

between the particles.Has high permeability.

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In rainy condition, water quickly seeps

among soil particles.

As a result, non-cohesive soil cannot

retain water.

Examples: sand and gravel.

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Sand has particles from 0.06mm to2.0mm.

Normally consists of quartz and feldspar.

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Rock fragments consisting of quartz,feldspar and other minerals.

The size is from 2mm to 60mm.

The rock fragments have rough surfaces.

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THE DIFFERENCES BETWEEN THE

CHARACTERISTICS OF COHESIVE AND

NON-COHESIVE SOIL

Fine-Grained Soil

(Cohesive soil)

Coarse-Grained Soil

(Non-cohesive Soil)

High void ratio Low void ratio

Cohesion between particles No cohesion between particles

No friction between particles Friction between particles

Plastically Non plastic

Almost impermeable PermeableCompressible Low compressibility

The rate of settlement is low and

takes longer time

Immediate settlement occurs

when subjected to load

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Formed as a result of the decomposition of

organic materials, plants and decaying

organisms.Its also formed from the formation of humus due

to the reaction of bacteria and fungus which

decay the organic waste.

Humus is a biochemical element which causesorganic soil to change colour into grey and dark.

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Has low density and low capacity.

It is because of its loose particle

packing and brittle but is able toretain water with very high moisture

content.

Has high plastic limit and liquid limit,acidic, soft and compressible.

Not suitable for supporting load.

Examples: Peat soil.

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Consists of organic material, fibrous or

amorphous.

Not suitable in supporting structurebecause it is not stable and has low

bonding and friction force.

The soil is fibrous and highlycompressible.

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