Soils are formed by weathering of rocks due to Mechanical disintegration or Chemical decomposition. When rock surface are exposed to atmosphere for considerable period of time,
( contineous heating and cooling of rock ) result in disintegrates or decomposes to form soil.
Formation of Soil also happens due to physical reaction and chemical reaction over the surface
1. Physical Disintegration
2. Chemical decomposition of rocks
Soil Classification is separation of soil into classes or groups each having similar characteristics and behaviour. Classification for engineering purpose should be based mainly on mechanical properties.
Like: Permeability, Stiffness, Strength etc.,
Classification based on Grain Size
Soil particles
1.Fine soil
- below 0.002mm are clay
- between 0.002 to 0.075mm are silt
- between 0.075 to 4.75mm are sand
- between 4.75 to 80mm are gravel size
What is Compaction?
Compaction is said to be compression of soil by expulsion of air from voids. It is a quick process, requires short term loading. Dynamic loading is applied during compaction, both cohesion and cohesionless soil can be compacted. Compaction is always done to get maximum dry density, which helps in improving bearing capacity. Compaction is done before start of construction. Mostly done in Construction of roads, Embankment, dam etc.,
What is Consolidation?
Consolidation is said to be compression of soil by expulsion of water from voids. It is a slow process, requires long term loading. Static or constant loading is applied (some times happen naturally), only cohesive soil can be consolidated. Consolidation is done naturally by structural loads from foundation. Consolidation is done naturally during the process of Construction. (Some times happen with natural settlement)
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| Clay |
Cohesion is said to be attraction between particle of same type or origin, type of soil where there is inter-particular attraction. In these type of soil particles are very fine and it is governed by surface fore rather than its self weight. Also, the friction between the soil will not happen hence shear strength will be contributed by only cohesive force and not internal friction.
Example: Clay
Non-cohesive soil -soil with out cohesive force, has coarser particles with self weight governing their behaviour. The soil particle has internal friction and shear strength depends on internal friction between their sand particles.
Example: Sand
Most natural soil have both cohesive and frictional force contributes shear strength.
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| Sand |
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