Soil in an engineering sense is a relatively loose agglomerate of mineral and organic materials and sediments found above bedrock. Texturally the soil is divided into two primary groups.
Coarse grained soil
Fine grained soil
The behavior of coarse grained soil is different from fine grained soil. The method of describing coarse grained soil is different from fine grained soil. Let us discuss the primary differences between them.
Coarse Grained Soil
Coarse grained soils are identified primarily on the basis of particle size or grain size. Individual particles are visible by naked eye.
Coarse grained soils are divided into two groups, Sand & Gravel. Particles having diameter larger than 4.75 mm is called Gravel and particles having diameter in between 4.75 mm to 75 micron is called Sand.
Verbal description of coarse grained soil is done on the basis of its gradation (well or poor), particle shape (angular, sub-angular, rounded or sub-rounded) & mineralogical components.
Coarse grained soil exhibit a good load bearing capacity.
Coarse grained soil posse’s good drainage qualities.
There is no volume change with change in moisture condition.
There is no appreciable amount of change in strength characteristic by change in moisture condition.
Vibration accentuates volume change in loose state, by arranging the soil fabric.
Engineering properties are controlled by the grain size of the particles and their structural arrangement.
When touched by hand it feels gritty.
Fine Grained Soil
Fine grained soils are identified on the basis of its plasticity. Individual particles are not visible by naked eye.
Fine grained soils are also divided in two groups, Silt & Clay. Particles having diameter in between 75 micron to 2 micron are called Silt and particles having diameter smaller than 2 micron is called Clay.
Verbal description of fine grained soil is done on the basis of its dry strength, dilatancy, dispersion and plasticity.
Fine grained soil exhibit a poor load bearing capacity.
Fine grained soil is practically impermeable in nature because of its small particles size.
Volume change occurs with change in moisture content.
Strength changes with change in moisture condition.
Fine grained soil is susceptible to frost action.
Engineering properties are controlled by mineralogical factors.
When touched by hand it feels smooth, greasy and sticky.