🅢🅞🅘🅛 -ORIGIN AND CLASSIFICATION OF SOIL
INORGANIC SOILS
Formed by weathering of rocks.
(eg., gravel, sand, silt, clay)
⦿ Physical weathering
‣‣temperature
‣‣wedging action of ice
‣‣plant root growth
‣‣abrasion
⦿ Chemical weathering
‣‣Hydrolysis
‣‣Carbonation
‣‣Oxidation & Reduction
- Clay forms due to chemical weathering. Therefore it has special properties (swelling, shrinkage, plasticity, & thixotropy)
ORGANIC SOILS
Formed by decomposition of organic matter.
(eg., humus, peat)
- The process of formation of soil is called PEDOGENESIS.
GEOLOGICAL CYCLE
➼➼weathering ➼➼ transportation ➼➼deposition ➼➼ upheaval➼➼
Soil classification based on Geological cycle
⦿ Residual or Sedentary soils: deposited at the same place of origin. (eg. Black cotton soils)
⦿ Transported or Sedimentary soils: deposited away from their origin.
Soils based on the source of transportation :
‣‣Wind or Air: Aeolian deposits (eg. Loess, Sand dunes)
‣‣Lake water: Lacustrine soils (eg. Varved clay)
‣‣Running water or Rivers: Alluvial soil (eg. Loam)
‣‣Marine water: Marine soils (eg. Marine clay, Marl)
‣‣Gravity: Colluvial or Elluvial deposits (eg. Talus)
‣‣Glaciers: Glacier deposits. (eg. Drift & Till)
Loamy Soil
⁃ a mix of sand, silt & clay in almost equal proportions.
⁃ best suitable for agriculture.
Varved Clay
⁃ alternate thin layers of clay & silt.
Collapsible Soil
⁃ reduction in volume by wetting.
⁃ Aeolian deposits (Loess: silty clay)
Caliche (Calcrete)
⁃ a mix of gravel, sand, & silt.
Moorum (Red soil)
⁃ a mix of gravel & clay.
⁃ best suitable for WBM pavement.
Black Cotton Soil
⁃ chemically weathered residual clay.
⁃ high swelling, shrinkage & plasticity due to Montmorillonite clay mineral.
Bentonite Clay
⁃ decomposed volcanic ash.
⁃ high swelling, shrinkage & plasticity due to Montmorillonite.
Golden fact: % of montmorillonite is more in Bentonite clay than Black cotton soils.
Comments
Post a Comment