DIFFERENT TYPES OF SOILS, THEIR DEFINITIONS AND BASIC PROPERTIES - SOIL MECHANICS (StudyCivilEngg.com)
DIFFERENT TYPES OF SOILS - THEIR DEFINITIONS AND BASIC PROPERTIES
SUBJECT : SOIL MECHANICS
Bentonite : It is a type of clay formed by decomposition of volcanic ash. It contains a high percentage of clay mineral montmorillonite. It is highly water absorbent and exhibits high degree of shrinkage and swelling characteristics.
Black Soil or Black Cotton Soil : It is a residual soil containing a high percentage of clay mineral montmorillonite. It has very low bearing capacity and exhibits high degree of shrinkage and swelling characteristics. The name black cotton soil is derived from the fact that cotton grows well in this soil.
Boulder : Boulders are rock fragments of large size, more than about 300 mm in size.
Boulder Clay : It is an unstratified deposit of soil formed by melting of a glacier. The deposit consists of all sizes of rock fragments ranging from boulders down to finely pulverised clay materials. The soil is generally well graded. It can be easily densified by compaction. It is also known as ‘Glacial till’ or simply ‘Till’.
Calcareous Soils : These are the soils which contain large quantity of calcium carbonate. These soils effervesce when treated with dilute hydrochloric acid.
Clay : It is a fine grained cohesive soil which consists of microscopic and sub-microscopic particles of size less than 0.002 mm. It is derived from the chemical decomposition of rocks and contains large quantity of clay minerals such as ‘Kaolinite’, ‘Illite’ and ‘Montmorillonite’. It can be made plastic by adjusting the water content, and depending on the degree of plasticity it may be called ‘lean clay’ or ‘fat clay’. It exhibits considerable strength when dry. Organic clay contains finely divided organic matter and is usually dark grey or black in colour. It is highly compressible and its strength is high when dry. 'China clay’, also called ‘Kaolin’, is a pure white clay, used in the ceramic industry.
Cobbles : Cobbles are the water-worn smooth rounded stones of large size in the range of 80 to 300 mm.
Diatomaceous Earth : Diatoms are the minute unicellular marine organisms. Diatomaceous earth is a fine, light grey, soft sedimentary deposits of the silicious remains of the skeletons of the diatoms. 10. Dispersive Clays. These are the special types of clays which defloculate in still water. Such soils erode if exposed to low-velocity water. Susceptibility to dispersion depends upon the cations in the soil pore water.
Dune Sands :These are wind-transported soils. These are composed of relatively uniform fine to medium sand particles.
Expansive Clays : These are prone to large volume changes as the water content is changed. These soils contain the mineral montmorillonite.
Fills : All man-made deposits of soils and waste-materials are called fills. Such deposits are made in the depressions on the ground surface in order to raise their level to that of the adjacent higher ground surface. The properties of the fills depend upon the type of soil, its water content and the degree of compaction.
Gravel : Gravel is a loose mixture of pebbles and rock fragments coarser than sand. It is a coarse-grained cohesionless soil with particle size ranging from 4.75 mm to 80 mm.
Hardpans : These are dense, well-graded, cohesive aggregates of mineral particles, which remain hard and do not disintegrate when submerged in water. Boulder clays or glacial tills may also be called hardpans. Since hardpans are densely cemented soils, they are very difficult to penetrate or excavate.
Humus : It is a brown or black organic part of the soil resulting from the partial decay of plant and animal matter. It is of little significance in engineering works.
Kankar : It is an impure form of lime stone. It contains calcium carbonate mixed with some silicious material.
Laterites : These are dark brown soils of cellular structure, easy to excavate but gets hardened on exposure to air due to the formation of hydrated iron oxides, which have cementing action.
Loam : It is a mixture of sand, silt and clay approximately in equal proportions. It sometimes contains organic matter.
Loess : It is a deposit of wind blown silt or silty clay, yellowish brown in colour. It is generally of uniform gradation with the particle size in the range of 0.01 to 0.05 mm. It exhibits cohesion in the dry condition, which is lost on wetting. Near vertical cuts can be made when the soil is in dry condition.
Marl : It is a crumbly mixture of clay, sand and limestone usually with shell fragments, with clay content not more than 75% and lime content not less than 15%. It is also designated as marine calcareous clay and is usually of greenish colour.
Moorum : It is a mixture of gravel and red clay.
Muck : It is a mixture of fine grained soil and highly decomposed organic matter. It is black in colour.
Peat : It is an organic variety of clay having fibrous aggregates of macroscopic and microscopic particles. It is formed from vegetal matter under the conditions of excess moisture, such as swamps. It is recognised by its dark colour, odour of decay and very low specific gravity (0.5 to 0.8). It is highly compressible and not suitable for foundations.
Sand : It is a coarse grained soil having particle size between 0.075 mm and 4.75 mm. The particles are visible to naked eye. It is cohesionless and pervious.
Silt : It is a fine grained soil which is finer than sand with particle size between 0.002 mm and 0.075 mm. The particles are not visible to naked eye. Inorganic silt consists of bulky, equidimensional grains of quartz. It is generally non-plastic and is cohesionless. It may, however, exhibit slight plasticity when wet and slight compressibility if the particle shape is plate-like. Inorganic silt is also called ‘Rock flour’. Organic silt contains certain amount of fine decomposed organic matter. It is dark in colour and has peculiar odour. It exhibits some degree of plasticity, cohesion and compressibility.
Top Soil : It is a surface soil which supports plant life. It contains large quantity of organic matter.
Tuff : It is a fine grained soil composed of very small particles ejected from volcanoes during explosion, and transported and deposited by wind or water.
Tundra : It is a mat of peat and shrubby vegetation that covers clayey subsoil in arctic regions. The deeper layers are permanently frozen and are called permafrost. The surface deposit is the active layer which is alternately subjected to freezing and thawing.
Varved Clays : Varve is a term of Swedish origin meaning thin layer. Thus varved clays are sedimentary deposits consisting of alternate thin layers of clay and silt. The thickness of each layer seldom exceeds 1 cm. These clays are of glacial origin, i.e., deposits of soil formed by melting of glaciers; and also lacustrine deposits, i.e., soils deposited in lake beds.
FAQs COVERED IN THIS POST
What are the different types of soils?
What are different types of soils and their properties?
What is Black Cotton Soil?
What is Boulder Clay?
What is Calcareous Soil?
What is Caliche?
What is Clay?
What is Silt?
What is Tuff?
What is Top Soil?
What is Varved Clay?
What is Moorum?
Define Gravels and their properties
What is Peat and mention its properties?
What are Dune Sands? Define and mention its properties?
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