[GATE NOTES] Geotechnical Engineering GATE, IES, Govt Exams - Handwritten Notes

GEOTECHNICAL ENGINEERING

GATE, IES, GOVT EXAMS – ACE ACADEMY HANDWRITTEN NOTES

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Origin of soils :

Soil is a naturally occurring unconsolidated earth material present above the bed rock.

Karl Terzaghi is known as father of soil mechanics.

Origin of soils is due to the following :
1. Weathering of rocks (disintegration inorganic soils) ex : gravel, sand, some type of silts, clays
2. Decomposition of organic matters (organic soils or cumulose soils ) ex : humus, muck, peat

Weathering of rocks are of two types :
Physical weathering which is due to physical effects like temperature change, abrasion (grinding action of flowing water and wind) and splitting action due to ice, rain, penetration of plant roots. Physical weathering produces soils like gravel, sand, non plastic silt.

Chemical weathering which is due to chemical actions like oxidation, carbonation, hydration , solution, hydrolysis. Chemical weathering produces soils like clay, plastic silt.
Transportation of soils : It is due to
Wind – Aeolion soils – Transported and deposited by wind.
Water – Alluvial soils – Transported by water and deposited along river bed.
Glacier – Glacier Deposit – Transported by glaciers.
Gravity – Colluvial soils – Transported and deposited by gravity.

Lacustrine soils – Transported by water and deposited in lakes.

Marine soils – Transported by water and deposited in seas.
Classification of soils :
Residual soils – Soil which remains at or near the parent rock.
Transported soils – Transported away from parent rocks.
Popular field names of soils :
1. Black cotton soils : a residual clayey soil. Highly plastic. Exhibits high swelling and shrinkage due to present of montmorillonite clay mineral. Parent rock is basalt.
2. Loam : a mix of sand silt and clay.
3. Morrum : a gravel mixed with red clay.
4. Bentonite : a decomposed volcanic Ash. A clayey soil, highly plastic and highly water absorbant. Bentonite slurry is called drilling mud.
5. Varved clay : contains alternative thin layer of silt and clay. Lacustrine deposits.
6. Loess : Aeolian deposit. Contains silt sized particles. Weakly cemented by calcium carbonate particles.
7. Sand dunes : Aeolian deposits. Particle size is same.
8. Humus : Half decomposed organic soul. Amorphous in nature.
9. Muck : contains fine inorganic particles with decomposed organic materials. Black in color.
10. Peat : Highly decomposed organic matters. Fibrous in nature. Dark brown to black color. Bad odour
11. Fill : a manually deposited soil (a man made deposit)