Soil Formation | How Does Soil Form?
Depending on the method of formation, the soil can be classified as residue and transport.
The remaining soils are formed by the weathering of the rocks and remain in a place of origin with little or no movement of practically isolated soil particles.
Carried soils are formed in one place (like residual soils) but are shipped and deposited in another place.
Remaining Soil
Climatic (due to weather effects) and leakage of water-soluble materials in rock are the geological processes in the formation of these soils.
However, The rate of degradation of the rocks is higher than the rate of erosion or transport of weathering material and the accumulation of residual soils.
Moreover, As the leaching action decreases with depth, the climatic environment gradually decreases from the surface downwards, thereby decreasing the soil formation, until eventually the unchanged rock is encountered (Figure 1.2).
Residual clays usually cover a wide range of particle sizes, shapes, and compositions. Generally, the climate is higher in warm, humid areas than in cold, dry areas.
However, Humid, warm areas are favorable for chemical weather. Also, due to the presence of vegetation, decomposed material is less likely to be transported into the sediment.
However, The remaining soils exist in different parts of the world, such as Asia, Africa, Southeast North America, Central America, and South America.
Sowers (1963) reported that the residual soil depth generally varies from 6 to 25 m and in southern India from 7.5 to 15 m.
Carried Soil
Climatic material has been moved from one or more transport locations to new locations, such as water, glacier, air, and gravity, and stored to form transported soil.
However, Such deposits are further classified based on the mode of transport that leads to the deposit.
Soils that carry water. Fast-flowing water is capable of moving substantial amounts of soil. The soil can be transported in the form of suspended particles or by rolling and sliding at the bottom of the stream.
The particle size of the suspension is related to the velocity of flowing water. The particles transported by water vary in size from rocks to clay.
However, Coarse particles are left when the stream or river is deep, widening, or changing the direction of the water. The fine particles remain in the suspension and are deposited in the quiet water below.
This is a typical case of a stream moving downstream, passing over a valley, and eventually reaching a large body of water. Soil that is carried and stored by rivers is called alluvial deposits. River deltas are formed this way.
The soil, carried by rivers, enters the lake, collecting all the rough particles due to the sudden decrease in speed. Such coarse clay deposits are known as lake deltas.
But fine particles move to the center of the lake and settle when the water is calm.
Such, Alternate layers are formed with the season and such lake deposits are called lacustrine deposits. These deposits are fragile and narrow and cause problems for foundations.
However, If coarse and fine-grained deposits are formed in seawater, they are called marine deposits. The marine sediment is made up of earth and ocean contributions.
However, Earth’s contribution consists of shoreline erosive particles, as well as minerals, either in real or colloidal solution, and this contribution decreases in proportion and grain size with increasing distance from the shore.
The contribution of the sea is represented by the organic and inorganic remains of dead marine life and it usually increases with time (Iyer, 1975).
In marine reserves, marine organisms and the environment play a more important role than the salt concentration of water. Soil particles absorb some of the chemicals from the organism, which can extract minerals from seawater.
Moreover, Some acids produced by the digestive tract of marine organisms can change soil composition Minerals (Iyer, 1975).
Marine clay deposits (excluding deep deposits that are subject to many changes and are covered by other deposits) are generally weak, narrow, and problematic for foundations.
However, If such a deposit is exposed to sea level and the sodium leaks from freshwater percolation, it is very sensitive to disturbance.
Glacial soils transported from rivers by melting glacial waters create deposits of graded glacial drift and are called glacial fluvial deposits or graded drift.
Glacial deposits. Ice compaction and re-crystallization lead to the formation of glaciers.
The growth and movement of the glacier depend on the formation of the iceberg. Glacial deposits from a large group of transported soil.
The glacier is very moving, primarily but distorts and filters the surface and bedrock it passes. The melting of the glacier leads to the accumulation of all materials, and such deposits known as Naka.
The topography or topography of the glacier after it has been repelled is called the ground moraine or plain till. The deposits overlapped by glaciers consist of coarse particles and form fine construction material.
Soils deposited by surface and sub-surface glacial rivers remain in the form of long-winding ridges called escars. They can vary in height from about 10 to 30 m and from about 0.5 km to several kilometers.
The isolated mounds of ice remnants of about 10 to 70 m in height and 200 to 800 m in length are called drumlin. Large rocks are picked up by a glacier, transported to a new location, and are called erratics.
Glacial deposits provide a poor foundation for optimal foundations. In many places, it is commonly found that the material is dense and contains considerable amounts of sand and gravel.
Therefore, Glaciers are believed to have covered much of the earth during the Ice Age.
Northern USA, Northern Europe, and Canada are subject to glaciers. Glaciers now cover approximately 10% of the Earth’s surface. Almost all glaciers are now concentrated in Greenland and Antarctica.
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However , Soil is transported by air. Like water, air can erode, transport, and deposit fine-grained soil.
Soils carried by air are subsequently deposited as aeolian deposits. The dunes are formed by the deposition of such air-deposited sands.
Mounds are commonly found in the desert areas of Africa, Asia, and the USA. Sand from dunes can be used in limited quantities for construction purposes.
Micro-grain soils such as silt and clay can be transported by air to dry areas. Losses and clays deposited by air deposited with some cementing minerals in loose, steady-state are classified as loess.
However, Loss deposits have low density, high compressibility, and poor bearing resistance when wet.
Loess is classic sediment consisting of a homogeneously divided mixture of silt, fine sand, and clay-sized particles. The formation of the Los deposit is accompanied by a decline in saturation.
Gravity deposits. Gravity can only move objects a short distance. Since motion is limited, there is no significant change in the moving material.
The gravitational deposits are called the talus. They contain material at the base of rock and landslide deposits.
The talus material in the rock is formed by degradation and subsequent failure. The face of the cliff. These pieces are usually loose and porous. Swamp and marsh deposits.
However, Water table fluctuation and vegetation growth are possible in areas where water is stagnant, and swamp and marsh deposits develop.
Soils transported and deposited under this environment are soft, high in organic matter, and have an unpleasant odor.
Storage of partially or completely rotted water bodies in swamps or swamps Known as muck or peat.
Moreover, The muck is a completely rotten material, spongy, low in weight, highly compressed, and not suitable for construction purposes.
Desiccated Soils
If fine-grained soils are exposed to the atmosphere, water is drawn from the inside to the surface. From the surface, the water evaporates.
Therefore, This type of drainage is called drainage by dehydration. In the process, the soil hardens and eventually hardens.
The point at which evaporation stops depends on the relative humidity of the surrounding air. Under field conditions, dehydration can occur when the soil surface is not permanently flooded.
Due to periodic dehydration, fine-grained sediment sands also show clear cohesion. Because clear cohesion is so large, even long-term precipitation cannot eliminate cohesion altogether.
This phenomenon of dehydration is most pronounced in soils of semi-arid and arid areas. Such soils are often mistaken for soft rocks.
However, In the case of soft clay, dehydration proceeds very slowly from the open surface to form a thicker crust and the thickness grows with age.
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