What Is The Difference Between Residual Soil And Transported Soil?

What Is The Difference Between Residual Soil And Transported Soil?

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There are a lot of types of soils around as, and every one of them has its own characteristics. Some soils are being made by nature and depend on climate and other natural factors, and there are some that are being transported. So the question is what is the difference between residual soil and transported soil?

Residual soils are products of chemical weathering whose characteristics depend upon environmental factors of climate, parent material, topography and drainage, and age. Transported soil is weathered soil deposits transported from one place to another by natural agents like water, wind, and more.

There are a lot of characteristics, examples, and types of both residual and transported soils. This kind of knowledge is very important for engineers and others who want to get the most out of their land and produce the best products possible. There are some benefits to residual soils, but there are some to transported soils as well.

What is Residual Soil

The definition of residual soils is that these soils are the material resulting from the in situ weathering of the parent rock. Residual soils are widely spread throughout many regions of the world, such as Africa, South Asia, Australia, Central, and South America, Southeastern North America, and some regions of Europe.

The largest areas of these soils are generally common in humid tropical regions, such as Brazil, Nigeria, Sout India, Singapore, and the Philippines.

Residual Soil Characteristics

Residual soils are those soils made as to products of chemical weathering and thus their characteristics are dependent upon environmental factors such as climate, parent materials, topography and drainage, and age. 

As I mentioned before, the diversity exhibited by residual soils is mainly due to external factors such as climate, topography, and vegetation cover, and not so much to the lithology of the original rock. There are some main characteristics of residual soils:

  1. The mineralogical composition of the soil is closely related to the original bedrock beneath it.
  2. The soil grains are irregular, sharp, and lack roundness.
  3. The residual soil contains fragments of the original rock.
  4. The residual soil thickness depends upon the depth of weathering, climatic conditions, nature of rocks, topography, and age.
  5. The presence of a complete soil profile reflects the gradual change from the original rock at the bottom to topsoil at the surface.

Example Of Residual Soil

The residual soils are the products of rock weathering that are still present at the same place of origin. For example, bentonite is a type of chemically weathered volcanic ash that is present on the parent rock from which it is former. So any type of soil that is still present at the place of origin, or the parent rock is an example of residual soil.

Types Of Residual Soil

There are a few types of residual soil that we must mention. There are regions where the climate, topography, age, parent material, and drainage are optimized, for example in the tropics where well-drained regions produce reddish lateritic soil. Others, such as poorly drained areas tend towards montmorillonite expansive black clays. 

There are andosols that develop over volcanic ash and rock regions. These soils are rich in allophane and metastable halloysite. It is important to mention that the geological origins affect the resulting engineering characteristics of any soil.

What Is Transported Soil

The definition of transported soil is that it is weathered soil deposits that are transported from one place to another by natural agents such as water, wind, and glaciers. There are a few types of transported soils: water transported soils, wind transported soils, gravity deposited soils, and glacier deposited soils.

Types And Examples Of Transported Soil

The soils carried and deposited by water are called alluvial deposits. The alluvial deposits made in the lake are called lacustrine deposits. On the other hand, when these deposits are carried to the sea or ocean, it is called as marine deposits.

There are also deposits transported by wind and are called aeolian deposits. There is also a type of silt deposited by wind and it is called loess. This kind of soil has a low density and is highly compressible. It also lacks sufficient bearing capacity.

One more type of transported soil is the one transported by glaciers. There are some soils called till. Those kinds of soils are made by the melting of glaciers. Others, that are either directly or indirectly made by glaciers are called drifts.

The types of soils transported or deposited by the gravitational force are called the talus. Lastly, there are transported soils that get deposited by combined agents as well.

Water-deposited Soils

Water is one of the major transporters of soil deposits. It is important to mention that the size of the soil deposits carried by water depends on the velocity of the moving water. For example, water with a considerable velocity can erode the hills and deposit the same in the valleys.

There are two ways of how high swift water can carry a large amount of soil, and it’s by suspension or through rolling. The coarser particles get deposited as the velocity decreases. Further decrease in the velocity makes finer soils to deposit. A delta is formed at the receiving body of still water when the velocity almost moves to zero.

Wind-transported Soils

The wind-transported soils are the soils deposited by wind and are also called aeolian deposits. It is important to mention that the size of particles transported depends on the velocity of the wind. There are some areas such as arid regions and leeward sides of seas, where there are large dunes being formed due to wind.

Glacier-deposited Soils

There are large glaciers that carry soils of various sizes to huge boulders during their movement. That soil gets mixed up with the glaciers and gets transported to large distances. These kinds of soils made by glaciers are called drifts. There are also soils that are formed by the melting of glaciers and they are called till.

Other deposits formed by glaciers are called glaciofluvial. These kinds of soils are made by melting water and possess stratification as well. These kinds of deposits of glacial till possess high shear strength and can also be compacted to sufficient dry density.

Gravity-deposited Soils

There are also some soils that can be transported and deposited by the action of gravity. It is important to mention that the movement might be a very small distance. For example, there is the movement from a steep slope under the action of gravitational force.

The type of colluvial soil that is deposited or transported by the gravitational force is called the talus. These types of gravity-transported soils consist of good coarse-grained particles and rock pieces which are highly demanded in engineering works.

Soil Transported By Combined Agents

Lastly, there are soils that can be transported by two or more agents. An example of soil transported by combined agents is the soil that is deposited by the wind which can fall through a slope due to the gravitational force. This deposit can be picked up by water and get transported somewhere else.

How Is Transported Soil Different From Residual Soil?

The main difference between the transported soil and the residual soil is that the transported soil is blown or washed away from its parent rock. The residual soil is the one that remains a place of formation. Residual soils remain above their parent rock, and their characteristics depend on the characteristics of the parent rock.

Transported soils are the weathered pieces of rocks that have been carried by several or combined agents like water or wind, and finally, break down into small pieces to settle down. These soils are very fertile as they consist of minerals from a variety of transported rocks.

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