Types of Soil: Soil particles, Different Tests and Soil Pollution

What are the Different Types of Soil

Different types of soil in India can be classified based on different parameters, like their strength, durability, location, use, and many other characteristics. But here we will discuss the types of soil based on its formation in the aspect of geotechnical engineering. As we know, the formation of soil takes place through many cyclic processes like weathering, transportation, deposition, and upheaval. The formation of soil can take place either due to some physical process or chemical process, which can be understood with the help of the following diagram:

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Based on the formation of soil, soil can be classified as follows:

Alluvial Soils: This soil is generally found along the banks of rivers. It is transported soil through running water by the action of physical weathering.

Marine Soil: It is the soil that is deposited from the suspension in seawater. It is transported soil generated due to physical weathering by the action of flowing water.

Lacustrine Soil: It is the soil that is deposited from the suspension in fresh still water for the lake. It is residual soil generated due to physical weathering.

Aeolian Soil: This soil is the deposition of soil particles due to transportation through the wind. It is transported soil generated due to physical weathering.

Colluvial Soil: This soil is formed due to rocks' weathering and the transportation's gravitational forces. This soil is also known as talus soil. This type of soil is generally found in hilly areas at the bottom of the valleys. It is transported soil generated due to physical weathering.

Glacial Soil: It is a transported soil that is transported by the action of flowing ice. It is also generated due to physical weathering.

Loess Soil: It is uniformly graded wind-blown silt that is slightly cemented due to calcium compounds. It is transported soil and generated due to physical weathering.

Marl Soil: This soil is generated due to chemical weathering. It is a fine-graded calcium carbonate soil of marine origin formed due to the decomposition of bones and aquatic creatures.

Bentonite Soil is formed by volcanic ash and generated due to chemical weathering. This soil has its application as a lubricant during drilling works.

Peat Soil is chemically weathered soil that is very fibrous and highly compressible. It is highly organic that almost consists of vegetative matter in different ratios.

Laterite Soil: It is the soil that is formed due to the leaching process. Leaching can be defined as washing out siliceous compounds. It is generated by chemical weathering.

Muck Soil is also chemically weathered soil found in areas with inadequate sewerage facilities. It is a fine particle mixture of inorganic and black decomposed organic soil.

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Types of Soil Particles

Soil particles are the constituents of soil that make it soil. Types of soil can also be classified based on their particle size. Generally, soil can be classified into coarse-grained soil and fine-grained soil based on particle size distribution. Different soil characteristics like liquid limit, plastic limit, permeability and shear strength parameters, etc. are depends on the size of the soil particles.

Soil particles are considered in the soil when their size is less than 80 mm. Further, the particle size of coarse-grained soil ranges from 80 mm to 0.075 mm and lesser than this size falls into the category of fine-grained soil. Further, classification of the types of soil based on their particle size distribution are classified as follows:

Types of Soil Tests

Soil is a material that does not have much strength to take tensile and compressive loads; it is resistant against shear to some extent. The type of soil test can be classified into field and laboratory tests based on where it is conducted. Various types of soil testing are available to determine the different soil parameters. These parameters are used to define the strength of the soil. These parameters consist of a compaction test, shear strength test, percolation test, consolidation test, etc. Different tests have been done to determine soil parameters like Water content, Specific gravity, Grain size distribution(Hydrometer test), Liquid limit, Plastic limit, Swelling index, etc. Here are a few tests of soil given below to define different parameters of soil.

Specific gravity: Specific gravity is defined as the relative density of soil concerning the density of water. It is an important soil parameter because it is used to analyze many other parameters. A hydrometer test is conducted in the laboratory to determine the specific gravity of the soil.

Dry density is equally important to the specific gravity; it can be determined in the field and laboratory. Many tests are available for determining dry density, like the proctor compaction test, sand replacement test, etc.

Atterberg’s limit: These are the parameters of the fine-grained soils; these include liquid limit, plastic limit, shrinkage limit, etc. Fine-grained soils are further classified based on these limits.

Moisture content: It is also one of the important parameters of soil characteristics. There are many methods available for the determination of moisture content in the field as well as in the laboratory. This test includes Oven dry method, Calcium carbide method, Radiation method, etc.

Soil Strength tests: Before the placement of the foundation over the soil, it is necessary to find its strength parameters which include the Standard penetration test, Cone penetration test, Triaxial test, etc.

Here you can find a detailed video about the Classification of soil which makes a better understanding of the type of soil.

PH of Different Types of Soil

pH is one of the important parameters of soil, which governs its strength of soil pH, representing its acidity and alkalinity characteristics. Soil can be either acidic or alkaline in nature based on its pH value. pH affects the growth of plants; hence it is important for the soil having irrigation. It also affects the strength of soil as the acidic or alkaline nature of soil affects its bearing capacity.

A pH measures hydrogen ion concentration in the soil on the logarithmic scale because hydrogen ion concentration varies in a wide range. Generally, soil pH varies from 3.5 to 10 for many types of soils. Soil can also be classified based on its pH value as follows:

Types of Soil Erosion

Soil erosion is the movement of the top layer of soil and its transportation by different agents like water and winds. It is a form of soil degradation which occurs gradually throughout time. Soil erosion affects the growth of plants as some nutrients are removed during the movement of the top layer of soil. Soil erosion is the main cause of land degradation. The different types of soil erosion are mentioned below:

• Rill erosion
• Rain-drop erosion
• Sheet erosion
• Gully erosion
• Ephemeral erosion

Cause of Soil Erosion:

• Deforestation
• Overgrazing
• Agrochemicals
• Construction and recreational activities

Types of Soil Pollution

Soil pollution is a type of pollution that implies the presence of unwanted ingredients in the soil. These ingredients are harmful to the soil and other organisms in the ecosystem. These ingredients include some chemicals which may be toxic in nature. There can be anthropogenic or natural causes for the pollution of soil. Soil pollution can be caused due to pesticides, Mineral fertilizers, organic fertilizers, etc. Here are some types of soil pollutants given below:

• Biological agents
• Radioactive materials
• Industrial waste
• Urban waste
• Agricultural pollutants

Types of Soil Water

Water in soils is required for the growth of plants, and it also governs the strength of the soils. It also requires the survival of many soil organisms. Many nutrients are available in the soil water, which is useful for the growth of plants. The water-holding capacity of different soil types depends upon the soil's intermolecular structure and surrounding temperature. Crops grown in different types of soil depend on the available moisture content and the holding capacity of the soil. Based on the retention parameters of water in soils, it can be classified into the following types:

Gravitational water: It is the water that is not available for the growth of plants, it is drained under the action of gravity and reaches the groundwater table.

Capillary water: It is the water that is present in the pores of the soils under the action of negative pressure. It is available for the growth of plants and can be extracted at any time.

Hygroscopic water is the water present in the intermolecular structure of the soil. It is the water bonded between the molecules of soil particles and it can not be extracted by the plants.

Types of Soil for Agriculture

Soil having a high retention capacity of water content is best suited for the purpose of agriculture. A sufficient amount of nutrients is also required for the proper growth of plants. So soil having an optimum amount of water and nutrients are suitable for agriculture.

Loamy soils are suitable soil for agriculture. It is ideally suited for the garden as loamy soils hold a sufficient amount of water and at the same time it also drains the water in an optimum way, and hence it ensures the proper flow of air within the soil.

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