Difference Between Cohesive & Non-Cohesive Soil

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Cohesive and non-cohesive soils differ in texture and consistency.

Part of the process for constructing a building or road involves analyzing the soil on which building will take place. Soil environments provide the physical foundation for a building or road to stand on for years. The engineering aspects of soil composition examine the differences in texture, strength, and consistency that distinguish cohesive soils from non-cohesive soil environments.


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Soil Mechanics

Soil mechanics, also known as geotechnical engineering, involves the use of soils as engineering materials. This line of study enables engineers to identify suitable soil environments for building and construction purposes. A soil's ability to compact and maintain its consistency under pressure determines whether it will provide a suitable foundation for building. In effect, engineers examine the physical characteristics of a soil environment as part of the pre-planning process involved with construction projects. As a result, differences between cohesive and non-cohesive soil play a significant role in determining whether a particular area will work with a building's plan.


Texture Differences

Texture differences in soils result from the types of rock that make up a particular area. Over time, the effects of weather and water erosion break down preexisting rocks into soil particles. Texture differences appear in the shapes, sizes and arrangement of particles that make up the soil. The presence or absence of clay or fine particles determines the cohesive qualities found within a soil environment. In effect, clay and fine particle materials act as binding agents that hold soil together. So non-cohesive soil environments contain little to no clay or fine particles while cohesive soils contain high amounts of clay and fine particles.


Compaction Differences

A soil's ability to compact has to do with the size of its particles and the amount of clay present in the sample. As a material, clay tends to readily absorb water when compared to a sand-type material. This absorption factor increases a soil's capacity to compact into a mold. Geotechnical engineers may analyze a soil sample to gauge its plasticity, or how well it molds together. So differences between cohesive and non-cohesive soils appear as high versus low plasticity properties with cohesive soils scoring higher. In effect, the higher a soil's plasticity properties, the more likely it will hold its shape when subjected to additional weight or pressure.


Consistency Differences

Non-cohesive soils consist of large or irregular-sized soil particles with little to no clay content. As a result, these soils tend to shift or change in consistency under different environmental conditions. Rain and wind conditions cause water and air materials to move in and out of soils. These conditions create spaces in between soil particles. In the case of water absorption, large soil particles with low cohesive properties tend to change in shape and consistency as water evaporates. With cohesive soils, clay and fine particular materials maintain a certain binding capacity that works to retain a soil's shape and consistency.


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