Soil cohesion is a fundamental component of civil engineering and geotechnical engineering, providing an important means of understanding how soils behave under the forces of gravity, shear, water, and climate. Cohesive soil is defined as soil that can be cut or held together when wet and deformed under force or pull.
Soil cohesion is a result of the attraction between soil particles. These attractions are due to the charged nature of soil particles, which are typically negative. The magnitude of the attraction between particles is influenced by many factors, including the type of soil, the amount of water present, and the amount of clay present. When the attractions between particles are strong, the soil is said to be cohesive. When the attractions are weak, the soil is said to be non-cohesive.
Some cohesive soils are
- Clay
- Silt
- Peat
- Loam
Clay particles are the smallest of the soil particles and have the highest surface area to volume ratio. This means that there are a lot of attractions between clay particles and water molecules. When clay particles are wet, they swell and become even more attractive to water molecules. This swelling puts pressure on the clay particles, making them cling together. This is why clayey soils are often referred to as “sticky” soils.
Sandy soils are the largest of the soil particles and have the lowest surface area to volume ratio. This means that there are fewer attractions between sandy particles and water molecules. When sandy particles are wet, they do not swell and do not become more attractive to water molecules. This means that sandy soils are not “sticky” like clay.
While cohesive soil has many benefits, it can also pose challenges for civil and geotechnical engineers. One challenge is that cohesive soils can be difficult to excavate and handle. Another challenge is that when cohesive soils are saturated with water, they can lose their strength and become unstable. This is why it is important for engineers to have a thorough understanding of the properties of cohesive soils and how they are affected by water.
When designing structures that will be built on or in cohesive soil, engineers must be aware of the potential for instability. They must also be sure to design foundations that can resist the lateral forces that can be exerted by cohesive soils when they are saturated with water.
Cohesive soils can be found all over the world, in a variety of environments. They are a vital part of the environment and play an important role in many engineering designs. By understanding the properties of cohesive soils and how they are affected by water, engineers can optimize their designs to take advantage of the benefits of these soils while minimizing the challenges.