What are the differences between coarse-grained and fine-grained soils?
The correct answer and explanation is :
Coarse-grained and fine-grained soils differ primarily in their particle size, texture, and behavior, which significantly influence their engineering properties.
1. Particle Size:
- Coarse-grained soils consist of larger particles, typically with diameters greater than 0.075 mm. These include gravel and sand, which can be seen and handled easily.
- Fine-grained soils have smaller particles, with diameters less than 0.075 mm. These include silt and clay, which are much finer and often require a microscope to observe their individual particles.
2. Texture and Composition:
- Coarse-grained soils tend to have a granular texture and consist mainly of sand and gravel. These soils are often more permeable due to the larger size of their particles, allowing water to move through them more easily.
- Fine-grained soils are smooth and can form a compact structure. Silt and clay particles are very small and can hold water tightly. The small size of their particles results in lower permeability and higher plasticity (ability to be molded or shaped when wet).
3. Engineering Behavior:
- Coarse-grained soils usually exhibit good drainage characteristics because the larger particles allow water to flow through easily. They tend to be more stable under load but can be prone to erosion or shifting when water is present.
- Fine-grained soils are less permeable, meaning they retain water and are more prone to swelling, shrinkage, and cracking. They can be more difficult to compact and are sensitive to changes in moisture content. Fine-grained soils, especially clay, are prone to plastic flow and can undergo significant changes in volume when wet.
4. Application in Construction:
- Coarse-grained soils are often preferred for foundations and drainage systems because they provide better stability and water flow.
- Fine-grained soils are used in applications where low permeability or specific plasticity is needed, such as in clay liners or certain types of foundations.
In summary, the distinction between coarse-grained and fine-grained soils lies in their particle size and physical properties, which greatly affect their behavior in construction and engineering contexts.