Coarse-Grained and Fine-Grained Soils: FAQs and Key Differences

Introduction of Coarse-Grained Soils Vs Fine-Grained Soils

Soil is one of the most important components which should be check and tested before doing any kind of construction on the site. As a civil engineer, it is very necessary that you should know the difference between coarse-grained soils and fine-grained soil so that you can design the structures accordingly.

The soil mainly divided into two types which are as follows

1. Coarse-Grained Soils
2. Fine-Grained Soils

In this article, you will get to know the Difference between coarse-grained soils and fine-grained soil. The behavior of both coarse-grained soil as well as fine-grained soil is different from each other.

What Is Coarse-Grained Soil?

The coarse-grained soils are mainly identified on the basis of grain size of the particle size of the soil mass. One of the thumb rules which is used for the identification of coarse-grained soils is that the individual particles of the coarse-grained soils can be seen with our naked eye.

One of an example of coarse-grained soils are sand and gravels. We can easily see the particles of the sand and gravel with our eyes. The particles whose size are larger than 75 mm is known as gravel and the particles whose size are less than 4.75 mm up to 75 microns are known as Sand.

The coarse-grained soils have a good load-bearing capacity as well as drainage quality. There is no volumetric changes are seen in the coarse-grained soils in the moisture condition.

The coarse-grained soil feels gritty when we touch it with our hands. The moisture change in the coarse-grained soil does not affect the strength of the soil. The shape of the coarse-grained soil is generally angular or sub-angular.

What Is Fine-Grained Soil?

Fine-grained soils are generally identified based on their plasticity. The fine-grained soils cannot be seen by our naked eye. The fine-grained soil is basically divided into two groups which are silt and clay.

The particles whose size ranges between 75 microns to 2 microns are known as Silt and the particles whose size smaller than 2 microns is known as clay.

The load-bearing capacity of fine-grained soil is low as compared to coarse-grained soils. The permeability of fine-grained soil is very low. The reason of very low permeability of the fine-grained soil that because of its size of the particle are very small due to which it retains water.

Strength of the fine-grained soil changes with respect to the change in the moisture or the water content of the soil. If you touch the fine-grained soil with your hand you will feel it smooth, greasy, and Sticky.

Difference Between Coarse-Grained Soil and Fine-Grained Soil: Respect to the Void Ratio

1. Void ratio is defined as the ratio of the volume of voids to the volume of solid. Void ratio is basically a measure of voids in a particular soil mass.
2. You may think that the soil particles present in the fine-grained soils are very closely packed with each other so that it may have less void ratio. But in fact, the fine-grained soil has more void ratio as compared to the coarse-grained soil.
3. It is because of the concept of the surface area of the particle. The surface area of the fine-grained soils with respect to the soil mass is more as compared to the surface area of the coarse-grained soil.
4. The voids created in the fine-grained soils are more with respect to soil mass because of its more surface area whereas in the case of the coarse-grained soils there are less voids are created with respect to their soil mass.
5. The clay has a more void ratio as compared to sand

Coarse-Grained Soils Vs Fine-Grained Soils

The difference between coarse-grained soil and fine-grained soil are as follows.

FAQs about Coarse-Grained and Fine-Grained Soils

What are coarse-grained soils?

Coarse-grained soils consist of particles visible to the naked eye, such as sand and gravel. They are categorized based on particle size, typically ranging from 4.75 mm to 75 microns.

What are fine-grained soils?

Fine-grained soils, like silt and clay, are not visible to the naked eye. They are identified by their plasticity and have particle sizes smaller than 75 microns.

How does moisture affect coarse-grained soils?

Moisture content has minimal effect on the strength and volume of coarse-grained soils due to their good drainage and low water retention properties.

What is the permeability of fine-grained soils?

Fine-grained soils have very low permeability, which means they retain water and have poor drainage capabilities.

Which soil type has a higher void ratio?

Fine-grained soils typically have a higher void ratio compared to coarse-grained soils. This is because the smaller particles create more voids relative to the soil mass.

How can I identify these soils on-site?

Coarse-grained soils feel gritty when touched, while fine-grained soils feel smooth and sticky. Additionally, coarse-grained soils can be seen with the naked eye, whereas fine-grained soils cannot.

Which soil type is better for construction?

Coarse-grained soils generally have better load-bearing capacity and drainage qualities, making them more suitable for construction than fine-grained soils.

Are there any specific engineering considerations for each soil type?

Yes, engineers must consider factors like strength variation with moisture content for fine-grained soils and the stability and compaction requirements for coarse-grained soils during construction planning.

What are some examples of each soil type?

Examples of coarse-grained soils include sand and gravel, while silt and clay are examples of fine-grained soils.

How does particle shape differ between coarse-grained and fine-grained soils?

Coarse-grained soils typically have angular or sub-angular particles, whereas fine-grained soils tend to have flaky particles.