The first question that comes to our mind is, What is a soil structure? Let me explain it, basically, different types of soil have different geometrical arrangements of soil particles, and this geometrical arrangement of soil particle form soil structure.
Types Of Soil Structures
Soil structures may be many types but in geotechnical engineering, there are mainly 6 types of soil structures that civil engineers consider while their construction work.
- Single Grained Structure
- Honeycomb structure
- Flocculated Structure
- Dispersed Structure
- Coarse-Grained Skeleton
- Clay Matrix Structure
Single Grained Structure
The first type of soil structure that is single grained structure deposited under a gravitational force. This type of soil structure is basically present in gravel and sand in other words we can say that the single-grained soil structure is basically present in cohesion-less soil (The soil whose strength depends on the friction between practical is called cohesion-less soil).
As we know that cohesion less soil has less surface force and more gravitational force, so when we put some soil such as gravel or sand on the ground then it is going to settle down through the gravitation force rather than surface force because gravitation force is more compare to surface force.
When the soil completely settles down to its final position then such structures are called single-grained soil structures.
Here are some important notes– first the single-grained soil particles must have a void ratio between 0.35 to 0.9. While selecting the soil for construction purposes we have to keep the void ratio as minimum as possible because when we select soil with a more void ratio that is less dense the soil has less stable which is not good for building construction.
More Read-Disturbed And Undisturbed Soil Sample
Honey Cumb Structure
Basically, the Honeycomb soil structures are present in fine sand or silt while the single-grained structure is present in gravel or sand.
When these types of soil going for settling down on the ground then the soil particle attracts each other and form a bridge-like structure.
Due to the bridge-like structure, a large void is formed between those bridges and making the soil very weak and loose in nature. The Honeycumb soil structures can not handle the building vibration and heavy loads of building which may cause heavy damage to the building.
Flocculated soil structures are present in the clay particles. Basically, these clay particles are charged particles that possess a positive charge on the edges and a negative charge on the face of the particles.
When the positive charge particles attract toward the negative charge particles the Flocculated soil structures are formed.
The flocculated soil structure is light in weight, has high shear strength, a high void ratio due to edge-to-face orientation, and low compressibility.
The best example of the flocculated soil structure is the clay present in the marine area.
Dispersed Soil Structure
The dispersed soil structure is one of the types of soil structure. The dispersed soil structure is the less permeable and more compressible
Just like Flocculated Structure, the dispersed soil structure is also present in the clay particles but one little difference is when the clay is remolded.
Due to the remolding process of the clay particles, the net attractive forces between the particles reduce, and the repulsive force increases. Hence due to the repulsive force between the particle, the edge-to-face orientation turns into face-to-face orientation and dispersed soil structure forms.
When time passes the loss of strength due to the remolding process is achieved and the process of achieving the strength is called thixotropy.
A coarse-Grained Skeleton soil structure is basically present in both fine and course-grained particles. The formation of coarse-grained skeleton soil structure happens when the percentage of coarse-grained particles is more than the fine-grained particles that is why it is called coarse-grained skeleton soil structure.
While the formation of a coarse-grained skeleton the coarse-grained particles form a bridge-like structure and the void in the bridges is fulfilled by the fine-grained particles.
Clay Matrix Structure
Just like the Coarse-Grained Skeleton soil structure, the clay matrix soil structure is also present in the composite soil which is both in coarse and fine-grained particles but the percentage of the coarse-grained particle is less than the fine-grained particles.
The clay matrix soil structure is very stable and it can handle heavy loads of buildings.
Soil formation is basically a cyclic process and it is formed in two ways the first way is the organic way and the second way is the physical and chemical weathering of rocks.
In the Organic way of soil formation, the plants and animals decompose over time and become soil.
In the physical weathering of rocks, the rocks fall on the ground under the action of gravity force and water, air, etc break them into small pieces, these small pieces of rock are called soil.
In the chemical weathering of the rocks, the rocks decompose by oxidation, hydration, and carbonation and break the rocks into small pieces called fine soil such as silt and clays.
Let’s Discuss more about the soil formation either by-
- Physical Weathering or Mechanical Weathering.
- Chemical Weathering
Soil Formation By Physical Weathering Or Mechanical Weathering
In the physical weathering of soil or mechanical weathering of soil formation, the rock breaks into small pieces in the following ways-
- Temperature Change
- Action Of Ice
- Action Of Plants Roots
1- Soil Formation By Temperature Change
All types of rocks behave differently in different temperatures because the size of the different objects changes differently in different temperatures. Due to this, the rock gets an unequal expansion and elongation with a change in temperature. When this process is repeated several times, the rocks break into small pieces and form soil.
2- Soil Formation By Action Of Ice
The rock contains empty spaces and these empty spaces get filled by the water. During freezing temperatures, the water starts freezing, and the volume starts increasing. Due to the increase in the volume, the rocks get cracked and when these cracks increase the rocks break into small pieces and form soil.
3- Soil Formation By Action Of Plants Roots
The roots of plants or trees grow in the crack of the rocks and force these rocks and break it into small pieces and through this process, the formation of the soil is done.
4- Soil Formation By Action Of Abrasion
The word abrasion means “the process of scrapping or wearing something away”. The movement of the water, air, and glacier over the surface of the rock will result in abrasion, and due to this process, soil formation has happened.
Soil Formation By Chemical Weathering
In chemical weathering, the hard rocks easily transform into soft rocks and after some time become soil. Here are the following chemical weathering which happens in the rock.
1-Soil Formation By Hydration
In the hydration process, the water combines with the mineral of the rocks and form a new chemical compound due to the chemical reaction, the volume of the rock change, and the rock breaks into small pieces and form soil.
Here is an example of hydration creation that takes place inside the rocks-
SiO2 +2H2O ——– Si(OH)4
2- Soil Formation By Carbonation
In the carbonation process, the carbon dioxide of the atmosphere is combined with water and form carbonic acid, and this carbonic acid act on the rock and break the rock into pieces, and form soil. Sedimentary rocks are a good example of soil formation by carbonation.
3- Soil Formation By Oxidation
In the process of soil formation by oxidation, the oxygen ion is combined with the rock mineral and starts breaking the rocks by the process of oxidation and at the end forms the soil.
4 -Soil Formation By Hydrolysis
As we know that hydrolysis is the process in which water breaks into H+ and the OH– ions. The H+ ions replace the metallic ions such as calcium, potassium, and sodium in rock minerals and form a new compound, and due to this new compound, the rock starts breaking into pieces and forming soil.
Types Of Soil
As we all know soil forms from the disintegration of the rock through chemical and physical weathering processes. Here are the different types of soil-
- Type Of Soil Based On Grain Size
- Type Of Soil Based On Origin
1-Type Of Soil Based On Grain Size
On the basis of the grain size soil is divided into 6 parts namely clay, silt, sand, gravel, cobble, and boulder.
The particle size of the soil is between .002mm to .075mm is classified as silt size.
The soil particle size between 0.075 to 4.75 mm is classified as sand size. And the sand size is further subdivided into three parts Fine Sand between 0.075mm to 0.425 mm, Medium Sand between .425mm to 2mm, and Coarse Sand between 2 to 4.75mm.
The particle size of soil between 4.75 to 80mm is classified as gravel. It is further subdivided into two parts Fine gravel between 4.75mm to 20mm in size, Coarse gravel between 20mm to 80mm in size.
The soil particle size between 80 to 300mm is classified as cobble.
A soil particle size above 300mm is classified as a boulder.
Type Of Soil Based On Origin
On the basis of origin soils are classified into two parts-
- Residual Soil
- Transported Soil
Residual soils are those soil that remains in the place of formation. Basically, these types of soil are present near the weathered rocks from which the soil form. The Residual soil does not affect by wind, water, ice, etc which means they do not move from its birthplace by any external agent.
2- Transported Soil
Transported soil is those soil that is transferred from its birthplace to another place by any external agent such as wind, water, ice, etc.
Frequently Asked Questions (FAQ)
What is soil formation in geotechnical engineering?
In geotechnical engineering, soil formation is defined as the formation of soil throgh physical or chemical weathering.
What are the 6 types of soil structures in Geotechnical engineering?
Here are the 6 types of soil structures in geotechnical engineering. 1-Single Grained Structure, 2-Honey Cumb Structure, 3- Flocculated Structure, 4- Dispersed Structure, 5- Coarse-Grained Skeleton, 6- Clay Matrix Structure
What is the difference between the Single Grained Soil Structure and Honey Cumb Soil Structure?
The main difference between the single-grained soil structure and the honeycomb soil structure is, the single-grained soil structure is present in the gravel or sand while the honeycomb soil structure is present in the fine sand or silt.
What is the difference between the Coarse-Grained Skeleton and Clay Matrix soil Structure?
The main difference between Coarse-Grained Skeletons and Clay Matrix soil Structure is, in the coarse-grained skeleton the amount of coarse-grained particles is more while in the clay matrix soil structure, the clay-grained particles amount is more.
What is the definition of residual soil in geotechnical engineering?
The residual soils are those formed soil that remains at the same place where they were formed. Basically, they do not move or transport to other places after the formation of the soil.
What is the definition of transported soil in geotechnical engineering?
The transported soil is the soil that is formed in other places and after the formation, it is transported to other places through the air, water, ice, or any other transporting agent.