What is Soil Structure? Types of Soil-Structure | Soil Aggregation
What is Soil Structure?
Soil structure refers to the way individual soil particles (sand, silt, and clay) assemble together to form aggregates (or peds). These soil particles are cemented together by chemical, physical, and biological processes to form layers. The aggregates vary in size and shape from small crumbs through to large blocks.
Soil texture is a classification method used both in the laboratory or field to determine soil classes based on their physical texture. Soil texture can be established by using qualitative ways like the texture of the soil by feeling, and quantitative ways like hydrometer instruments.
Aggregation process of soil particles can happen in different ways and patterns, therefore will result in different soil structures. Water circulation in the soil varies significantly depending on the structure of the soil
Importance of Soil Structure
Soil structure is much more than every particle of silt, sand, and clay. Typically, the soil should be one-half solid materials including sand, silt, clay, nutrients, minerals, organic materials, and biological life and one-half pore space that contains water and the other half being air space
Soil is vital for human wellbeing because over 95% of human and animal food production relies on the soil. Normally, a ‘good’ agricultural soil is thought to consist of around 50% solids, 25% air, and 25% water, but this will vary according to soil type.
Soil is also home to a quarter of all terrestrial species.
Soil plays a crucial role in storing carbon and water, which helps mitigate climate change and prevent flooding.
Different Types of Soil Structure
Soil structure determines the water and air penetration through the soil and vastly influences the ability of the soil to allow and treat wastewater.
It describes the arrangement of the solid components of the soil and of the pore space found between them.
Soil structure is determined by how small soil granules clump, bind together, and the aggregate that results in the arrangement of soil pores between them. Soil structure influences air and water movement, biological activity root growth. There are several different types of soil structure. It is inherently a dynamic and complex system that is affected by different factors.
Soil structure is classified by type (shape), class (size) of peds, and grade (strength of cohesion) of aggregates.
The size, shape, and strength of aggregates determine how porous the soil structure is and how easily water, air, and roots penetrate through soil layers.
Soil structure is most usefully described in terms of grade (degree of aggregation), class (average size), and type of aggregates (form). In some soils, different kinds of aggregates may be found together and they are then described separately.
The grade of structure can be defined as the degree of aggregation, expressing the differential between adhesion between aggregates and cohesion within aggregates.
As these properties vary with the moisture content of the soil, the grade of the structure should be determined when the soil is neither extremely moist nor dry. There are four major grades of structure;
Structureless has no observable aggregation or no definite orderly arrangement of natural lines of weakness.
Massive structure (coherent) where the entire soil horizon appears cemented in one great mass.
Single-grain structure (non-coherent) where the individual soil particles show no tendency to cling together, such as pure sand.
A weak structure is poorly formed from indistinct aggregates that can barely be observed in place. When removed from the profile, the soil material breaks down into a mixture of very few entire aggregates, many broken aggregates, and much-unaggregated material.
How Soil Structure Deteriorates
Factors that can deteriorate or destroy soil structure include, for example:
- Removal of vegetation
- Moving and handling of soil
All soil is vulnerable to erosion. And during the construction process, the soil becomes loose and loses its stability. To help decrease any problems caused by erosion, one method is limiting the space where the soil is moved around during the excavation process.
Types of Soil in Construction & How it Matter in Foundation of the House
Clay & Black Cotton Soil
Clay is an expansive soil, which means it expands when wet and shrinks when dry. These changes cause a great deal of pressure on foundations and can cause them to move up and down, and eventually crack. For this reason, clay is usually not a great soil to construct a home on.
Peat is a dark brown/black soil formed by decomposed organic material. It’s usually found near wetlands and is especially porous. Like clay, peat shrinks and expands depending on weather conditions and has a low bearing capacity, making it a poor support material.
When compacted with gravel and other materials, and does not retain water and therefore will not cause any structures above it to shift. However, over time, sand particles can lose their friction and be washed away, creating gaps beneath a foundation.
Varieties such as bedrock, limestone, and sandstone have exceptionally high bearing capacities, which make them suitable for supporting buildings and homes. It’s imperative that a rock surface is at a level before a foundation is constructed, otherwise, the foundation must be held into place with anchors.
Loam & Red Soil
Loam is an ideal surface for the foundation. Typically, loam is a combination of sand, silt, and clay, and is crumbly/soft to the touch. Loam handles moisture in a balanced way and will generally not expand or shrink enough to cause damage.
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If you’re planning a construction project, it’s best to figure out what kind of soil you’ll be working with and understand its properties.