Structures, such as buildings, bridges, and tunnels, are founded either below or on the surface of the earth. To ensure the structure is secure and stable, the quality and suitability of its foundation, the soil, must be assessed. The geotechnical properties of the soil must be analyzed to ensure the proposed structure will be suited to the environment.
What are the geotechnical properties of soil?
- Specific gravity
The ratio of the mass of soil solids to the volume of water in the soil is referred to as the specific gravity. The higher the level of specific gravity, the stronger a foundation will be.
- Density index
Density index is related to how densely compact soil is. For example, the degree a fine grain soil is compact can be measured against the shape, size, and gradation of soil. This property is particularly useful when calculating the safe bearing capacity of soils with a high sand concentration.
- Consistency limits
Fine-grain soil can pass from a liquid state to plastic and solid-state. Different soils will have a different change of state based on its water contents. Determining how much water content is needed to change the state of a soil is known as its liquid, plastic and shrinkage limit (the consistency limits).
- Particle size analysis
The particle size of soil needs be to analyzed, as how rounded or sub-rounded the soil solids are will affect the strength of the soil. For example, angled, rigid soil particles will interlock more easily, increasing the shear resistance of the soil.
Analyzing soil compaction is completed by placing compactive energy on the soil to rearrange the soil solids more closely together. The higher the compaction, the higher the strength of the soil and the lower the permeability.
When soil is subject to compressive stress, usually due to a new structure, particles rearrange which may cause particles to be crushed. This can cause the soil to crack which causes functional and aesthetic problems. Calculating the soil’s consolidation, its immediate and time-dependant compression will predict how the soil will react once a structure is constructed.
The permeability of soil, its amount, distribution, and movement in water, has a big influence on how soil reacts. The permeability of soil should be measured in relation to atmospheric pressures to determine whether a structure built on the soil will need additional draining.
- Shear strength
The friction and interlocking properties of particles are known as the shear strength of the soil. The shear strength of soil depends on stress, drainage conditions, the density of the soil solids and multiple other factors. Soil with higher shear strength is more stable for construction projects and structures.