INDEX PROPERTIES OF SOIL

You can ask yourself what is the index properties of soil? Is it helpful to know the index properties of soil?

The answers of above questions can be answered as described below

INDEX PROPERTIES OF SOIL

These are properties of soil which are not primary interest to Geotechnical Engineers but which are indicative of the engineering properties of soil, these properties of soil have nothing to be used in design but they are helpful in one way or another.

The following are examples of index properties of soil which can be indicative of engineering properties of soil.

1.      Specific gravity

Specific gravity of soil (G) is ratio of density of soil to density of standard material (water).

Specific gravity of soil help geotechnical engineers to know the porosity of soil and to predict whether the soil will be stable to support the structure and allow proper drainage.

2.      In-situ bulk density

This is the density of undisturbed soil (soil with its water content) from site, in situ bulky density can indicate the porosity and compaction of soil, bulk density considers both the solids and the pore space (that covered by both air and water).

For example the bulk density- 1960kg/m3 the soil is strong than the soil with bulk density-1260.

3.      Water content

This is the amount of water found in the soil, this property of soil can also used to give an overview on porosity, strength, permeability of soil.

The amount of water that the soil can hold defines the size of particles that the soil has, due to the fact that the soil with fine particles holds more water for a time and has high capillarity (allow water to rise from underlying layers).

 For example when water content 20% the soil is sand, water content 40% the soil is clay.

4.      Relative density

Relative density is the measure of compactness of cohesionless soil. Relative density or density index is the ratio of the difference between the void ratios of a cohesionless soil in its loosest state and existing natural state to the difference between its void ratio in the loosest and densest states.

Determination of relative density is helpful in evaluating compaction state of coarse grained soils and also assessing the safe bearing capacity in case of sandy soils.

5.      Particle size distribution

This is the one of soil classification method which classifies the soil according to their size, this involves determining the percentage by weight of soil particles in different size ranges, and particle size distribution is done sieve analysis or hydrometer analysis

From Particle size distribution, here we can find the coarseness and fines of the soil particles. By knowing the coarseness and fines of soil particles can bring the following view on the provided soil as follows.

ü  Coarse-grained soils have good load-bearing capacities and good drainage qualities, and their strength and volume-change characteristics are not significantly affected by changes in moisture conditions.

ü   Fine-grained soils have poor load-bearing capacities and poor drainage qualities, and their strength and volume-change characteristics are significantly affected by changes in moisture conditions.

6.      Consistency limits

Consistency of soil id the degree of firmness of the soil in relation to water content that a soil contains, the soil consistency is described in the following states liquid state, plastic state, semi solid state and solid state.

The consistency limits of soil consist of liquid limits, plastic limits are used to determine the Plasticity Index (PI) soil, where by higher PI indicate weak soil and more fines.

This help to know the strength of soil materials to hold together themselves also resistance of soil to deformation and rupture.

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