Geotechnical Engineering

The degree of saturation denotes the actual relationship between the weight of moisture existing in a space and the weight that would exist if the space were saturated.

It can be also said as the percentage of water that occupies the pore spaces present in soil and is said to be degree of saturation. Basically, the soil has three phases soil solid, water and air. If the pore and void space in the soil is fully occupied by water, then it is fully saturated and the degree of saturation is 100%. If the void space in the soil is partially occupied by water, then it is said to be partially saturated.

Generally, shear strength is a term used in soil mechanics to describe the magnitude of the shear stress that a soil can sustain. The shear resistant of soil is a result of friction and interlocking of particles, and possibly cementation or bonding at particle contacts. Due to interlocking, particulate material may expand or contract in volume as it is subject to shear strength. If soil expands its volume, the density of particles will decrease and the strength will decrease; in this case the peak strength would be followed by a reduction of shear stress.

As we know,
Density = Mass / Volume

Here, Soil density is defined in two well accepted concepts as particle density and bulk density. In the metric system, particle density can be expressed in terms of mega grams per cubic meter (Mg/m3). Thus if 1 m3 of soil solids weighs 2.6 Mg, the particle density is 2.6 Mg / m3 (since 1 Mg =1 million grams and 1 m3 =1 million cubic centimeters) thus particle density can also be expressed as 2.6 g / cm3.

Particle Density :-

The weight per unit volume of the solid portion of soil is called particle density. Generally particle density of normal soils is 2.65 grams per cubic centimeter. The particle density is higher if large amount of heavy minerals such as magnetite; limonite and hematite are present in the soil. With increase in organic matter of the soil the particle density decreases. Particle density is also termed as true density.

Bulk Density :-

The oven dry weight of a unit volume of soil inclusive of pore spaces is called bulk density. The bulk density of a soil is always smaller than its particle density. The bulk density of sandy soil is about 1.6 g / cm3, whereas that of organic matter is about 0.5. Bulk density normally decreases, as mineral soils become finer in texture. The bulk density varies indirectly with the total pore space present in the soil and gives a good estimate of the porosity of the soil. Bulk density is of greater importance than particle density in understanding the physical behavior of the soil. Generally soils with low bulk densities have favorable physical conditions.