Introduction

For the help of foundation engineer, soils are classified based upon physical properties,  Those properties which is helping to predict the behavior of soils is called INDEX PROPERTIES. These properties can be determined easily and quickly which shows the strength or bearing capacity, swelling and shrinkage and settlement. The properties are related to soil grains or soil mass. The former are from disturbed samples and the latter from in-situ.

The important physical properties are soil color, soil structure, texture, particle shape, grain specific gravity, water content, in-situ unit weight, density index, particle size distribution, and consistency limit.

Soil Color

Soil color may vary from white through red to black. it mainly depends upon the mineral matter, quantity and nature of organic matter and the amount of coloring oxides of iron and manganese.

Iron compounds, gives the color red, brown, or yellow. Manganese compounds and organic matter gives black color. Green and blue colors imparted by pyrite. Water content is also helps to impart lighter shades.

Particle Shape

This is an important qualitative property. In the case of coarse grained soils including silts, the grains are bulky in nature. The particle shape of bulky grains are angular, sub-angular, sub-rounded, rounded and well-rounded. Silt particles are not less than one micron (.001mm). Clay particles are less than 2 micron. The clay minerals shows sheet structure and flaky shape.

Specific Gravity of Soil Solids

It is useful in the determination of void ratio, degree of saturation, critical hydraulic gradient and zero air voids in compaction. It is also useful in computing the unit weight and in the determination of particle size by wet analysis.

Water Content

Water content of a soil has a direct bearing on its strength and stability. For maximum compaction there is an optimum moisture content.