Physical Properties of Soil
Here are some of the physical properties of soil:
The texture of soil is based on the size distribution of the constituent particles. In simple terms, the relative percentage of clay, sand, and silt in a soil mass determines its texture. Furthermore, the soil texture determines the water retention capacity of a soil sample. Sand particles have the largest diameter, whereas clay particles have smallest diameter, among the three soil constituent particles. The American Association of State Highway Officials (AASHO) and the USDA divide soil texture into twelve classes which are shown in the corresponding figure. Depending upon the percentage of sand, silt and clay in soil, it is defined as coarse, fine, or medium aggregate soil.
Soil structure refers to the arrangement of sand, silt, and clay particles within a soil mass. Air and water movement through a soil mass directly depends upon the structure of soil mass. Symmetry leads to stability, so if a soil mass has symmetrical or good structure, water and air movement through it will be smooth. However, if the structure is asymmetrical, water and air movement will not be smooth and the soil will be unstable. By knowing soil structure, the moisture content of the soil mass can be worked on, which is equally important for engineering and agricultural works.
Color of Soil
Generally speaking, soils are classified as dark and light colored soils. By looking at the color of a soil mass, a rough idea of the moisture content of the soil, drainage properties, and degree of oxidation can be obtained. A dark color reflects poor drainage, high organic content, and low annual temperatures. On the other hand, light colored soils have better drainage, high annual temperatures, and highly leached conditions. However, these are rough estimates that only help engineers and agriculturists to adopt suitable measures to study soil properties in detail.
Permeability and Porosity of Soil
The ease with which soil will allow water to pass through it is called permeability, which is a very useful value for civil engineers. Constructing a building on highly permeable soil means that water proofing techniques have to be put in place before digging a foundation or raising columns. On the other hand, the porosity of a soil mass means the pore space or void space in a soil mass. It affects the strength of a soil mass and it depends upon other physical properties of the soil like texture, structure, and presence of organic matter in soil.