Mechanical Properties of Soil

Soil is a granular medium that varies in composition from organic peat to gravel and that may contain various amounts of water. The soil physical system is continually being subjected to external forces and is, therefore, dynamic. These external forces may be environmental (climate, plants, animals, and micro-organisms) or mechanical (forces applied by man using some type of machine). The specific reaction of the soil to these forces is of interest. The forces provide the means for changing soil from one condition into another and the reaction indicates the kind and degree of change. If one is to be able either to maintain a soil condition or to change it to a more suitable condition, he must first have an understanding of soil behavior; this behavior must eventually be properly described. Soil conditions and properties, widely varying types of forces, and widely varying types of behavior must all be included in any description before the description can be satisfactory.

Friction

All tillage operations involve a sliding action of soil over some surface of the tool. Friction of soil against a tool having large contact areas represents a significant component of the draft requirement. Friction is also involved when two rigid bodies of soil move with respect to each other.

Adhesion

Adhesion is defined as the force of attraction between two unlike bodies. In soil, adhesion is due to the film of moisture between soil particles and the surface contacting the soil.

Compressibility

Failure of a soil by compression is generally associated with a reduction in volume.

Erodibility

Fine grained materials are easily transported, but clays are difficult to initially erode due to cohesion.

Permeability

It is defined as the ease with which water flows through the soil. Fine grained materials are less permeable.

Corrosion

It is defined as the tendency to corrode materials and structures, esp. metals, laid in the ground.