Soil compaction is the compression of soil due to outside pressure. The effect of soil compaction is an increase in the density of a soil and a corresponding reduction in the amount of air present in the spaces between soil particles. This process can be caused by a number of factors and may be harmful or beneficial depending on the circumstances.
When undertaking almost any construction project, soil compaction is usually performed in a purposeful way. Road construction, in particular, benefits from soil compaction, as it provides a stable base for the roadway. Failure to compact the soil below a road prior to construction can result in the development of uneven areas as the soil settles and compacts due to the cumulative weight of passing vehicles.
Other large construction projects often employ soil compaction for a similar reason. It provides a more stable underlying base for the structure to be built upon and helps prevent buildings from sinking into the soil under their own weight, causing the building to lean or crack. A building or other structure can also experience other problems due to settling, such as leaking pipes.
In natural and agricultural settings, soil compaction is a problem rather than an asset. Soil compaction reduces the ability of a particular soil to hold water and air, both of which are important to the health and growth potential of trees and other plants. Forested areas that are harvested for timber may be slower to recover due to the compaction of the soil from the passing of the heavy equipment used in logging operations. Repeated heavy rains or floods can also contribute to soil compaction. This can slow the growth of new trees that naturally take root or that are planted in the harvested area and of crops in areas under cultivation.
Farmers combat soil compaction by tilling their fields which keeps the soil loose, promoting good root growth for their crops. The presence of pockets of air between soil particles encourages the roots to grow as they are easily able to extend into these spaces. It also improves the ability of soil to hold moisture as well as to allow excess moisture to pass through and drain into the underlying subsoil and water table. Fields are tilled yearly because the soil gradually settles and compacts under its own mass. Compacted subsoil is common due to the mass of surface soils, but this is a natural occurrence and is not usually regarded as a problem, although it can make digging holes or other excavations that penetrate to the compacted layers a challenge.