Soil Classification & Its Bearing Capacity

Soil Classification

• Soil classification proceeds in a similar way as plant and animal classification. Soils are divided into 12 orders defined by the predominant characteristics of the soil, such as texture, structure, organic matter, color and water-holding capacity. A soil is also classified by how deep it is and what material it was formed on. The soil classification system is refined enough to pick out all of the major properties of a soil. Depending on a soil's classification, you can estimate its bearing capacity.

Bearing Capacity of Soil

• Determining the bearing capacity of soils is complicated. The amount of moisture in the soil can alter its bearing capacity. How compacted the soil is or what its temperature is can also change how much weight it can bear. You can change the bearing capacity of a soil by using specialized equipment. Compacting a soil decreases the amount of its volume that is occupied by air. Soil compaction by mechanical means is carried out with vibration equipment and heavy rollers. The amount a soil needs to be compacted will depend on the bearing capacity that is required for the construction project.

Clayey Soil

• Clayey soils are those with a dominant percentage of clay-sized particles in the fine material of the soil. The fine material of the soil is defined as everything less than about a quarter of an inch. Clay soils can become very dense. However certain kinds of clay can become very unstable depending on the amount of moisture in them. Clay soils are easy to compact and can have very high bearing capacities.

Sandy Soil

• Sandy soils have more than 70 percent sand. Because of the relatively large size of sand particles, these types of soil are more difficult to compact. Sandy soils are typically loose and have low bearing capacities. If there is a significant amount of clay in a sandy soil, they can be quite hard, but this does not mean that their bearing capacity will be high enough to build on. Sandy soils are also easily penetrated by water, which makes them more susceptible to erosion.