Civil and Building Engineering.

The first information of interest to any designer of foundations is the soil and rock profile in which the foundations are to be constructed. This information often is the major factor that determines the type of foundation because foundations perform in different ways in different soil types and because the typical problems encountered during construction also vary in different types of soil and rock.

For purposes of foundation engineering, current design methods for determining the axial capacity of deep foundations generally classify soil and rock into five types (note that the following definitions are for foundation engineering, not for geology or other purposes). The five classifications for soil types are:

•  Cohesive soils, including clays and cohesive silts.
•  Cohesionless soils, including sand and gravels of moderate density.
•  Cohesive intermediate geomaterials. This soil type consists of cohesive materials that are too strong to be classified as cohesive soils and too weak to be classified as rocks. It includes saprolites, partially weathered rocks, claystones, siltstones, sandstones, and other similar materials.
•  Cohesionless intermediate geomaterials. This soil type consists of highly compacted granular materials, including very tight sand and gravel; naturally cemented sand and gravel; very tight mixtures of sand, gravel, and cobbles; and glacial till. Excavation in cohesionless intermediate geomaterials usually requires heavy equipment, specialized tools, and occasional blasting.
•  Rock includes all cohesive materials that are too strong to be classified as cohesive materials. Rock types are further classified according to their mineralogy, fracture pattern, and uniformity.

The purpose of using these five classifications is to establish a system of soil descriptions covering the range of earth materials from the softest and most compressible to the hardest and most incompressible.

This same classification of soil types can be used for the design of foundations subjected to lateral loading. It is used to describe the soil types, but additional information on the position of the water table and the results of shear strength testing in the laboratory or field are also needed so that the proper load-transfer models can be selected by the foundation engineer.