Soil Formation

Engineering soils are particulate materials that have been formed naturally by physical, chemical and biological processes and artificially by humans. Fine-grained and coarse-grained soils that are deposited by sedimentation are covered in classical soil mechanics. Mineral soil formation processes within the geological cycle include weathering (physical, chemical and biological), erosion (by gravity, water, ice or wind), deposition (from ice, water or wind), and lithification (compaction and cementation). Mineral soils can exist at several stages in the geological cycle. They include primary minerals (silicate and silica minerals), that is minerals found in soil but not formed in soil, and secondary minerals formed in soil. These soils can include fragments of rock which can be formed of primary and/or secondary minerals depending on the source rock, or completely weathered rock in the form of clay minerals. Organic soils are formed by paedogenesis processes (weathering, leaching, humification, eluviation, illuviation and pedoturbation). Anthropogenic activity (e.g. urbanisation, forestry and farming, mining and quarrying, and construction) creates anthropogenic soils. Anthropogenic soils, organic soils, sulphate acid soils, soluble ground, mudrocks, arid soils, glacial soils, tropical soils, collapsible soils and expansive soils are often referred to as problematic soils because their behaviours do not fit the classical theories of soil mechanics.