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For instance, soils with a small amount of expansive clay minerals will not expand as much when exposed to moisture as a soil with a large amount of the same clay minerals. [5] If a soil is composed of at least 5 percent of these clay minerals by weight, it could have the ability to shrink and swell. [3]
Expansive clays have an expanding crystal lattice in a 2:1 ratio; however, there are 2:1 non-expansive clays. [2] Mitigation of the effects of expansive clay on structures built in areas with expansive clays is a major challenge in geotechnical engineering. Some areas mitigate foundation cracking by watering around the foundation with a soaker ...
Vertisols have a high content of expansive clay minerals, many of them belonging to the montmorillonites that form deep cracks in drier seasons or years. In a phenomenon known as argillipedoturbation, alternate shrinking and swelling causes self-ploughing, where the soil material consistently mixes itself, causing some vertisols to have an extremely deep A horizon and no B horizon.
Mapping of the distribution and extent of natural vegetation of South Africa started in 1918 when the Botanical Survey of the Union of South Africa was established. Maps by Pole-Evans (1936), Acocks (1953), and Low and Rebelo (1996) preceded the current system, which is the combined effort of participants from various centres in the country. [2]
Fluvisol profile along Agula'e River, Ethiopia Distribution of Fluvisols. A fluvisol in the World Reference Base for Soil Resources (WRB) [1] is a genetically young soil in alluvial deposits. Apart from river sediments, they also occur in lacustrine and marine deposits. [2] Fluvisols correlate with fluvents and fluvaquents of the USDA soil ...
Clay cannot be resolved by optical microscopes as its particles are 0.002 mm (7.9 × 10 −5 in) or less in diameter and a thickness of only 10 angstroms (10 −10 m). [16] [17] In medium-textured soils, clay is often washed downward through the soil profile (a process called eluviation) and accumulates in the subsoil (a process called ...
Haplic Planosol profile near Abiy Addi in Ethiopia Distribution of Planosols Soil profile of a Eutric Planosol. A Planosol in the World Reference Base for Soil Resources [1] is a soil with a light-coloured, coarse-textured, surface horizon that shows signs of periodic water stagnation and abruptly overlies a dense, slowly permeable subsoil with significantly more clay than the surface horizon.
Distribution of nitisols. Nitisol, in the World Reference Base for Soil Resources (WRB), is a deep, red, well-drained soil with a clay content of at least 30% and a polyhedral structure or a blocky structure, breaking into a polyhedral or a flat-edged structure. The soil aggregates show pressure faces.