Tropical Soils

 

In humid tropical regions, rocky weather is more severe and extends to greater depths than the rest of the world. Residual soils grow as a result of climate, primarily a chemical environment (Rahardzo et al., 2004). As a result, climate (temperature and precipitation), source rock, water movement (drainage and topography), age, and vegetation cover contributed to the development of the soil profile.

Ferruginous and aluminous clay soils are frequent products of climate in tropical latitudes. They are characterized by the presence of iron and aluminum oxides and hydroxides.

Those compounds, especially those of iron, are responsible for the red, brown, and yellow colors of the soils. The soils may be fine-grained, or they may contain nodules or concretions. Where there are matrices in which the concretions occur, there are high concentrations of oxides in the soil. More extensive accumulations of oxide give rise to laterite.

Laterite is a residual ferruginous clay-like deposit that usually occurs beneath a hard ferruginous crust or hardpan (Charman, 1988). Ratios of silica (SiO2) to sesquioxides (Fe2O3, Al2O3) in laterals are generally less than 1.33, with ratios between 1.33 and 2.0 Lateritic refers to the soil, and more than 2.0 indicates non-lateral types.

During the dry season, the water level decreases. A small amount of iron, which is mobilized from groundwater to iron, is then oxidized, forming a gaitite if hematite or hydrated.

The movement of the water table leads to the gradual deposition of iron oxides at a given horizon in the soil profile. A cemented layer of laterite is formed that may be a continuous or honeycombed mass or nodules may be formed, as in laterite gravel. Concretionary layers
often are developed near the surface in lowland areas because of the high water table.

Laterite hardens upon exposure to air. Hardening may be due to changes in the hydration of iron and aluminum oxides. Laterite usually contains fractions of all sizes ranging from clay to gravel and sometimes even larger material (Figure 5.6). Generally, at or near the surface, the liquid limit of the literate does not exceed 60% and the plasticity index is less than 30%. As a result, the laterite has low and moderate plasticity.

The activity of laterite may vary between 0.5 and 1.75. Some of the values of common properties of laterite are given in Table 5.16. Lateritic soils, particularly where they are mature, furnish a good bearing stratum (Blight, 1990). The hardened crust has low compressibility and, therefore, settlement is likely to be negligible.

However, in such cases, the soil depth may decrease with increasing depth. Oxidation occurs more readily in the ferruginous soils where red earth or latosols remain. Most such soils are derived from the first cycle of supporting material weather.

Table 5.16. They are some common properties of laterites (after Madu, 1977)

Moisture content (%)                                        10–49

Liquid limit (%)                                                  33–90

Plastic limit (%)                                                  13–31

Clay fraction                                                        15–45

Dry unit weight (kN m -3 )                               15.2–17.3

Cohesion (kPa)                                                   466–782

Angle of friction (∞)                                           28–35

Unconfined compressive strength (kPa)        220–825

Compression index                                            0.0186

Coefficient of consolidation (m2-1a00)          262

Young’s modulus (kPa)                                     5.63  10∧4

 

They differ from laterite because they act as clay soil and do not have strong concrete. However, they will be graded as laterite. Black soil is typically developed in poorly drained plains with wet and dry seasons where annual rainfall is less than 1250 mm. In general, the clay content in this soil exceeds 50%, with silky materials varying from 20 to 40% and sand. Forming a residue.

The organic content is usually less than 2%. Black clay fluid limits may range from 50 to 100%, while plasticity indices may be between 25 and 70%. The shrinkage threshold is often 10-12%. Montmorillonite is usually present in the soil part and is the main factor determining the behavior of these soils.

For example, due to the montmorillonite content, they undergo significant volume changes upon wetting and drying. However, changes of this magnitude are limited to the critical zone on the soil, which is often less than 1.5 m thick. Below this, the humidity is more or less the same, for example, about 25%.

Thank you for reading the detail of tropical soils

Also Read: Ground Water Exploration

Also, Read Characteristics of the tropical soil.