*Tropical Soils: Considerations on Occurrence and Characteristics and Studies in Brazil DOI: http://dx.doi.org/10.5772/intechopen.103947*

soil enrichment of iron- and/or aluminum-hydrated oxides, and the permanence of kaolinite as predominant and almost always exclusive clay. These minerals give the soils a typical color: red, yellow, brown, and orange [7, 15].

The saprolitic soils (sapro, Greek: rotten) are those resulting from the decomposition and/or *in situ* breakdown of the matrix rock by the action of the timeless agents and that maintains the structure of the source rock. They can be considered genuinely residual, because the particles that make it up remain in the same place as the matrix rock and can be called young residual soils, in contrast to the lateritic surface mature soils [7].

Saprolitic soils form layers underlying the layer of lateritic surface soil (or possibly other soil) generally appearing on the surface of the soil due to soil erosion or excavation due to man-made works. These soils are more heterogeneous and consist of a complex mineralogy containing minerals still in decomposition phase.

The characterization and evaluation of the geotechnical properties of residual soils are a complex subject, and there is the need for studies on their peculiar behavior for different purposes such as foundation, roads, stability of taludes, construction of earthworks, among others.

**Figure 3** illustrates some variations that can be found in the intemperism profile of tropical soils and that contribute to the complexity of the approach, and **Figure 4** shows concretions formed by this material.

Field investigations of residual soils often relate to heterogeneous soil profiles vertically and horizontally, great structural complexity, and expected metastability due to the process of leaching and chemical decomposition, the presence of rock blocks immersed in matrix, among other aspects [21].

Despite the difficulties of naming these soils, there is a relative consensus that their characterization is made by conventional criterion, which is chemical, that is, would be lateritic soils all those in which the silica/sesquioxides ratio is greater than or equal to 2, and it is deeply weathered soil [22].

Despite the conventional definition, it is found in many situations that the behavior of these soils cannot necessarily be addressed by the conventional geotechnical project due to one or more of the following reasons [21]:


These difficulties of lifting and characterization are detached also by authors [23–25], and others, according to which the tropical grounds it has the reputation of there are "problematic soils" because of without being fitted in the classification systems usually used as they were developed for temperate climates; there is also the need to use adequate methods for them, since the destruction of the cement and its original structure compromises the analysis of its behavior.

Variability in its engineering properties implies, in many situations, a difficulty to meet traditional specifications or consecrated use. An example put forward by [8] is that these materials usually have gaps in the graduation curve (e.g., in the coarse sand fraction); high plasticity indices (PIs 15-20) and CBR values below the minimum 80% are normally specified. An interesting discussion about unconventional materials and their research can be seen in [26].

The geotechnical behavior of these soils is therefore influenced more by their unsaturated condition and by factors such as their structure, macro- and microporosity, anisotropy, and genesis than by their stress history [27–29].
