**3.2 Geotechnical properties of lateritic soils in some sites in Brazil**

As previously mentioned, lateritic soils can present quite varied behaviors, which requires the implementation of projects that take into account their geotechnical properties, obtained from field and/or laboratory tests. The growing urbanization and verticalization of cities in the center-south region of Brazil, as well as the increase in infrastructure works, lead to increasing challenges in foundation design, since the foundation elements must consider the high loads to be distributed frequently. For this, the use of piles has been the most common foundation option, since in some situations, geotechnical limitations occur due to soil properties such as high porosity and/or the collapsible character or excessive settlements in the face of loads, which do not allow the use of direct foundation.

**Figure 8.** *Site characteristic profiles [15].*

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

One example of this behavior is the soils of the city of Brasilia, located in the state of Goiás, which is located in an area of highly weathered tropical soil, with high levels of aluminum and iron. As a consequence of the high porosity of the cemented structure of this soil, known as "porous clay," it presents great structural instability and can sorer that is highly unstable and can suffer changes in volume (collapse) due to changes in saturation and stress state. The possibility of sharp deformations must be considered since this type of soil covers 80% of the area of the municipality [53–55].

**Figure 9** illustrates the SPT index strengths in the study conducted by [53, 54] and the strength parameters of unsaturated porous clay, according to Mohr-Coulomb criteria that can be considered as Cohesion angle ranging from 20 to 34 KPa, friction angle () between 25 and 28° and Young's modulus varying 1–8 Mpa, Coefficient of collapsibility is 0–12%, Coefficient of permeability is 10−06–10−03 cm/s [55, 56]. The tests to evaluate the granulometry of the soil composed of sieving and sedimentation, in addition to the Atteberg limits test, allowed the classification of the soil as CH by the Unified Classification system, with a plastic Index of 12% and a natural unit weight around 15 kN/m3 . This porous clay layer has a variable thickness of 20–30 m and NSPT indexes between 2 and 3 strokes with a deep water level, and in some cases reaching a depth of 5 m. Liquid limit LL = 50–80%, plastic limit PL = 35–50%, and water content w = 35–55%. The clay fraction, that is, the percentage of soil particles less than 2 μm lies between 70 and 55%. The percentage of fines (less than 60 μm in diameter,) varies from 70 and 80% [55].

Considering the characteristics observed in the drilling and laboratory tests, the authors state that a foundation option that has been used in the city of Brasilia and neighboring cities is the Alluvial Pile Anker, a new type of small diameter foundation characterized by fast execution, with technical and economic advantages over precast piles. It consists of drilling small diameter piles, where a 2 ½″ tube, 50 cm longer than the depth of the hole, with a cutting tip (**Figure 10**), is installed in the ground at very high speed, and the soil is drilled through rotation. The hole is filled with cement, and after it has been drilled, the capping is made with precast-reinforced concrete or steel sheeting on each pile. A gravel backfill is placed between the capstones at the same height, and a geogrid is placed over it, followed by a transition backfill that acts as a stress dissipator [53, 57].

It should be noted that in foundations embedded in lateritic or collapsible soils, the rigor in the design process and in the design should be greater, because the behavior of these foundations often differs from the classical models adopted and presented in the technical-scientific literature, being possible to observe a nonlinearity of the soil behavior due to variations in the soil parameters that control its behavior: modulus of deformation and shear modulus of the soil [58]. It is fundamental for pile foundation design like aspects such as the relative stiffness of the lateritic soil of the first layer when not saturated; the collapsibility of this soil, especially if the piles are totally embedded in this layer and the evaluation of the ultimate strength, due to its own executive process, be taken into consideration.

Studies conducted in collapsible lateritic soils in the city of Campinas, state of São Paulo, where most of the foundations employed are deep, with auger piles being the most commonly used, show the use of foundations executed as staked foundations, for example, a foundation element where the piles under the radier are interrelated may have greater efficiency in the reduction of settlements, because the greater contact of the surface foundation element contributes to the performance of load capacity and settlement reduction for the system [59, 60].

**Figure 9.** *Stratigraphy and SPT-SPTT results [53].*

**Figure 10.** *Alluvial Anker pile construction process [57].*

In the city of São Paulo, the construction of an extensive subway network allowed obtaining geotechnical parameters of soils existing in the São Paulo Basin from the study of 12 different sites, which demonstrated the heterogeneity of the profiles, comprising alternating layers of sandy clays and clayey sand with silt fractions. However, the horizontal stress index (Kd) revealed values greater than 2, confirming the overconsolidation of the variegated soils, which had been previously reported in the literature [22]. The *in situ* tests allowed obtaining information about the stress history of the sampled soils and despite the variability of the soils, authors point out that the corrections obtained are consistent with results presented in the technical literature, confirming the potentiality of the piezocone and dilatometer (DMT) tests [33].

It is noteworthy that lateritic soils can also present variation in their behavior as a function of matrix suction variation, and therefore, their geotechnical investigation should be careful [21, 26, 33, 58, 61, 62].

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

Furthermore, one must consider the resistance variation presented by laterite soils that vary considerably with depth, according to the influence of such factors as parent rock, depth of the water table, topography, degrees of decomposition, laterization, and desiccation, as well as mineralogical composition. Also in relation to mineralogy, if the clay present in the soil has the presence of iron oxide in ferric state, the soil is essentially stable and no changes are expected and therefore, standard tests can be employed for soil characterization [8, 32, 63].
