Pile Groups and Piled Footings Bearing in Weakly Cemented Residual Soil

In engineering practice, it is usual to adopt pile groups as a foundation solution, whereby the block only distributes the loads from the superstructure to the piles. However, the blocks generally have contact with the ground and this portion of strength can be significant. Thus, the concept of piled footing arises. These foundations are composed of deep and shallow foundation elements and can promote technical and economic advantages over a traditional design. The efficiency of the shallow element contact depends on the type of soil. The residual soil weakly cemented existing in Brazil and other tropical countries has peculiar characteristics and is little addressed by traditional geotechnics. Thus, the paper aims to study piled footing foundations supported in this soil, in comparison with traditional pile groups. Seven full-scale load tests were carried out on different foundations executed on the experimental site. Also, simplified methods were applied (PDR-Poulos, Davis & Randolph and Mandolini et al.) to predict the piled footings behavior. The results showed that the contribution of the footing contact reduced the settlements and increased load capacity (reaching 148% of failure load improvement), providing a significant reduction in foundation cost in relation to traditional design in pile groups. It was also found that the bearing capacity for the piled footing is on average 85% of the sum of the bearing capacities of the individual elements (pile group + footing). The simplified methods were satisfactory in representing the behavior of the piled footings on residual soils, especially Mandolini et al.