The use of helical piles as tower foundations in Brazil has increased considerably during the last five years. A number of these piles are installed in unsaturated structured soils, which cover a significant part of the Brazilian territory. However, the installation of helical piles in such soils produces a breakdown of the natural soil structure that affects the pile performance for tension applications. This scenario motivates the present work, in which a comprehensive pile load-test program was carried out on helical piles composed of a single helix or multihelices, installed in an unsaturated tropical residual soil. Eleven full-scale pile axial load tests were carried out, including two compression and nine tension tests. In addition, cone penetration tests were performed close to the piles after installation, and undisturbed soil samples were collected at the depth of the helices. The aim of these additional tests was to contribute to the understanding of the effect of helical pile installation on soil structure. The results of the tension load tests showed that the changes in the structure of the porous tested soil result in particularly low pile uplift capacities. In contrast, the load-settlement curves of the pile compression tests indicate a peculiar failure mechanism due to the sensitive soil structure associated with the high void ratio of the intact soil beneath the bottom plate.
Helical piles have been widely used in Brazil to resist uplift forces of transmission line towers due to certain advantages compared with other foundations, such as resistance to both compressive and tensile loads, easy transport to remote sites, possibility of installation at batter angles, rapid installation with small equipment, and no need for concrete and formwork. However, in some sites the appropriate soil layer for the installation of the pile helices is too deep or too hard to be penetrated. In these cases, the use of helical foundations is not economically and (or) technically viable. One possible solution for this problem is to install the pile in a soil with low bearing capacity improved with cement injection. To evaluate the applicability of a soil-treatment method for helical piles, two different procedures of injection were tested in typical Brazilian residual soils of different geologic origin. For this investigation, 41 multi-helix piles (15 conventional piles and 26 with cement injection) were installed and submitted to tensile loading tests. The results reveal that both techniques can improve the tension capacity and produce a stiffer load–displacement response of helical piles under uplift loads.
À minha orientadora, Profa. Cristina Tsuha, por todo o apoio, amizade, dedicação e oportunidade de conduzir este trabalho.Agradeço à Vercon Industrial e à Vértice Engenharia pelo suporte no fornecimento de materiais, equipamentos e pessoal, durante todas as fases de realização deste trabalho.À CAPES pela concessão da bolsa de estudos.Aos técnicos e pessoal da administração do Departamento de Geotecnia da EESC-USP (Oscar,
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