Piled rafts with hollow auger piles for building foundations in sand deposits in northeastern Brazil

Wilson Cartaxo Soares, Roberto Quental Coutinho, Renato Pinto da Cunha

In the proceedings of: GEO2011: 64th Canadian Geotechnical Conference, 14th Pan-American Conference on Soil Mechanics and Geotechnical Engineering, 5th Pan-American Conference on Teaching and Learning of Geotechnical Engineering

Session: Deep Foundations

ABSTRACT: Usually, geotechnical projects predict load transfer to the ground by means of shallow or deep foundations. Conventional design approach does not provide the combination of these two types of foundation. The piled raft philosophy allows the association of both the soil elements, raft and piles, in order to obtain technical and economic advantages over the conventional design. The city of Joao Pessoa, in northeastern Brazil, has developed foundation practices with hollow auger piles in piled raft design. The coastal area of the city presents superficial soil layers with favorable conditions for using such technique. This paper shows results of instrumented load tests performed over foundations systems of hollow auger piles and piled raft. The case of a raft and a piled raft is evaluated with analysis of the load x settlement curve through extrapolation criteria. Instrumentation analysis describes the load distribution process between raft and pile during charging. Results indicate that the load is first absorbed by the raft and that soil-raft contact contributes significantly to the system™s bearing capacity. RESUMEM Generalmente, los proyectos geotécnicos predicen la transferencia de carga al suelo por medio de cimentaciones poco profundas o profundas. El enfoque de diseño convencional no ofrece la combinación de estos dos tipos de elementos estructurales. La filosofía de cimentación mixta losa-pilotes permite la asociación de ambos elementos del suelo, losa y pilotes, con el fin de obtener ventajas económicas y técnicas sobre el diseño convencional. La ciudad de Joao Pessoa, en el nordeste de Brasil, ha desarrollado prácticas de fundación con pilotes hollow auger en el diseño de losa pilotada. La zona costera de la ciudad tiene capas superficiales del suelo con las condiciones favorables para el uso de esta técnica. Este trabajo presenta los resultados de las pruebas de carga instrumentadas realizadas en los sistemas de grupos de pilotes hollow auger y losas pilotadas. El caso de una losa de cimentación y de losa pilotada se evalúa con el análisis de la curva de carga x asentamiento a través de criterios de extrapolación. El análisis de instrumentación describe el proceso de distribución de carga entre la losa y pilote durante la carga. Los resultados indican que la carga es primero absorbida por la losa y que en contacto con el suelo, esta contribuye significativamente a la capacidad de carga del sistema.

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