Unexpected behavior of long steel H piles in Santos City, Brazil

Faiçal Massad

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: The paper deals with an unexpected behavior of long steel H piles used as foundations of tall buildings in Santos City. The piles were driven through 10 to 12m of a medium to compact sand overlaying up to 50 m of alternated layers of soft to medium clays plus sands. Four piles were submitted to static vertical loading tests; two of them were instrumented. It is shown that: a) the piles behaved as floating piles; b) the unit shaft resistances reached their maximum values with movements of 3 to 8 mm, except in the upper sand layer, that required more than 40 mm; c) this upper layer exerted a pressure on top of the underlain soft clay, drastically reducing its unit shaft resistance; and d) the piles behaved as piled rafts. Based on a mathematical model, it is shown how to estimate the total shaft resistance in load tests without instrumentation.

RÉSUMÉ: Le travail traite un comportement inattendu des pieux d™acier de grande longuer, enfoncées à travers 10 à 12m dans une couche du sable compact superposé jusqu'à 50 m de couches alternées d'argiles molles à moyennes et sables. Quatre pieux ont été soumis à des essais de chargement; deux pieux ont etés instrumentés. Le travail montre que: a) les pieux se comportaient comme flottants; b) les frottements lateraux unitaires atteindrent leurs valeurs maximales avec des déplacements de 3 à 8 mm, sauf dans la couche de sable supérieure, qui exigeait plus de 40 mm; c) cette couche supérieure a exercé une pression sur le sommet de l'argile molle, réduisant considérablement son frottement lateral; et d) les pieux se comportaient comme fondations mixtes semelle-pieux. S™appuyant sur un modèle mathématique, il est montré comment estimer le frottement lateral total en essais de chargement sans instrumentation.

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