Volume 44, N. 2

April-June 2021

Interpretation of bi-directional tests on piles with the evaluation of stress relief at the pile toe

Technical Notes

Volume 44, N. 2, April-June 2021 | PAPER (42 downloads)


This paper presents the interpretation of bi-directional load tests performed on three auger piles, in the city of São Paulo, Brazil, using a method based on transfer functions for the shaft and toe. Elastic shortenings of the shaft were directly measured through a displacement indicator at the pile top and two telltales at the upper and bottom plates of the expansive cell. The equivalent top-down load-settlement curves were estimated and compared with two other methods from the literature, one which considers the pile infinitely rigid; and the other, which takes the pile elastic shortening into account. The curves resulted in good agreement considering the pile compressibility. Yet for the infinitely rigid pile, the settlements resulted in up to 75% smaller. Furthermore, the influence of stress relief on the toe behavior due to shaft lifting was investigated. For the cases studied, involving bored and auger piles with the slenderness ratio (Ls/r) greater than 20, the percentage of this effect was generally small, up to 5% of the toe load, being negligible for practical uses.

Keywords: Bi-directional test, Expansive cell, Equivalent top-down curve, Elastic shortening, Stress relief,

Submitted on January 07, 2021.
Final Acceptance on May 19, 2021.
Discussion open until August 31, 2021.
DOI: 10.28927/SR.2021.062021