Interpretation Of Reaction Pile Influence On 45 Mn Static Pile Loading Test And Implications For Design

D.J. Tara

Dans les comptes rendus d’articles de la conférence: GeoVancouver 2016: 69th Canadian Geotechnical Conference

Session: FOUNDATION DESIGN - II Driven Piles

ABSTRACT: Recent major bridge projects in Metro Vancouver showcase the experience of local geotechnical engineers. Large static pile loading tests have been carried out on a number of projects including the Pitt River Bridge, Golden Ears Bridge and Port Mann Highway One projects where the spacing between the test pile and reaction piles was less than the ASTM D1143 recommended five clear diameters. This paper briefly discusses an analytical approach that employs the small strain shear modulus to assess the influence of reaction piles on a test pile in a conventional, top down, static loading test and then reviews how this approach could be applied to interpret the results of a 45 MN static pile loading test completed in late 2007 for the Pitt River Bridge Design Build project. The paper considers the influence of the reaction piles on the initial stiffness of the test pile and demonstrates how to correct the measured load movement response such that the data can be used in pile group analyses.

RÉSUMÉ: Récents grands projets de ponts dans la région métropolitaine de Vancouver mettent en valeur l'expérience des ingénieurs géotechniques locales. Les grands essais de charges statiques des fondations profondes ont été effectués sur un certain nombre de projets, y compris le pont Pitt River, pont Golden Ears et Port Mann Highway One projets où l'espacement entre la pieux de test et des pieux de réaction a été inférieure à la D1143 ASTM recommandé cinq diamètres clairs. Le présent document décrit brièvement une approche analytique qui emploie le module de cisaillement à petites déformations pour évaluer l'influence des pieux de réaction sur un pieu d'essai dans un classique, de haut en bas, essai de chargement statique, puis examine comment cette approche pourrait être appliquée pour interpréter les résultats d'une 45 MN pieu statique essai de chargement terminé à la fin de 2007 pour le projet de construction du pont Pitt River. Le document examine l'influence des pieux de réaction sur la rigidité initiale du pieu de test et montre comment corriger la réponse du mouvement de la charge mesurée de telle sorte que les données peuvent être utilisées dans l'analyses d'un groupe de pieux. 1 BACKGROUND There currently are two distinctly different design philosophies based on elastic methods that are promoted for interpretation of static loading test (SLT) results and their application to design of pile groups. These methods are the equivalent linear elastic approach, which is based on the secant modulus (Poulos and Davis 1980, Fleming et al. 1992) and the linear elastic approach which is based on the initial stiffness augmented by the measured movement (Randolph 1994, Fleming et al. 2008, Viggiani et al. 2012). Although both methods have a similar basis, they differ significantly in application. This paper will demonstrate the use of these methods for a published case history for the Pitt River Bridge 45 MN static pile loading test (Tara 2012, Tara and Coulter 2015). To more accurately assess this local case history, the influence of the reaction piles will be taken into consideration in the analysis. 2 METHODS OF ANALYSIS Elastic methods of analysis have been available to the geotechnical community for many years (eg. Poulos and Davis 1980 and Fleming et al. 1992). The software program PIGLET (Randolph 2003a) is one example of this method of analysis. PIGLET was developed to model the elastic response of single piles and pile groups subject to compression, tension and lateral loading. A detailed example of its application to the prestigious My Thuan bridge project in Vietnam is provided in a recent Rankine Lecture (Randolph 2003b). Program inputs include the soil and shear modulus along the pile shaft and at the pile toe, and the pile dimensions and elastic modulus. The soil model and program inputs are defined as shown in Figure 1. (a) Floating Pile (b) End-bearing Pile Figure 1. PIGLET soil model showing variation of shear modulus with depth (Fleming et al. 2008). Depth Depth GL/2 Shear Modulus GL GL/2 GL Gb L L/2 L L/2 Shear Modulus

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