Response Prediction for Axially Loaded Fixed Head Pile Groups

Abstract

SUMMARYThe aim of this paper is to evaluate the influence of the interaction between the piles of a group fixed in a pile head on both bearing capacity and stiffness. For this purpose, numerical analyses were carried out to establish the load-displacement relationships for different 3*3 layouts of pile groups. The results are compared with those of the pile test carried out for the purposes of the project and the numerically established load-displacement curve of the single pile. Based on these non-linear analyses, the effect of the interaction was quantified for the pile group layouts examined, and was compared to proposed empirical relationships and reduction factors resulting from linear elastic analyses based on the principle of superposition. INTRODUCTIONThe effect of the interaction between the piles of a group under axial loading has been the subject of many researches during the past three decades. Based on the experience gained through these studies, empirical relationships were proposed to estimate the reduction factors on both, the bearing capacity and the stiffness of a group due to the interaction between the piles. Moreover, specific values for these factors have been proposed in tabular form resulting from simplified analyses based on elastic continuum analysis and the principle of superposition, Poulos and Davis /1 /, Poulos 121. An alternative approach is proposed by Lee 13/ in which the response of the single pile is simulated using the load-transfer (t-z) method, and the interaction between the piles is assessed using Mindlin's solution /4/. Another simplified approach providing a methodology for estimating the settlement of a pile group is the representation by an equivalent pier (Randolph /5/; Horikoshi and Randolph 161). Most of the above methods involve soil profile simplifications and other idealisations rendering them computer cost-effective with the drawback however of limited accuracy in many cases. Numerical methods such as Finite Element or Finite Difference Method, taking 27 Brought to you by | Western University Authenticated Download Date | 6/9/15 7:16 PM

Μέθοδος Απλουστευμένης Τριδιάστατης Αριθμητικής Ανάλυσης Πασσάλων Υπό Συνδυασμένη Φόρτιση

“…Η αξιοπιστία της εν λόγω εξίσωσης διερευνήθηκε για δεδομένες εδαφικές συνθήκες και αξονική απόσταση ίση με 3.0D. Προκειμένου να εξεταστεί περαιτέρω η ισχύς και η αποτελεσματικότητα της προταθείσας σχέσης, η Μπαρέκα (2007) και οι Comodromos και Bareka (2005 αξιοποίησαν τα αποτελέσματα εκτεταμένης τριδιάστατης μη γραμμικής αριθμητικής ανάλυσης που περιλάμβανε επιπρόσθετες διατάξεις πασσάλων σε διαφορετικούς εδαφικούς σχηματισμούς, καλύπτοντας τύπους συνεκτικών εδαφών, από μαλακές έως στιφρές αργίλους και μη συνεκτικών εδαφών από χαλαρές έως πυκνές άμμους. Η σχέση προσαρμόστηκε κατάλληλα δίνοντας ιδιαίτερα ικανοποιητικά αποτελέσματα, με εξαίρεση την περίπτωση πυκνών αμμωδών εδαφών, όπου η εφαρμογή της οδηγούσε σε πιο συντηρητική πρόβλεψη σε σχέση με την πραγματική συμπεριφορά της ομάδας πασσάλων.…”