Interpretation of failure load of helical piles

Mohammed Sakr

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Earth Walls and Foundations

ABSTRACT: Helical piles has gained a wide acceptance in the industry as a robust foundation option in the last few years. As a result of that, numerous full-scale helical pile load tests were documented and reported in the literature. One of the key aspects in analyzing the pile load test results is the selection of the most suitable failure criterion. A large number of failure criteria are available and used to interpret the failure load of piles which had resulted in a wide spectrum of failure loads for a certain pile load test. This paper compares the capacities of helical piles estimated using number of methods including Davisson, L1-L2, FHWA (5%) and ISSMFE (10%). criteria. Total of 31 axial pile load tests were used in the study to assess pile capacities and to validate a relevant definition of helical pile failure loads. The paper also highlights factors that affect determination of helical pile capacities such as soil properties, pile geometry including the number of helices, embedment depth, helix and shaft diameter ratio and load path (i.e. tension or compression). RÉSUMÉ Piles à denture hélicoïdale a acquis une large acceptation de l'industrie comme un fondement solide option au cours des dernières années. À la suite de cela, de nombreux pleine échelle hélicoïdale tas tests de charge ont été documentées et signalées dans la littérature. L'un des aspects essentiels de l'analyse de la pile résultats de test de charge est la sélection des plus aptes critère de défaillance. Il y a un grand nombre de critères de défaillance disponibles et utilisées pour interpréter l'échec de charge des piles qui ont abouti à un large spectre de l'échec des charges pour un certain tas test de charge. Ce document compare les capacités des piles à denture hélicoïdale estimées en utilisant plusieurs méthodes, incluant Davisson, L1-L2, la FHWA (5 %) et ISSMFE (10 % ). Les critères. Total de 31 axial tas tests de charge ont été utilisés dans l'étude pour évaluer les capacités tas et de valider une définition pertinente du tas à denture hélicoïdale panne charges. Le document met en lumière les facteurs qui affectent les détermination de tas hélicoïdale capacités comme propriétés des sols, tas géométrie y compris le nombre des helices, encastrement profondeur, helix et le diamètre de l'arbre ratio et chemin de chargement ( c'est-à-dire la tension ou la compression). 1 INTRODUCTION There are a large number of failure criteria used to interpret the axial compressive capacities of piles from static pile load test results such as Davisson's criterion, Brinch Hansen, L1-L2 method, FHWA (5%) and ISSMFE (10%). Generally; load-displacement curves from axial compression tests on helical piles can exhibit any of the three shapes shown on Figure 1 (Kulhawy and Hirany; 1989). The peak of A and the asymptote of B define the failure load of piles. However for curve type C, the failure load is not clearly defined. A helical pile (Figure 2) consists of a central shaft that is made from round or square sections with one or more formed steel plates (helixes) welded to the shaft. Helical pile sizes varies considerably depending on the required pile capacities and soil conditions. For example typical shaft diameter vary between 73 and 965 mm, while helix diameters vary between 152 and 1219 mm. A single helix or multiple helixes may be used depending on the soil conditions and the required pile capacities. The load displacement curves of helical piles is a function of soil properties and pile configuration since helical piles geometry is considerably different than traditional steel driven piles. Figure 1. Typical load displacement curves for deep foundations (Kulhawy and Hirany 2009)

RÉSUMÉ: pretation of failure load of helical piles

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Cite this article:
Mohammed Sakr (2014) Interpretation of failure load of helical piles in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper187,author = Mohammed Sakr,title = Interpretation of failure load of helical piles ,year = 2014}