Design and load tests of helical piles

Mustapha Zergoun, Bernie Vaughan, Steven Lewis

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

Session: Earth Walls and Foundations

ABSTRACT: d load tests of helical piles Mustapha Zergoun, Ph.D., P.Eng. Thurber Engineering Ltd., Vancouver, BC, Canada Bernie Vaughan, P.Eng. and Steven Lewis, P.Eng. Metro Vancouver, Burnaby, BC, Canada ABSTRACT This paper presents a case history of the design and load tests of helical piles for a regional water pumping station. Helical piles were selected to reduce construction noise for a neighboring residential area. Pile resistance for both compression and uplift was required to support heavy gravity loads and address buoyancy concerns under flood conditions, respectively. The subsurface conditions consisted mainly of lightly over-consolidated silty clay of low to medium plasticity and sensitivity. The method recommended in the 2006 Canadian Foundation Engineering Manual (CFEM) was followed for design. The CFEM method uses the undrained shear strength Su in cohesive soil deposits. The Su design value was derived from field vane and static cone penetration tests. Two contractors specializing in helical pile installation independently load tested preliminary helical piles in order to submit their design-build bid. Various helical pile sizes and configurations were used and both compression and tension static load tests were carried out in accordance with ASTM testing standards. In all cases, the results indicated resistance values significantly lower than the values calculated using the selected Su design value. The discrepancy was so large that the helical pile foundation system became uneconomical and a thick concrete raft foundation was preferred instead. RÉSUMÉ Cet article présente une histoire d'un cas de design and d'essais de pieux à hélices pour une station régionale de pompage d'eau potable. Les pieux à hélices ont été choisis afin de réduire le bruit pour un voisinage résidentiel. La résistance des pieux était requise en compression et en tension pour supporter, respectivement, des charges lourdes et éviter le soulèvement de la structure en cas d'inondation. Le profile des sols consiste principalement d'argile silteuse légèrement surconsolidée de plasticité et sensitivité moyenne. La méthode recommandée dans le Manuel Canadien de Fondations 2006 (MCF) a été suivi pour le design. La méthode du MCF utilise la résistance au cisaillement non-drainé Su pour les sols argileux. La valeur de design Su a été dérivée d'essais au scissomètre et au pénétromètre statique. Deux entrepreneurs spécialisés dans l'installation de pieux à hélices ont indépendamment fait des essais statiques sur des pieux préliminaires dans le but de soumettre leur offre de design et construction. Plusieurs pieux à hélices de différentes dimensions et géométrie ont été utilisés en compression et en tension suivant la norme d'essai ASTM. Dans tous les cas, les résultats ont indiqué des valeurs de résistance nettement inférieure aux valeurs calculées en utilisant la valeur de résistance au cisaillement choisie pour le design. La divergence était si grande que le système de fondation sur pieux à hélices est devenu non économique et un radeau de fondation en béton a été préféré. 1 INTRODUCTION Over the past few years significant advance has been made on the design and testing of helical piles in both sand and clay deposits. However, the design and performance of such piles still require load tests for quality assurance. This paper describes a case history of the design and load tests of helical piles for a regional water pumping station located in Maple Ridge, about 50 km east of Vancouver, British Columbia. The proposed pump station is located at the end of 120A Avenue, on the boundary of Pitt Meadows and Maple Ridge, near the north ramp approach to the Golden Ears Bridge, as shown in Figure 1. The site has a trapezoidal shape and is bounded by residential properties to the east, Lougheed Highway to the south, a golf course to the west and Fortis BC Gas right-of-way to the north. At the time of the site investigation, the site grade elevation ranged from El. 2.0 to 3.6 m (geodetic datum). The proposed pump station is a one storey building of about 72 m by 23 m. The underside of the floor slab is set at El. 0.6 m. The Landscape grade surrounding the building is set at about El. 3.25 m. Figure 1 Site location. SiteNorth

RÉSUMÉ: gn and load tests of helical piles Mustapha Zergoun, Ph.D., P.Eng. Thurber Engineering Ltd., Vancouver, BC, Canada Bernie Vaughan, P.Eng. and Steven Lewis, P.Eng.

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Cite this article:
Mustapha Zergoun; Bernie Vaughan; Steven Lewis (2014) Design and load tests of helical piles in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper362,author = Mustapha Zergoun; Bernie Vaughan; Steven Lewis,title = Design and load tests of helical piles,year = 2014}