Capacity of driven precast prestressed concrete hexagonal piles: a Winnipeg region geotechnical study

Ryan Belbas, Ken Skaftfeld, James Blatz

In the proceedings of: GeoSt. John's 2019: 72nd Canadian Geotechnical Conference

Session: Pile Foundations

ABSTRACT: Driven precast prestressed concrete hexagonal piles have been used to support industrial, commercial, and residential buildings in Winnipeg and the surrounding area since 1961. Pile design was originally governed by the National Building Code of Canada which stipulated the use of various methods, including static load tests, the Hiley dynamic pile driving formulae, and local experience. Governance of PPCH pile design was superseded in 1964 by the Metropolitan Corporation of Winnipeg By-law 711 which introduced maximum design capacities for specified pile sizes installed under ideal soil conditions. These capacities eventually became known locally as the values and provide the basis for the current state of local practice for geotechnical design of this pile type. The historical values were based on driving the piles to practical refusal in very dense silt till (hardpan). However, the historical capacities may not be appropriate where hardpan is absent and where sand inclusions under high porewater pressure may be present. The By-law was succeeded by the Manitoba Building Code in 1977 which omitted the historical values, although they are still commonly used today. This paper investigates the capacity of PPCH piles driven to practical refusal (estimated from dynamic pile load testing results) at three sites with varying till conditions to quantify potential differences between measured nominal capacities and those which would be derived from historical (allowable) capacities. The results demonstrate that there may be significant variability in the nominal capacity of PPCH piles driven to practical refusal in till indicating that the historical capacities may not account for this variability.

RÉSUMÉ: Depuis 1961, les immeubles résidentiels, commerciaux et industriels à Winnipeg et les alentours ont été soutenu par des pieux battu de béton précontraint hexagonaux. Initialement, le design de ce type de pieu était réglementé par le Code national du bâtiment du Canada. Ce dernier prévoyait une variété de méthodes pour le design, incluant les résultats sur design des pieux HBMP a été remplacer en 1964 par le règlement administratif 711 de la Metropolitan Corporation of Winnipeg qui a introduit des capacités de design maximum pour des tailles spécifiques de pieu installer dans des conditions du sol idéal. Éventuellemenusage local la base pour le design géotechnique pour ce type de pieu. Les données historiques étaient basées sur le refus calcin). Cependant, les capacités historiques pourront être appropriées ou non si règlement administratif était suivi par le Code du bâtiment du Manitoba (CMB) qui omettait des données historiques, ois sites de condition de till variée pour quantifier les différences potentielles entre les capacités nominales mesurer et celles qui seront remaniées de capacité historique (admissible). Les pieux HBMP dans du till indiquant que ces capacités historiques ne peuvent pas tenir compte de cette variance.

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