IN-SITU AXIAL LOAD TESTS OF DRILLED DISPLACEMENT STEEL PILES

Fazli Shah, Lijun Deng

In the proceedings of: GeoQuébec 2015: 68th Canadian Geotechnical Conference & 7th Canadian Permafrost Conference

Session: Foundations IV / Fondations IV

ABSTRACT: Drilled Displacement Steel Pile (DDSP) is an innovative pile type that fully displaces the soil during installation. DDSP consists of a conical tip with steel blades and a steel tubular pipe. Compared to conventional drilled displacement piles, this pile type has many advantages that include rapid installation, immediate usability, and greater pile capacities. Consequently, DDSP has recently been widely used in varieties of engineering applications in Western Canada. However, the axial behaviour of DDSP has not been well understood due to the lack of research, and a design guideline has not been developed. A series of in-situ load tests of full-scale piles were conducted at two testing sites in Alberta. Three axial compression and two tensile tests were conducted on heavily instrumented piles. The paper evaluates the axial capacities and the load-transfer mechanisms during axial loading tests and compares the existing design methods adopted for other pile types.

RÉSUMÉ: : Le pieu foré en acier (Drilled Displacement Steel Pile, DDSP) est un type novateur de pieux qui déplace complètement le sol lors de son installation. Le DDSP est formé d™une pointe conique avec des lames et un tube en acier. Par rapport aux pieux forés conventionnels, ce type de pieu possède de nombreux avantages incluant une installation rapide, une exploitabilité immédiate et de plus grandes capacités. En conséquence, le DDSP a récemment été largement utilisé dans diverses applications de l™ingénierie dans l™ouest du Canada. Cependant, le comportement axial du DDSP n™a pas été bien compris vue le manque de recherche et vue qu™aucun guide de conception n™a été établi. Un ensemble d™essais de chargement en place a été réalisé à l™échelle réelle en deux sites en Alberta. Trois essais en compression et deux essais en tension ont été réalisés sur des pieux largement instrumentés. L™étude évalue les capacités axiales et le mécanisme de transfert de charge pendant des essais de chargement axial et compare les méthodes de conception existantes adoptées pour d™autres types de pieux. 1. INTRODUCTION The use of piles to transmit the structural loads to underlying soils is a conventional method in foundation engineering. There has been continuous improvement in the pile design and construction with regards to the material, methods of installation and design procedure. Pile foundations can be classified into three categories: non-displacement piles, partial displacement piles and displacement piles (Salgado 2008). Drilled displacement piles are one of the most commonly used partial displacement piles. Basu and Prezzi (2009) summarized existing drilled displacement piles available in the industry, such as the Auger Pressure-Grouted Displacement piles (Brettmann and NeSmith 2005), Atlas (Bottiau 2006), De Waal (Huybrechts and Whenham 2003), Fundex (Van Impe 2004), Olivier (Holeyman and Charue 2003), and Omega piles (Bottiau et al. 1998). Typically, the drilling tool of conventional drilled displacement piles contains: a) soil displacement body, b) a helical, partial-flight auger segment and c) a specially designed sacrificial tip attached to the bottom of the tool. The partial auger assists in penetration, the displacement body provides the densification of the soil and the sacrificial tip is released once the drilling is complete. The concrete or grout is placed as the drilling tool is withdrawn and the piles will develop the pile axial capacity after the curing of the concrete or grout (Salgado 2008). The growing economy of Western Canada requires pile foundations that can be installed and loaded in a short period. Drilled displacement steel piles (DDSP) are an innovative pile type that has recently been used in North America in the past decade. DDSP is composed of a conical tip and steel tubular pipe shaft. The conical tip is welded with blades and cutter teeth to drill and transport the soils from the pile tip during installation and thus reduces the installation resistance. Unlike conventional drilled displacement piles, DDSP are made of a specially design conical tip welded to the tip of steel tube, which drills and transports the soil and the steel tube pushes the soil radially to complete the displacement process. DDSP provides a viable alternative to conventional drilled displacement concrete piles, especially in the cases where lateral capacity is required such as in case of seismic loading (Tuladhar et al. 2008). DDSP has higher structural

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