Performance of Insturmented Composite Helical Screw Piles Seismic Systems in Layered Soils

Yasser Abdelghany, M. Hesham El Naggar

In the proceedings of: GeoManitoba 2012: 65th Canadian Geotechnical Conference

Session: T2A - Foundations III

ABSTRACT: The axial and lateral monotonic and cyclic behavior of helical pile foundations was investigated and new helical screw systems suitable for seismic loadings were developed. More than one hundred full scale field load tests were conducted on instrumented helical screw piles installed in cohesive soil. The piles included: plain helical screw piles (P-HSP); grouted (G-HSPs); fiber reinforced polymer FRP-G-HSPs; and reinforced grouted RG-HSPs. The RG-HSP piles axial capacity was more than twice that for P-HSP, with minimal reduction after cyclic loading, and their lateral capacity was more than 3 times the P-HSPs capacity. A 3-D finite element model was established.

RÉSUMÉ: Le comportement monotone axiale et latérale et cyclique des fondations sur pieux hélicoïdaux ont été étudiées et de nouveaux systèmes de vis hélicoïdale adaptée pour les charges sismiques ont été développés. Plus d'une centaine à la pleine échelle des tests de charge sur le terrain ont été effectués sur des pieux instrumentés vis hélicoïdale installés dans des sols cohérents. Les piles incluses: plaine pieux vis hélicoïdale (P-HSP); injectés (G-HSP); polymère renforcé de fibres de PRF-G-HSP et renforcé injectés RG-HSP. Les pieux RG-HSP capacité axiale a été deux fois plus que pour P-HSP, avec une réduction minimale après le chargement cyclique, et leur capacité latéral a été de plus de 3 fois la capacité P-HSP. Un modèle par éléments finis 3-D a été établi. 1. INTRODUCTION The performance of single helical anchors and group action was studied experimentally and theoretically by several researchers with regard to their installation torque and uplift resistance. However, their performance under axial compressive or lateral loading is not well characterized and their seismic performance was not investigated. The majority of the research on helical piles focuses on the load carrying capacity with little pile response to other loading modes such as cyclic loading effects or to full scale models. Among numerous researchers Clemence (1983, 1984) conducted laboratory testing investigations; Mooney et al. (1985) conducted field and laboratory testing; Hoyt (1989), Ghaly and Hanna (1992), Hoyt et al. (1995), and Ghaly and Clemence (1998) conducted theoretical and experimental testing, Puri and Vijay (1984), Ghaly et al. (1991), Huang et al. (1995), Johnston (1999), Perko (2000), and Pack (2000) conducted theoretical analyses. Rao and Prasad (1993), Prasad and Rao (1994), Shaheen and Demars (1995), and Frangoulides (2000) conducted experimental testing; Vickars and Clemence (2000) studied the performance of helical piles with grouted shafts experimentally. 2. SS175 HELICAL SCREW PILES The SS175 pile is a segmented deep foundation system with helical steel bearing plates (helices) welded to a central steel shaft. Load is transferred from the shaft to the surrounding soil through the bearing plates. Segments or sections are joined with bolted couplings. Installed depth is limited only by soil resistance. A helical bearing plate or helix is one pitch of a screw thread. All helices regardless of their diameter have a standard 75 mm pitch (Fig.1). The helices have true helical shape and therefore, they do not auger into the soil but rather screw into it with minimal soil disturbance.

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