Innovative seismic resistant helical screw piles (FRP-G-HSP - fiber reinforced polymer grouted and RG-HSP reinforced grouted steel fibers novel systems)

Yasser Abdelghany, M. Hesham El Naggar

Dans les comptes rendus d’articles de la conférence: GeoMontréal 2013: 66th Canadian Geotechnical Conference; 11th joint with IAH-CNC

Session: Foundations III

ABSTRACT: : The axial and lateral monotonic and cyclic behavior of helical pile foundations was investigated and new innovative helical screw systems suitable for seismic loadings were developed and patented. 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. The results of 3-D finite element modeling were used to establish the load transfer mechanism and a design methodology for the considered piles. RÉSUMÉ: Le comportement axial et latéral monotone et cyclique des hélicoïdaux fondations sur pieux a été étudiée et de nouveaux systèmes de vis hélicoïdales innovantes adaptées pour des chargements sismiques ont été mis au point et breveté. Plus d'une centaine de tests de charge sur le terrain en grandeur réelle ont été menés sur instrumentés hélicoïdaux pieux vissés installés dans un sol cohérent. Les piles incluses: pieux vissés hélicoïdaux simples (P-HSP); injectés (G-HSP); polymère renforcé de fibres FRP-G-HSP et renforcés cimentée RG-HSP. Le RG-HSP piles capacité axiale était plus de deux fois le P-HSP, avec une réduction minimale après le chargement cyclique, et leur capacité latéral était plus de 3 fois la capacité P-HSP. Un modèle par éléments finis 3-D a été établi. Les résultats de la modélisation 3D par éléments finis ont été utilisés pour établir le mécanisme de transfert de charge et une méthode de conception pour les pieux considérées. 1. INTRODUCTION AND LITERATURE REVIEW Helical (screw) anchors have been utilized in tension loading and have gained popularity for bearing load applications. Helical piles represent an overall cost effective alternative to conventional piles for new construction and repair applications. The helical piles speed and ease of installation, less noise during installation added advantage with regards to their efficiency and reliability for underpinning including re-support and reconstruction of distressed and damaged foundations for either stabilization or rehabilitation. The 5 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 these bearing plates. Segments or sections are joined with bolted couplings. Practically installed depth is limited only by soil resistance and economics. 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 (Figure.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. However, the pile slender square shaft is susceptible to buckling under loading conditions. The performance of single helical anchors and group action were studied experimentally and theoretically by several researchers, the researches focuses on the installation torque and uplift resistance. Some researches focus on the load carrying capacity with little pile response to cyclic loading effects or to instrumented full scale field testing. Helical piles axial compressive or lateral loading still is not well characterized and needs more analyses and their seismic performance was not investigated. For such this research was initiated in 2005 to investigate the helical piles monotonic and cyclic performances under axial and lateral loadings to consider their usage in different applications in seismic zones. Among the several researchers, Clemence (1983); Mooney et al. (1985) conducted field and laboratory testing; Hoyt (1989), Hoyt et al. (1995), and Ghaly and Clemence (1998) conducted theoretical and experimental testing, Puri and Vijay (1984), Huang et al. (1995), Perko (2000), and Pack (2000) conducted theoretical analyses. Rao and Prasad (1993), Prasad and Rao (1994), conducted experimental testing; Vickars and Clemence (2000) studied the performance of helical piles with grouted shafts. 2. RESEARCH OBJECTIVES AND METHODOLOGY I. To develop efficient guidelines for the field installation of (P-HSP) and grouted (G-HSP) and

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