Field investigation of lateral monotonic and cyclic performance of reinforced helical pulldown micropiles

Abstract

Different forms of grouted helical piles are increasingly used to support new and existing foundations. In particular, different methods are used to enhance the lateral and cyclic performance of helical piles for applications in seismic regions. This paper presents a field study on the lateral monotonic and cyclic behaviour of steel fibre–reinforced helical pulldown micropiles (RHPM) and fibre-reinforced polymer – steel fibre–reinforced helical pulldown micropiles (FRP–RHPM). The study shows that the grout shaft and (or) the fibre-reinforced polymer (FRP) sleeve significantly improve the helical pile lateral performance. In addition, the piles showed a significant ductility (no observed failure up to 75 mm displacement or 50% of pile diameter). Two-way cyclic loading resulted in overall degradation in pile response relative to its static performance. Degradation is found to stem from the formation of gaps between the pile and soil, rather than soil stiffness degradation. Formation of gaps leads to the piles having a “preferential direction” with one side providing higher resistance (i.e., stiffness) than the other side. Design charts of various pile configurations are presented.