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

Helical piles are used increasingly to support new and existing foundations. This paper presents a field study on the axial monotonic and cyclic behaviour of steel fibre-reinforced helical pulldown micropiles. Test piles consisted of a round corner square helical pile with three helices attached to it, and a steel fibre-reinforced grout shaft. To assess the grout shaft contribution, one helical pile without a grout shaft was tested. Piles were instrumented with strain gauges to evaluate the load-transfer mechanism. This paper discusses the load-displacement response of this pile system, and load-sharing mechanism between the grout shaft and lead section. The study shows that the grout shaft significantly improves the helical pile axial performance. It was found that the load-transfer mechanism within the lead section is through individual bearing of each helix. Also, the findings demonstrate that the behaviour of this pile system is satisfactory under one-way cyclic loading conditions. The results suggest that the reinforced helical pulldown micropile is a viable deep foundation option for axial monotonic and one-way cyclic loading applications.