Field Lateral Behaviour of Full-Scale Screw Micropiles in Cohesive and Cohesionless Soils.

A screw micropile is a multi-sectional pile typically consisting of a smooth segment at the top, a threaded segment in the middle and a tapered segment at the bottom. Although the axial behavior of this pile type has lately been studied, response to lateral loading and contribution of the threads to lateral capacities are yet to be investigated. To facilitate the design of this pile type for applications where wind or seismic loads are concerned, there is a necessity to examine the lateral behavior and capacities of screw micropiles and effect of the threads on the lateral capacities. Hence, lateral load field test programs were carried out on six types of screw micropiles at two cohesive soil sites and a cohesionless soil site. Selected piles were instrumented with bending moment strain gauges along the pile shaft. A geotechnical site investigation was carried out at each site to obtain soil profiles and properties. The lateral load versus displacement curves and the bending moment distribution were obtained. The lateral capacity and failure mode of the piles were determined from existing methods and analysis of the field test results. The lateral capacities of the piles were estimated using the Broms method without considering the effects of the thread. The estimated and measured lateral capacities were in a good agreement. This suggested that the effects of the threads on the lateral capacities were minimal. In addition, the effects of the tapered segments on the lateral response of the piles were negligible. This research was the first one for screw micropiles subjected to lateral loading and the outcome may support the engineering of the piles and further studies on soil-screw micropile interaction. [ABSTRACT FROM AUTHOR]