Electronic Thesis and Dissertation Repository


Doctor of Philosophy


Civil and Environmental Engineering


M. Hesham El Naggar


Helical piles are a deep foundation system that can be used to support pipelines, telecommunication and transmission towers, and low- and medium-rise buildings. Advantages of helical piles include: short installation time with minimal noise and vibration levels; can be installed with ease in limited accessibility site; and onsite quality control by measurement of installation torque.

The main objective of the current research is to assess the performance of steel fibre-reinforced helical pulldown micropiles (RHPM), and fibre-reinforced polymer-steel fibre- reinforced pulldown micropiles (FRP-RHPM) under axial and lateral monotonic and cyclic loading conditions.

The research methodology involved conducting full scale field testing on: one plain helical pile, 12 RHPM and 12 FRP-RHPM. Piles were subjected to axial static and one-way cyclic loading, and lateral static and two-way cyclic loading. The axial test results were then used to calibrate a three-dimensional finite element model. To calibrate the lateral test results, moment-rigidity curves for the tested piles were generated through three-dimensional finite element models. Along with test results, these curves were used to calibrate a finite difference model.

The experimental investigation under axial loads shows that these pile systems behave as composite pile systems. The grout shaft significantly improves the helical pile axial performance. Cyclic loads resulted in degradation of the shaft resistance, however, resulted in an improvement of the lead section resistance. The overall pile cyclic response was found to stabilize after a few cycles of loading. Finally, the cyclic loading was found to improve the axial capacity of these systems.

The experimental investigation under lateral loads shows that the grout shaft and/or the FRP sleeve significantly improve the plain helical pile lateral performance and ductility. Two-way cyclic loading resulted in overall degradation in pile stiffness and capacity.

A design procedure for FRP-RHPM and RHPM under axial compression loading conditions is presented. For the lateral direction, a series of design charts that can be used in conjunction with available numerical programs to design such systems are provided.

In general, the RHPM and FRP-RHPM are viable foundation options for axial and lateral monotonic and cyclic loading applications.