Date of Award

Spring 5-10-2025

Level of Access Assigned by Author

Open-Access Thesis

Language

English

Degree Name

Master of Science in Civil Engineering (MSCE)

Department

Civil Engineering

First Committee Advisor

Aaron P. Gallant

Second Committee Member

Keith Berube

Third Committee Member

Luis Zambrano-Cruzatty

Abstract

Helical piles are gaining popularity due to several advantages over traditional foundation elements such as drilled concrete shafts. Their design makes them a cost-effective solution for supporting axial loads. However, the lateral and torsional capacity of helical piles is often minimal, as small shafts are typically preferred for efficient design. Consequently, helical piles are excluded from many applications that require significant lateral and torsional resistance.

Recently, a novel device called the "Collar Vane" has been proposed to effectively enhance the lateral and torsional capacity of helical piles. This device consists of a finned, hollow pipe or collar that is installed near the ground surface and wraps around the helical pile shaft. Both elements are bolted together at the pile head to transfer the additional resistance mobilized by the collar vane to the helical pile.

A comprehensive field study demonstrated the performance and feasibility of this device in enhancing the lateral and torsional capacity of helical piles. However, the lateral load tests conducted were limited to purely lateral forces. Since one potential application of modified helical piles with a collar vane is to support lightweight transportation infrastructure, such as roadside signs, the influence of overturning moments must also be investigated. Additionally, a framework for analyzing and aiding in the design of laterally loaded helical piles with collar vanes would be highly valuable to practitioners and designers. Regarding the practical implementation of this technology, the force required to install different collar vanes into the ground remains unknown, which is an important factor in selecting appropriate installation equipment.

This study extends previous research on modified helical piles with a collar vane by: (1) conducting additional full-scale, instrumented load tests to evaluate their performance under monotonic lateral loads with substantial overturning moment (overturning load test) and comparing them to typical drilled shafts; (2) developing a numerical method for analyzing these elements under lateral loads; and (3) quantifying the axial force required to install the collar vane elements.

The results of the overturning load test demonstrated that the collar vane significantly increases the capacity of the helical pile and considerably reduces the bending moment along the shaft. Furthermore, the performance of helical piles modified with collar vanes can be comparable to, or even better, that of conventional foundations used to support roadside sign structures. A nonlinear Winkler model is proposed, calibrated, and validated against field data. The model suggested the presence of a concentrated force acting on the shaft at the level of the collar's bottom edge, which may result from shaft–collar contact and/or soil intrusion. This scenario was further explored using 3D finite element simulations, and the results also support the occurrence of a concentrated force at that location. Finally, the required installation forces increased as the collar vane size increased, reaching up to 170 kN in clay and 260 kN in sand.

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