Date of Award

2018

Degree Type

Thesis

Degree Name

Master of Science in Civil and Environmental Engineering

Department

Civil and Environmental Engineering

First Advisor

Aaron S. Bradshaw

Abstract

Helical anchors (or helical piles) are currently being considered for anchorage of floating offshore wind turbine platforms. Maximizing the geotechnical efficiency of these types of anchors will help to minimize the overall cost of the mooring system. One measure of efficiency of a helical anchor is the torque factor, defined as the ratio of the pullout capacity to the installation torque. The objective of this study is to evaluate available analytical models from the literature that may be used to predict the torque factor of a helical pile, consisting of a pipe pile with a single helix attached to the bottom. Three different analytical models were evaluated using data collected from small-scale load tests on helical piles in sand. The models included Ghaly & Hanna (1991), Perko (2001), and Tsuha & Aoki (2010). Interface shear tests were also performed to characterize the residual interface friction angle for the small-scale anchor tests. Both the Ghaly & Hanna (1991) and Perko (2001) models tended to overpredicted the measured torque factors in most cases with significant variability. The Tsuha & Aoki (2010) model yielded the best predictions, which only requires the dimensions of the helix and the residual interface friction angle of the foundation soil.

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