Distributed Fiber Optic Sensing of Helical Pile Loads in Pile-Reinforced Rail Applications
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Authors
Sherlock, Sam
Date
Type
thesis
Language
eng
Keyword
Helical piles , Pile reinforcement , Railway rehabilitation , Soil arching
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Abstract
Localized areas of weak subgrade under rail tracks can lead to increased damage to the rail and rail sleepers, and rapid deterioration of the trackbed geometry requiring frequent maintenance. One solution to mitigate this problem is the installation of piles under the rail in the ballast, which would then allow for the loads from the tracks to bypass any low stiffness subgrade materials. However, there are uncertainties regarding the distribution of loads in this system, which require improved measurements of pile behaviour to understand. The objectives of this thesis are to a) develop a technique for measuring axial load and bending along the full length of helical piles, and b) use these measurements to understand the load distribution in a pile-reinforced rail foundation. To protect the distributed fibre optic sensors during pile installation, a PVC insert method was adopted, whereby a series of distributed fibre optic strain sensors were installed on a PVC pipe, which was then placed inside a steel helical pile, and the two were epoxied together. The strain measurements were then used to calculate both the axial loading and bending along the length of the pile. Four prototypes were constructed to examine the impact of pile diameter and fibre type, and in-air eccentric axial load testing was completed. The strain measurements from the PVC inserts were in good agreement with strain measurements from fibres mounted to the outside of the pile. A fullscale laboratory test setup involving a single railway tie supported by four helical piles was used to investigate the impact of ballast depth on pile load. Four load tests were completed on the system at ballast depths of 900, 635, and 350 mm, with three of the tests having three cycles up to 50 kN applied, and the final test having one cycle up to 90 kN. The response of the system during the loading was monitored using the developed PVC insert sensor system and a series of settlement plates. The distributed measurements of axial and bending moment showed a transition between negative and positive skin friction at a simulated low stiffness layer, and end bearing. The pile group was found to carry approximately 8% of the total load at a ballast depth of 900 mm and 20% of the total load at the depths of 635 and 350 mm.
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Copying and Preserving Your Thesis
This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner.
Attribution-NoDerivs 3.0 United States
ProQuest PhD and Master's Theses International Dissemination Agreement
Intellectual Property Guidelines at Queen's University
Copying and Preserving Your Thesis
This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner.
Attribution-NoDerivs 3.0 United States