Distributed Sensing for Monitoring Cast Iron Pipe Behaviour

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Date
Authors
Simmons, Josh
Keyword
Cast Iron , Pipe , Distributed Sensing , Fibre Optics , Differential Ground Movement , Frost Heave , Four-Point Bending , Parallel Plate Loading
Abstract
The objectives of this thesis were to investigate the material performance and field behaviour of small diameter cast iron water pipes. Exhumed pipes were provided by the Cities of Kingston, Hamilton, and Toronto in Canada. Four of these 150 mm diameter pipe specimens, with a length of 2.2 m, were instrumented with distributed fibre optic sensors (three circumferential fibres around midspan and five longitudinal fibres along the crown, springlines, and invert) and tested in four-point bending to identify the circumferential and longitudinal strain distributions before failure. Additionally, 48 parallel plate loading tests were conducted on 25- and 100-mm ring samples to identify the variation in behaviour over the length of a pipe specimen. Samples from both tests exhibited linear strain patterns up to 50% of ultimate load, after which the strains increased non-linearly with load. In parallel-plate loading, the ring specimens generally sustained more load when the wall thickness at the failure location was larger. In bending, peak tensile hoop strains at midspan occurred at the crown while compressive strains occurred below the springlines down to the invert due to Poisson’s effects. The pipes under four-point bending did not fail at locations of observed peak tensile strain, indicating that cast iron pipes can fail at locations without physical signs of deterioration or damage. A field study of two sites in Kingston, Ontario was conducted to investigate the relationship between pipe leakage and differential ground movements. Seasonal ground movements were monitored using total station and Light Detection and Ranging (LiDAR) surveying equipment. Ground movements of 23 to 30 mm were detected from a roadway repair required to fix a water main break, suggesting that both technologies are capable of detecting ground movement of this magnitude. Additionally, the LiDAR results indicated ground movements of 25 to 30 mm around a confirmed leak, however it was difficult to distinguish this area versus noise in the data set. The total station data was able to confirm the profile of the ground movement but not the magnitude (due to conflicting signs) around the confirmed leak.
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