The Response of Glass Fibre Reinforced Polymer Pipe Subject to Longitudinal Bending in the Form of Vertical Ground Deformation

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Williams, Jan
Permanent Ground Deformation , Buried Pipeline , Pressurized Pipe , Normal Fault , Glass Fibre Reinforced Polymer , Full Scale , GFRP Pipe
Glass fibre reinforced polymer (GFRP) pipe is a light weight alternative to steel pipe for oil and gas distribution pipelines that is corrosion resistant but whose material properties vary based on production technique and whose failure mechanisms are not well understood. These pipelines may cross through unstable terrain and be subject to flexural bending caused by ground motion causing split and leakage of their contents into the environment. This study examines the response of GFRP pipe to permanent ground deformation and the failure mechanisms exhibited by GFRP material. A series of full-scale tests were performed using the Split Box at the Queen’s University GeoEngineering Laboratory, a facility that can simulate a normal ground fault to mimic permanent ground deformation. Three 5.6 m long GFRP pipe segments were pressurized to zero, 300, and 1000 kPa respectively and subject to 120 mm of differential settlement, causing longitudinal bending at the crown and invert near the fault line. Fibre optic sensors installed longitudinally along the length of the buried samples reveal zones of peak strain and curvature. These zones located on either side of the fault line are shown to be asymmetrical with higher strains recorded on the stationary side of the fault line. The position and magnitude of peak curvature zones changed with increased pressure, shifting further away from the fault line with decreased curvature. The samples did not reach an ultimate limit state, however at 110 mm fault offset the buried pipe wall split resulting in water leaking at the peak curvature zones and pressure loss. Three four-point bending tests were also performed on similar pipe segments 1.8 m long. The flexural tests were used to establish a relationship between curvature and moment for the GFRP pipe which was then used to estimate the lengthwise moment distribution of the buried samples. Comparisons were also made to the flexural responses of the buried pipe.
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