Experimental Evaluation of Internally Pressurized GFRP Pipes Subjected to Vertical Ground Slip

While glass fiber-reinforced polymer (GFRP) tubes have emerged as a corrosion-resistant alternative to buried steel pipelines, they are not as well understood or widely used. This study examines the response of ±55° angle-ply filament-wound GFRP pipes to ground deformations in the form of vertical fault offset. Full-scale tests were conducted on 5.65-m-long buried pipes of 141-mm diameter (D) and 4.1-mm wall thickness (t), with internal pressures of 300 and 1,000 kPa, and results were compared with an identical unpressurized pipe from a separate study. A special 7.3 × 1.8 × 1.8-m split-box apparatus able to simulate a vertical fault plane at the midlength of the pipe with up to 120-mm offset was employed. Strain gauges and optical fibers were used to construct lengthwise and circumferential strain profiles. The GFRP pipes withstood a fault offset of 110 mm (0.8D) before failing in the form of pressure loss due to pipe weeping after GFRP matrix cracking. The total length of the pipe subjected to curvature and bending was only 2.85 m (20D) in the vicinity of the fault, a length apparently independent of fault offset and internal pressure. The maximum curvature occurred on the stationary side, about 1.4D–2D from the fault line. This curvature was 43%–70% higher than the peak curvature on the moving side. The internal pressure of 1,000 kPa resulted in 25% and 35% reductions in peak curvatures at the stationary and moving sides, respectively. Upon excavation, tension failure was apparent at the crown (the point at the top of the circular pipe cross section) on the stationary side of the pipe, and compression failure, also at the crown, was observed on the moving side. These locations correspond to the estimated locations of peak curvature.