Longitudinal Bending and Failure of GFRP Pipes Buried in Dense Sand under Relative Ground Movement

Pipelines extend thousands of kilometers for transport and distribution of oil, gas, and other chemical products. With the ever persistent challenges often faced with corrosion, relative rigidity, and other issues characteristic to steel pipes, the need to explore the use of new pipeline materials, such as glass fiber-reinforced polymers (GFRP), increases. The pipe-soil interaction and the longitudinal behavior of such pipes resulting from relative ground movements is poorly understood. In this study, a series of GFRP pipe bending experiments have been conducted on 115-mm-diameter and 1,830-mm-long GFRP pipes buried in dense sand. The pipe ends were pulled by two parallel cables attached to a spreader beam outside the test region, which was pulled by a hydraulic actuator. The study investigated the effect of laminate structure of pipe, including a cross-ply and angle-ply laminates, on the strength, deflections and failure modes, at different burial depth-to-diameter (H/D) ratios of 3, 5, and 7. Results were also compared with steel control pipes of comparable dimensions and pressure rating. The peak load was shown to increase as burial depth increases, and was generally associated with soil failure, except for the angle-ply pipe at H/D=7 that experienced a structural failure. At peak loads, the net deflections of GFRP pipes were 4-7.5 times those of the equivalent steel pipes, with the cross-ply pipes being stiffer than angle-ply pipes.