Stability of Buried Steel and Glass Fibre Reinforced Polymer Pipes Under Lateral Ground Movement
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As vast networks of high pressure buried energy pipelines traverse North America and other continents, the stability of such essential buried infrastructure must be maintained under a variety of earth loading conditions. The pipe-soil interaction and the longitudinal behaviour of buried pipes due to relative ground movements is poorly understood. This thesis presents full scale testing and numerical modeling of steel and Glass Fibre Reinforced Polymer (GFRP) pipelines to better understand the flexural performance of buried pipes subjected to lateral earth movement. For the experimental phase of the study, a series of pipe bending experiments have been conducted on 102 mm nominal diameter and 1830 mm long steel and GFRP pipes buried in dense sand. Pipe loading was carried out by pulling pipe ends using two parallel cables attached to a spreader beam outside the test region, using a hydraulic actuator. The different tests covered burial depth-to-diameter (H/D) ratios of 3, 5 and 7. During the steel pipe testing phase, special consideration was given to assess the effect of boundary limits, friction within the pulling mechanism, and consistency of results using repeated tests. For the GFRP pipes, the experimental work investigated the effect of the laminate structure of the pipes, including both cross-ply and angle-ply laminates. Test results showed that burial depth significantly influenced the ultimate pulling forces, longitudinal strains, and pipe net deflection at mid-span. The results were also compared between the two types of pipes. The failure mechanism for all tests was consistently governed by soil failure, except for the angle-ply GFRP pipe that failed at a burial depth of H/D=7. For the numerical analysis, the study presents the development and verification of two and three-dimensional numerical models including material constitutive models for both the pipe and for the soil using a stress-dependent modulus. Calculations are presented for different burial depths and are compared to experimental data. It was shown that the numerical model can successfully capture the pipe-soil interaction behaviour for both pipe types in terms of load-displacement responses and net bending deflection. Also, the effect of material variation and laminate structure were in agreement with test data.