Mitigation of pipeline uplift ratcheting in silty sand

Ryan Phillips, Andrew Cuff, Sylvia Bryson, Rodney McAffee, Michael Martens

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Infrastructure

ABSTRACT: of pipeline uplift ratcheting in silty sand Ryan Phillips, Andrew Cuff, Sylvia Bryson, Rodney McAffee C-CORE, St, John's, NL, Canada and Michael Martens TransCanada, Calgary, AB, Canada ABSTRACT The soil response around a high temperature pipeline proposed for construction in northern Alberta was evaluated. A medium-scale laboratory model testing program was used to gain a better understanding of the thresholds at which silty sandy backfill infilled around a pipeline when subjected to cyclic upward loading. Soil movement fields were identified. Various mitigation techniques were evaluated in order to both delay and reduce the net downward soil movement from pipe displacement cycles. RÉSUMÉ La réponse du sol entourant un pipeline à haute température qui est proposé pour construction au nord de l'Alberta a été évaluée. Un programme de tests de laboratoire à moyenne échelle a été effectué afin de mieux comprendre les limites pour lesquelles le remblai limoneux sablonneux se dépose autour du pipeline lorsque ce dernier est soumis à un chargement cyclique vertical et dirigé vers le haut. Les champs de mouvements du sol on été identifiés. Plusieurs mesures de mitigation ont été évaluées dans le but de retarder et de réduire le mouvement vertical net du sol dirigé vers le bas causé par les déplacements cycliques de la conduite. 1 INTRODUCTION The soil response around a high temperature pipeline proposed for construction in northern Alberta was evaluated. A unique field testing program was conducted to gain a better understanding of the engineering properties of the backfill material placed in the trench around a pipeline when subjected to cyclic thermal loading, McAffee et al. (2014). A horizontal plate load test was used to measure the strength and stiffness of backfill materials to improve the predictions related to pipe restraint and movements. The thermal cycling of the proposed pipeline may also cause infilling under the pipeline and its upward ratcheting during successive vertical movements. Neilsen et al. (1990) report the failure of an offshore buried pipeline from upheaval buckling that was likely initiated by thermal cycling ratcheting. They proposed a limit of 20 mm upward movement during each thermal cycle to prevent such failures. Finch (1999) and Cheuk et al. (2008) assessed such upward displacement limits from medium scale physical model tests for infilling during large upward monotonic motions. Thusyanthan et al. (2011) considered the limited information available on upward ratcheting to propose regimes for ratcheting based on pipeline diameter and upward mobilisation of pipe, Figure 1. Their proposal was based on the geometry of the angle of repose of soil in the void created under a pipe for a given upward movement. A medium scale physical modelling program was undertaken to assess the onset of infilling under small vertical cyclic movements, and the consequential loss of subsequent uplift shear resistance. Two mitigation strategies using geotextile and geofoam were also evaluated. A subsequent program also evaluated the latter strategy for mitigation of infilling by cyclic lateral movements. Figure 1. Proposed regimes for ratcheting, Thusyanthan et al, (2011). 2 MODEL TESTING PROGRAM A one-third scale test was made of the proposed 762 mm outside diameter pipeline with 2 m of submerged soil cover. The pipe was simulated using a 254 mm PVC pipe. The model PVC pipe system had a specific gravity of 1.09 as compared to the proposed bitumen filled coated pipe system of 0.83. Axial feed in of the pipeline into bends may be reduced by roughening the outer HDPE on the straight line pipe outside of the bends. Smooth and sand-coated rough model pipe sections were used to simulate the different HDPE pipe external coatings. The test tank is about 0.9 m square in plan and 0.75 m deep, as shown in Figure 2. The 2 acrylic viewing windows are about 0.53 m by 0.5 m. The soil cover was slightly less than the targeted equivalent of 666 mm submerged soil cover due to spatial restrictions of the test

RÉSUMÉ: ation of pipeline uplift ratcheting in silty sand Ryan Phillips, Andrew Cuff, Sylvia Bryson, Rodney McAffee C-CORE, St, John's, NL, Canada and Michael Martens TransCanada, Calgary, AB, Canada ABSTRACT The soil response around a high temperature pipeline proposed for construction in northern Alberta was evaluated. A medium-scale laboratory model testing program was used to gain a better understanding of the thresholds at which silty sandy backfill infilled around a pipeline when subjected to cyclic upward loading. Soil movement fields were identified. Various mitigation techniques were evaluated in order to both delay and reduce the net downward soil movement from pipe displacement cycles. RÉSUMÉ La réponse du sol entourant un pipeline à haute température qui est proposé pour construction au nord de l'Alberta a été évaluée. Un programme de tests de laboratoire à moyenne échelle a été effectué afin de mieux comprendre les limites pour lesquelles le remblai limoneux sablonneux se dépose autour du pipeline lorsque ce dernier est soumis à un chargement cyclique vertical et dirigé vers le haut. Les champs de mouvements du sol on été identifiés. Plusieurs mesures de mitigation ont été évaluées dans le but de retarder et de réduire le mouvement vertical net du sol dirigé vers le bas causé par les déplacements cycliques de la conduite. 1 INTRODUCTION The soil response around a high temperature pipeline proposed for construction in northern Alberta was evaluated. A unique field testing program was conducted to gain a better understanding of the engineering properties of the backfill material placed in the trench around a pipeline when subjected to cyclic thermal loading, McAffee et al. (2014). A horizontal plate load test was used to measure the strength and stiffness of backfill materials to improve the predictions related to pipe restraint and movements. The thermal cycling of the proposed pipeline may also cause infilling under the pipeline and its upward ratcheting during successive vertical movements. Neilsen et al. (1990) report the failure of an offshore buried pipeline from upheaval buckling that was likely initiated by thermal cycling ratcheting. They proposed a limit of 20 mm upward movement during each thermal cycle to prevent such failures. Finch (1999) and Cheuk et al. (2008) assessed such upward displacement limits from medium scale physical model tests for infilling during large upward monotonic motions. Thusyanthan et al. (2011) considered the limited information available on upward ratcheting to propose regimes for ratcheting based on pipeline diameter and upward mobilisation of pipe, Figure 1. Their proposal was based on the geometry of the angle of repose of soil in the void created under a pipe for a given upward movement. A medium scale physical modelling program was undertaken to assess the onset of infilling under small vertical cyclic movements, and the consequential loss of

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Ryan Phillips; Andrew Cuff; Sylvia Bryson; Rodney McAffee; Michael Martens (2014) Mitigation of pipeline uplift ratcheting in silty sand in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper388,author = Ryan Phillips; Andrew Cuff; Sylvia Bryson; Rodney McAffee; Michael Martens,title = Mitigation of pipeline uplift ratcheting in silty sand,year = 2014}