Uplift Capacity of Reinforced Buried Pipelines on Sand

Priscila Cardoso Santiago, Fernando Saboya Jr., Rodrigo Martins Reis, Sérgio Tibana

In the proceedings of: GEO2011: 64th Canadian Geotechnical Conference, 14th Pan-American Conference on Soil Mechanics and Geotechnical Engineering, 5th Pan-American Conference on Teaching and Learning of Geotechnical Engineering

Session: Buried Structures & Subsurface Systems

ABSTRACT: The use of buried pipelines in urban areas has experienced impressive growth during the last decades. This has happened mainly because the high demand for basic services has forced the expansion of the pipeline nets which transport gas, oil, communication and electrical cables amongst others. The main reasons for the use of buried pipelines for such services are the low installation costs, low environmental impact and protection of the facilities. However, the success design of buried pipelines is highly dependent on the good knowledge of the soil x pie interaction mechanism and also on the knowledge of the risks involved during their lifetime. This work has as the main aim to study the behavior of buried pipelines regarding their resistance against the uplift and, therefore, to come up with a proposal for a new anchoring system in order to avoiding these upwards movements, using geogrid reinforcement. Therefore, this paper has as the main aim to show results from a study carried out on reduced scale buried pipeline in geotechnical centrifuge, where a special and innovative anchor using geogrid, is proposed. The study was conducted using the UENF geotechnical centrifuge at 10G. Two different relative densities were considered for the sandy backfill (23 and 70%). Also, two different reinforcement widths attached to the pipelines were considered. The pipelines were tested at three different depths. Therefore, a total amount of 24 tests were carried out. For each test using reinforced pipeline an adjacent unreinforced pipeline was also pulled out in order to allow a direct comparison to each other. The results have shown a high efficiency of the proposed anchoring system due to the changing in the failure mechanism avoiding, thus, the soil grain flow around of the pipe. This is particularly significant for pipelines buried at shallow depth in loose soil

RESUMEN: El uso de tuberías enterradas en las zonas urbanas ha experimentado un crecimiento impresionante durante las últimas décadas. Esto ha ocurrido principalmente debido ala gran demanda de servicios básicos que ha obligado a la expansión de las redes de gasoductos de transporte, combustibles, cables eléctricos y de comunicación, entre otros.Las razones principales para el uso de tuberías enterradas son los bajos costos de instalación,el bajo impacto ambiental y protección de estos servicios. Sin embargo, El éxito del proyecto de tuberías enterradas depende en gran medida del dominio y conocimiento de los mecanismos de interacción del suelo y la tubería, también como, de los riesgos durante su vida útil. Este trabajo tiene como principal objetivo estudiar El comportamiento dela stuberías enterradas en lo que concerniente ala resistencia contra las fuerza de izamiento, para proponer un sistema de anclaje con refuerzo de geomalla con el finde evitar el levantamiento de las tuberías. Por lo tanto,este trabajo muestra los resultados Del estudio llevado a cabo em escala reducida em centrifugadora geotécnica de tuberías enterradas, donde fue utilizado un sistema innovador de anclaje mediante geomalla. El estúdio se realizo em la centrífuga geotécnica de la UENF a 10G. Fueron considerados dos densidades diferentes de arenas para El relleno (23y70%). Además fueron considerados dos anchos diferentes de refuerzo unido alas tuberías. Las tuberías fueron enterradas a diferentes profundidades. Por lo tanto, el número total de ensayos fueron de 24. Para cada ensayo de izamiento realizado con la tubería reforzada, también fue ejecutado otro con solamente la tubería, esto con el fin de permitir una comparación directa entre sí. Los resultados han mostrado una alta eficiencia del sistema de anclaje propuesto debido a los cambios en los mecanismos de ruptura, así como, del flujo de granos de arena al rededor de la tubería. Esto es particularmente significativo para las tuberías enterradas a poca profundidad en terrenos sueltos o poco compactados 1. INTRODUCTION In the last decades several studies have been conducted to investigate the geotechnical and structural behavior of buried pipes. Geotechnical studies have been almost all concerned to type of soils, embedment, backfill compaction, buckling amongst others (Katona, 1988; Phares et al. 1998, Rogers, 1988, Rogers, 1987; Conrad et al. 1998). Nowadays these studies are mostly directed to a better understanding of the failure mechanisms when these pipes are subject to upward movements (White et al., 2000, Cheuk et al, 2008). Pipes transport a great variety of products with different characteristics, densities, pressures and temperature. Therefore, the pipe is submitted to efforts which depend on what product is being transported. However, most important pipelines in the world transport basically gas and oil. These pipelines are generally buried for safety reasons which encompass mechanical and thermal protection. On the other hand, they are light in relation to the weight of the backfill and, thus, are prone to suffer upward movements due to uplift forces that come from temperature gradient or groundwater rising. There are a group of problems related to the stability of pipelines when subject to uplift forces. For that reason

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