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Geobag Stability for Riverbank Erosion Protection Structures
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- Author / Creator
- Thompson, Angela
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Erosion along the banks of the Brahmaputra River in Bangladesh and India leads to both the loss of infrastructure and land, consequently forcing many of those who live along the riverbanks into poverty. Because of the limited availability of hard materials that are traditionally used to protect riverbanks, such as rock, geotextile sand filled bags (geobags) have emerged as an economic solution to this devastating problem. Over the last twenty years geobags have been used to create revetments which have begun to systematically stabilize large reaches of the Brahmaputra river system. Geobags are required to be stable against current loading in order to avoid failure of these erosion preventing structures, which can be many kilometers long. While flexible geobags have been studied extensively for coastal applications, there are limited studies regarding their stability in rivers. This study was designed to address the problem: when do geobags undergo incipient motion under current loading? Using a combination of physical and numerical models, this study approached the problem of incipient motion via the method of permissible velocity, as well as, the method of critical shear stress. The physical model study, performed at Northwest Hydraulic Consultants laboratory in Vancouver, Canada, used scaled geobags which are large enough to replicate the flexibility of the bags used in the field. Results from the physical model study were used to improve the current sizing formula by using the thickness rather than the cube root of the volume as the characteristic diameter. Additionally, the stability coefficient was suggested to be a function of the filling percentage of the geobags because the stability of the bag appears to be dependent on the flexibility and fill of the bag. The physical model study was recreated in a three dimensional numerical model, which was then used to find the shear stresses on the geobag surface. There was not enough data to confidently find a Shields parameter for geobags to use in a design capacity; however, first results imply the value to be around 0.09. These first results also imply that the Shields parameter varies with fill percentage of the geobags.
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- Subjects / Keywords
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- Graduation date
- Fall 2019
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- Type of Item
- Thesis
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- Degree
- Master of Science
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- License
- Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.