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Estimating the mechanical contribution of willows and balsam poplar in soil bioengineering projects in Alberta
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- Author / Creator
- Ishii, Cassio
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After the floods in 2013 in Alberta, the effort towards reducing the impact of conventional approaches on the environment and improving the desirable effects of vegetation protecting the water bodies has been an increasing trend in most cities. Soil bioengineering designs with fast-growing plants and natural or synthetic support materials for reinforcement and reducing soil erosion have been becoming common alternatives to conventional engineering to treat streambank failures, banks where pipelines cross water bodies and road rehabilitation among other applicatio. Moreover, recovery of riparian vegetation with these techniques has increased in the last decades in response to concerns over water quality, fisheries, wildlife, flooding damages and aesthetics. However, despite the policies promoting greener solutions, the lack of precise technical information about the effect of plant roots on soil strength and the associated uncertainties means engineers are resistant to recommend the use of soil bioengineering, and then maintain the preference for conventional approaches even where soil bioengineering is appropriate. Therefore, the move from the use of traditionally “hard” elements to “greener solutions” as a functional material in streambank soil stabilization has been challenging for decision makers.
The focus of this study was to quantify the strength provided by roots of species commonly used in soil bioengineering projects in Alberta, such as willows (Salix spp) and balsam poplar (Populus balsamifera).
We built a large-scale shear box to validate models calibrated with data from the mentioned species. We also assessed root architecture and strength variation, often called ‘biological uncertainties’ under engineering perspectives. The results indicated that the mechanical contribution to the soil stabilization of mature willows (Salix spp) and balsam poplars (Populus balsamifera) assessed increased the soil cohesion up to around 0.3 m deep, where we found the majority of roots. The large-scale direct shear tests suggested that Fiber Bundle Model (FBM) and Wu and Waldron Model (WWM) consistently underestimated the total force from the plant roots.
Systems to calculate slope or streambank stability that includes models for plant root contribution should incorporate factors of strength variation so they can help us move beyond overly conservative factors of safety and provide engineers with the data required to make informed decisions about the strength of soil treated with soil bioengineering. -
- 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.