UBC Undergraduate Research

"Forest bridge design and scour potential" Ebadi-Angorani, Amir

Abstract

Scouring is the removal of sediment materials such as sand or rock which are used to support the foundation of bridge structures through rapidly moving water over time. Scour prevention depends on the proper design, construction and maintenance of a bridge. This process involves the experience and knowledge of professional foresters and professional engineers. When selecting the type of bridge and the site in which it will be built in, professionals will need to consider factors that lead to scouring. The bridge structure influences scour by obstructing a water way channel with sections such as the abutments and pier. The abutments and piers of bridge structures narrow the channel by reducing the cross sectional area in which water will flow. This consequently increases the velocity of water as narrowing occurs to pass through an obstructing bridge structure. High water velocity as well as volume during flooding events leads to scouring through hydraulic forces such as the formation of horseshoe and wake vortex at the foundations of bridge structures, specifically piers. The constant hydraulic forces against the bridge can remove bedding material that the structure’s foundations are set on. Over time, the excess removal of underlying material such as soils and rocks through scouring will weaken the foundations of the bridge, making it lose stability and eventually leading to collapse. To decrease bridge vulnerability to scour, professional can take several countermeasures. The site where the bridge is desired needs extensive and careful assessments of the physical characteristics of the stream and its impacts on the existing bedding material. Using measurement and calculation based methods such as the erodibility index method (EIM), the vulnerability of the bedding material to scour can be found. Technological devices such sonar, the rotating erosion rate apparatus (RETA) and the scour erosion rate flume (SERF) used to assess scour vulnerability can help design a more cost-efficient bridge, but they have limitations such as operability at a large scale. Periodic inspections of bridges are also necessary to ensure safety and operability. Inspections would be optimized for data collection and observations if done during flood events, but safety precautions require inspections to occur after flood events. Inspections can happen from the bridge or by underwater diving, but underwater diving has limitations such as visibility, hazardous floating debris or aggressive water flow that deem it unsafe.

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Attribution-NonCommercial-NoDerivs 2.5 Canada

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