- 1st November 2018
- Posted by: Sophie Smith
- Category: Blog
Andy Collier, Principal Engineer, was at the University of Exeter yesterday for the RAMB dissemination workshop. Looking at the assessment of debris related scour risks to bridges, the event covered the approach and other findings from an Engineering and Physical Sciences Research Council (EPSRC) funded project. Below, Andy highlights his takeaway points of the event.
When looking at risk assessments for masonry bridges, debris is a major factor in bridge failure as scour, lateral and uplift forces are increased.
Kevin Dentith, from Devon County Council, noted that it is not uncommon to have up to 500 tonnes of debris up against one bridge at any one time. This does seem pretty high to me, although his photos were compelling. He determined the worst time for debris build up to be late summer – around July/August.
Assessing debris-induced scour
Dr Mohsen Ebrahimi went on to discuss assessing debris-induced scour. He commented that debris can increase scour depth by 2 to 3 times and that the area scoured is also significantly increased. He believes surface debris causes more scour than submerged debris and has tested non-flood flows that he defined as ‘subcritical at or within the structure.’
Sketches that I took are shown (indicative only) and highlight the impact of floating debris and scour depth. Grey = scour depth/area.
Dr Ebrahimi further went on to suggest that floating debris could be modelled as spanning between the soffits of a multi-span bridge for one pier only. For a short span single arch, it would be full width. For submerged debris, such as a piled-up wood dam, you’d use a single arch.
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