Structural Bio-Engineering at Magdelen
This project was to replace a failing hard revetment on the banks of the River Cherwell where it runs through the historic Fellows Gardens, part of the grounds of Magdalen College.
The existing timber and concrete revetment had failed in several places and was collapsing into the river. Aside from age the principle cause of the problem was the large population of Signal Crayfish present in the river burrowing into the soft banks weakening them, increasing erosion, undercutting of the bank and collapse.
Due to the depth of the water and the crayfish burrowing a hard structural revetment was required below water level but what was on view above was designed to be much more in keeping with the beautiful and historic surroundings.
Due to the historical significance of the gardens and the very restricted access the works were carried out from a modular pontoon craned into the river in pieces and assembled. Large tracked plant for pile driving along with the sheet piles and other materials were then loaded onto the pontoon from a temporary loading dock constructed on the river bank.
The new sheet piles were driven to just below mean water level and the old concrete revetment was then removed, broken up and recycled as fill behind the sheet piles along with imported free draining crushed stone.
A stone filled gabion basket was used as the interface between the backfilled sheet piles and the ʻgreenʼ revetment above.
The ʻgreenʼ revetment was achieved using a reinforced earth design consisting of parcels of compacted, consolidating fill material including a degree of organic material such as topsoil which are faced with pre-established wildflower turf, very in keeping with the neighbouring water meadow famous for itʼs fritillaries!
