Hollow Bar DYWI Drill Soil Nails stabilize an embankment on the River Severn
As part of the project known as ‘Unlocking the Severn’, Land & Water Ltd constructed one of the four fish passes along the River Severn in Worcestershire. DYWIDAG supplied DYWI Drill Soil Nails to stabilize the embankment.
Context
The project is one of the largest river restorations of its kind ever attempted in the UK. The fish pass is essential for the rare migratory fish species known as Shad to travel to their natural spawning grounds upriver. It will also benefit other varieties of migratory fish, such as salmon and lamprey.
Funded by the National Lottery Heritage Fund and the European Union LIFE programme, ‘Unlocking the Severn’ also aimed to deliver ambitious heritage, educational, and science programmes.
The environmental engineering company ‘Land & Water Ltd’ was instructed by the ‘Canal & River Trust’ and the principal framework contractor, Kier Group, to deliver a pre-design package of works, including, but not limited to, the construction of a large, deep, vertical slot within the river boundary to enable the construction of a fish pass at Holt Weir.
Land & Water’s on-site scheme of works included establishing site access and compounds upstream of the weir. The construction of a small slipway and offloading point, as well as the installation of a large temporary dam structure within the river, were also required to prevent water ingress into the works area.
Solution
Land & Water instructed DYWIDAG’s preferred specialist drilling contractor, M&J Drilling Ltd, to install 318 R32-250 hollow bar soil nails within the pre-prepared cut slope to the west of the downstream weir area. The nails were, on average, drilled 9 meters into the cut. This area of the river embankment had a history of slope failure, so a ‘nailed retention’ solution was specified within the temporary works design.
The DYWIDAG R32 76mm diameter arc-shaped button carbide drill bit EYY was specified to drill through the tough, dense gravels in order to reach a socket within the layers of mudstone further back into the embankment. This is typical geology for the banks of the Severn in this location.
DYWIDAG’s testing services completed suitability testing on eight soil nails, with loads up to 118kN. This met the client’s design specification, after verifying the data reference against the working load originally specified within the initial ULS of the design. Much depended on the structural integrity of the ‘nailed cut,’ as it would ultimately form part of the overall fish pass structure.
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