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.
The fish pass is essential for the rare migratory fish species known as Shad, to travel to their natural spawning grounds up river, and will also benefit other varieties of migratory fish i.e. salmon and lamprey. The project is seemingly one of the largest river restorations of its kind ever to be attempted in the UK.
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 principle framework contractor Kier Group, to deliver a pre-design package of works, including and notwithstanding, 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 scheme of works on site included establishing site access and compounds upstream of the weir. The construction of a small slipway and offloading point, and the installation of a large temporary dam structure within the river, were also required to prevent water ingress into the works area.
Land & Water instructed DYWIDAG’s preferred specialist drilling contractor M&J Drilling Ltd to install 318no. R32-250 hollow bar soil nails, within the pre-prepared cut slope to the west of the down-stream weir area. The nails were, on average, drilled into 9mtr of the cut: this area of the river embankment had a history of slope failure, so within the temporary works design, a ‘nailed retention’ solution was specified.
DYWIDAG R32 76mm dia. arc shaped button carbide drill bit EYY was specified, to enable the tough, dense gravels to be drilled through, 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 8no. ‘soil nails’, Suitability’ tested up to 118kN loadings. This met the client’s design specification, after checking the data reference against the working load, which had been originally specified within the initial ULS of the design. A lot was resting on the structural integrity of the ‘nailed cut’, as it would ultimately form part of the overall ‘fish pass’ structure.