- 30th June 2017
- Posted by: Sophie Bunker
- Category: Projects
Following the Boxing Day floods in 2015, a significant area of bank erosion occurred immediately downstream of the A6026 road bridge. The bank scour was within proximity to the highway bridge. The bridge not only carried the A6026 over the river, but also carried significant infrastructure within the highway, including data transfer services to a local data centre. The need to maintain vehicular access in the area, as well as the integrity of the services, meant that protection works were given the highest priority. Calderdale Council installed a series of 1 tonne filled bags within the scour hole as emergency works to provide a short-term method of protection. Whilst this took place a permanent solution was designed by JBA under the Engineering Framework.
The solution needed to involve the reconstruction of the failed length of bank wall, along with a method of preventing the wall from being undermined in the future. This required the design of an appropriate foundation detail and scour protection.
Several solutions were examined. The preferred option involved the installation of interlocking steel sheet piles along the top of the river bank and extending down to bedrock. The sheet piles also had the benefit of creating a temporary works cofferdam to allow excavation for the proposed Allan Block wall foundation to be completed in the dry. In addition to the sheet pile wall, a double layer of rock armour was placed within the river bed to infill the scour hole and prevent further scour.
The solution meant that the new section of wall would be fully protected from scour failure in the future. Sheet piles were also driven across the front the existing bridge apron which had become undermined as a result of the flood. The resultant void below the apron was filled with mass concrete. As the river channel is approximately 4m below the adjacent ground level, significant enabling works were required to gain access for plant. This provided a safe working area for the piling works and construction of the foundation for the Allen Block wall. The wall was then constructed and backfilled with imported granular material reinforced with layers of geo-grid.
Both the immediate temporary protection and the permanent solution helped secure an important structure. Plus, it ensured access was maintained for the public and services were maintained. This was particularly important given the extent of the damage resulting from the flood event.
In addition, the installed works reinstated an area of public open space adjacent to the canal moorings. A long-term scour protection solution was also provided to the bank with the added benefit of providing scour protection to the highway bridge by preventing any further undermining of the invert.