Case Study: Alleyn Park Bridge - Wing Walls Strengthening
Client: Network Rail
Designer: Donaldson Associates
Main Contractor: BAM Nuttall Ltd
Working closely with the Southern Zones Construction Partnership (a Network Rail/BAM Nuttall alliance), BAM Ritchies strengthened the bridge wing walls at Alleyn Park in London. The bridge carries Eurostar lines over a wide residential road.
The brick wing walls showed signs of severe distress including cracking and displacement, possibly related to bombing in WWII. Previous repairs, including the installation of tie bars, had failed to arrest movement and the development of further cracks.
The proposed strengthening comprised inclined ground anchors and waling beams with cast in situ concrete facing. BAM Ritchies was appointed to review the proposals and investigate alternative solutions. Working with designer Donaldson Associates, the condition of the wing walls was analysed and the design proposals refined to include improvement to the existing foundations, installation of additional tie bars and a concrete facing.
BAM Ritchies installed 29 300mm piles to 5m depth, reinforced with circular hollow sections.
12 ‘Double Corrosion Protected’ permanent tie bars were used, six between each pair of wing walls. The tie bars were installed using a DB100 rig to drive open-ended casing through the fill material. The casing was then cleaned using augers before coring through the brickwork and reinforced concrete in the opposite wing wall.
BAM Nuttall constructed new mass concrete footings to support the concrete facing. Temporary support to the walls was provided by propping off the piles.
A reinforced concrete facing to the wing walls was applied using a dry sprayed concrete technique, to accommodate the curved and inclined wall profile. This was carried out using Reader Spraycrete 40. The excellent quality of the surface finish meant that no additional facing was required for aesthetic purposes.
Careful attention to temporary works and sequencing enabled all of the works to be completed within the restricted site with no possessions and minimal disruption to road.