A47 Longthorpe Footbridge
This TensarTech structure combines complex geometry and lightweight fill to create wheelchair friendly shallow access ramps within a very restricted space, constructed with minimal disruption, and without the need for expensive foundation works.
Benefits
- No piles or deep foundation required due to the use of reinforced structures with lightweight structural fill
- Major road remained open throughout - construction of the TensarTech TW3 walls required no deep excavation, enabling the A47 to remain open
- Fewer trees removed due to the compact construction footprint made possible by the zigzag ramp design and construction method
- Aesthetically attractive structure - important for this large, highly visible structure in a residential area.
The existing footbridge had become costly to repair. National Highways decided on a replacement and committed to improve accessibility for cyclists, walkers, and wheelchair users. The site contained mature trees and the client wanted to remove only the minimum that was necessary. Ground conditions were variable, the potential for differential settlement between the ramps and piled abutments was a concern. In addition to this, the busy A47 had to be kept open throughout as well as the exiting footpath, due to the bridge being heavily used by school children and their parents. The site was very restricted as only two sides of each ramp had good access to build the walls.
TensarTech TW3 wall construction was adopted to support the access ramps. Using a zigzag geometry, 3.5m wide ramps were built with a gentle 1:20 gradient, all within a very tight construction footprint. By using lightweight aggregate for the reinforced fill, bearing pressure was minimised, avoiding the need for deep excavation or piled foundations.
