Method Led Design - Upgrading Lee Valley Viaduct - Span 35 over River Lee
Options for construction of the new river span were severely limited due to restricted access and buried and overhead services such that crane erection or sliding-in of a pre-fabricated span was not possible. In addition, the existing abutments were not adequate to support the increased loadings from a modern bridge carrying ballasted track. The design was therefore arranged for delivery of smaller components and piece-small assembly of the new deck at low level directly beneath the existing span on new foundations. Piles, installed using low-headroom rigs working within a portable dam, to support the heavier new steel plate girder composite deck were installed for abutment extensions in front of the existing walls. Weathering steel plate girders were delivered individually to the side of the existing bridge at low level and formed into braced pairs before being slid along the top of the pile cap. Once all steelwork was placed the deck slab, including ballast retention side walls, was constructed. After waterproofing, the deck was raised to the underside of the existing bridge using climbing jacks, two per abutment and supported on the permanent bearings fixed to the upper portion of temporary steel trestles. After piece-small demolition of the existing span climbing jacks were used to raise the deck to the final level and the trestles completed. The trestle system, once encased in reinforced concrete integral with the new piled foundations, formed the permanent new piers that were then faced with brickwork.