By Michael Rothenborg
Here’s a paradox: When cities strive to solve congestion problems, the problems only worsen while the cities
try to solve them. Repairing a road or a railway usually means shutting it down – fully or partially – causing even more congestion for months or even years.
This is why rail and road authorities the world over are increasingly demanding that daily traffic must continue to flow while existing infrastructure is upgraded.
Three cases from Europe’s most congested city, London, show that such smooth operations are possible.
When Langdon Park Station on the Docklands Light Railway needed to be upgraded as a central part of a regeneration plan, precast and prefabricated elements were constructed to fit around the existing train line and thus keep the station operating throughout the project.
Designing the platforms, a new footbridge and the lifts required careful planning and 3D modelling to ensure the geometric fit of the different elements. To reduce the foundation works, engineers modified the footbridge at an early stage, thus saving substantially on steelwork tonnage.
Ramboll is also involved in a similar, still on-going rail project, the Bermondsey Dive Under – a key component of the Thameslink project to make London Bridge station more accessible, reduce congestion and increase passenger capacity by 50%.
The dive-under project involves untangling the old track on the approaches to London Bridge, the key technical challenges of which are to develop designs that minimise disruption to the live railway and coordinate with the existing structures.
Yet another example is the refurbishment of the Hammersmith Flyover, a vital link in West London, carrying over 70,000 vehicles per day. The post-tensioning system had suffered significant erosion that threatened to close the flyover unless the system was repaired. This is probably the first time an all-new, pre-stressing system has been installed in a bridge where the original could not be removed. Here too, planning and 3D scanning eliminated programme and safety risks, speeding up repairs and thus minimising disruption to the public.
Managing Director Paul Bottomley from the post-tensioning sub-contractor Freyssinet calls the work in this complex, EUR 130-million programme unique:
“Fully replacing all the old post-tensioning without first removing it on such a significant structure is truly impressive,” he says.