St John’s Hill Bridge carries the A 3036 over multiple railway tracks on the approach to Clapham Junction station. FM Conway was asked by Wandsworth Borough Council to reinforce and strengthen the current spans, allowing us to self-deliver with five of our divisions.
Our team always had the safety of the pedestrians and railway in mind. Due to the 8-tonne weight limit on the deteriorated span, FM Conway opted for lightweight, remotely operated, Brokk plant to eliminate any risks to the deck. “We had to be millimetre precise due to the existing deck infill being the wrong shape.” Says FM Conway Projects Manager, Toby Allen. Any works that might cause falling debris were undertaken at night or during a two-day track possession to prevent any risks to trains and the railway, and trackside spotters were used throughout the project.
All of the asphalt was supplied by FM Conway’s Heathrow Asphalt Plant.
The strengthening works were initially planned for just span three of the bridge, and included removing and replacing the bridge deck waterproofing, strengthening the concrete bridge deck and renewing the footway paying and road surfacing to ensure the continued structural integrity of the bridge. Once work started however, our team soon realised this was a bigger job than expected.
Project Manager, Toby Allen explains: “Once the asphalt was removed it was clear that the area of strengthening needed to be increased not only in span three but also the adjoining span two. The extent of the works increased from 84m2 to 160m2.”
The team also discovered that the centreline crown and camber was not formed by asphalt but by the bridge deck itself, requiring precision concrete to be poured at various different levels. The new concrete bridge deck needed to be reinforced and connected to the existing deck below. To achieve this, long L-bars were fixed into the beams under the bridge and two layers of steel reinforcing bars were laid in a mesh-lie formation. The new concrete was then poured around the reinforcement.
Our kerb line was removed, along with the existing waterproofing membrane, so the whole bridge deck could be waterproofed using a spray applied two-part system.
The St John’s Hill Bridge project illustrates FM Conway’s self-delivery capability with, the business’ Traffic Management division handling the bridge closure and diversions so the Structures team could take over the bridge and carry out the civil engineering works, including the concrete removal. The Surfacing division completed the planning and laid new asphalt, while the Term Maintenance division installed the new kerbs and footways, including the re-laying of the block paving. All of the asphalt was supplied by FM Conway’s Heathrow Asphalt Plant.
Even with the extra works, the combination of FM Conway’s self-delivery capability, working weekends and bringing in additional resources meant the job was finished 20% faster than the 10-week original plan.