Threading the needle

Another one of my Bob the Builder stories. This one concerns London Bridge station, a station I know well. We often travel up to London Bridge because there are lots of lovely restaurants and interesting places to explore. It is also just round the corner from where we got married.

Anyway the trainline I catch into work is one London's main North South rail routes and gets horrendously congested. Thankfully it is now being upgraded to the tune of £6 billion 

In order to relieve one of the major congestion points on this route they realised that they needed to create two new railway lines going in and out of London Bridge station. The only problem was the route of the railway lines ran via an elevated track over a bustling open air market on a series of cast iron bridges and brick viaducts. This elevated railway line passed close to a large number of listed occupied Victorian buildings. There was no room on this existing structure to take the new lines. These lines were an integral part of the upgrade and could not be put off as too difficult.

To help matters worse just 200m away Europe’s tallest building (London Shard – 87 storeys) is currently under construction. (A mere baby The Shard will only be occupied up to 72 stories – Eureka tower in Melbourne is occupied up to the 88^th storey!) 

The Shard website 

The main tower is due to be finished in 2012 after which the entire concourse for the London Bridge station will be rebuilt together with an additional mid rise office block. Because of the associated congestion with these works it was decided that the new railway lines had to be completed before work started on new concourse and associated office block. This has meant that the bridge is being constructed now which is 6 years ahead of when the rerouting of the new railway lines through London Bridge will be completed

The solution was to insert a new elevated viaduct on piles over and beside the existing buildings and build a new bridge across Southwark Road.

Among other things the builders had to lop one storey off an existing pub to allow the new viaduct to pass over. A new roof is being built for the pub and a single storey extension provided to replace the lost space. At another point the new viaduct passes within 157 mm of an existing building.

The new viaduct is supported on 8 irregularly placed piles 2.4m in diameter. These piles required a 90 tonne piling rig to drive them into the ground. The trouble was the access road used to drive the piling rig into place wasn’t strong enough to take the weight of the rig. So they had to remove the top of the road and expose the Victorian brick arches underneath so that these could be strengthened and allow the piling rig to be manoeuvred into place

Before each pile could be dug a 5m deep archaeological excavation had to be completed – one such dig uncovered a 17C delft pottery plate

One of the 2.4m piles had to be drilled into a 3m zone beside one of the tunnels for the London underground – that’s only one foot either side of the pile. The piles in another area had to be double sleeved to avoid transferring loads to the adjacent tunnel carrying one of the escalators down to the platform station. Throughout this work the tube lines running beside the new piles remained open. All the tunnels and escalator shafts were continually monitored by automatic theodolites mounted in the ceiling to measure any deflection

The 1200 tonne 71m single span truss crossing Southwark Road couldn’t be fabricated off site and trundled up the road and craned into position because a service tunnel and old cast iron water main underneath the road could not take the imposed load of the truss and multiwheeled transporters. Southwark Road was deemed to busy to allow it to be closed for the time that would be needed to strengthen the road. Another solution had to be found – this involved building the truss piece by piece on top of the new narrow viaduct 4 storeys up in the air beside an operational railway line and within a metre of an occupied building.

On April 30 it will then be winched out over the Southwark Road, rotated slightly to clear an neighbouring building and then lowered onto the waiting piles on the other side of the road. Southwark Road will only planned to be closed for one week

The market underneath has remained open 3 days a week throughout all of this work.