Over the weekend of the 15 - 18th September, a major milestone in the delivery of the London Underground Northern Line Extension (NLE) was achieved. Having constructed the enlarged tunnel around the existing cast iron lined tunnel of the operating Northern line tunnel (Charing Cross branch), at each of the two locations where the NLE connects with the current railway, the existing cast iron tunnel rings were removed above existing track level. The newly created enlarged sections of tunnel, known as step plate junctions, then became integral in the operating Northern Line.
The removal of the existing Kennington loop cast iron tunnel rings, which were built in 1926, required this section of the Northern line to be put out of service for 52 hours over separate weekends for NLE works to be done. Two such weekends were set for removing existing linings.
A particular challenge in the planning process was determining how the existing tunnel rings were to be removed. The lifting operations were complex so it was imperative to ensure the majority of the operation was mechanised to reduce the level of risk involved. During the months leading up to the work, the methodology was developed with the team involved at the workface and BIM was used to model the step plate junction area and lay out the plant locations.
At 00:45 hours on Saturday 16 September, the break in service began. There was a fantastic collaborative effort by the whole team; FLO, designer, subcontractors, London Underground (LUL) project and operational staff and the TfL engineering team ensured that the possession was taken safely and the worksite was adequately protected. The team of 120 people worked in shifts throughout the weekend to maintain the works nonstop for the 52 hours. The final segments were removed from the tunnel at 00.30 hours on the Monday morning.
Once all the rings had been removed, the worksites were cleaned of all debris, extraneous metalwork and dust. LUL track inspectors confirmed the loop was safe to run trains through and signalling technical officers ensured that the system was correctly reinstated. The possession was handed back to the Northern line controller at 0320 on Monday 18th September.
As a result of the huge planning effort and some fantastic teamwork, 220 tonnes of old tunnel rings were successfully dismantled in a single weekend possession (101 rings at Kennington Park, 117 at Kennington Green), without any incident. There were no injuries of any sort and no damage to any plant and equipment. Early engagement with the local community ensured that the works were completed without complaint or disturbance. This was outstanding.
David Darcy, Project Director, said “Reflecting on the first possession of the Kennington loop and the many months of planning in the lead up to this project milestone, it is amazing to appreciate the achievements of the team, as well as seeing how our people have grown, overcoming challenges. This is a huge landmark for the Northern Line Extension, achieved with the highest regard for the health and safety of every team member. This, for me, is a most satisfying aspect of this complex operation – not one incident, no-one with even a scratch in difficult handling of 220 tonnes of cast iron. I sincerely thank everyone involved, from FLO, the supply chain and LUL, for their hard work, exemplary collaboration and dedication to safety in completing this key piece of work over this September weekend. The exemplary performance in that single weekend means further weekend possession time that had been provided for the dismantling work is now used for preparatory works for the 10 days blockade at Christmas, reducing the risk involved in the intense works to be done in those 10 days.”