There is little margin for error for engineers working on Transport for London's 17-week Bank Station Capacity Upgrade blockade, with just a matter of days leeway to complete the work.

The 17-week Bank Station blockade on the Northern line begins in January and the contractor has now revealed that there are only “a matter of days” of float in the event of delays or complications.

Bank is the third busiest station in London, with 120M users annually and up to 100,000 per hour during rush hour. The upgrade will increase the station’s capacity by 40% with a new ticket hall, concourses and an entirely new southbound tunnel and platform. Dragados commenced tunnelling on the project back in 2017 and has been progressing without major disruption to the station’s operation.

The coming blockade will stop Northern line services on the Bank branch, between Moorgate and Kennington, for almost four months as the new tunnels are connected to the old tunnels the new platform is made functional and a new concourse created. Once the blockade is complete in May 2022, the new southbound platform and tunnels will be in operation. A new ticket hall and banks of escalators will open later in the year.

Speaking at NCE’s Tunnelling Festival about the pressure of completing the objectives within the allotted 17 weeks, Dragados tunnels manager Donal Kelly said: “We’re comfortable in what our progress rates are. There is a small bit of float in our little programme for the tunnelling.

“Once we hand over to the wider team – to do the fit out, the testing, commissioning – that’s where the real challenge is. So, there is a matter of days, maybe about seven days at the end."

He added: “But, put it this way, our programme has achieved 96% of our activities in the past. So we’re fairly confident in what we’re doing, and we like to set the bar at a reasonable level; not being too optimistic.”

Kelly also took the opportunity to fully reveal the details of the work that will be done during the 119 day blockade.

Already constructed are 1.3km of tunnels that weave around the existing station, as well as 18 connections to the existing tunnels. A temporary access shaft from Arthur Street down to the tunnels has also been constructed to allow workers, equipment and materials into the work site.

However, there are more connections to be made, particularly at the ends of the tunnels. This will be the first phase of work during the blockade, which lasts for 44 days.

During this phase, 99m of new tunnels – 55m at the south end and 44m at the north end – will be created to tie in the new platform tunnel with the existing tunnels of the northern line. The work site with all the equipment will be based within the new southbound tunnel.

The first step is to remove the rails from the old tunnel, install formwork and backfill it with foam concrete. The concrete is pumped down to the tunnels trough a hollow pile.

The 99m of connective tunnels between the new platform tunnel and the existing tunnels will then have to be excavated. Once opened up, a single pass spray concrete lining (SCL) will be installed, followed by the casting of the first stage concrete and finished with a sprayed regulating layer.

Phase two spans 19 days and will see the installation of 712m of new track. The first stage of this is to complete the track bed through the tunnel up to where it connects to the existing Northern Line.

The rails will be laid out with a tracked rail transporter and the blocks/baseplates put in place with a telehandler and mini digger. The rail will be placed on top of this and clipped in place. The track then has to be aligned to its final design position.

Concrete from the Arthur Street shaft will be put in place to shore up the track. The final stages are to install conductor rail, signalling equipment, traction power and train radio.

The project then has 11 days to demobilise the tunnelling equipment. It will first backfill the hollow pile, and the portal to the tunnel will be waterproofed and have a second lining installed. The muck chamber is the next to go, as it will be emptied and filled with foam concrete.

Finally, all plant will be removed through the 40m deep Arthur Street shaft. The shaft will then be in-filled, but a support structure has to be built and a framework erected before concrete can be poured. Once the concrete has cured, the former portal will be waterproofed.

With the construction of the tunnel then complete, the project moves on to the 39-day phase four: fitting out the platform tunnel and installing the systems. This involves removing the hoardings and protections, and putting in place the new coping stones and floor finish. Lights will also be installed in the new tunnel.

The platform will then be furnished with CCTV, staff telephones, WiFi, furniture, services speakers and advertising frames.

Concurrent to phases three and four is the 96-day conversion of the old southbound platform tunnel into a concourse. This first involves infilling the old southbound track bed to bring the floor up to the level of the concourse. Storage rooms for equipment will be created in part of the old tunnel.

Mechanical, electrical, public health and comms installations will be completed before architectural finishes are applied and signage and furniture are installed.

Finally, 42 days are allotted for phase five, where Dragados hands over to TfL and third parties carry out all the testing, commissioning and systems integration. The station staff will also be given time to familiarise themselves with the new station.

With all running smoothly and the seven days of float being sufficient to sustain any delays, the new southbound tunnel and platform will open for operations in mid-May.

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Tagged with: Bank station Bank Station Upgrade Programme Dragados TfL

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