|Project:||Bank Capacity Upgrade Project|
|Client:||London Underground; Main Contractor: Dragados|
Project in focus
The two main objectives of the Bank Station Capacity Upgrade project with London Underground were to increase capacity at the station and minimise journey times. They would do so by, they would do so by installing a new station entrance, three ticket halls, six lifts. 10 line platforms, 15 elevators. Added to this were two 94m travelators allowing step free access and a 570m tunnel and platform for the Northern Line.
Working for Dragados our role was the creation of a 570m tunnel for the Northern Line. This tunneling works would reduce the planned closure of the line by 5 weeks. To achieve this we had to control flows and articulate 11 joints inside Low Level 2 sewer beneath the station to allow it to move without being damaged when tunnelling commenced. Access was only possible through a 600mm manhole and down a 20m shaft. We couldn’t use traditional stoppers to control flow due to access problems & flow rates. Also sustained rainfall was a major risk with a serious possibility that emergency evacuation would be needed. Of course the issue of Silt build-up was very problematic. Finally with everything else also going on we had to Adhere to a very strict schedule of works.
Planning & Works
From the very start extensive planning and meetings were held to make sure that everything would run as smoothly as possible.
By constructing 11 articulation joints in a 70m long section of the Low Level 2 sewer, with a further 2 joints in the connecting cascade prevented damage to the sewer. Steel cages and geotextile liner were also put in at various locations to address the risk of existing sewer lining spalling. For the danger of water build up rubber seals were fitted over the top of each joint and secured with steel bands to provide a flexible seal that will prevent both infiltration and exfiltration. A 600mm diameter free-in-air UV liner was installed and cured to act as a flume to divert flows. We were able to keep on top of the weather by Using the Thames Water’s ICM Live weather system.Further to that high pressure cleaning of the sewer and use of specialist tankers helped to remove silt. Also two semi-circular steel plates were fabricated & installed upstream to act as baffles to prevent further silt depositing. To reduce disruption, the site works were delivered by three teams working alternating shifts. Each team worked 8 hrs a day 7 days a week, with work continuing 24 hrs a day.