Last year we were proud to accept the United Kingdom Society for Trenchless Technology (UKSTT) award for Large Renovation. The award was given for our work on Bank Station London. Bank and Monument Stations, as it is now known, was built in 1900 in King William street, London. It is the fourth busiest Transport for London station with nearly 96,000 people going through it every day. Served by the Central, Northern, Waterloo and City lines the station is a key gateway into London and is also one of the world’s most complicated underground railway stations.
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. 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. This wasn’t the easiest process in the world however. 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.
Those problems of course we not going to hold us back. As mentioned above our construction of 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. Credit must go to Dragados’ as our adoption of their ‘one-team’ approach really helped with this project. 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.
For those of you are interested here are some interesting facts about the project. This was London Underground’s first Innovative Contractor Engagement (ICE) project. Working in full alliance with London Underground, Dragados saved its client £60 million. They achieved through the use of innovative solutions to difficult problems. Something we fully endorse and look to do with all our projects.
This works act was one of the largest scale upgrades of any underground station. It including 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 of course most importantly a 570m tunnel and platform for the Northern Line.