Silvertown Tunnel in depth


Now that the winners of Transport for London's (TfL) £1bn Silvertown Tunnel project - procured through a Design, Build, Finance and Maintain contract - have been announcedHighways speaks to TfL to find out more about this flagship scheme.

1) The financial risk for construction and an initial maintenance period will sit with the private sector rather the public sector. How long does the consortium's 'initial maintenance period' last?

Once completed, the consortium will operate the tunnel for 25 years. Riverlinx will be incentivised to ensure that the tunnel is open and operating smoothly at the most busy periods. Under the terms of the agreement signed, TfL will only start paying for the tunnel once it is operational, limiting its financial exposure on this project. Responsibility for the tunnel will then pass to TfL after the 25 years.

2) Are you building a digital twin of the tunnel for future maintenance support?

TfL has set high level requirements in relation to asset and information management to encourage innovation and high standards of future maintenance. The details of how this is to be delivered are for the consortium to agree and develop. 

We would be happy to share more information this work once the Riverlinx team mobilises and begins this process later this year.

3) Are you using the heat generated from drilling to power anything? This was discussed for Crossrail but never happened in the end, we understand.

We are not intending to do this. Due to the large diameter and shallow depth of these tunnels under the river, and the nature of road traffic, the heat that might be generated from this project does not justify the investment required to install equipment to recover it.

4) What are you doing with the waste materials?

A comprehensive waste management plan will now be developed by Riverlinx to detail how waste will be managed through construction. We have set high level requirements on Riverlinx through the Project Agreement to ensure proper application of the waste hierarchy and mitigate the environmental impacts of construction. For example we will require that 100% of suitable excavated materials and at least 55% of all materials by weight will be transported by river.

5) Do you know what drilling machines will be used yet?

We expect that an Earth Pressure Balance (EPB) type Tunnel Boring Machine will be used to construct the main tunnel drives. The actual machines however will be procured by Riverlinx.

6) How many people will be involved in construction?

The exact details of the workforce will further detailed with Riverlinx through the next stages but we anticipate that at peak roughly 1,000 people will be involved in construction. We have committed to employing at least 25% of the workforce from the local community, as well as to creating apprenticeships and training opportunities.

7) What percentage of the cost allows for optimism bias?

The financial risk for construction and maintenance sits with Riverlinx; however we have worked closely with tenderers during the procurement process to ensure appropriate allowances have been made for risk and other factors.

8) To avoid the issues that Crossrail saw, will you be changing any of the ways information is passed between the consortium, TfL and the mayor, and then made public?

Riverlinx will be fully responsible for design, construction and maintenance and everything that is required to integrate the various sub-contracts they will establish to deliver the scheme. The financial risk for this also sits with Riverlinx who are not paid until the tunnel is open and meets out quality standards.

Despite this, we have set a number of requirements on Riverlinx to record and report information on construction performance. This will cover progress as well as environmental performance, community engagement and other related matters. As the Riverlinx team mobilise over the course of this year, we will be working closely with them to finalise the details of how we will report this information between Riverlinx, TfL, the mayor and the public.

9) What is the design life of the asset?

The tunnel has a design life of 120 years although certain equipment or elements of it will need to be replaced, renewed and maintained within that timeframe.

10) Is the tunnel being designed to support future connected or autonomous vehicles? If so in what way?

Although the technology/infrastructure that might be required to support this is still somewhat uncertain, we have made provision for ‘dark’ fibre cables and spare cable capacity to be installed throughout the tunnel to allow future installation during the maintenance period. This gives us flexibility to respond to future requirements as and when we might require them.

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