Thames Tideway Tunnel

At 25 km (15.5 miles) long, spanning 14 London boroughs and with an internal diameter of 7.2 metres wide enough to park three London buses side by side the Thames Tideway Tunnel is planned to be one of the deepest tunnels ever built in the UK. It will take the sewage flows, currently discharged into the River Thames, out to east London for treatment before they go back into the Thames in a safe, clean form.

The potential environmental and health benefits of the project are as monumental as the structure itself. And with such a huge-scale venture in such a heavily-populated and historically built-up area, the risk management approach also needs to be on a major scale. Its a risk process designed to guard against, quite literally, the sewage hitting the fan, as Sue explains.

Weve gone through conceptual design, and design for planning, and through that process have identified potential risks and looked at how we develop mitigation measures at the planning and procurement stages and what we leave for the contractor to do. Weve built our risk register and will manage that as we go, says Sue, who set up the projects third party infrastructure team in 2010. The team has conducted extensive research along a wide corridor of London to look at the existing and planned assets and evaluate and assess the predicted impact of the Thames Tideway Tunnel on these structures which include such significant landmarks as Tower Bridge.

Its been very much a risk-based approach, emphasises Sue, Looking at the ground conditions we know about, the type of tunnel boring that well specify the contractor should use and so on. If our initial assessment showed there might be issues we looked at these in a lot more detail, with more sophisticated analysis, to really understand the likely effects on these structures as we come underneath them.

The plans have ended up with the tunnel being quite deep, partly because were a gravity system and have to fit around the existing infrastructure, and partly because we're so big we ended up crossing over two of our (Thames Waters) existing assets in the west and beneath the London Underground Tunnels through central London and in the east. Were planning to go 65 m deep in the east, which is deeper than Crossrail and the Eurotunnel. This brings more complex tunnelling risks, such as management of groundwater and difficult ground conditions. We start off in the west in clay, then go through the Lambeth Group and Thanet Sands through central London to the chalk in the east. The Lambeth Group, presents difficulties when you start working in it so that has influenced our design.

In some cases this risk-based approach has already resulted in mitigation measures for example two of Thames Waters tunnels are being relined to guard against damage as the boring machine for the Thames Tideway Tunnel passes by. The development phases have also helped the team adapt plans to ensure the optimum health and safety measures are in place during construction phase and beyond.

Weve built an extensive ground model and our risk process means that as time has gone on weve changed the planned alignment to minimise the impacts on third party assets and also and how the tunnel connects with the shaft at Blackfriars, having considered work methods in the ground conditions there and the potential significant health and safety risks, explains Sue.

The team has drawn on risk management lessons learned during other significant infrastructure projects, such as Crossrail.

Mitigating the risks of unexploded ordnance has been a significant consideration for us in terms of the works at surface level and in the river, Sue continues. Early engagement with Crossrail helped us develop an appropriate approach to assessing this risk. Weve also liaised with the Crossrail team and others in terms of how theyve managed the challenges of construction traffic and cycle safety, and have been learning from schemes theyve implemented such as putting sensors and other safety equipment on the lorries. This will help us be very specific with our contractors about the high standards they must achieve.

Although the construction phase poses the main risk considerations for Sues team, the project team has also been mapping out future inspection measures to ensure the integrity of the tunnel is maintained while safeguarding other people and other existing infrastructure. The tunnel is being designed for a 120-year life and a 10-yearly principal inspection regime of the entire tunnel and associated shafts, using heavy lifting equipment. The team is looking at remotely-operated vehicles that minimise the need to put people into potentially risky situations. It is also taking into account the health and safety of people conducting regular surface-level maintenance of valves, etc.

Ultimately, as with any project, the Thames Tideway Tunnel risk management process is about ensuring safety and quality is at a high level to protect people and assets whilst providing value for money for Thames Waters customers.

Its all about having a high specification now, and a sensible handover/completion period that means we can test it thoroughly and ensure we can safely inspect and maintain it, emphasises Sue.

So has the team followed a tried-and-tested risk management route or developed a bespoke process for this large-scale project? I would say its pretty standard, Sue confirms. Weve followed the established processes for establishing predicted ground movements based on extensive experience of excavation and tunnelling works within London, including recent major tunnelling projects such as the Jubilee Line Extension and the Channel Tunnel Rail Link (High Speed 1). Workshops are held to identify risks, actively managing them through risk reviews with the specific teams, allocating the risks to a specific owner, developing and tracking a mitigation plan and ensuring the top risks get reviewed by the executive management team at least once a month.

Were trying to capture all the working levels within and across the project. Its not just sitting with the management although they have a certain level of responsibility. Its also about ensuring everyone, including the junior level people working on the project, are bought into and understand the risk management process.

So whats next for Sues team as the project moves from planning to construction stage?

At the moment were transitioning to prepare for delivery and are currently in the process of procuring contractors to undertake the works. Its a design and build contract so once appointed, the contractor will need to validate the impact assessments weve done for the existing assets or provide their own to account for time elapsing and existing conditions and structures might have changed. Were looking for the contractor to be responsible for and excel in risk management.. Well be maintaining a relationship with all third parties including the local communities, through which the tunnel passes to make sure the way the contractor manages those works and stakeholder relationships are managed effectively and not detrimental to Thames Water.

About the Thames Tideway Tunnel
Londons sewerage system dates back to Victorian times and no longer has sufficient capacity for the increased population, spilling enough sewage into the tidal section of the River Thames every year to fill the Albert Hall 450 times over. The Thames Tideway Tunnel is designed to help protect the river from increasing pollution and will run approximately 25 km from Acton in west London to Beckton in east London. It will tackle the problem of overflows for at least the next 100 years, and enable the UK to meet European environmental standards.

The tunnel broadly follows the line of the river below ground with vertical shafts projecting upwards at specific points to capture flows and give access to the tunnel. These meet the surface at 24 separate locations, via some sensitive sites in the centre of London such as by Blackfriars Bridge, Victoria Embankment and where the boat race starts in Putney. The projects goal is to integrate this infrastructure seamlessly and safely into the urban fabric of London and, where possible, create vibrant new public spaces.

Under the Flood and Water Management Act, a new Infrastructure Provider is to be created to finance and deliver the tunnel, independent of Thames Water. Thames Tideway Tunnel Ltd, a new regulated utility company, will design, construct and finance the tunnel. The company will have its own licence with revenues determined by the regulator Ofwat, and will collect bill payments for the tunnel via Thames Water.

Investors interested in bidding for Thames Tideway Tunnel Ltd are being invited to take part in a competitive procurement process, being run by Thames Water. This process is a new way of forming a utility company and has been done to ensure customers get the best value for money.
Thames Tideway Tunnel Ltd will enter into contracts with construction companies for three geographical areas in east, west and central London, to build the project.

There are currently around 350 people working on the Thames Tideway Tunnel project. This is expected to rise to around 500 by the end of 2014 ready for construction work to begin in 2016. At the peak of construction, the project will create more than 9,000 direct and indirect jobs. The project is scheduled for completion in 2023.

Biography
Sue manages an in-house Thames Water team of 18 staff, in addition to multiple consultant teams contracted to assess the impact of the Thames Tideway Tunnel works on existing infrastructure. Sue is also responsible for managing the relationships with a number of key Stakeholders such as TfL, Network Rail, utility companies and the PLA. She is a chartered civil engineer and has worked in project management roles on a number of flagship projects for Thames Water, including the first desalination plant in the UK. Prior to her current role, Sue was the site investigations manager for the Thames Tideway Tunnel project involving extensive ground investigations in the marine environment as well as on land.

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This article first appeared in Project magazine. APM members can read all feature articles from Project magazine over recent years by accessing the Project magazine archive.

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