All eyes are now on CTRL Section Two, stretching 39km between Fawkham Junction in Kent and St Pancras station in London.
With more than 50% of Section Two complete, 'so far, everything is going to plan', says Alan Dyke, managing director of client Union Railways North.
This part of the Channel Tunnel Rail Link (CTRL) runs between Fawkham Junction in Kent and a new terminus at St Pancras in London. It involves the construction of railway stations at St Pancras, Stratford and Ebbsfleet, more than 20km of tunnels, 3km of viaducts and numerous access and road bridges.
On a project which will spend $48M every fortnight for the next two to three years, forward planning is essential. With detailed design only about one month ahead of work on site, the programme is extremely tight.
Threading TBMs around the many existing tunnels, sewers and utility cables beneath London and building diversion routes where roads have had to close, has contributed greatly to the complexity.
Dealing with stakeholders associated with land near or on the route has been a challenge.
'When you're working in a city the size and complexity of London, you can't just do what you want to when you want to, ' says Walt Bell, who until May was managing director of Union Railways North.
'I had to speak with 23 potential interfaces on a daily basis:
borough councils, English Heritage, British Waterways, Network Rail and London Underground, which all have the right to say 'no'.' And yet, on a project the size of the CTRL, there have been relatively few complaints, and to Bell's relief, 'no placard wavers'.
'Warning stakeholders in advance is important, ' says Bell.
'If we're tunnelling under industrial sites where vibrations cannot be tolerated, we advise they shut down over that period.'
With the huge potential for planning procedures to run on and on, a management structure was created to ensure that information was passed to the people who could act most quickly. As in Section One, splitting the project into separate contracts with few interfaces helped each team to work more autonomously, says Bell.
The 100 series contracts were centred around work on St Pancras, the 200 series included tunnelling east to Stratford and the Stratford box itself, and the 300 series included piled slabs across the Thames Valley, the Thames tunnel and Ebbsfleet station.
'Across both sections of CTRL, civil works have been going well, but finding suitable contractors for the systemwide works was difficult, ' says Dyke.
'The contracting industry was inexperienced in such widespread interfaces. So contracts have been split into a number of smaller ones, with RLE as project manager, ' he says.
With the number of people working at any one time, 'we have maintained an extremely high level of safety awareness', says Ian Galloway, RLE project director for Section Two.
'We have a long thin construction site which runs alongside roads and railways and under homes, so it is not just our people on site that we have to consider, ' adds Dyke.
Work in and around St Pancras is one of the biggest challenges on Section Two. It is effectively four stations in one; serving international Eurostar trains, domestic CTRL services, Thameslink and the Midland Main Line services.
Platforms are being extended and work on a new steel framed roof is in full swing. Fifteen new platforms are needed plus underground links to a new Tube ticket hall. All of this must be done while maintaining normal services.
The maze of underground utilities and the St Pancras cemetery just outside the station have complicated the project. And as home to one of Britain's first gas distribution centres, three Grade II listed gas holders have had to be dismantled.