With construction costs now 8% over budget, London’s 25-kilometer the Thames Tideway joint venture contractor completed the first tunnel breakthrough this month, with construction still on course for on-time completion in 2022.

The breakthrough by the team of Balfour Beatty, Morgan Sindall and BAM Nuttall completed the 1.1-km-long, 2.6-m-dia spur between Wandsworth and Fulham.

Elsewhere, three of four larger TBMs are driving the main 6.5-7.2-m-dia east-west tunnel from Acton to Abbey Mills, with the fourth machine due to start next year. Bazalgette Finance plc., the private sector project owner, now puts the construction cost at $4.9 billion.