The construction of transport tunnels is one of the largest, most ambitious and most challenging types of infrastructure projects you can do, and every element from the tunnel boring machines to the vulcanisation services needs to be optimal in order to avoid potential delays.

There are a lot of factors that can affect delivery, as has been seen recently with news that work on the Euston Tunnel portion of High Speed II will be paused in favour of other parts of the huge infrastructure project due to inflation increasing manufacturing costs.

However, few projects will match the sheer chaos that was the Boston Central Artery/Tunnel Project, often known colloquially as the “Big Dig”, which was a road tunnel project that took 25 years from its initial inception to final completion, at a total cost of $22bn.

From its initial inception, it faced an uphill struggle, as the initial project was a merger of two projects that both business leaders and the Boston city authorities wanted, and would only receive funding in 1987 after then-President Ronald Reagan’s veto was overturned.

The next obstacle was gaining environmental agency approval, as the planned tunnel route went through reclamation land, two subway tunnels, utility lines, pipes, debris from a glacier, the foundation of houses lost to time and even a sunken ship or two in the reclaimed land.

However, eventually it would receive the approval it needed with a plan to complete by 1998. In practice, it was nearly 2008 before it would be finished and would cost nearly ten times its initial $2.8bn.

Part of the reason for this was that it would have to be designed whilst disrupting as little traffic as possible, a feat described by Bostonians as akin to a person running a marathon whilst receiving open-heart surgery.

At one point, when the Central Artery tunnel reached South Station Railway, the soil was so unstable that refrigeration units were brought in to freeze the ground. 

In 2001, an underwater section of the tunnel had started leaking and the only solution was to flood the entire tunnel to equalise the pressure and avoid sheer catastrophe.

In 2006, a motorist sadly died when four concrete slabs fell, which in 2007 was found to be caused by inadequate epoxy glue and was the subject of one of many lawsuits caused by the project.

Whilst seen as an expensive disaster, time has helped the challenges fade from history. The removal of the aboveground highway, replaced with a set of parks known as the Greenway has helped to rejuvenate downtown Boston, carbon monoxide lowered by 12 per cent and the city is in rude health.