It took some first-rate machinery to dig one of the world’s most famous tunnels.
We are hearing a lot about various landbridge projects again. The fabled Bahrain-Qatar causeway is still a long way from being started, let alone finished and the assortment of other spans, such as that mooted from between Egypt and Jeddah drift into the realms of vapourware occasionally.
The too-ing and frow-ing is reminiscent of the Channel Tunnel project in the UK. The idea was first mooted as far back as 1802, though as the development of steam drills was still some way off, it is unclear how chipping through 40km of limestone was to be achieved.
The project resurfaced several times in the late nineteenth century, Interestingly, all of these early plans had to include a method of flooding the tunnel, should the French get any big ideas about invading.
It took another 100years, before the political will was there, but even then the project was founded on the proviso that it was to be 100% privately funded.
Needless to say, the money ran out faster than a drunk in Vegas, and the bill ended up being footed by the tax payer, which overran by some 80%, and that was before a high-speed rail link connecting London to the tunnel was built. As such, the whole operation was highly politicised and the royal opening (on which a train broke down) was mired
in controversy.
This was a shame as the machines used to build the tunnel and the engineering behind them was astounding. The project consisted of two primary tunnels and one smaller access tube.
The five TBMs that were built for the project were state-of-the-art by any standard. Supplied by a firm named Robbins, machines were deployed on both sides of the tunnels in December 1987.
The three French seaward TBMs encountered water inflows almost immediately, forcing the use of the sealed mode of operation much earlier than anticipated.
The sealed cutterheads of the machines could withstand 10 bar (145 psi) of water pressure; however, additional measures were required to seal the remainder of the machines against water inflow.
The U.K. machines also experienced some difficult tunneling conditions at the outset. Unforeseen water inflows in a 3.2 km (2.0 mi) stretch caused the machines to slow their progress as each section of tunnel had to be grouted in advance of boring.
After passing through this section of tunnel, the machines experienced no further difficulties and began averaging 149m (490 ft) a week.
The machines on the U.K. side averaged 873 m (2,864 ft) per month and set world records for a best day of 75.5 m (247.7 ft), a best week of 428 m (1,404 ft), and a best month of 1,719 m (5,640 ft) all of which have yet to be beaten by any other tunnel project.
In December 1990, the French and British TBMs met in the middle and completed the Channel Service Tunnel bore. In all of the tunnels the French TBM was dismantled while the U.K. TBM was turned aside and buried, where it remains to this day.
The Main Rail Tunnels met on May 22, 1991 and June 28, 1991. Both accomplishments were celebrated with breakthrough ceremonies to commemorate the building of one of the world’s longest and most ambitious undersea tunnels.