World’s ‘biggest, fastest’ tunnel machine completes 9km dig

The mighty “Caucasus” tunnel boring machine breaks through to what will become one of the tunnel’s entrances (CRTG)
The world’s biggest tunnel-boring machine has dug the 9km-long Gudauri tunnel in the mountains of the Caucasus state of Georgia.

It’s part of the 23km “KK Highway” linking the cities of Kvesheti and Kobi, north of the capital, Tblisi.

The 8,860m tunnel will allow the road, which is 2,400m above sea level, to remain open in winter.

It will also cut the drive time between the two cities from an hour to 20 minutes.

A 2019 report by the Asian Development Bank, one of the project’s funders, said the old road couldn’t handle the 3,000-4,000 vehicles that used it each day, causing congestion, pollution and accidents.

It said: “Up to 35% of all traffic is delayed, a number that is expected to double in the next 15 years.”

The project was carried out by China Railway Tunnel Group (CRTG), a subsidiary of China Railway Group and the largest civil engineer of its kind in the country.

It used “Caucasus” a 182m-long tunnel-boring machine that has an excavation diameter of more than 15m, which the company says is the biggest of its kind in the world.

It’s also the fastest, CRTG said, which allowed it to finish the dig ahead of schedule.

“With a maximum monthly advance of 426m, Caucasus set a new record in large diameter tunnel construction, surpassing the previous estimate of ‘no more than 320m per month’ in the industry,” the company said.

It added that the speed was also due to the innovative design of Caucasus, which is able to carry out “synchronised excavation and assembly”.

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