Highlights

With 6,000 tons of thrust, the machine performs the task with ease. “That’s enough thrust to get sixty Boeing 747s off the ground,” adds Kupkowski by way of comparison.

Each boring machine is also a mobile tunnel factory.

To prevent the ground from subsiding during the drilling, the soil is strengthened with Bentonite, a mixture of water and clay that is pumped ahead of the cutting wheel. The spoil is fed through pipes to a separating plant above ground, where the Bentonite is separated from the sand and gravel and returned to the construction site.

But digging is only part of the job. Each boring machine is also a mobile tunnel factory. As the machine advances, workers to the rear of the working face are busy constructing the actual tunnel tubes. Using a vacuum suction lift, reinforced concrete sections are offered up one by one by a remotely operated crane and placed precisely in position. Seven of these so-called tubing segments plus a key stone form a ring – 7.30 meters in diameter, 1.50 meters wide, 40 centimeters thick and 38.5 tons in weight. This is how the new tunnel is built, ring by ring. The narrow gap between the soil and the tubing is filled with mortar. This avoids cavities and thereby prevents settlement and the attendant damage to buildings above ground. While the ring is being installed, the machine stops. Only when the key stone is secure does it resume its progress.