The endless fascination of BORING MACHINES

It is the world’s biggest drill, a massive Tunnel Boring Machine that dwarfs the ones used for Sydney’s Metro West project. It can gnaw through 30 metres of rock a day – and leaves a finished tunnel behind.

There are few more impressive displays of mechanical and geological engineering prowess than to see Daphne and Beatrice, Sydney’s twin TBMs (tunnel-boring machines), as they break through solid rock, still side by side after cutting a 4.3-kilometre tunnel from The Bays to Five Dock. Daphne breaks through first, the rock peeling away like an eggshell pushed from within, revealing the cutting heads spinning around a massive rotating circular face: it is the height of a two-storey building.

Beatrice now appears, fast catching up with Daphne, the two mechanical moles ripping away rock side by side, each one leaving a tunnel of 7 metres in diameter behind it, wide enough to accommodate the tracks, the trains, the pipes and cables of the Sydney Metro West project.

The TBMs were built by a German company, Herrenknecht, part of a package worth almost $1.96bn that was awarded to an Australian joint venture.

The world’s biggest drill

But these Sydney mighty moles are mere earthworms for Herrenknecht; they are dwarfed by the pride of the company’s excavation fleet, the Herrenknecht S-880.

The S-880 is a giant among giants. Tunnel-boring machines are some of the biggest, most powerful, and heaviest machines in existence. The Herrenknecht S-880 can drill through 7500 cubic metres of rock in one working day, enough rubble to fill 250 large dump trucks (or 2000 small ones). The drill’s diameter of 17.6 metres means a cutting face with an area more than six times those of Beatrice or Daphne. As it drills through the ground it leaves a tunnel wide enough for four lanes of traffic.

Rise of the machines

Before tunnel-boring machines, digging was done first by hand and then aided by explosives and pneumatic drills. The forerunners of modern TBMs saw the light of day in the mid-1800s. In 1853, American