Herrenknecht tunnel boring machines

What it is

Herrenknecht AG designs and builds tunnel boring machines (TBMs), the giant rotating drills that excavate tunnels for railways, metros, roads, water and energy lines. The family-owned company was founded by Martin Herrenknecht, who set up an engineering business in 1975 and established Herrenknecht GmbH in 1978. Its headquarters and main assembly plant are in Schwanau, in Baden in south-west Germany.

How it works

A TBM combines a rotating cutterhead, which breaks up rock or soil, with a shield that supports the ground, a conveyor that removes the spoil and an erector that places concrete lining segments behind the machine as it advances. Herrenknecht builds different types for different ground. Gripper TBMs brace against hard rock walls. Earth Pressure Balance shields hold up soft ground by keeping the excavated soil under pressure in front of the machine. Mixshields use pressurised slurry to tunnel safely below the water table; Herrenknecht introduced large-diameter 6 m Mixshields in 1985.

Why it stands out

The company's machines have been involved in some of the most demanding tunnels ever built. Four Herrenknecht gripper TBMs drove a total of about 85 km of the Gotthard Base Tunnel in Switzerland, the longest railway tunnel in the world. In 2014 the company accepted a machine with a diameter of 17.6 m, built at its plant in Guangzhou for a road tunnel in Hong Kong. Herrenknecht says it can supply mechanised tunnelling technology for all geologies and diameters, from small utility tunnels to the largest road tunnels.

Where you meet it

If you travel on a modern metro, a new high-speed rail line or an urban road tunnel, there is a fair chance a Herrenknecht machine dug part of it. The company's TBMs are also used for sewers, water mains and cable tunnels, the hidden infrastructure that cities depend on.