The Mechanized Digging Revolution
Tunnel boring machines (TBMs) have revolutionized the way underground infrastructure projects are carried out around the world. Powerful, mechanized devices capable of excavating through virtually any ground condition, TBMs have allowed tunneling projects to be completed faster, safer, and at a lower cost compared to traditional drilling and blasting methods. They have become indispensable for ambitious underground transportation and utility projects.
How Tunnel Boring Machine Industry Work
Most modern Global Tunnel Boring Machine are either open- or closed-face machines depending on the ground condition. An open-face TBM has a large rotating cutterhead at the front that chips away at the material in its path. The muck or debris is then transported out of the tunnel through a conveyor belt system running inside the hollow machine. Closed-face machines instead have a self-advancing, pressurized, closed chamber in front of the cutterhead that traps material as it is excavated. The chamber then transports the material out of the rear of the TBM. Behind the cutterhead, the main body of the machine contains functions like electrical systems, hydraulic systems, operator cabins, and temporary tunnel support segments installed as the machine advances. Propulsion systems allow TBMs to either be slided forward or occasionally be jacked ahead after each excavation cycle. Some machines can bore through over 15 meters of ground per day.
Applications Around the World
Due to their mechanized precision and ability to bore through almost any ground type, TBMs have enabled ambitious tunneling projects on every continent. Europe is a pioneer, with many early-2000s projects like the Channel Tunnel between UK and France and more recent ones like the Gotthard Base Tunnel in Switzerland built exclusively using giant TBMs. In North America, important transportation arteries like New York City’s Second Avenue Subway extension and Seattle’s Sound Transit network expansion rely heavily on tunnel boring. Asian nations are also increasingly adopting mechanized underground infrastructure to solve urban transportation and flood management challenges, with China building hundreds of kilometers of metro tunnels using TBMs each year. Even large water supply and hydroelectric projects in South America and Australia now favor tunnel boring over conventional drilling. As sub-Saharan African cities expand rapidly and climate change impacts water security worldwide, TBM use in those regions is also expected to rise significantly in the coming decades.
Tunnel Boring Machine Industry Engineering Challenges
While TBMs have radically improved underground construction capabilities, operating these complex machines in variable ground conditions still presents significant engineering challenges. For soft ground tunneling, maintaining stability of the tunnel face during constant material removal requires precision control of slurry pressures, ground treatment ahead of the machine, and timely installation of temporary linings. Soft clay and silt layers prone to squeezing further increase support requirements. Hard rock excavation on the other hand relies more on robust cutterhead design, bearing thruster pressures, and muck removal systems to counter high torque loads. Unexpected rock discontinuities and faults also require contingency response plans. Groundwater control is critical in water-laden soil and fractured rock environments to prevent flooding and stabilize the face. TBM steering and guidance technologies have evolved to deal with tight curves, but negotiating 90-degree bends without excessive wear still proves difficult. Addressing such intricate geotechnical and machine operation issues through continuous innovation will be key to pushing the limits of tunnel boring into even more demanding ground in the future.
Large-Scale Machines for Big Projects
As tunneling projects worldwide target ambitious depths and length records, tunnel boring machines have grown larger in turn to accommodate these technical needs. At over 17 meters in diameter, the gargantuan machines excavating Turkey’s Istanbul Canal tunnels will be among the largest ever built. Japan’s Chuo Shinkansen maglev tunnel project will deploy TBMs measuring more than 15 meters across to efficiently bore through dozens of kilometers of strong crystalline rock. The landmark Strait of Gibraltar tunnel linking Africa and Europe, if ever constructed, may require tunnel boring machinery approaching 20 meters in diameter to withstand subsea pressures during the multi-year crossing. With careful engineering, such future mega-machines could truly stretch the boundaries of what is possible beneath the earth’s surface. Continued size increases may however pose challenges for transportation, assembly, and maintenance logistics within tight urban worksites.
New Technological Directions
As the field of tunnel boring continues its relentless march forward, researchers are exploring diverse technological developments to further enhance safety, speed, controllability and cost-effectiveness of underground construction. Automated operation, advanced digital modeling, and remote robotic maintenance systems aim to reduce human intervention risks within hazardous tunnel environments.
