A tunnel boring machine (TBM), also known as a "mole", is a machine used to excavate tunnels. TBMs are an alternative to drilling and blasting methods and "hand mining", allowing more rapid excavation through hard rock, wet or dry soil, or sand (although each requires specialized TBM technologies). TBM-bored tunnel cross-sections extend up to (through June 2023). TBM tunnels are typically circular in cross-section. Specialized tunnel boring machines have been developed to excavate non-circular tunnels, including rectangular and horseshoe-shaped profiles.Commercial websites that reference the same types of material include:
Much narrower tunnels are typically bored using trenchless construction methods or horizontal directional drilling rather than by TBMs.
TBMs limit disturbance to the surrounding ground and produce a smooth tunnel wall, which reduces the cost of lining the tunnel and allows for tunneling in urban areas. Large TBMs are expensive and challenging to construct and transport, and have fixed costs which become less significant for longer tunnels. Tunneling speeds generally decline as tunnel size increases, but tunneling speeds using TBMs have nevertheless increased over time. TBM speeds excavating through rock can, in the 21st century, reach over 700 meters per week, while soil tunneling machines can exceed 200 meters per week.
History
1800s The first successful tunnelling shield was developed by Sir Marc Isambard Brunel to excavate the Thames Tunnel in 1825. However, this was only the invention of the shield concept and did not involve the construction of a complete tunnel boring machine, the digging still having to be accomplished by the then standard excavation methods.
The first boring machine reported to have been built was Henri Maus' Mountain Slicer. Commissioned by the King of Sardinia in 1845 to dig the Fréjus Rail Tunnel between France and Italy through the Alps, Maus had it built in 1846 in an arms factory near Turin, Italy. It consisted of more than 100 percussion drills mounted in the front of a locomotive-sized machine, mechanically power-driven from the entrance of the tunnel. The Revolutions of 1848 affected the funding, and the tunnel was not completed until 10 years later, by using less innovative and less expensive methods such as pneumatic drills.
In the United States, the first boring machine to have been built was used in 1853 during the construction of the Hoosac Tunnel in northwest Massachusetts. Made of cast iron, it was known as Wilson's Patented Stone-Cutting Machine, after inventor Charles Wilson. It drilled into the rock before breaking down (the tunnel was eventually completed more than 20 years later, and as with the Fréjus Rail Tunnel, by using less ambitious methods). Wilson's machine anticipated modern TBMs in the sense that it employed cutting discs, like those of a disc harrow, which were attached to the rotating head of the machine.Bancroft 1908, p. 65.Wilson, Charles. "Dressing stone," (issued: March 13, 1847).Wilson, Charles. "Machine for tunneling rocks, etc.," (issued: March 18, 1856). In contrast to traditional chiseling or drilling and blasting, this innovative method of removing rock relied on simple metal wheels to apply a transient high pressure that fractured the rock.
In 1853, the American Ebenezer Talbot also patented a TBM that employed Wilson's cutting discs, although they were mounted on rotating arms, which in turn were mounted on a rotating plate.Talbot, Ebenezer. "Machine for tunnelling or boring rock," (issued: June 7, 1853). In the 1870s, John D. Brunton of England built a machine employing cutting discs that were mounted eccentrically on rotating plates, which in turn were mounted eccentrically on a rotating plate, so that the cutting discs would travel over almost all of the rock face that was to be removed.Brunton, John D. "Improved machine for sinking shafts," (issued: July 21, 1868).
The first TBM that tunneled a substantial distance was invented in 1863 and improved in 1875 by British Army officer Major Frederick Edward Blackett Beaumont (1833–1895); Beaumont's machine was further improved in 1880 by British Army officer Major Thomas English (1843–1935).David William Brunton and John Allen Davis, Modern Tunneling: With Special Reference to Mine and Water-supply Tunnels (New York, New York: John Wiley & Sons, 1914), p. 182.Frederick Edward Blackett Beaumont, U.K. Patent no. 1,904 (issued: July 30, 1864). (See: Patents for Inventions. Abridgments of Specifications relating to Mining, Quarrying, Tunnelling, and Well-sinking (London, England: Office of the Commissioners of Patents for Inventions, 1874), p. 247. ).F. E. B. Beaumont, U.K. Patent no. 4,166 (issued: Dec. 2, 1875). (See: Patents for Inventions. Abridgments of Specifications. Class 85, Mining, Quarrying, Tunnelling, and Well-sinking (London, England: Patent Office, 1904), p. 169. ).Thomas English, U.K. Patent no.s 4,347 (issued: October 25, 1880) and 5,317 (issued: December 5, 1881); "Tunneling-machine," (filed: June 4, 1884; issued: October 28, 1884). In 1875, the French National Assembly approved the construction of a tunnel under the English Channel and the British Parliament supported a trial run using English's TBM. Its cutter head consisted of a conical drill bit behind which were a pair of opposing arms on which were mounted cutting discs. From June 1882 to March 1883, the machine tunneled, through chalk, a total of 1,840 m (6,036 ft). A French engineer, Alexandre Lavalley, who was also a Suez Canal contractor, used a similar machine to drill 1,669 m (5,476 ft) from Sangatte on the French side. However, despite this success, the cross-Channel tunnel project was abandoned in 1883 after the British military raised fears that the tunnel might be used as an invasion route.Terry Gourvish, The Official History of Britain and the Channel Tunnel (Abington, England: Routledge, 2006), Chapter 1, § 2: The commercial possibilities: Lord Richard Grosvenor, Sir Edward Watkin and the 'Manchester to Paris Railroad'. Nevertheless, in 1883, this TBM was used to bore a railway ventilation tunnel – in diameter and long – between Birkenhead and Liverpool, England, through sandstone under the Mersey River.
Construction of the Uptown Hudson Tubes for the Hudson & Manhattan Railroad took place intermittently between 1890 and 1908, using a Greathead Shield. The project used air compressed to to reduce cave-ins. However, there were many workers that died via cave-in or decompression sickness.
1900s During the late 19th and early 20th century, inventors continued to design, build, and test TBMs for tunnels for railroads, subways, sewers, water supplies, etc. TBMs employing rotating arrays of drills or hammers were patented.See: Bancroft 1908, pp. 66, 125, 127, 146. Thales Lindsey, "Improved machine for tunneling rock," (issued: June 12, 1866). Pedro Unanue, "Tunneling machine," (filed: December 23, 1901; issued: June 30, 1903). Russell B. Sigafoos, "Rotary tunneling machine," (filed: May 18, 1907; issued: October 20, 1908). George A. Fowler, "Tunnel driving machine," (filed: July 30, 1907; issued: June 23, 1908). TBMs that resembled giant hole saws were proposed.See: Bancroft 1908, pp. 66, 85, 106. Wilson, Charles. Machine for excavating tunnels," (issued: June 23, 1857). Stanley, Reginald. U.K. Patent no. 1,449 (issued: February 1, 1886); "Tunneling-machine" (issued: August 7, 1894). Mitchell, Jonas L. "Tunneling-machine," (filed: April 3, 1893; issued: April 23, 1895). Other TBMs consisted of a rotating drum with metal tines on its outer surface,See: William F. Cooke and George Hunter, U.K. patent no. 433 (issued: August 10, 1866). Available online at AditNow. . Patents for Inventions. bridgments of Specifications relating to Mining, Quarrying, Tunnelling, and Well-sinking (London, England: Office of the Commissioners of Patents for Inventions, 1874), p. 275. . or a rotating circular plate covered with teeth,See: Bancroft 1908, pp. 146, 165. John P. Karns, "Tunneling-machine," (filed: November 29, 1905; issued: March 26, 1907). Olin S. Proctor, "Tunneling-machine," (filed: February 17, 1908; issued: October 13, 1908). or revolving belts covered with metal teeth.See: Bancroft 1908, p. 145. William A. Lathrop, "Machine for cutting headings," (filed: August 31, 1903; issued: April 3, 1906). However, these TBMs proved expensive, cumbersome, and unable to excavate hard rock; interest in TBMs therefore declined. Nevertheless, TBM development continued in potash and coal mines, where the rock was softer.For example: In Germany, the Eisener Bergmann (iron miner) was developed in 1916 by Schmidt, Kranz & Company for potash mines; its boring head consisted of a large rotating roller that was fitted with cutters. See: . In the U.S., the McKinlay Entry Driver, a track-mounted TBM or "continuous miner", was invented in 1918 for use in coal mines. Its boring head consisted of metal tines on two, side-by-side rotating arms. See: Thomas W. Garges (November 13, 2003) William N. Poundstone lecture: "Underground Mining Technology Evolution", p. 8. Available online at: Benjamin M. Statler College of Engineering and Mineral Resources, West Virginia University. .
A TBM with a bore diameter of was manufactured by The Robbins Company for Canada's Niagara Tunnel Project. The machine was used to bore a hydroelectric tunnel beneath Niagara Falls. The machine was named "Big Becky" in reference to the Sir Adam Beck hydroelectric dams to which it tunneled to provide an additional hydroelectric tunnel.
2000s
The TBM known as Bertha, reportedly the largest earth pressure balance machine and second largest TBM in general (as of June 2023), has a bore diameter of , and was produced by Hitachi Zosen Corporation in 2013. It was delivered to Seattle, Washington, for its Highway 99 tunnel project. The machine began operating in July 2013, but stalled in December 2013 and required substantial repairs that halted the machine until January 2016. Bertha completed boring the tunnel on April 4, 2017.
Two TBMs supplied after the 2013 acquisition of Germany's Aker Wirth (Aker Solutions) TBM and shaft-boring technology by China Railway Tunnelling Equipment (CRTE), now CREG (China Railway Engineering Equipment Group)-Germany, Note, the acquisition was sans Wirth's newer Mobile Tunnel Miner technology developed with Codelco and Rio Tinto, see article. CREG-Wirth units with boring diameter of , were used to bore two tunnels for Kuala Lumpur, Malaysia's Metro system. The medium excavated was water "saturated sandy mudstone, schistose mudstone, highly weathered mudstone as well as alluvium". By the company's commercial description, its products achieved an advance rate of "more than 345 meters [1,130 feet] per month".
Reportedly the largest hard rock machine and fourth largest TBM overall (as of June 2023), a machine known as Martina, was built by Herrenknecht AG. Its excavation diameter is , and total length ; excavation area of , and thrust value 39,485 t, total weight 4,500 tons, and total installed capacity 18 MW. Its yearly energy consumption was about 62 GWh. Martina was used by the Italian Toto Group construction company (Toto S.p.A Costruczioni General) to bore a 2.4 km tunnel of the Variante di Valico project near Florence, Italy, in 2013. This project created the Sparvo gallery of the Italian Motorway Pass A1 ("Variante di Valico A1"), near Florence. As of this date, Martina was still owned and operated by the Toto Group.