By Susanna McLeod
Special to Ontario Construction News
Blasting, excavating, and digging by hand to construct a tunnel was dangerous, time-consuming work. Inventors envisioned machines that could work through the earth like moles to create a pathway for a train or pipework. The first tunnel boring machine (TBM) was developed in the early 1800s. The one-metre diameter TBM was miniature compared with today’s over 14-metre- diameter Big Becky and more advancing machines.
Avoiding surface disturbances of terrain and urban areas, tunnel boring machines are valuable assets for drilling under mountains, beneath waterways, and below city streets. As the TBM churns through the rock and inches ahead, it leaves a smooth wall for easier completion.
However, invention doesn’t always run smoothly.
Excavating a tunnel under the Alps from France to Italy, Henri-Joseph Mauss developed one of the first boring machines in the 1840s, using revolving cutters. “An excavating machine, called a ‘mountain slicer’… was composed of a truck with a frontal system of percussion excavators activated by cables which transmitted energy from a hydraulic engine installed at the mouth of the tunnel,” described Giorgio V. Dal Piaz and Alessio Argentieri in Italian Journal of Geosciences 2021; 140 (2).
“As excavation advanced, these trolleys had to become longer and longer, and they would also pose problems of technical management.” A rebellion ended the project for years.
Half a world away, Charles Wilson’s Patented Cutting Machine launched into excavating the Hoosac Tunnel in northwest Massachusetts in the 1850s.
Wilson’s boring machine weighed 75 tons, and was designed to make a 7.31 metre diameter circular cut that was 31 cm wide, and 2.4 m deep. When the depth was reached, the TBM “would be pulled back and black powder explosives implanted to loosen the material inside the ring,” said Giles Lambertson in Construction Equipment Guide, December 5, 2019. The plan was to repeat the process, “powered by a 100-hp steam engine.” Wilson’s machine carved just over 3 m then failed. The cutting was difficult—the mountain’s base is composed of hard granite gneiss and quartz.
Within decades, engineers devised tunnel boring machines that carved longer distances, such as the 2 km railway ventilation tunnel under the Mersey River, and parts of the English cross- channel tunnel in the 1880s. Projects for TBMs abounded, with tunnels required for subways, sewer systems, mining, water projects, and more. Research and development produced an interesting array of tunnel borers with belts, plates, and rotating drums. Soft rock was much easier to cut through; hard rock presented problems… until Big Becky was built.
Preparing to increase electrical power production at OPS’s Sir Adam Beck Hydroelectric Plant, Austria’s Strabag AG was contracted to manage the Niagara project. The firm hired The Robbins Company in Ohio to build an enormous tunnel boring machine.
Specializing in innovative technologies, the American firm holds many world performance records. The TBM for the Niagara project set records then as well, as the world’s largest hard- rock machine. First dubbed the Beck after the hydroelectric facility, the boring machine was changed to the endearing Big Becky.
Manufactured in 2006, Robbins HP 471-316 tips the scales at 2,000 tons. Costing over $30 million, the enormous machine “is powered by 15 electric motors that generate 6,375 horsepower,” according to Niagara Tunnel Project, “and is able to chew through rock at the rate of up to 1010 feet per hour.” The TBM’s cutter head design “consists of a six-piece bolted and doweled hard-rock configuration that includes 12 muck buckets with radial face and gage openings.” The completed cutter head with 85 discs weighs over 440 tons.
Another first for Robbins was assembling pre-built components of Big Becky on the jobsite to save time and money. (The TBM was constructed to meet a 12-month deadline.) The remarkable machine excavates a 14.45 m diameter tunnel with the finished measurement of the concrete- lined tunnel of 12.5 m.
Gnashing through the difficult rocky environment with relative ease, the Niagara tunnelling machine still faced challenges. Specialized to cut solid rock, Becky “encountered a stretch of loose, crumbling material that was unsuitable for tunneling,” noted John Spears in The Star, May 13, 2011. The change of terrain “forced a long and expensive detour.”
Scarborough subway extension is the next tunnelling project to use a massive TBM, although the machine is smaller than Big Becky. Manufactured by Herrenknect Ag in Schwanau, Germany, the boring machine features a cutter diameter of 10.7 m, large enough for trains to operate in both directions.
As with the Niagara boring machine, the tunneller’s components arriving at the Port of Oshawa will be assembled and welded at the job site. The 2,000-tonne “TBM had to be disassembled into parts and shipped in 15 containers,” stated Jack Landau in blogTo, along with 86 pieces too big for containers.
Excavating through hard rock? TBMs will find the light at the end of the tunnel. END 800 words
© 2022 Susanna McLeod. McLeod is a Kingston-based freelance writer who specializes in Canadian History.
“Patent # US97441, an example of early plans for a tunnel boring machine in 1853, by Ebenezer Talbot, Connecticut,” Google Patents. Retrieved from https://patents.google.com/patent/US9774A/en