Dive Brief:
- Tunneling projects underneath major cities are on the rise due to new machinery that can bore more efficiently and safely, according to The Wall Street Journal.
- Herrenknecht AG, a leading tunnel boring machine (TBM) manufacturer, told The Journal that the number of buyers for its $50 million TBM’s has increased from approximately 20 in 2000 to 100 this year.
- Today's TBMs are so fast and capable that Michael Horodniceanu, president of capital construction for New York City’s Metropolitan Transportation Authority, said that it cost the city $1 million per foot to manually dig a problematic tunnel recently, while a 3-mile stretch using a TBM cost $19,000 per foot.
Dive Insight:
Tunneling technology experienced a sea of change when engineers in the 1970s developed TBMs that could automatically install a precast concrete lining as they made their way through rock or even under water. Electronic sensors and monitors also allow modern TBMs to avoid existing structures as they’re digging. The machines can also emit chemicals that can loosen or harden soil as necessary during tunneling operations. All of these innovations have made it possible for tunneling to be put to use in areas that were previously considered unsafe or impassable, such as a recent traffic tunnel in Miami, which had to be carved out of wet sand and coral, according to The Journal.
Tutor-Perini and Seattle Tunnel Partners haven’t had much luck with their tunneling operations underneath Seattle since the TBM, dubbed Bertha, broke down in December 2013, which put Bertha out of commission for two years. After a few days of resumed digging in January of this year, tunneling operations were stopped again because of a sinkhole that formed near Bertha’s boring path. As a result, Washington Gov. Jay Inslee ordered a halt to all boring operations and only released the order when Tutor Perini, which called the stop-work order "wrongful and unjustified," came up with a plan to improve monitoring of tunneling operations.
Another "tunnel-challenged" endeavor is the California High Speed Rail Authority’s bullet train project, which will, eventually, have to bore 36 miles through the San Gabriel and Tehachapi Mountain ranges, as well as through earthquake faults and other untested areas. So daunting and expensive was the prospect that the authority sidelined that segment of the rail system for the time being and has decided to start on a more topographically friendly route in Northern California.
