With the assistance of a tunnel-boring machine (TBM) dubbed Angeli, construction crews have completed work on the first of two tunnels for the 1.9-mile, $1.7 billion Regional Connector rail project in Los Angeles, according to Engineering News-Record.
After making its way through a tangle of utilities and other obstacles — with the help of BIM, wireless sensors and natural gas detectors — the 1,000-ton, 350-foot-long Angeli will be taken apart and readied to begin work on the second tunnel this fall.
The new connector will allow commuters on the Los Angeles Metro's Blue, Green, Gold and Red lines to transfer more easily and will open east–west travel in the metro area. Project completion is scheduled for late 2021.
According to a 2016 report from The Wall Street Journal, advances in TBM technology are driving more cities to build tunnels as part of their transportation systems. This is good news for TBM manufacturers, one of which saw sales of its $50 million machines rise from 20 in 2000 to 100 in 2015.
It's also good news for cities looking to reduce their tunneling costs. A New York City Metropolitan Transportation Authority official told The Journal that manually digging one tunnel project cost nearly $1 million per foot while use of a TBM on another cost just $19,000 per foot.
That's not to say the use of TBMs never presents challenges. A TBM used to dig a tunnel beneath Seattle as part of the Alaskan Way Viaduct project broke down in late 2013 after reportedly hitting a steel object. It took crews almost two years to repair the TBM. After resuming operations, a sinkhole formed overhead near the tunnel's path, prompting Washington Gov. Jay Inslee to shut the project down. Operations resumed after the project team came up with a new plan to monitor tunneling work.
In April, that TBM, Bertha, completed its 1.75-mile trip under Seattle, a process that took four years and $2.1 billion in all. The project finished 29 months behind the scheduled completion date, mostly because of repair-related delays. Bertha is the world's largest TBM yet.