How do they do that? is a series for The Source that explores the technology that helps keep Metro running and passengers and other commuters moving. Some of it applies directly to the trains, buses and freeways and some of it runs in the background — invisible to nearly everyone but essential to mobility in our region.
Lowering tunnel boring machine into the ground — Dec. 15, 2005 — for construction of Metro Gold Line Eastside Extension.
With the Crenshaw/LAX line, the Metro Regional Connector and the Purple Line Extension readying for construction, there will be plenty of digging going on in L.A.County. But how do you dig a subway tunnel? Dynamite? Giant corkscrew? Spoon?
In the U.S. we’ve been mining subway tunnels for more than a century. At first there were men and shovels and dynamite and excruciating physical labor. (Think Holland Tunnel under the Hudson River between New York and New Jersey. Think pressurized compartments holding workers who had to be depressurized at the end of a shift to avoid getting the “bends.”) Fortunately, we now have machines to do the heavy work.
During the past 20 years Metro has constructed three sets of tunnels: one for the Metro Red and Purple lines, another for two stations of the Metro Gold Line Eastside Extension and a third to carry the Expo Line under the busy Figueroa-Exposition Boulevard intersection.
For the Gold Line Eastside Extension, two tunnel boring machines nicknamed Lola and Vicki (see video above) were lowered into the ground in Boyle Heights to bore twin subway tunnels from First and Boyle to First and Lorena streets at a depth of 50 to 60 feet. Each TBM weighed more than two million pounds and was 344 feet long. Each built a tunnel that was 21 feet in diameter.