For obvious reasons, ground collapse is the enemy of a successful tunneling project.įiguratively, the TBM is like a giant coffee can on its side but instead of a lid there is the rotating cutter head face with teeth that chew up the soil. This type of TBM maintains enough pressure on its face to prevent the surrounding ground from collapsing during construction.
As it did for the Gold Line Extension, Metro will again use “pressurized face” tunnel boring machines. (On the Eastside Extension the Mariachi Station shaft was used as the boring machine entry point.) Then the TBM goes to work. 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.ĭuring 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.įor cut and cover, the surface street is removed, a temporary road deck is installed to maintain traffic, a trench is dug, the station box is constructed in the trench and, finally, the street restored.įor TBM tunneling, a shaft is sunk and the boring machine lowered to the depth of the tunnel. (Think Holland Tunnel under the Hudson River between New York and New Jersey. At first there were men and shovels and dynamite and excruciating physical labor. we’ve been mining subway tunnels for more than a century. But how do you dig a subway tunnel? Dynamite? Giant corkscrew? Spoon? 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. 15, 2005 - for construction of Metro Gold Line Eastside Extension.
Lowering tunnel boring machine into the ground - Dec. 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.
METRO 4 PIECE CORKSCREW SET SERIES
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.
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