The Anatomy of a Subway Excavation Method #1 Tunnel-Boring

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Posted on May 3, 2017 by dartdallas
Did you know the first underground subway in the U.S. was built in 1897? Luckily, technology has helped us since the 1890’s develop easier and less-invasive ways to dig a transportation tube nearly one hundred feet below the surface.  DART is leveraging this new technology to help make the D2 Subway a reality. This week, we’ll explore one of these innovative excavation methods DART will use to construct the D2 Subway. The tunnel boring method is executed by a large piece of equipment known as a Tunnel Boring Machine (TBM) that creates long tunnels beneath the surface. A TBM has already been used effectively to create the DART North Central Corridor tunnel, the Melbourne Metro Rail project and New York City’s Second Avenue Subway line. This machine, also known as a “mole”, has a tubular shape and can bore through hard rock and respond to geological conditions beneath the surface. So why is using a TBM an option for the D2 Subway? Great question! Used as an alternative to drilling and blasting, TBMs can limit the damage or disturbance to the surrounding areas.  DART is planning to use a TBM when excavating the D2 Subway’s underground tunnel. However, the TBM can only tunnel in areas that contain stronger, competent rocks that provide significant geological stability, since these machines tunnel without significant structural support. Choosing the right method for the right location is critical and we need to make sure geological conditions are ideal when using a TBM. That’s a big part of our environmental review. Check back next week to learn what other methods DART engineers may employ when constructing the D2 Subway if there are alluvial soils, or softer soils, that can’t support TBMs. Want to learn more about Tunnel Boring Machines? Check out this video from the Melbourne Metro Rail Project and discover how TBMs work!
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