The Anatomy of a Subway Different Ways to Dig!

Posted on May 11, 2017 by dartdallas
Digging a tunnel is a big deal. Excavating something so large underground may cause some impacts above-ground, especially during construction. DART wants you to have all the information before we hit the ground (literally) in the construction phase. As a member of the North Texas community, we want to create transit projects that bring value to our entire region, while making sure we remain a conscientious neighbor during the construction process. Creating a safe and serviceable tunnel is an engineering feat, and DART is pulling back the curtain, letting you in on some of the thinking and strategy we use when we consider different excavation methods. Last week we told you about the tunnel-boring method. This week, we are looking at the two other excavation methods DART will employ when building the D2 Subway. Sequential Evacuation Method You may have already guessed, the Sequential Evacuation Method (SEM) is a construction method that is executed just like it sounds.  A tunnel is divided into sections and the soil in the tunnel is moved in a specific order to create space underground.  Equipment, such as a backhoe, is used to help mine this space sequentially.  Conditions must be dry in order to complete this type of excavation.  Why would DART consider using this method when building the D2 Subway? While this process is slower than the tunnel boring method, it can be useful when trying to navigate around underground infrastructure such as a sewer system or utilities. Cut and Cover Method Finally, the cut and cover tunneling method is very common in subway construction, especially for digging shallower tunnels, creating stations, or inserting portals.  This method starts by breaking through the surface and utilizing trenches to remove soil.  Most similar to road construction, this method starts from the ground and goes MUCH deeper than your normal freeway. When a large portion of a subway is constructed using the cut and cover method many times, a temporary road deck is used to allow traffic to continue to flow above the work site.  DART may use the cut and cover method when creating stations or when creating portals that shift the tunnel from below-ground to an above-ground track. Curious about how stations are constructed? What should North Texans expect to encounter below ground when hopping aboard the D2 Subway and what parts will they see above-ground? Stay tuned for our next piece in the series Anatomy of a Subway: Exploring Stations!
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