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JULY 19, 2019

How Is a Tunnel Built?

Look inside a similar state-of-the-art machine that RiverRenew will use to construct its tunnel system.

RiverRenew features a new network of tunnels and sewers that will connect to the four combined sewer outfalls in Alexandria. The system will capture millions of gallons of sewage mixed with rainwater that currently pollute our waterways on rainy days.

To build the new tunnel system, RiverRenew will use a state-of-the-art tunnel boring machine (TBM) that will:

  • Allow us to build long tunnels 100 feet below ground without digging up major portions of the city;
  • Dig out the soil deep below ground and install a new tunnel in the void that’s created; and
  • Remove soil through the TBM and along the newly created tunnel, then lift it to the surface via an elevator at AlexRenew’s Water Resource Recovery Facility.

So, how exactly does a TBM do all that? We’re glad you asked!

A Rare Look Inside

Silicon Valley Clean Water (SVCW) is conducting a project similar to RiverRenew. They recently hired a German manufacturer to build a TBM to their program’s specifications and visited the factory to test the different elements of the machine. Their TBM, named “Salus” after the Roman goddess of safety, was dismantled, shipped overseas through the Panama Canal, and is nearly assembled at the project site.

SVCW developed a self-guided tour of the TBM which can be viewed at the thumbnail on the right.

The tour takes you through the following components:

  • Cutterhead, which rotates to excavate soil
  • Shield, the cylinder that houses the machine’s components
  • Trailing gear, which is almost a football field-and-a-half long!
  • Rear of the shield, where concrete rings are placed to build the tunnel in segments
  • Operator’s room
  • Inside the shield, where you’ll see the inner-workings of the TBM
  • And, if you’re still watching, you’ll walk all the way to the other end.

Get a rare look inside this underground factory!

To take the SVCW tour, click the thumbnail above and hit "Play."