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The City of Portland, Oregon

Environmental Services

working for clean rivers

Phone: 503-823-7740

Fax: 503-823-6995

1120 SW 5th Ave, Suite 613, Portland, OR 97204

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Microtunneling

Microtunneling is a trenchless method of sewer construction. It is effective in soft, unstable, and wet soils and can crush large boulders. It is similar to the Jack and Bore method, except the tunneling process is remotely controlled, not manually controlled. And Microtunneling can be used to install larger diameter pipes and longer pipe runs than the Jack and Bore method. Crews dig a sending pit and a receiving pit to install a new sewer pipe. They place a microtunnel boring machine in the sending pit and cut a hole underground horizontally from the sending pit to the receiving pit, without disturbing the surface above. As the machine drills the hole, a jacking rig functions like a jack hammer to push the new sewer pipe in place between the boring machine and the jacking rig.

The work involves the following steps:

  • Dig a sending and a receiving pit to the required depth
  • Place a microtunnel boring machine into the sending pit
  • Use the machine to cut a hole through the ground and push the new sewer pipe in place
  • Remove the microtunnel boring machine and the jacking rig
  • Connect the new pipe to the existing public sewer
  • Cover open pits with steel plates—or secure the pits with fencing—at the end of each day as needed while work is in progress
  • Backfill pits with sand or gravel and apply temporary asphalt patches
  • Conduct quality control inspections
  • Complete permanent pavement restoration of patched pits after work passes inspections