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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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Pilot Tube Microtunneling

Pilot Tube Microtunneling is a trenchless method of sewer construction. It is effective where pinpoint accuracy is needed for the line and the grade of the sewer pipe installation—where several underground utility lines exist in close proximity, for example. It is similar to the Microtunneling method, except that crews will place steel tubes to guide the installation of the new sewer pipe. Crews dig a sending pit and a receiving pit. They place a pilot tube microtunnel boring machine in the sending pit and install steel tubes between the sending pit and the receiving pit, without disturbing the surface above. As the machine installs the tubes, a jacking rig functions like a jack hammer to push the new sewer pipe in place behind the steel tubes.

The work involves the following steps:

  • Dig a sending and a receiving pit to the required depth
  • Place a pilot tube microtunnel machine into the sending pit
  • Install steel tubes that will establish the desired line and grade for the new sewer pipe
  • Use the machine to push the new sewer pipe in place behind the steel tubes
  • Remove the pilot tube 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