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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 is an effective method of installing pipelines beneath highways, railroads, runways, harbors, rivers, and environmentally sensitive areas where a maze of underground utility lines already exist. Microtunneling is a digging process that uses a remotely controlled microtunnel boring machine (MTBM) combined with the pipe jack-and-bore method to directly install pipes underground in a single pass. This process avoids the need to have a long stretch of open trench for pipe-laying. Microtunneling includes these steps:

  • Microtunnel ShaftExcavate launching and reception shafts at opposite ends of the tunneling drive.
  • Hydraulic jacks in the launch shaft push a microtunnel boring machine (MTBM) into the earth.
  • Pipes containing slurry water transport excavated spoils to the surface
  • Retract the jacks and disconnect slurry lines and control cables.
  • Lower a pipe or casing into the shaft and insert it between the jacking frame and the MTBM.
  • Reconnect slurry lines and control cables and advance the MTBM another drive.
  • Repeat the process until the MTBM reaches the reception shaft.
  • Retrieve the MTBM and trailing equipment.

In addition to a hydraulic jacking system to advance the MTBM and pipe, most microtunneling operations require a lot of equipment on the construction site, including:

  • A closed loop slurry system to transport excavated spoils
  • A slurry cleaning system to remove spoils from the slurry water
  • A lubrication system to lubricate the exterior of the pipe during installation
  • A guidance system to provide line and grade control
  • An electrical supply and distribution system to power equipment
  • A crane to hoist pipe sections into the jacking shaft
  • Trucks and loaders to transport spoils off site

What to Expect During Microtunneling

  • The equipment is loud and causes vibration that you may feel in your home or business. This is standard for this method of construction.
  • Both preparation and post micro-tunneling work can take a few weeks to complete. 
  • Shafts are usually too large to cover safely with steel plates during non-construction hours. Site fencing is necessary to secure these areas during non-construction hours.
  • There may be road closures and lane restrictions.
  • There may be inactivity bewteen some phases of this process.
  • Typical work hours are 7:00 a.m. to 6:00 p.m. Monday through Friday, but the contractor may schedule work during the same hours on Saturdays.