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:
- Excavate 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.