Pilot Tube Microtunneling
Pilot Tube Microtunneling (PTMT) is a trenchless method to install new service lines and gravity flow sewer tunnels with pinpoint accuracy. This method requires a multi-step sequence of accurately installing a pilot tube, followed by upsizing stages to the final product pipe diameter.
- Pilot tubes are accurately installed from the launch shaft to the receiving shaft with tooling selected based on the ground conditions encountered.
- Small diameter cased augers are connected to the installed pilot tubes and advanced from the launch shaft.
- Excavated material is removed by the augers and transferred to the launch shaft for removal.
- As the cased augers advance, pilot tubes are thrust into the reception shaft where they are disassembled, cleaned, and placed into storage containers.
- If the product pipe matches the diameter of the temporary cased augers, the product pipe is connected to the last casing. The pipe then thrusts out the temporary cased augers into the reception shaft for storage until the drive is complete.
- If the product pipe is larger, a Powered Cutting Head (PCH) or Power Reaming Head (PRH) is used to increase the cut diameter to match the final product pipe. Excavated soil is removed by reversing the direction of augers and transferring the excavated material to the reception shaft.
- Accuracy: Acceptable accuracy is +/- 1-inch from the design grade and +/- 3-inches from the design alignment at any location.
- Ground Conditions: PTMT is most suitable in displaceable soils with shallow water levels or low permeability soils.
- Product Pipe: Up to 48-inch flush wall jacking pipe.
- Drive Length: Typical drive lengths are 400ft of less. Longer drives lengths have been achieved.
- Shaft Size: 8ft to 16ft typical. Shaft size is dependent on product pipe length and equipment.
The City of Minneapolis’s sewer system was originally constructed in the 1890s and in need of capacity upgrades and new extensions as part of the Nicollet Mall re-imaging effort in the heart of downtown. The highly urbanized region had many subsurface utilities and above ground buildings and structures. Read more