Tunnel Boring
Tunnel boring is a construction method used to install utility tunnels through the ground. Mechanical excavation of the ground is done by a cutterhead that is pre-selected based on the soil conditions prior to launching the machine. An operator located inside of the TBM controls all TBM functions including cutterhead rotation, spoil conveyance, and steering for line and grade accuracy. Excavated material from the cutterhead is conveyed to an electrically driven haul unit that transfers material to the launch shaft when full.
Pipe Jacking Mode
The TBM is advanced from the launch to reception shaft by thrust forces transmitted through the product pipe by a main jacking unit located at the launch shaft.
- Accuracy: Tunnel laser guidance. Suitable for gravity flow installations.
- Diameters: 48-in to 114-in are typical.
- Product Pipe: Pipe jacking requires a product pipe to be reinforced to handle anticipated thrust loads for the project. A flush bell and spigot design is required. Most common diameters of trenchless jacking pipe in North America are 48-in, 54-in, 60-in, and 72-in.
- Ground Conditions: Pipe jacking TBMs are most suited for non-pressurized ground to weathered rock up to 15,000 psi UCS. Various cutterheads are available such as closed-face attachments. Pressure Balance Modes are available up to 1-bar in certain diameters.
- Drive Lengths: Drive lengths are dependent on ground conditions and diameter. Typical pipe jacking projects range from 400 to 800lf. Contact representative for typical installation lengths based on project information.
Two-Pass Mode
The TBM is advanced by propulsion cylinders located inside a secondary shield at the machine. Thrust forces are transmitted to a liner that is hauled into the TBM and erected at the tail section of the shield.
- Accuracy: Tunnel laser guidance. Suitable for gravity flow installations.
- Diameters: 72-in to 168-in are typical
- Liner Type: Steel liner plate, Rib & Board – Most Common
- Ground Conditions: TBMs are most suited for non-pressurized ground to weathered rock up to 15,000 psi UCS. Various cutterheads are available such as closed-face attachments. Pressure Balance Modes up to 1-bar are available in certain diameters.
- Drive Lengths: Drive lengths are dependent on ground conditions and diameter. Two-pass installations can exceed 1,000lf. Contact representative for typical installations based on project information.
