Direct Steerable Pipe Thrusting (DSPT) is a trenchless method where a thruster pushes a steel pipe string and microtunnelling machine along a designed bore path that can include both horizontal and vertical curves between shallow pits.
This is in comparison to conventional microtunnelling, which uses pipe jacking from a shaft to incrementally launch and jack individual pipes behind a microtunnelling machine.
This DSPT system was first developed and patented by an equipment supplier as the DirectPipe® method in 2007. In the system, a slurry microtunnelling machine excavates the soil and is steered along a planned alignment. The machine is welded to the front of a continuous steel pipe that advances through the ground at the same time. The thrust to advance the pipe and the microtunnelling machine is provided by the pipe thruster at the launch pit – allowing the pipe to be prepared as a continuous string before installation. The pipe thruster has a clamping unit to grip the pipeline and two hydraulic cylinders to provide the thrust. The excavated materials are removed by a closed slurry system within the installation pipe. A separate system injects bentonite lubrication into the annulus surrounding the pipe. The system can install large diameter pipes in a single pass and only a small annular gap is provided around the pipe during installation – which eliminates the possibility of a borehole collapse.
The method also limits the major space requirements for site work and installation to only one side of a crossing. If the space on the launch side of the crossing is also partially restricted, it is possible to weld two or more different sections of pipe string together during the installation process.