Microtunnelling is a trenchless construction technique for creating small diameter tunnels used for the installation of small to medium sized pipes ranging from 0.61m to 1.5m (2ft to 5ft).
Microtunnels are constructed using specialized boring equipment called microtunnel boring machines (MTBMs) which, due to their small size, are remotely controlled as opposed to having an operator in the machine itself. The system used to operate these machines is called a remote control system.
Trenchlesspedia Explains Microtunnel
The MTBM which creates the microtunnel is first inserted at an entry point called the entry eye and the pipes to be installed are pushed behind the machine causing it to advance. This process is referred to as pipe jacking and is repeated until the MTBM reaches the end of the shaft.
During advancement, the cutting head removes the soil by grinding it into smaller particles while mixing it with a slurry mixture which is pumped to the head. The soil and slurry mixture is pumped back to the surface via discharge pumps to a separation system which recycles the slurry back to the cutting head.