Mako Trenchless Pilot Displacement Microtunnelling
The pilot soil displacement microtunnelling system is generally used to bore sewer pipework over short to medium distances in reasonably friable materials. The system is a two stage system:
Initially a line of hollow steel 'pilot' rods jacked into the ground from the bore shaft or pit. These pilot rods displace the earth hence 'pilot displacement'. Direction of these rods are controlled from the bore pit by frequently rotating the head which has a one sided wedge. Forward movement places a side pressure on the head encouraging it to move off line. By monitoring the head with the aid of a theodolite the head can be rotated so that its location is controlled within a fine tolerance.
This process is continued until the target shaft or receival pit is encountered. Accuracy is generally within +- 20mm over a distance of 50 to 80 metres, although better results are common. However, this depends on ground conditions and obstructions which maybe encountered.
When the first pilot rod has arrived in the receival pit, an auger system and pipework is connected to the last pilot rod that has been inserted at the bore pit. The product pipe is generally used to case the auger system which extracts material from the auger head to make way for the larger diameter pipe. Pilot rods are progressively disconnected in the receival pit.
PVC pipe sizes of 150mm and 225mm diameter are generally used in line with the majority of sewer pipe sizes. Pipe grades meet the requirements of the Australian Standard.
The pilot displacement type of microtunnelling is ideally suited to dry sandy ground conditions where line and grade are critical. However, other soil types can be accommodated.
Mako has a quality multiple stage jacking system which delivers speed accuracy over longer distances than many other machines of similar type. The system is more cost efficient for longer distances as the establishment cost becomes a significant factor in short distances. However, frequently distances of 15 to 20 metres in length are undertaken.
Mako is able to provide a complete service to clients including project management, approvals, construction, connection and authority handover and approval. However, Mako is also pleased to work with other contractors in the delivery of projects and is pleased to provide specification of bore pits and site requirements so that these can be prepared as part of other works. Please refer to the Pilot Pit section.
The system is limited to a 225 diameter pipe and should be undertaken in reasonably dry or de-watered conditions.
The length of drive is dependant on ground conditions and is generally in the 30 to 50 metre distance but would generally not exceed 80 metres.
Due to the displacement requirement of the pilot head, highly compact or cementitious ground can cause extreme difficulty and abandonment of the bore. Geotechnical investigation is always recommended as part of the planning for any project requiring trenchless technologies.
The Mako slurry shield system is better suited to situations requiring longer drives and wet adverse ground conditions.