Microtunneling

A key DM Civil trenchless technology capability is our range of slurry microtunnelling machines which are capable of installing pipes from DN150 up to DN1800 into soils up to 5MPa strength and rock up to 100MPa strength. This class of microtunneling machine utilises a slurry shield system that can operate in dry or water charged ground conditions.

A mud slurry is batched adjacent to the boring pit, transferred into a slurry tank and pumped through a charge line to the head of the microtunneling machine, where it is mixed with the cuttings from the cutting head. The mixed cuttings and slurry mix is then sucked out through a discharge pipe back up to the boring pit. The discharged material it is then pumped up to a vibrating screen separator located on top of the slurry tank. Solids are discharged off the end of the vibrating screens and the fine mud slurry falls through to the tank and reused at the cutting head.

The rotating cutting head is driven by an electric motor in the boring head. The head can also be articulated horizontally and vertically by hydraulic rams to allow steering corrections to be made remotely by the operator. Steering of the machine is adjusted to maintain a laser light set up to line, level and grade in the boring pit, on the centre point of a target in the boring head.

A welded steel casing or rubber ring jointed clay, concrete, GRP or GRC jacking pipe is installed behind the boring head. These are inserted with slurry charge and discharge pipes, electrical cables, hydraulic lines and communications cables in 2.0m, 2.4m, 3.0m, 4.0m or 6.0m lengths.

In 2014, DM Civil constructed the Yanchep DN500 gravity sewer utilising DN800 steel casing attached to our Rockman TRW800 microtunnelling machine, into which the DN500 GRP sewer pipe was sleeved, and the annulus grouted.

This technology has the capability installing bore lengths up to 300 metres with an accuracy of +/- 20mm using additional in-line booster pumps and intermediate jacking stations.

This technique is a very cost-effective methodology used for bores under roads, railway lines, services and structures, in wet or dry ground conditions, where line, level and grade are critical.