.Low pressure sewers comprise of a small collection tank and a grinding pump on each site, a pipe through the property to a boundary kit that allows each site to be isolated when required, and a main reticulation line that transports the ground slurry from the boundary kit to a pumping station or local treatment plant.

The pump is activated when required, and because it pressurises the pipe, the pipe location is not as restrictive as for a gravity sewer. The pipe itself is polyethylene and of relatively small diameter, with lengths of pipe welded together to provide a sealed system. This type of system lends itself to installation by directional drilling, which minimises ground disturbance. The availability of directional drills with rock heads allows sewerage to be installed on rocky and/or hilly conditions. Directional drilling also has advantages in areas with a high water table, as only the entry and exit pits need to be dewatered.

Infrastructure Constructions a large fleet of 12 directional drills and has become a specialist in low pressure sewer installations in Australia – encompassing all aspects of this work, including design and construction. In fact; Infrastructure Constructions has the capability to take on ‘turn-key works’ offering a one stop shop to its clients. This approach has been recognised overseas with work currently being taken in Samoa with other possible locations being considered.

The recent acquisition of a number of rock capable directional drills – Ditch Witch JT2720 AT and JT3020AT, Vermeer D100x120 Series II – gives Infrastructure Constructions the ability to install low pressure sewer systems in most ground conditions. This fleet is complemented by excavators and trenchers for pit construction and open trenching work where more appropriate, and vacuum trucks for removing site waste.

To date Infrastructure Constructions has completed over 53 km of low pressure sewers and nearly 5 km of gravity sewer and rising main using trenchless methods.

One such project – Bega Valley’s Low Pressure Sewerage Project – required the installation of over 34 km of low pressure sewerage pipe in four townships in the Bega Valley Shire, involving 747 boundary kits.

The project began in September 2005 and was completed in April 2007, two weeks ahead of schedule.

This work was required due to an upgrade from the old style pump-out sewerage systems to a low pressure sewerage system that will pipe all the effluent to sewerage treatment plants located in the townships of Cobargo, Wolumla, Candelo and Kalaru.

The reticulation pipe works were constructed using Polyethylene pipe with sizes ranging from 40 mm through to 140mm. The main reticulation line was joined using electro fusion collars with the bulk of the pipe being supplied in 50 m to 200m lengths.

Both horizontal directional drilling (HDD) and conventional trenching methods were used during the construction period. The ground conditions changed from town to town and varied from loamy soil to decomposed granite, which didn’t initiate any major concerns except that the wear factor on the ground engaging equipment used on the HDD machine would increase.

During the construction period minimal disturbance was caused to the local residence. This was helped by using the HDD machine in all areas that had heavy traffic flow. This also minimised the ground required to be re-instated due to excess excavations.

Projects such as this demonstrate that Infrastructure Constructions has become a one stop shop for projects involving a mixture of conventional and trenchless methods ensuring they remain the leader in underground and civil constructions.