In recent times a large amount of infrastructure development has taken place in Sydney’s western metropolitan area. In 2004, the NSW Government allocated an estimated $A8.7 billion to be spent on roads, rail, bus networks, education and health services, linked to the staged release of land for new homes in the northwest and southwest areas of Sydney.

In particular, the area around Sydney’s northwest is experiencing a huge period of growth with a multitude of newly open residential land sites. Included in this development are a number of new transport projects, with two of these being the Orbital M7 stretching from Liverpool to Baulkham Hills and the new Transit Way being built along Old Windsor Road. Residents of western Sydney were eagerly awaiting the completion of both of these projects and they are expected to attract popular usage throughout the community. Currently both of these projects are crossing paths at the intersection of Old Windsor Road and Norwest Boulevard, Norwest Business Park.

The scope of the Telstra contract involved relocating the existing Telstra fibre network running from Norwest Boulevard, Bella Vista across into Meurants Lane, Glenwood. This relocation would cross a major arterial road (Old Windsor Road) and finish in the residential area of Glenwood. Due to the large amount of construction taking place by other contractors, the project being completed by Infrastructure Constructions had to be constructed with minimal disruption. An added difficulty for the worksite came due to the crossing of a major set of traffic lights, which were expected to upset the location system used for the drill head location. Along with all of this was the fact that all of the projects being conducted in the area were being managed by different companies, meaning strong communication networks between Telstra, Abi-Leightons, RTA, Daracon and Infrastructure Constructions were required.

One major section of the relocation work was to install eight 110 mm diameter conduits under Old Windsor Road and exit along side residential properties along Meurants Lane, Glenwood using Horizontal Directional Drilling. The total length of the bore was 256 m and had to be completed at a minimum 7 m below the proposed pylons required for the construction of the new overpass. This meant a minimum bore depth of 15 m was required. As the current topography of the landscape/road way was to change due to the construction of the M7 and RTA Transit way, a pre-bore plan had to be designed. This would ensure correct bore depths for current and future land levels including pylon construction. If the bore was not at the correct depth/location then damage may occur to the newly installed conduits when pylon installation commenced for the roadways.

Due to the ground conditions it was decided to use the Ditch Witch 4020 with a 3 inch Wenzel mud motor fitted with a 123 mm PCD (Poly Crystalline Diamond) bit. After years of drilling through many different types of rock Infrastructure Constructions have found that in certain rock formations, like Sydney sandstone, the PCD bit gives a better penetration rate and life length than a traditional tri-cone bit. To locate the drill head a Digitrak Eclipse was to be used fitted with a wire-line sonde system due to the depth of the bore.

With information supplied by Dial Before You Dig, all existing utilities were located and exposed. Next the entry pit was excavated and the pilot bore began. The first 80 m of the pilot bore followed the existing footpath and no initial problems occurred. At this point the depth was over 16 m deep with the traffic light intersection of Windsor Road next to be crossed. It was suspected that the traffic loop was going to interfere with the signal being received by the Digitrak Eclipse and unfortunately this was correct. This was predicted after initial site visits and a solution was in place to counter act this problem. The interference caused both incorrect drill head position (left to right) and depth readings. To ensure correct depth was maintained during the crossing of the intersection the drill head was brought to an almost horizontal position and tracked using its pitch. As the Eclipse can locate the sonde from well ahead (or behind) the drill head’s actual position, the receiver was walked as far in front and behind the drill head as the signal strength would allow. This gave Infrastructure Constructions a reference point and running off existing marks allowed the drill head to be successfully located for its duration under the signal loop. While this may sound easy it actually took several attempts and slightly different methods until the drill head was correctly steered under the traffic loop.

Once the drill head had crossed the intersection and correct readings were once again located, the depth was shown at 19 m and the alignment was right on target. The bore then had to be steered to the right and began its assent to the exit pit. With 120 m to go several utilities were still to be crossed including a water main, communication conduits and gas lines.

With the pilot hole finally complete and mud motor removed, a series of fluted back reamers were pulled through the bore till a 500 mm hole was established. The eight 110 mm diameter Telstra conduits were then connected via a large swivel and slowly pulled back up the borehole until finally exiting the original entry pit.

Along with the bore was the installation of up to twelve 110 m diameter conduits through trenches, pits and manhole construction along with fibre hauling and splicing. A total of approximately 7 km of Single Mode Optical Fibre is being laid along with approximately 3 km of copper cable 200 – 2,400 pair. All conduits placed under existing roads through trenching had to be concrete encased and reinstated to RTA/council specifications.