For the residents of Wisemans Ferry they also have the graceful Hawkesbury River lapping at their door step. Situated 85 km from Sydney, Wisemans Ferry is cloaked in history with many relics still visible today including The Great Northern Road which was constructed in 1836 to join Sydney with the Hunter Valley. Today Wisemans Ferry is still as beautiful as ever with the weekends being a great place for local Sydney residents to relax and have lunch by the Hawkesbury.

But with the increase in population comes an increase in infrastructure.

Recently Integral Energy undertook a project to upgrade its overhead mains from Wisemans Ferry to the Lower Macdonald area to help improve the reliability of the current electrical supply. Included in this project was the requirement to install an 11 kV cable from the Wisemans Ferry side of the Hawkesbury River (south side) across to the northern side of the river to allow the upgrading of overhead mains to continue along the Lower Macdonald area. Two options were available for crossing the Hawkesbury. The cables could be strung between poles over the river or the other option was to install conduits under the river bed using horizontal directional drilling.

Underground civil construction company Infrastructure Constructions was one of the companies selected to investigate the possibility of installing conduits under the Hawkesbury River for Integral Energy. As Infrastructure Constructions thought this project was quite challenging but practical, a few specialised pieces of equipment were purchased to help survey and complete the bore. The option to drill under the Hawkesbury River called for the installation of two 140 mm HDPE conduits. The Wisemans Ferry side allowed for a fairly open entry point with room for machinery and all required equipment. The exit side positioned on the northern bank was a different story. As the northern side included the main road running to the Lower Macdonald, the continuation of the mountain range and the northern river bank, only a relatively small exit area was available (approximately 2 m long).

Due to the river itself being approximately 290 m wide and the ground formation to be encountered being mainly rock, a pre-bore plan had to be compiled to ensure that the bore was feasible. To begin, a survey was taken of the river bed using a depth sounder. These readings showed a very disturbing picture. A 22m deep channel was recorded running along the northern side of the river. This was going to make hitting the exit point extremely difficult. With all the survey distances and depths recorded, a bore plan was compiled using the atlas bore planner. Due to the ground formation and the requirement of a mud motor to penetrate the rock, a minimal bend radius was needed to be included to again ensure that the bore could be achieved. The result showed that a bore depth no shallower than 25 m below the river bed was required to ensure the exit point could be reached. This will have the drill head exiting the ground at approximately 45 degrees.

IC successfully tendered for the project and began preparations for construction to start five weeks later. Due to the difficulty of the project, it was decided to purchase the new Digitrak SST Advanced Guidance system. This system works via a wireline cable attached to the transmitter and fed through the internal diameter of the drill string which is connected to a remote display and laptop positioned next to the operator station. Due to the sensitivity of the system, two non-magnetic rods and adaptors were required to be positioned either side of the transmitter housing to ensure that the information being received from the transmitter was accurate as anything magnetic near the transmitter could cause a incorrect or false signal. Again, due to the difficulty of the bore it was decided to manufacture new non-magnetic adaptors to minimise of failure in the drill string.

The horizontal directional drill chosen to complete this project was IC’s largest machine, the Vermeer D80 x 100. With 80,000 lbs of thrust and 10,000 ft/lbs of torque, this machine had the ability to complete this project with ease. As the D80 x 100 has a relatively small foot print and is self contained, no problems were encountered manoeuvring the machine onto site. Working in conjunction with the D80 x 100 was the DFE-LE-2000 mud mixing and recycling system. This was going to allow all the drill slurry to be recycled and re-used minimising requirements for extra fresh water when mixing drilling fluids.

Before drilling could commence an accurate surface survey was completed giving several reference marks on both sides of the river. These were required to accurately calculate the entry and exit point for the Digitrak SST system. A bore plan was then entered into the laptop as a guide for the Digitrak SST. Once this was completed drilling could begin. For the first 23m only silt and clay were encountered so a conventional drill head was used. Once rock was encountered, the conventional drill head was removed and a mud motor was fitted along with a PCD bit. Drilling below the river bed and guided by the Digitrak SST, the motor mud was accurately steered to the exit point entering the pit at forty three degree angle. The exit point was spot on the money with the guidance system proving its worth.

It was then discovered that the product initially chosen to be installed may not be able to handle the critical buckling pressures required for this installation due to its depth under the river bed. Therefore it was decided, with help from the Integral Energy design team, to install a larger, thicker walled material that could handle the pressures expected at such a depth. This called for a single DN160 PE100 PN16 polyethylene pipe to be installed.

The mud motor was then removed along with all the non-magnetic rods and replaced with a 320 mm back reamer. To minimise the potential risk of the bore hole collapsing, trailing rods were connected behind the reamer as it was pulled through the pilot hole. Unfortunately, with 70 m of rods left, the coupling between the reamer and trailing drill string broke. Fortunately for the trailing rods all downhole equipment was successfully retrieved. This now meant that the hole had to be re-traced so the conventional drillhead was again fitted with the non-magnetic rods and through the Digitrak SST followed the original pilot hole. At 67m in the original pilot hole erratic readings were being received from the transmitter. It was decided to retrieve the drill string and investigate. Once all the rods had been retrieved it was discover one of the newly manufactured non-magnetic adaptors had given way, causing the conventional drillhead, one non-magnetic rod and adaptor to be dislodged from the rest of the drill string. On investigation it was noticed that the box thread in the transmitter housing was damaged and that the remaining non-magnetic adaptor on the machine side of the transmitter housing was also loose. Closer investigation proved that the material used to manufacture the non-magnetic adaptor was inadequate for its requirements and had caused the threads to stretch thus becoming loose and separating from the box thread. One very fortunate position was that the transmitter housing holding the transmitter was retrieved.

Unfortunately the conventional drillhead and non-magnetic rod were lost under the river bed so it was decided to quickly get two new non-magnetic adaptors manufactured along with a new non-magnetic rod. These were not off-the-shelve items and had to the sourced from interstate. After approximately two weeks of patiently waiting for new parts, the retracing for the pilot bore could recommence. This time the mud motor was again required as a new bore path had to be drilled until the position of the original lost drillhead was past. Once this point was past, the mud motor was steered back onto its original course until the exit point was once again reached. Again the mud motor and non-magnetic rods were removed and reamer fitted with trailing rods connected. This time the total distance was successfully back reamed. After several passes with the back reamer through the bore hole to ensure a clean hole was achieved, the DN160 PE100 PN16 polyethylene pipe was connected and successfully pulled through to the entry pit.

After a very difficult and tough bore (more so than expected), everyone could sit back and view the finished product. With the machine and equipment removed from site, all disturbed surfaces were returned back to original conditions. To take on the tough bores is not just a challenge but sometime a test of endurance and ability to resolve problems that don’t normally occur.