Sunday, June 23, 2024

Undergrounding power cables through rock in Australia

R&R McClure use a Tracto-manufactured 28N+ GRUNDODRILL with a GRUNDOROCK low flow mud motor to drill the pilot bore

Guildford is a small settlement situated on the Loddon River some 124 km north-west of Melbourne, in the State of Victoria, Australia. It is located on the Midland Highway between the towns of Daylesford and Castlemaine. At the last census in 2016 the population of the town was recorded at 333.

As part of works to place underground the town’s power supplies to overcome local environmental impacts, the power authority responsible for the area required a new cable duct installation beneath a local rail track. Due to the obstacle of the track an open cut option for the undergrounding work was not possible so a trenchless solution was desired. It was decided to utilise the horizontal directional drilling method. Contractor R&R McClure Excavations Pty Ltd was awarded the contract to plan and execute the project.

Whilst only a single bore, the installation was not an easy one and took particular planning to execute successfully. This was because the bore was over a length more than 100 m for the installation of 110 mm diameter cable duct with a 63 mm carrier duct alongside as a pipe bundle. Not too difficult you may think.

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However, the elevation difference between the start and reception pits was 6 m and ground conditions comprised sandstone and ironstone rock near the surface at both ends of the bore with included quartz layers throughout the bore route

Rock Drill

To ensure the successful installation McClure decided to utilise a Tracto-manufactured 28N+ GRUNDODRILL with a GRUNDOROCK low flow mud motor to drill the pilot bore. This was the preferred configuration because of the PDC drill bit diameter which in this case was selected at 6½ in (165 mm), the low mud flow requirement and short length which offered a good steering angle for the drilling crew to work with. The mud motor was also adaptable to the company’s other Tracto-manufactured drills with no modifications needed. The contractor also utilised a drilling mud recycler, an AMC 500R unit, to aid in the handling of the drilling mud. Steering control and bore location monitoring was provided by using a Digi Trak F5 system with a pressure sonde in the drill housing. The installed HDPE pipe was provided on 100 m long coils at the 110 mm diameter required.

Once the launch site had been prepared and the machine set-up completed the pilot bore was started and completed in just 8 hours at a rate of around 3 to 5 minutes per drill rod.

The selection of the correct drilling configuration meant that the pilot bore was all the drilling that was necessary as the diameter of bore was sufficient to pull back the product pipe bundle without the requirement for further reaming. This configuration also meant the impact on the local populous was minimised as the drill rig with the rock drill could be located within a limited easement that was allowed by the planning process.

Ultimately the project was completed to the full satisfaction of the client and without any notable difficulties despite the hard ground conditions.

Commenting on the project for R&R McClure Tim McClure, Managing Director said: “We were very happy to use the TRACTO Grundodrill 28N+ HDD rig and the GRUNDOROCK low flow mud motor at this location. From previous experience drilling in this area we knew that the combination of these two systems would provide an effective and efficient trenchless solution to the project’s requirements in the hard ground.”

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Newsdesk
Trenchless Works bringing you balanced journalism, accuracy, news and features for all involved in the business of trenchless and no-dig from around the world

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