From the magazine, HDD

Drilling across the nation

Codmah initially began operating in Sydney and across New South Wales, and has since expanded to undertake private and government-funded projects in the ACT, Queensland, the Northern Territory, Victoria and Tasmania.

The company has a range of HDD equipment which can cater for small tight access bores, mid-sized bores, and large diameter rock bores. Their fleet includes Vermeer 24×40, 36×50 and D100x120 drilling machines. All rigs include their own vacuum sucker truck and recycling units as required.

The case boring division of the company currently has six rigs which can install steel or concrete jacking pipes in sizes ranging from 300 to 1,350 mm in diameter; and the company also has two pipe jacking rigs that can install larger diameter pipes starting from 1,500 mm.

Penrith to Emu Plains primary gas main

Codmah is currently undertaking an HDD project which involves a crossing under the Nepean River and an under-rail bore crossing at Emu Plains. The rail crossing is under the main Western rail line, and involves approximately 70 m of thrust boring and pipe jacking to install a 375 mm reinforced concrete jacking pipe to accommodate the 200 mm steel gas main.

The HDD installation of the pipeline across the Nepean River from Penrith to Emu Plains involves the installation of approximately 583 m of 200 mm steel primary mains under the Great Western Highway at two locations. Codmah is planning to use their Vermeer D100 x120 HDD rig for the bore.

The geotechnical report for the bore shows that there is a significant layer of cobblestones on both sides of the bore. The cobblestone layer makes the bore difficult for the following reasons:

  • Construction – the cobbles and the surrounding ground will be very unstable and will continually collapse on the drill rods, head or reamer. This will make trying to maintain the integrity of the hole impossible regardless of the drilling fluids that are used. It is highly unlikely that a pipe could be pulled back through these ground conditions.
  • Environmental – the cobbles and the surrounding ground will make the retention and return of drilling fluids almost impossible. There is a high likelihood that there will be a loss of drilling fluids through these permeable ground conditions which could result in frac outs.

To address these issues, Codmah has decided to install a 600 mm steel case pipe by case boring on both the entry and exit points of the bore. The steel casing is to be installed through the initial layer of silty clay/sand, and then through the layer of gravel/cobbles. It will stop when it strikes the laminate (sandstone) layer, as per the geotechnical report.

Using this method will fix the HDD entry and exit point, leaving a very narrow window and reducing the chances of actually hitting the exit casing pipe. In order to overcome this problem, Codmah are now looking at using two HDD rigs. The Paratrack Guidance System will drill a pilot hole to a planned intersection point midway, and the second rig will drill an intersection hole from the exit point.

After intersection of the pilot shot is achieved and a complete drill string is established from entry to exit, normal reaming operations will commence and the 200 mm gas pipeline line will be installed.

Wakehurst Parkway

The recently completed Wakehurst Parkway job involved the decommissioning of an existing 375 mm medium pressure steel pipeline, and construction of a new 250 mm diameter polyethylene (PE) gas main, into an 11 km section of the existing steel gas main between Frenchs Forest Road and North Narrabeen. This was to boost the secondary gas system in the Northern Beaches area of Sydney.

The innovative method used was to pull the new PE pipe through the existing gas pipe. The upgrade required the pipe to withstand operating pressures of 1,050 kPa.

An approximately 158 m string of welded pipe was installed by HDD, allowing the rods to be inserted through the pipe section – a proven method for attaching and pulling back PE pipe.

Codmah used their Vermeer D100x120A HDD rig as the primary piece of machinery, together with Vermeer 24x40A rigs.

Codmah carried out all traffic control on this project, which involved extensive night works leading to the partial closure of a two lane major RTA road.

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