Infrastructure Constructions rises to the challenge
Trenchless Australasia — March 2005
Since the introduction of Horizontal Directional Drilling into Australia a wide range of different utilities have been successfully installed using this technology. One company that has risen to the challenge of HDD installation is Sydney based Infrastructure Constructions.
Established in 1998, Infrastructure Constructions (IC) is a wholly owned Australian company and has become synonymous in the HDD industry with its experience, knowledge and resources in providing underground civil construction.
Rail Infrastructure Corporation Toongabbie Railway Station
Rail Infrastructure Corporation (RIC) contacted IC to investigate the possibility of using HDD to install four 140 mm diameter class 10 electrical conduits over a distance of 115 m.
RIC had requested that the project take place without altering normal train
schedules, with minimum interference to commuters and with no damage to the local environment. Another factor increasing the difficulty of this bore was the existence of another HDD bore that had previously been attempted by another company but failed due to continuous frac-outs.
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The first step was to have the site surveyed and a geotechnical investigation report compiled. This report showed a very compacted clay formation down to at least 4500 mm deep. Due to the bore path being on an alignment that intersected the walkover bridge for commuters and a well-preserved landscape garden, an electronic bore path pre-plan was compiled to help during drill head location and to show RIC personnel where the bore path (including depth) was to be drilled. After some consultation with RIC personnel an agreed route was finalised and put in place. All IC personnel involved in the project were site inducted and ticketed to work within railway property. At all times during the project at least one RIC personnel member was present.
Entry and exit pits were excavated and shored due to the close proximity of the railway line. The 10 X Grundo drill was chosen to complete this project due to its small foot print and powerful pullback capacity. A vacuum truck was also placed on site to ensure any waste water was contained and removed from site. The location of the existing bore was unknown but was believed to be no more than 1500 mm below the surface, and so a minimum depth of 3000 mm was to be observed during the bore.
The 10 X was moved on site and had the pilot bore completed within one day. An
180 mm diameter fluted back reamer was then pulled back through the hole. This procedure was then repeated with an 280 mm diameter and an 380 mm diameter reamer. Once the hole was bored out to the correct size, the four conduits were attached to the 380 mm diameter reamer via chains and a swivel, then slowly pulled back through the hole while slowly rotating. In total five days were required to drill and install the product.
Once the conduit was successfully installed, all the excess slurry was removed from the entry and exit pits via the vacuum truck, and the work site was cleaned up to original condition. No frac-outs or environmental damage occurred, and train schedules were uninterrupted and all commuters were able to travel freely to and from the railway station.
Hunter Water –Cockle Creek Project
A recent project successfully completed by IC for Hunter Water Corporation involved replacing an existing 280 mm diameter PVC water main with a 315 mm diameter PE100 PN16 pipe across Cockle Creek, Boolaroo over a distance of 110 m. The current 280 mm diameter PVC pipe had been laid across the top of the river bed and secured in place by concrete blocks. Over its life length of only 5 years the tide, weather and sun had slowly weakened the pipe,
rendering it useless as a supply line. This pipeline is used as a back-up water supply to the Teralba area and also supplies water to the Gosford/Wyong Council Water Authority. If the main supply line was to fail then the 280 mm diameter pipe would have to handle all the water flow to these areas. HDD was not the first option considered for completing this project, as it was initially considered not possible, but after some discussions and proposals, including a bore path pre-plan, Hunter Water Corporation agreed to allow Infrastructure Constructions to attempt this installation.
After all safety procedures and site
investigations had been completed the JT4020 HDD was placed on site and began the pilot bore. Due to the proximity and sensitivity of the waterways a stringent environmental plan was set in place to ensure no foreign materials such as drilling fluid entered the water system. As the river bed was very silty and was expected to continue down several metres below the river bed, the bore path was pre-planned to reach a depth of approximately 8 m deep. This ensured the product remained securely in place over its life expectancy (20 years) and also limited the chances of any frac-outs.
Once the pilot bore had been completed, an 250 mm diameter fluted back reamer was pulled back through then repeated once again with an 450 mm diameter reamer. The 315 mm diameter pipe (supplied in 12 m lengths) was joined together using electro fusion. Once boring and fusing was completed the product was attached to the 450 mm diameter reamer via a swivel and slowly pulled back up the bore into position. Once in position, the pipe was pressure tested, connected to the existing valves, concrete encased and the surrounding area re-established with grass. The project was completed to Hunter Water Corporation specifications and within budget.
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