Earlier this year Nacap successfully completed its engineering, procurement and construction contract for Stage 2, Supply System 5 Murray – Culgoa, which formed part of GWMWater’s Wimmera Mallee Pipeline Project (WMPP).
The WMPP is a bold and exciting project which, when complete, will replace the existing earthen channel and storage system in the Horsham region of western Victoria with approximately 9,000 km of underground pipelines and synthetically lined storages.
This Stage 2 contract was significant not for its size, but for the innovation it provided to the water industry in regard to the installation of small bore polyethylene (PE) pipelines. Nacap used its innovation to provide for improved levels of safety, environmental and landowner outcomes, as well as providing a superior quality asset at a lower capital and operational expenditure. This was achieved by the use of innovative vibratory plough construction techniques, which was a first for the water industry in Australia. The technique is also significant because it provides opportunities for the gas industry, particularly for gathering and flowline pipeline systems.
At the height of Supply System 2 pipeline construction, progress peaked at 17 km in one day. Plough technology coupled with a strong emphasis on stakeholder engagement contributed to this outstanding effort. A dedicated team of land liaison and environmental managers ensured that there were no landowner complaints or cultural heritage incidents recorded throughout the project.
Innovation – ploughed high density PE
The opportunity to trial and use the vibratory plough installation technology was inspired by Hugh Boyd, who is a Senior Superintendent for Nacap Australia. Mr Boyd did not see the logic or responsibility toward the environment when installing long lengths of small bore pipe using traditional pipeline construction techniques, so the challenge was to find a better solution. Nacap had to work with various technical providers, independent engineers, pipe suppliers and survey experts as well as interface with GWMWater in order to adapt a new technology. Together, all parties worked in a climate of innovation and a highly successful project followed.
Nacap mobilised two vibratory ploughs to install PE pipe of 110 DN and less, to a minimum required grade. The vibratory plough consists of a bulldozer with a hydraulically powered vibrating plough attachment.
The plough unit is similar to a flat bladed ripper that cuts rather than rips the ground. The boot of the ripper is fitted with a hole reaming device that has a larger OD than the PE pipe being installed.
The vibrating action of the plough effects an oscillating vibration at the boot that creates a round hole of pulverised fine material through which the PE pipe is towed. The bulldozer acts as the tow unit whilst the vibrating boot does the significant portion of the work (to pull harder doesn’t increase installation rates). Vibratory plough installation of PE pipe has the distinction of being a rapid rate pipe installation method that could be classed as a semi-trenchless technology due to its low environmental impact.
Automatic level control was provided by a GPS system into which horizontal pipeline alignment data was placed and which controlled the installation depth whilst the machine operator ensured correct alignment.
Nacap conducted various field installation trials during the tender and pre-award period in soils similar to those expected on the project. The pre-award field trial was witnessed by WorleyParsons (engineering), Calder Harris (surveyors) and representatives of GWMWater (client) with acceptance gained from all proponents.
The construction process
Preparation of the right of way (RoW) involved a less intrusive process than that involved in open cut pipe laying. Preparation included stripping vegetation and topsoil for vibratory plough works only in areas where the RoW had localised elevation changes. This required removal for pipeline performance reasons or where the vertical profile was unsuited for ploughing such as at washouts, dry channels and water courses. The significant advantage of the vibratory plough is preventing the need to excavate bulk soil strip topsoil in most cases and mix soil horizons. Soil remains in-situ during the pipe installation phase with only minimal disturbance.
Pipes were then delivered in coils to the RoW and laid out in preparation for ploughing.
Jointing of pipe was undertaken at jointing pits, excavated prior to ploughing. These pits had sufficient length to provide for overlapped pipe ends to be cut and stress free connection of the pipe. Jointing methods were by either electro-fusion or butt weld. Not one weld failed over the course of 519 km of high density PE (HDPE) pipe installed and tested.
Immediately following the compaction of the rip line and installation of appurtenances, the reinstatement of the RoW was conducted.
Effectiveness in improving safety
With any activity in pipeline construction there is an associated risk. It is the responsibility of all people involved to identify, assess and, when required, act to reduce the risk. The risks associated with using the vibratory plough proved relatively few when weighed against the alternative of open cut installation.
The vibratory plough removes the requirement for clear and grade, trenching, pipe laying, bedding/haunching and reinstatement activities on a large scale. Each of these activities have associated risks including fast moving machinery on clear and grade, and reinstatement, slips, trips and falls around open trenches and manual handling hazards such as sprains and strains associated with pipe laying.
In addition, the less people involved in the project obviously equates to a lesser probability of a safety incident.
Most importantly, Nacap said that the safety performance of this installation method was excellent with no lost time injuries incurred throughout the entire vibratory plough operation.
Application to gas industry
With the technology in very early stages Nacap said that it is clear, based on the multi-fronted success of this project, that there is a place for this technology within the Australian pipeline industry. A brief review of current projects in Australia point to the possible application of this installation method in the field of coal seam gas extraction, whilst the dearth of water projects will see the vibratory plough and associated safety benefits employed on a far wider scale.
Nacap has trialled the installation of larger diameter pipe from 160 mm through to 315 mm diameter HDPE with excellent results. There clearly exists a huge potential for this technology in Australia where cross country pipelining is ploughing ahead.