The BulletPlow plough uses vibration of a steel bullet head to pulverise a hole underneath the ground, through which pipe is installed using free-passage towing.
“As a safeguard mechanism, a special weak link between the pipe and the machine will release well before any stress is applied to the pipe, preventing pipe damage,” said Mitchell Water Engineer Ross Bennett. “The vibrating shank and bullet head also causes fine material to shake down around the pipe, providing a good bedding environment.”
The BulletPlow is capable of working from 600 mm minimum cover down to 1.4 m deep. The current model is able to plough pipe from 63–315 mm diameter. Smaller diameter pipe is installed from coils, however, pipe with diameters exceeding 125 mm can be butt fusion-welded and ploughed in as if it were on a coil.
How the BulletPlow works
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For diameters less than 125 mm, pipe is delivered in coils, which are then loaded onto purpose-built trailers from a Hiab truck. Entry and exit holes are excavated before the pipe is attached to the head of the plough, fed from the coils into the ground, and towed behind the BulletPlow. The pipe is pulled into a hard-glazed tunnel that is compacted by a vibrating bullet, so there is very little friction between the displaced earth and the pipe.
“This method is unlike underground boring where there is a great deal of pressure on the pipe,” said Mr Bennett. “BulletPlow creates very little friction allowing the installation of long-distance pipelines without the need for frequent entry and exit holes.”
Mr Bennett said that an additional advantage of the BulletPlow technique is that the tunnel created acts to protect the pipe from being distorted during back-rolling.
“As the pipe is back-rolled, fine soils fall down the rip line and encase the pipe, giving it firm bedding and surround,” said Mr Bennett. “The ripper blade is only 35 mm in thickness and knifes through the earth as it travels along the route, so once it is back-rolled it will never sink or subside.”
Two stabilising hydraulic cylinders connect the plough attachment to the bulldozer, which are in turn operated by an automatic GPS satellite guidance system.
“This system allows the bulldozer to plough the pipe to grade with almost centimetre accuracy,” said Mr Bennett.
After the pipe is ploughed in, the bulldozer or backhoe backtracks along both sides of the rip line, completing the section.
For pipe diameters of140 mm and greater, pipes are strung and welded using quality-assured butt fusion welding. After a pipeline string is installed in the ground, each string is then joined using electrofusion welds.
Environmental benefits
Mitchell Water said that the BulletPlow offers unique environmental benefits and is highly successful in sensitive areas.
“The BulletPlow’s trenchless construction method is fast and efficient, with no soil erosion or sinkage issues, no danger to stock from open trenches, and no need to grade the surface in front of the plough or repair the ploughed surface,” said Mr Bennett.
Environmental consultant Jim McGuire said “[With the BulletPlow] you are not removing top soil – that means that you’re not effecting the vegetation that grows on the top soil, and it’s not being exposed to wind and water erosion, etc."
In addition, cultural heritage co-ordinator Les Bennett said “There have been 29 scatter sites [on the Wimmera Mallee Pipeline] for which the BulletPlow was an accepted method of pipe installation, approved by the local aboriginal communities.
“As the sites were already disturbed from farming, it was a lot better to use the BulletPlow instead of disturbing them and destroying them further by putting a grader through. The BulletPlow significantly reduces the footprint, minimising disturbance and any likelihood of loss of our cultural heritage artefacts.”
Ross Bennett said “When it’s minimal environmental and ground disturbance that counts, the BulletPlow delivers.”
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