Friday, May 27, 2005 - Greg Keane (published courtesy of Constructionequipmentnews.net)
TO PARAPHRASE Mark Twain, reports of the death of the scraper have been greatly exaggerated. Sydney contractor Brett Kelly, of Kelly & Shepherd, is one person who believes in its future and has done a lot to refine the way it is used in subdivision development.
In league with New South Wales Topcon dealer Laserquip, Kelly has applied the System 5+ machine control system to dozers and scrapers. System 5+ uses both US and Russian satellite systems, greatly reducing the timeframe in which the GPS signal can be lost due to inappropriately positioned satellites, to provide an accurate position for a machine. Kelly & Shepherd has pioneered machine control (as opposed to guidance) on scrapers in response to the need to control layer thickness when building the ground up to level. The machine control is used only for the final 100mm, with a guidance display used to build the levels up prior to that stage.
Kelly has a rural background, and many of the principles that he applies have been learnt from his father, with the twist of old methods being applied to modern equipment. Kelly believes the key factors in good soil preparation to be mixture, moisture and layer thickness. He uses scrapers because they provide greater control over layer thickness than dumpers, with this advantage enhanced by the use of GPS machine control and good operator training and supervision.
The other two factors are being addressed through the use of a modified offset disc plough towed by a Caterpillar Challenger tractor. The plough has a fibreglass water tank on top, with a water receiver above to accept refills from a water truck cannon; and an onboard pump and spraybars to inject water into the soil in the plough zone. As the plough can cut up to 280mm deep, and mixes the soil vertically, this provides even water content throughout the soil and minimises loss from spray drift, evaporation and run-off.
The plough is working with eight twin-engine scrapers, two compactors, a grader, a dozer and two water carts at Penrith Lakes (the largest construction materials quarry in Australia, supplying 65% of Sydney's sand and gravel requirements). It works behind the scrapers and ahead of the compactors, which seal in the moisture.
While the Challenger and plough combination involves an extra machine and operator, its existence is justified by being able to work wet ground earlier (by between a half and a full day), and being able to reach the required moisture content earlier on dry ground, minimising idle time for other equipment. (In dry conditions, Kelly believes using the plough avoids the need to bring in a third water truck.)
Ploughing wet ground greatly increases the surface area of soil that is exposed to air, which speeds up the drying. It also avoids having a greasy surface layer that is difficult for the scrapers and grader to gain traction in.
The plough provides an additional benefit in chopping two layers into each other, resulting in better mixing.
Current daily production of 8000-10,000 cubic metres is comfortably handled by the plough, and Kelly believes it could handle 13,000-15,000cu.m a day.
The Challenger travels at 12kmph, with the plough working an area 3m wide and 200mm deep.
Some further refinements to the water system are planned, with a swinging discharge arm to be mounted on the water trucks; the pumping system on the plough to be upgraded from 600 litres per minute to 1500l/m; more holes to be added to the spray bars to handle the increase; and an automatic on/off valve to be added to the spray system.
Work will also be done to quantify the savings using a plough, and formalise the benefits that Kelly knows from experience exist.
Kelly & Shepherd is no stranger to innovation in equipment. It has used a snow plough (with a ground pressure one eighth of a swamp dozer's) to thinly spread soil from a silt pond, then seed it with lucerne to take moisture out of the soil.
Kelly's blending of agricultural and earthmoving expertise, along with a willingness to "think outside the square", is paying dividends.