Kelly & Shepherd's second major innovation on this project has been its development of its "Optimum Moisture Plough", designed to overcome compaction issues where material is poorly mixed and has insufficient moisture.
The Optimum Moisture Plough consists of a Ennor agricultural offset disc plough, manufactured in Deniliquin, NSW, substantially modified for construction use. It incorporates spray bars front and rear, a high-pressure water pump, and a 7000 litre water tank, above which is mounted a filler tank into which water can be pumped while under way by a slightly modified water cart. The plough is towed by a Challenger agricultural tractor, at speeds of up to 8 km/h.
High flotation tyres, as used on Boeing 737 aircraft, can be lowered to lift the ploughing discs off the ground for travel between different parts of the worksite. They can also be part lowered when lesser ploughing depths are required.
In use, the moisture plough is simply driven along the area to be mixed and watered, with a water cart alongside to keep the water tank filled. As the ploughing discs mix the material, high-pressure jets of water are sprayed down into the mix, ensuring moisture is mixed right through it - to depths of 300 mm.
The rate of water delivery can be adjusted depending on the moisture levels required.
Compaction occurs immediately afterwards, using either a vibrating padfoot self-propelled roller or high-speed compactor.
The three key factors in achieving correct compaction are:
Typically, if moisture needs to be added to material, it will be sprayed on by a water cart.
However, this is frequently not an efficient process. The sprayed water will sit on the surface, and only penetrate a few millimetres below. In hot dry or windy weather, it will quickly evaporate off, while there is a lot of wasted water in the form of fine spray which blows off and settles elsewhere. This can be as much as 30% wastage - which in these times of extended drought and low rainfall is unacceptable and unsustainable.
The Optimum Moisture Plough delivers water to exactly where it's required: within the mix. There is no wastage, minimal evaporation and the moisture is right through the mix.
In hot, dry or windy conditions, failure to get moisture into the mix can hold up a fleet of equipment. Scrapers, dumptrucks, dozers and graders can all be sitting idle while a water cart and roller will be working to get moisture into a layer and compacting it adequately - ready for the next layer.
The moisture plough is able to achieve optimum moisture levels in a single pass, working at the same speed as our scrapers, minimising delays, hold-ups, unnecessary fleet waiting and ensuring correct compaction first time, every time.
In dry conditions, its use avoids the need to bring in a third water cart.
The Optimum Moisture Plough is also suitable for working wet or soggy material, helping it to dry out faster and mixing it in with drier material, ready for compaction. It allows wet ground to be worked up to a day earlier than would otherwise be possible.
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.
Mixing each layer of material is also imported, and the Optimum Moisture Plough does this in the process of adding moisture to the mix. In common with many cut/fill jobs, McCarthy's Terrace involves both local and imported materials, ranging from clay to silty clay to sandy clay and sand itself.
The plough mixes these materials thoroughly, eliminating the need to run over them with a dozer or grader to mix them.
Current daily production of 8000-10,000 cubic metres is comfortably handled by the plough, and we believe it could handle 13,000-15,000 cu.m a day.
The Challenger travels at 12 km/h, with the plough working an area 3 m wide and up to 300 mm deep.
The thicker the layer, the harder it is to get moisture to the bottom of the layer. Scrapers, which Kelly & Shepherd primarily uses on this project, typically put down layers in 150 mm lifts. However, dump trucks, which are also being used, will put down material in 300-400 mm lifts.
The moisture plough allows us to thoroughly mix materials put down in 400 mm loose layers, compacted to 300 mm thick.
In summary, the Optimum Moisture Plough allows Kelly & Shepherd to minimise construction delays and achieve compaction quickly and efficiently, especially in hot, dry or windy weather conditions.