A defective wall at a Queensland, Australia mine was removed by two Aquajet Aqua Cutter robots, reducing what would have been a six-month job to just four weeks.
One of Australia’s leading Hydrodemolition specialist contractor’s, HiTech Industrial Services, has removed a defective section of blade wall from a mine in Mackay, Queensland using two Aquajet Aqua Cutter robots; a method that allowed continuous working despite the proximity of a railway line that placed restrictions on conventional demolition methods.
The problem had arisen when an incorrect batch of concrete had been poured for a section of the blade wall measuring 9.3 m high by 9.3 m long and with a thickness of 1 m.
Removal of the section was necessary, but had wire sawing techniques been used the deployment of the crane would have had to be scheduled around railway shutdowns.
“Using the two Aqua Cutter robots meant that our total time on-site was just four weeks, compared with an estimated six months or more that a crane and wire saw would have required,” says HiTech’s Operations Manager Damien Turner.
HiTech – which was formed in 1991 specifically to pioneer and specialise in high pressure Hydrodemolition and water jetting services – used an Aqua Cutter 710V Evolution and an Aqua Cutter HVD-6000 from Sweden’s leading Hydrodemolition manufacturer, Aquajet Systems AB; delivered through local distributor, Adelaide-based Metco Ltd.
The 710V Evolution robot was equipped with an 11m mast to enable it to comfortably reach the top of the wall. It has been designed for all horizontal, vertical and overhead operations, having a 3-D positioning of the front power head; giving the operator full freedom to reach all areas and to work in confined areas.
The HVD-6000, which has a similar 3-D feature, was fitted with a standard 5 m mast.
“There was a 32,000 volt rail line behind the site that is used to transport coal. The line is just 2 m behind the wall,” says Mr Turner. “We proposed placing an 8mm thick steel plate behind the wall, which was supported by formwork and props, to prevent flying debris hitting the trains. It also stopped the jet from hitting the power cables.
“Apart from the speed and convenience of the removal rate using Hydrodemolition techniques, the idea of the 8mm safety shield helped us to win the contract. It was important that the trains continued working. A full trainload of coal is valued at 3 million A$, so it was important to ensure there were no delays.”
Mr Turner says that although HiTech was on site for four weeks and working or on standby 24/7, the removal of the full 86m³ of defective concrete was achieved in just 172 blasting hours.
“There was a good deal of reorganising and other work going on at the site, and so much of our time was spent on active standby,” he said. “The actual work presented no unexpected problems for the Aquajet robots.”
The concrete being removed was 40 MPa, with the reinforcing bars being 32 mm diameter with generally between 150 and 200 mm spacing, although in some places the spacing was only 50 mm.
Use of Hydrodemolition ensured that the rebar was not damaged in any way whilst removing the defective concrete.
Mr Turner says that Hydrodemolition in Australia is still a relatively novel concept, but that with the technique proving to be so efficient, acceptance is spreading.