What might seem like a straightforward job to drill and install bridge piles for a river crossing, understates the difficulties of working on the water and the conditions below the riverbed itself. Not only did Caporn Piling have to negotiate drilling from a barge with one of the largest Bauer rigs in Australia, the BG 45, but it had to drill some very hard rock.
"We had to drill 1,500mm diameter piles in various depths up to 32m and socket the last 6.5m into very hard rock that was 150Mpa to 200Mpa, all from a barge," said Nigel Desert, senior project manager for Caporn Piling. "But what made it more challenging was that the rock face was sloping, so we had to carefully manage the deflection this could cause both to position and verticality of the piles."
Caporn employed two Bauer rigs on barges for the job, working from opposite ends of the bridge. The smaller Bauer BG 28, a tried and tested workhorse of the Caporn fleet, dealt with the same challenges. "For the BG 28 we had to drive the pile casing down to the rock, with the addition of an oscillator, while the new BG 45 just screwed the casing in with the KDK (drive head) without an oscillator due to its increased power and weight," said Desert.
Prior planning was key to Caporn achieving great results on the Nelligen Bridge Project. "We have exceeded tender production rates on this job", said James Morris, piling superintendent for Caporn Piling. "This has been down to many factors, for example, prior to the job we designed and built our own roller bit core barrel specifically for the conditions, plus we bought the new, bigger BG 45 from Bauer Equipment in preparation for this job.
"When you stand next to the BG 45, it just doesn't shake and vibrate in the hard rock", said Morris. "You can tell that there's no stress in the KDK (drive head), the Kelly bar or in the drill bits. It does the job much easier. In the hard rock it is drilling at 1m per hour faster production rates than the other rig. Even drilling from the barge, the extra weight makes the barge list, but this is easily compensated by the rig to achieve perfect verticality. The ‘V' kinematic (mast support) system on our Bauer is just superior in hard rock drilling," said Morris.
Choosing a larger Bauer unit is paying off for Caporn Piling, allowing the capability to increase production rates in hard rock, even in challenging conditions. "Looking back, it was absolutely the right decision to get the BG 45 into our fleet, the sheer power and stability is absolutely stunning," said Sam Kelly, general manager of Caporn Piling. "I'm really happy with our team and their performance at Nelligen and really happy with the performance of our new Bauer BG 45."
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