Moonbi Hill, granite floater reduction

Moonbi, NSW

A massive granite floater sat half way up a steep hill and was in danger of collapsing onto the New England Highway, taking half the hill down with it. Two years earlier the highway was blocked for two weeks by a much smaller floater.

The task was to reduce it in size safely, without endangering traffic below, or blocking the highway for more than 10 minutes in every 30 minutes.

No percussion drilling could be risked, the floater was in a highly precarious position, any vibration could have disturbed it, causing a catastrophy, diamond coring the option, using Nimbus granite segments, helped with sharp sand.

Equipment Used

  • Darda splitters
  • Hydraulic core drill (48mm core 650mm long)
  • Darda HCS6 Combi-Shears
  • Hydraulic packs for splitters & tools
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What happened

Firstly, we must apologise for the poor image quality, no one carried mega-pixel phone cameras in 2001 and the scan from images done then, were poor quality, however, you can still see what we faced. It did not help that original images and video were on a laptop that was stolen on a trip to New Zealand, images had to be recovered from old website. This big granite floater, seen from the top on the first image and from the bottom on second, clearly shows the potential for disaster.

Our first task was to drill horizontally 1.5 metres down from the top and a vertical hole from the top, at the back where we wanted the horizontal split to end, we needed to firstly reduce it's height, then take the front of it off by 3 metres. Without causing everything behind it to go on a tour of NSW.

Timing on use of the splitters, was crucial, if we got it wrong, a vertical split could cause the whole front of it to collapse onto the highway. What we did, was use a single C9 splitter on the back vertical one, 5 minutes later, engaged two C12 on the horizontal one. The idea being to have a flat top as we came down, leaving an upright section with weight at the back of it. This was then repeated another 1.5 metres lower, after the top section had been sliced, diced and walked off the end using HCS6 Combi-Shears.

We had put Jersey Barriers up at edge of road and excavated a ditch that we filled with sand, shrubbery and as much soft material as we could find. Square objects do not roll and once into soft stuff, they don't move.

Once we had reduced it's height by some 3 metres, we then took the nose off it, then came back in 1.5 mtres for another vertical split. It is estimated that the nose of it weighed around 9.8 ton and the other verticle section 14.6 ton, both can be seen in the final two photos. Photo 6 at around 1630 and being inspected by the world's supply of RTA staff at 0800 the following morning, when we were chopping it up into movable sections. Including very lengthy safety officer briefing at start of job, completed in 3 days. You can compare image 2 with image 5, to see just how much in height and depth we reduced it. The highway was never closed for more than ten minutes and no RTA safety officer verbally abused, for more than 4 minutes, at a time!!!

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