They should have used pantoons. Blocking was not good enough espacially near the edge of an enbankment which probably bulged out further below the enbankment.
chicopee,
What's a pantoon? Also, OSHA won't be involved, as this happened in New Zealand. Point taken though, the NZ safety authorities would likely have taken a similar approach as your OSHA.
Err, they did use Pontoons. The problem was with the underlying ground.
Not only was the existing ground saturated by being adjacent to water, but the fill they placed had been subject to torrential rains in the days preceding the lift.
Also, the signaler and operator took far too long to decide what to do with the load. It should have been put down immediately the ground problem was pointed out to he signaler.
That was not a ground strength failure, but rather a stability failure due to inadequate distance between the load and the top of the slope. Agree it was poorly planned, but you cannot rely on the signaller and operator to prevent this type of accident.
You're right in the sense that the support method was to blame, and should have been better designed.
From carrying out hundreds of lifts, I've found it's often the case that a problem can be mitigated by the response of the crew.
I have to say I think they could have responded better. I also recognize that they had about 40 seconds to make a decision. The only chance they had was to get some of the weight off those back outriggers. I think it still would have failed, but taking the time to try and bring the load back to the ground was the wrong one.
I'm no geotech, but have a look at the aftermath photos, especially the last one and see what you think.
They built a pad with sloping sides, then loaded it adjacent to the edges. Most of the load of the crane as well as the girder would have been on those two front outriggers, and the embankment was unstable under that type loading.
It looks like a classic rotational slope failure. Just from the pics in the 2nd link you can see the outrigger blocking is tilted back where it failed. The pics also show some large cracks in the trees below the crane, which looks like the toe of the failure. If you watch the video carefully ignoring the concrete beam and crane as it falls, you'll see a movement as the trees and toe of the slope shifts into the river.
It was a pretty good sized slope failure. Considering how much of a bulge the toe created, I'm guessing there was a good amount of structural fill built up the bank. Good structural fill over pudding.
