Cribbing on soft ground (lawn)

[ichudov]

I have a 36,000 lbs capacity Grove RT-60S RT crane. I have to take down some scrap components of huge dust collectors, unknown weight, guessed at 12-15k.

The problem is that two outriggers will have to be on a lawn, which is soft ground. A crane driving through this lawn leaves some ruts.

I have two sets of of wood crane pads, one set is 24x24, and another is about 40x40. Do you think that if I use 40x40 and a 24x24 on top, it will be enough?

Thanks

 

[lumberjack]

That's tough to answer, soft is a relative term. My crane will leave impressions in most any yard, although usually I only need my 2' square pads. I have 4x8 sheets (ground protection mats) I have stacked and used to spread the load as well as using 3 24" pads stacked in a pyramid.


I consider which outrigger(s) will see the highest load and accommodate those first. In my application it's not unusual for one outrigger to see nearly all the load while the others are just keeping the truck from rocking (the rest may be short jacked to allow traffic to pass, for example). Before taking a heavy pick on an uncertain foundation, I'll stretch out over the appropriate outriggers with the load low, see how they handle the weight, and adjust accordingly.

 

[ichudov]

Thanks. Most of what I do, involves taking things down, rather than putting them up. This is slightly safer, as after I pick the load, the radius would only decrease.

 

[Natman]

Yes, except, do you have it or does it have you! I have a horror story about a advertising sign that was supposed to weigh 2400 lbs., and ended up over 6,000. You can guess the rest, 100 foot high, jib out on the Manitex 22 ton, it didn't get away from me but I was dead in the water until help (a 50 ton crane) showed up the next day. The guys up top unbolted it except for the last two, so it was still up there but it shifted, about the time we realized this thing was a LOT heavier then we were told. and it was a very long night as when I came back I wasn't sure what I would find. The boom was side loaded, it had a real pretty bow to it due to the sign swiveling, no damage but it really gave me a heads up about latching onto things up high versus picking things up off the ground.

 

[crane operator]

Standard cribbing for me, for a crane that size, would be a 2'x3'. If crane leaves ruts when driving in around 6" deep, a 4' x 4' pad should hold that rig. If its so wet and soft that your boots sink in, and it kind of tries to grip them, and it seems there's no bottom (some clay gets "pumpy" the more you're on it the worse it gets) I've had to go to a 4'x8' pad to stay on top.

If you sink in to your knees, and it pulls your boots off- you really don't need to be in there with the crane.....

 

[Tradesman]

I posted this last fall. I'm 48500 # and the water was squishing up through the grass when we walked on it. The boom truck didn't leave a mark on the lawn. I have four plastic flotation mats and the rest was 3/4" fir plywood. Under the outriggers was a plastic mat a layer of 6x6 and 3'-0" plywood and lvl pad that I made and use daily. It felt like I was set up on a asphalt parking lot. Oops I lied its plywood under the 6x6.

 

[ichudov]

Thanks a lot, guys. The ruts are more like 3 inch deep, not quite 6 inches. The ground is not wet or soggy. I will use the 40x40 inch pads and smaller 24" pads on top of them.

What I need to do is take the top part of a dust collector off (guessed at 12-15,000 lbs), turn a little bit, lower it down almost to the ground, then when it is safely low, turn 150 degrees and set it to the ground to be torched into small pieces on the ground.

There is an electric substation nearby (high voltage into 4160 volts) and I would hate it if my crane fell on this substation.

 

[Knepptune]

You should be fine with 40" pads.

I will say, whenever your taking stuff down if its possible, loosen the bolts and make sure the crane has it before its completely cut loose. I had some guys cut a grain pipe loose on me that was still full of grain once. If i had been in a smaller crane like we had planned to send, it would have taken me over.

 

[ichudov]

Knepptune, this is exactly on how I plan on doing it -- keep four bolts, lift it and see if the entire perimeter rises up before cutting them. Great idea.