Lifting Damaged Concrete Lid

Pics or drawings would help visualize the situation.

Any military bases around that might have large nets to help out the local energy supplier? They may even throw in a heavy lift helo if it's a good photo op., good pr, etc. You know what glory hogs they are.

There's always lots of chain and lots of shackles, make your own custom net. You never have too much chain, you know.

Can't upload pictures right now...technology conflict.

It is about 18.5 ft long by 25 ft wide and weighs almost 60,000 lbs. Way too much for an aircraft even if you could get one close enough.

Picture a deep concrete vault set in the ground with about 3 ft above ground. The concrete lid is cast together with the rest so we will have to cut it off. There is a cast beam in the center that we can cut out also.

We have the means of boring some holes in the corners to allow the straps from a net to be connected to a crane. I feel that using the net and a lifting beam is the best method to remove it. Now if only I can find a net that could contain about 30,000 pounds of concrete rubble if the half I lift first crumbles.

Drew K

How big and how thick is the lid? how many lifting lugs on it and where are they located. Obviously you have access to the underside so a few through bolts to clamp a beam or two above and below to strengthen the lid should work.

I'm just trying to visualize getting a net under something you are afraid to lift.

The lid is about 8 in thick with no lifting lugs. We can drill through and bolt in some lugs.

We could clamp it with a beam but have concerns about damaging the suction hood (that was just put in 2 years ago) if the lid were to crumble.

Drew K

Use the expanding foam and plastic liner system for packaging. Lay in plastic sheeting for release purposes later, with ropes under that for lifting the foam cover you spray in to protect the hood. If the concrete crumbles, it falls on the foam layer.

That was my guess, a single layer of steel in the center. I perhaps misunderstood, I assumed that the spalled concrete had fallen on the hood without damaging it; had it fallen before the hood was installed?

Do you have room to put a temporary wooden platform below the lid?

I wonder how they installed the lid and how they intend to pick it without lifting lugs of some sort.

If it is continuously supported around the edge, you should be able to pick it with six pick points and coring holes should not send any but small debris down into the pit.

Just a thought.

It may be possible to find a pourable 2 part epoxy product that would permeate the concrete and restore hardness. From there, you could cut it into pieces and remove it in manageable chunks.

I can't vouch for this product, but it sounds kind of like what I'm talking about.

http://www.solvingconcreteproblems.com/dpsinformation.htm

Big suction cups?

This might seem a bit radical - maybe the problem can be split into two parts.

Initial Lift

Removal

To lift something crumbly like this you need a really good strong membrane to collect the bits. I would assume the worst - there will be bits everywhere. If you can hire suitable sized heavy material (woven fabric and double skin PVC) lifting pillow(s) and slowly use a compressor to inflate them, you will have a slow, steady, safe and immensely powerful lift, which will at the same time prevent the dead concrete falling in the pool - I have accidentally bent large steel frameworks with this method long long ago and can attest to its surprisingly large and controlled lifting force.

but then if its in one piece, at ~30 tons it might be a problem ( you don't say if you have ground access to the pond for a large crane)

Another idea is to introduce large polystyrene foam sheets equal to 3 times the thickness of the concrete ( so about 600mm) under a strong tarpaulin under the concrete, cut lid into sections, and then flood the pool. Use the water pressure to safely and slowly lift the concrete up enough to safely introduce cables under the slabs, every 3 ft. Binding the slabs will keep them together even if they do fail. Use a bit of 4" angle iron to distribute the load on the sharp edge. Interweave a rope around the perimeter to prevent the cables slipping inwards.

This looks like a lot of work but I think it may be easier than rigging a net.

Easier to remove as well. Once the perimeter rope is removed, the cables can be pulled out with the crane by detaching one end and simply lifting.

My concern with introducing point loads, drilling holes and using beams is that since the structural integrity of the concrete is in question, this sort of power lifting may result in a dramatic failure with unfortunate results. Crane drivers have a lot of power available and its not always possible to judge what will happen when something misbehaves, sticks, a rebar isn't cut fully thru etc.

I say slow and steady wins the race.

Good points, Capt. Moosie. My experience with concrete containing rebar is that once the rebar starts rusting the structure is fairly doomed. Before epoxy coated rebar was invented, rebar that already had started to rust was often cast into concrete. The rust does not improve adhesion, as someone tried to tell me, (a contractor) it acts like a release agent.

As we all know, once rust has started, it never stops. Concrete breathes enough to keep the corrosion going.

As the rebar rusts, it shatters the concrete as it expands. This cracking and shattering opens pathways for air and moisture to run down the rebar, destroying the slab.

So many times I see contractors setting 4" wire mesh in slabs. Even if it was up on chairs, by the time they are finished stomping around in the wet cement leveling it out, the wire has settled close to the bottom of the slab. Give it a little time, and the exposed wire on the bottom starts rusting. As the wire rusts and cracks the slab from below, the slab is destroyed. Planned obsolescence if I ever saw it. This all happens from below, so when the slab breaks up everybody is so surprised.

It sounds like you have something more like a precast concrete vault, not just a box with a lid on it...

Also, there are saw-cutting contractors that specialize in challenging concrete removal jobs. There should be several who could do a good job of it...

If you are hiring a crane, perhaps they can provide a professional rigger to set up the lift.

We got half of it out already; it came out in big pieces and the small pieces fell with no damage. We have the unit back online with a temporary cover and will deal with the rest of it (which wasn't as bad off) after the summer season.

Drew K