suction forces on CS's being lifted

[chicopee]

I am looking for references about suction forces on concrete slabs being lifted with a hydraulic crane. These slabs are stored and have settle a few inches in saturated soil. These slabs are to be relocated.

 

[Ltwine]

I think it is highly difficult to get a number for the lift. Rather, you should lift one edge first to loosen the contact, then you may change to a level lift if it is desirable.

For purpose of research, you may want to check into "apparent cohesion", or simply "cohesion", for cohesive soils.

 

[oldestguy]

I'd add in the atmospheric pressure times area to any cohesion you can come up with.

Reminds me of the time I loaned a pair of goulashes (buckled overshoes)to a friend who walked into a mud hole and proceeded to walk out of them. I had to go out and retrieve them. Same principles apply.

 

[Ron]

Drill a small hole through the slab and force compressed air in there. A few psi should do it. It takes about 1 psi to equalize the dead load of the concrete (if the slab is 12 inches thick, less if thinner).

 

[chicopee]

I guess an uneven leg sling will do the trick by lifting one side first to break cohesion. Thanks to the responders.

 

[apsix]

I guess an uneven leg sling will do the trick by lifting one side first to break cohesion.

It may also break the slab, depending on it's size and strength.

I'd at least dig around the edges to below the slab underside to minimise suction.

 

[Ltwine]

Before lifting, soak the slab with water, it may weaken the soil and the bond. I will try to drag, or push, the slab with slight tilt, then gradually lift it up after it has started to move. Be gentle, and make 100% certain the sling & hook have more than adequate capacity. The setup can kill if it fails.