Where did the soil go?

[AAEC]

We were demoing a concrete slab and when we remove the concrete cover, water was spraying in the air. We discover that a pressurize pipe was leaking under the slab for probably several years. This void was created due to the water leak. The volume of the void is about 5'x5'x3' deep. I am wondering where do the soil went? Did the small particles migrated to other areas thus creating the void?

 

[coloeng]

Is this the same concrete slab that you mentioned in the Civil Engineering topics that you demoed because it was damaged from "swelling of the soil"? If so, could it be that the soil didn't swell, but the water line break lifted the slab and the soil that is missing filled the void between the slab and the original ground?

 

[AAEC]

coloeng,

Yes, this is the same project along with the acid attacts on the Acid Trench Concrete. There were obviosly a chain of events that happen here. We suspected that it was the acid that initially cause this upheaving of the concrete. Now that we found the leak, the leak could be very well the initial cause of upheaving problem plus there maybe some acid leak from the trenches. The concrete slab above the leak actually did not have upheave problem since it create a void there. The surrounding concrete slab away from the leak is where the upheaving problem. Perhaps the water migrated to the surrounding area. My question is why one side did not have the upheave problem and the other side have? Is this due to the direction of the groundwater flow?

 

[Ron]

The acid did not likely cause swelling. The water leak found its path of least resistance and caused the slab to heave in an area where it could most affect it. It was likely an area where the water could no longer migrate laterally and built up hydraulic pressure under the slab.

It only takes a pressure of a couple of psi to lift a slab.