soil upheaval causing concrete to rise and crack

[AAEC]

We already demolished the concrete and plan on replacing with a new concrete slab but I am not so sure how to deal with the original soil that expanded when a 2" underground emergency eyewash/shower line leak. What should I do with the original soil? Do I need to excavate and replace it with new non-expansive soil? Can I re-condition and re-use the original soil and how do you re-condition such soil?

 

[Ron]

Assuming you have an expansive clay, about the only way to treat it is to use lime or flyash, well mixed. For a relatively small area, removal and replacement with a non-cohesive, non-expansive material would be easier.

 

[oldestguy]

Are you sure it is expansive soil? It does not take much water pressure to lift a slab. In doing so, it may have added water to the soil and later drying will cause settlement of the future slab. I'd look at the soil and if it is sloppy wet, of course change it.

As Ron says, if it is expansive clay, then replace or do the lime thing.

If you are unsure, I'd ask a local geotech expert or soils lab.

 

[csd72]

The other option is to use a waffle type slab with expansion voids under it. The theory is that much of the expansion will occur at the voids minimising (but not eliminating) movement.