Slab on grade, deep fill

[mtsnowrider]

I'm looking at the feasibility of filling in a concrete structure instead of replacing the rotting floor system. My idea was to fill with gravel and top it with a concrete slab at the existing floor level. The fill is pretty deep though, 17 feet. Even using the most suitable free draining material (3/4" screened rock according to the material supplier) and compacting sufficiently, I would still expect some settlement. If we compact to within 95% of max, if it settles the remaining 5% later that would equate to nearly a foot of settlement. 95% is probably pretty ambitious too considering we have to use a jumping jack. Aside from placing the fill and letting it sit for a year or 2, any ideas on abating the settlement without major structural overhaul?

Thanks

 

[Ron]

Consider flowable fill (controlled low strength material-CLSM) or cellular concrete such as Elastizell.

 

[BAretired]

Your concept is wrong. Use a structural slab.

BA

 

[dhengr]

BA..... you stole my thunder, so the only thing I have left is; form the slab and utilize the basement space in the building, it must be worth something per sq.ft.; or form the slab against the fill and save on forming costs. But, the fill process might cost almost as much as the forming work. Do you have a serious water table problem that you are worried about free draining fill down at -17'? And, where and how are you going to drain it?

 

[JAE]

And adding 17 ft. of fill overall like that you will most certainly cause global settlement of the entire structure in the area of the fill. In other words, not only will your 17 feet of fill consolidate, but the soils below that fill will now see very large pressures and respond accordingly by compressing.

 

[mtsnowrider]

The space below the floor serves no useful purpose. A small amount of water migrates through the wall in a few locations and drains out a hole at the bottom that can be left in place. The hole is concrete on all 4 sides and below, global settlement is not an issue. I could construct a steel framed floor system for alot cheaper than a concrete slab on columns and not have to worry about forming and removing the forms from underneath without access to the bottom. The fill idea is appealing because it is simple and permanent, and aside from the settlement, will yield far more allowable loads than a framed floor on columns.

 

[JAE]

global settlement is not an issue

So you know what the soil properties are below the basement and can make that statement based on facts?

I don't think you can just say that it isn't an issue.

 

[mtsnowrider]

The soil below the area is solid rock, as is the case with the entire structure. And the area is less than 5% of the total building area. So those facts make me comfortable with the global settlement concern.

It is sounding like I either have settlement, or I build a new floor system instead.

 

[bigmig]

There are all sorts of products that handle things like that. Check out chemical grouting, or call Concrete Stabilization Technologies at 303-748-2473 (Littleon, CO). Another contact is Hayward Baker for the chemical grouting (in phonebook). These guys fill mine shafts with yards and yards of cementious sand slurry that sets up with structural abilities. They would point you in the right direction.

Compaction Grouting, helical piers, micropiles, driven push pins + structural slab are all other options based on your experience, budget, and settlement allowance.