filling material for underground strucutre

[readyandsharp]

We have been tasked to close under ground storage tank in place. The tank was constructed but was never used. The tank top is made up with 1 ft concrete slab. The top of the concrete slab is 5 ft below the grade filled with soil. The tank is 130 ft long 35 ft wide and 25 ft deep (it's huge!)Void volume is close to 5000 cubic yard. One idea is to use cement/sand mixture which could flow. This is not done under any environmental law and we don't have to do any sampling.

Any comments on the idea of using cement/sand mixture? Any thoughts on how to implement it? What would be the cost of flowable fill per cubic yard?

Thanks for your responses!

 

[Ron]

So as to keep settlement down, you might want to consider using cellular concrete or lightweight insulating concrete for this application. Keep in mind that a sand-cement mixture will have a unit weight of 130 to 150 pcf. Cellular concrete will have a unit weight of about 50 pcf and lightweight insulating concrete will be in the range of 35-40 pcf.

Back in the early 1990's, I designed a similar application for a "major theme park" to fill the voids of very large artificial rocks. Worked well.

 

[oldestguy]

Take a look at the alternative costs, if that is important.

I'd bet it would be less expensive to break in the top slab and fill with ordinary earth handling equipment and hauled in earth than to work up mixtures and somehow get it into the tank and completely fill it.

 

[MTPipeliner]

Is it possible to remove the tank lid? Either whole or break it into pieces.

If you had the lid off, then you can just fill it with gravel, sand, etc.

If you have to leave the lid on then using a flowable fill of some kind seems like a good idea. You're probably talking some pretty serious money for that much flowable fill.

It seems like the cost of concrete varies quite a bit from location to location so you will probably get your most accurate answer on pricing by calling a local supplier.

Just had another idea. I'm not sure if it would work, but could you use a sand/water slurry, then devise a way to get the water out of the tank? You could pump the water out or poke a hole in the tank to let it drain out if the water table isn't too high.

 

[TDAA]

You could use a foamed sand. This will allow the material to spread, and when the bubbles break, the material consolidates. This has been used for filling near surface mines below housing in my area.

 

[AAEC]

I would recommend comparing these 3 options:
1. Flowable fill-material cost is high and labor cost is low since no mechanical compaction needed.

2. Well graded gravel - no mechanical compaction needed. Remove concrete cover. Fill the space up to the top of the concrete storage. Cover the top with non-woven geotextile. Place another geotextile with enough area to cover the rest of the gravel. The gravel layer above the concrete storage will be wrapped with the geotextile just like a "burrito wrapped". This geotextile prevents tiny particles migrating out of the sorrounding area into the gravel area.

3. Gravel mix-material cost is relatively cheap, hauling cost, and compaction cost.

Option number 2 I think is the best.

 

[Dozerman56]

Depends on your local materials but I'd bet it would be cheapest to fill with compacted local fill material. Personally I'd be careful about removing the entire top until I was sure the walls would stay in place.

 

[dik]

Do you need to fill it?

Secure/remove whatever access there was. Is it failing? If they need the space in future, there will be just more debris to remove.

Dik