Lateral Pressure of Flowable Fill concrete against a basement wall

[Ron247]

I have a situation where a house transitions from a crawl space to a basement. The crawl space area immediately adjacent to the basement wall was not backfilled and the first row of interior piers for the crawl space are very close to the 8'+ drop-off. There has been soil sloughing off over time near the piers.

I told the Owner of the possible remedies, and they decided they want to fill the area with flowable fill. I have suggested doing it in 3-4 lifts and letting each lift set up before installing the next lift.

I have questions:

1. Am I correct that once the concrete cures, the lateral form pressure from that pour is no longer present against the concrete basement wall other than any lateral soil pressure from the embankment that may have "shifted" during the pour?
2. I recommended placing plastic across the bottom and up each side at least equal to the total pour height to help prevent liquid/flowable fill from seeping into the finished basement area due to the pressure. Is that reasonable to expect? It looks like the concrete wall sets on stone, not a concrete foundation.
3. I did not design the concrete wall but it was a manufactured product that was installed by the supplier. I am having owner's get confirmation from supplier it is designed for lateral soil loads of the expected height. Is there more I should have them confirm?
4. The finished floor above is wood. I have recommended well ventilating the crawl space during curing to minimize effects from the heat and moisture from the drying process of the flowable fill. Is that a reasonable expectation.
5. Anyone ever do this before, and if so, what problems did you encounter?

Any advice is greatly appreciated.

 

[TRAK.Structural]

Here's my logic, and I'm totally happy to be corrected by someone smarter than me....

The wall therefore tries to relax back to its original (vertical) shape - however, the grout now restrains it
The grout therefore ends up in compression resisting the load from the wall trying to undo its deformation
Presumably the compression profile looks very similar to the original fluid pressure profile, but it has flipped from grout pushing the wall to wall pushing the grout

This.

Sounds like there is still load whether the grout is "pushing" or the wall is "pushing".

Because the wall can't move without the pressure vanishing. For a load to matter it has to keep applying load. It has to be capable of doing work.

Yes, subsequent lifts/pours would deform the wall and pressure from the previous lift/pour would decrease. In the case of a 1 pour scenario I don't think the load totally goes away. Shrinkage maybe helps to reduce the load but how can you quantify that? Also I think the main components of shrinkage would occur in the gravity direction and in the longitudinal direction.

 

[Ron247]

Apologies if this isn't the right place, but a few people have mentioned foaming, but no one has bitten.

This looks to me to be ideal for foamed concrete fill?

I saw this mentioned in some of the responses, but I am not familiar with it at all. Over the last few years, I have not kept up with advances in the field. I will look into it also.

 

[Tomfh]

In the case of a 1 pour scenario I don't think the load totally goes away.

It probably won't. I'm just not sure why it's even worth thinking about given the fluid state is critical. Once it's set, it's set.

 

[LittleInch]

I saw this mentioned in some of the responses, but I am not familiar with it at all. Over the last few years, I have not kept up with advances in the field. I will look into it also.

It's used a lot to just fill space where you can accept a lower compressive strength. They use it a lot to fill old sewers or large voids.

 

[Tomfh]

We’ve used it to top up old slabs when weight was critical. It can be hard to source in some markets. We could get it easy in Sydney for a while then the suppliers largely stopped.

In my experience you need a good reason to use it. Smaller lifts with concrete or stabilised sand is usually more economical for general jobs.