Gap under concrete border/deck

[cipher]

We have a 4 foot concrete border/deck that surrounds our pool which is then surrounded by our lawn. Late last year I saw both a racoon and a rabbit disappear into an opening where the lawn met the concrete border. At the time I thought they had dug out a bit of earth from under the concrete border and were using that area for shelter.

Fast forward to today and I finally decided to see if I could fill in these two openings and see if they did any damage. However, after digging a trench along one side of the concrete border and looking underneath I discovered there is about a half foot opening from the bottom of the concrete to the earth below it that extends most of the way around the pool. I'm assuming the earth settled this far down since the original owner had the pool built, but now I'm not sure what I should do. Is this something that people live with or do they fill in that gap if it develops over time. If so, what would I use to fill it in (soil, sand, stone etc)?


Here are some pics that give a better idea of what it looks like:



Here's the concrete border:

This is the trench I dug so I could see under the concrete:

Here is the gap under the concrete showing the pool wall at the back, the concrete/stone mixture on top and the earth on the bottom:

Another view of the gap:

 

[azdesertpool]

I'd fill the gap. It looks big enough that the concrete isn't supported and seems like its only a matter of time before it cracks if not catastrophically fails. I don't know what is best to use to fill it, because it seems like you need to compact whatever you do use so that is fully supports the concrete.

 

[ap2002]

Fill it in with sand, sand is thin all will fill all the small spaces down there, sand then water it down to push sand down as far as it can and repeat until it covered

 

[bmoreswim]

Mudjacking came to mind. I also thought of foam, then I searched. This could be a solution...

http://concretejack.com/erosion-under-concrete/

One of their scrolling pictures shows your exact situation.

But obviously any solution that someone else has to do will be more expensive than something you can do yourself. However, solutions you can do yourself have a greater likelihood of being less effective than those done by someone with the right equipment. Often times that's the conundrum.

 

[nu2pools]

I have the similar problem. Does anyone know of a business who can correct the sinking around the pool in northwest suburbs of Chicago?

 

[BigEinAZ]

Is that a gunite pool or liner? If it is gunite, you could pour CLSM (Controlled Low Strength Material). It's essentially a lean grout that can be excavated, with some effort, if the need ever arises. It is self leveling so it will fill all voids.

 

[cipher]

Thanks everybody for the ideas. I'm going to look a bit more into mudjacking to see what this might cost versus a DIY approach.

Is that a gunite pool or liner? If it is gunite, you could pour CLSM (Controlled Low Strength Material). It's essentially a lean grout that can be excavated, with some effort, if the need ever arises. It is self leveling so it will fill all voids.

Hi BigEinAZ, I'm not sure what a gunite pool is, but we definitely have a liner over the underneath structure which I just assumed was concrete.

 

[Pool Tool]

The CLSM, aka flowable fill, would be fine to use for a liner pool as well. It is a very wet mix and flows almost like water. It will fill all the voids and dry with little to no shrinkage. Typical concrete withstands around 3000 psi of force whereas most CLSM target ~100-150 psi yield strength meaning it can be removed "easily" if you ever have to remove it unlike typical concrete.