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Concrete Slab with Slight Slope - Will it Slide?

Concrete Slab with Slight Slope - Will it Slide?

Concrete Slab with Slight Slope - Will it Slide?

I am getting ready to pour a 14'x16' concrete slab.

About 10'x16' of the slab is on level grade and will be 5" thick.

The remaining 4'x16' of the slab slopes to about 7" thick in one corner and about 10" thick in the other corner.

The entire slab is reinforced with #4 rebar on 18" centers and the thicker portion of the slab has two layers of rebar.

My question is.....will the portion of the pad that slopes try to pull the rest of the slab down hill....or slide my pad?

I am installing a small workout pool on the 10'x16' area with about 2300 gallons of water.  Will the weight of the pool help anchor the pad?

Should I drive rebar into the ground to help anchor the pad?

I set on clay soils and the bedrock is about 30' down (30 feet!).

Any ideas are most appreciated.

Dallas, Texas

RE: Concrete Slab with Slight Slope - Will it Slide?

The simpler solution seems to me make the foundatian level, and the bottom of your pool a slab of constant thickness. I see the pool is quite small, in any case we are accustomed to thicker designs where I live.

You have 1/10 slope or so at worst under your pool, I see not big risk of your pool drifting, but some there is. Minimal movement from waves could soften adhesion by movent or unrelated undermining by some washing from rain or so, and this would overstress the zones having to take the brunt of the weight, normally this could mean a final inclination towards the slope, and then potential slippage.

You can deepen it unto the soil to nullify this effect. Anchors to the ground, well can help but I see worse than a level foundation.

In any case this and in clayey soil should not be a 3 min failure, you could see it happen and then anchor after re-leveling the thing with some jacks, your pool should be stout enough to not suffer much structural damage from such correction. But it is simpler to make it level.

RE: Concrete Slab with Slight Slope - Will it Slide?

What you are proposing does not present a significant sliding problem.  While some migration might occur over a very long time period, the most significant movement your ar likely to experience is the volume change in your near-surface clays, due to wetting/drying.

Yes, the pool will help to anchor the slab, but you don't really need to worry about it.

You should be aware that the slab you have described will be susceptible to cracking due to the thickness changes.  You should consider control joints, even though the slab is quite small and would not normally be jointed.


RE: Concrete Slab with Slight Slope - Will it Slide?

Even if you do decide to anchor the slab you should not do it by driving reinf bar into the ground. Eventually it will rust out and provide a corrosion path into the slab.

Chris Rohde
Editor, Structural D-zine

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