Sub-base for concrete compacting more than anticipated

[Dazzy50]

Hi all,

I am currently in the process of constructing a 15 x 11 concrete slab. Will house a 14 x 10 workshop.

Original plan was to have 3" of sub-base (standard MOT type 1 aggregate) and 3" of concrete in a 5:1 ratio.

I have clay soil that is pretty much dry (mostly).

I have laid all the sub-base today and began compacting it, but it's compacting the clay underneath more than anticipated, so now there's a bigger gap in my concrete shuttering than I had originally planned for.

I am not sure how to proceed.

I have 3" of compacted sub-base. Can I just fill the remaining with concrete or would it be best to fill with more sub-base?

Is this a typical feature of clay soils? Unless I was to lay it in the midst of summer in the baking heat there's always a bit of give in clay soil, so am not sure how this is usually done?

Many thanks in advance,

Daz

 

[^woody^]

Either. But I'd suggest that 100mm of concrete would be better than 75mm in any case.

 

[Dazzy50]

Thanks for the reply Woody. No issues with the concrete section being thicker than the MOT section then if I was to just fill the remaining shuttering up to the rim with concrete? I don't know if you need a certain ratio of thicknesses in the levels.

 

[^woody^]

There are no ratios.

The hardcore is just a more economical way of filling the gap left by the removal of the soft soil.

But do ensure that you have dug down to a firm layer of the soil. You don't want to be laying the base on soft soil if firmer ground is just a few inches below.

If the ground is the same for a good depth yet, then that will be OK.