compaction to achieve a bearing pressure of 70KN/M2

[osayamen87]

The uderneath concrete slab is to be treated to have a bearing pressure of 70KN/M2. The organic soil has been removed and replaced with broken stones with lots of fines. This was compacted using a roller. The ground is further required to be raised by 200mm to get to he formation level to receive the concrete slab.

What type of stone and roller/compactive effort are required to achieve the 70KN/M2.

Thanks
Yamen

 

[BigH]

First off, 70 kPa is not all that much - unless you are supporting the slab on soft clayey soil - in which case your 500 mm of so of "base" is of little use. I am not sure that the 70 kPa is dead and live load or just dead load.
Presuming of course, that you have "good" soil exposed (and it is to depth) after removing the organics, one usually would compact the underside fill to something like 95% modified Proctor dry density (I like to use modified when I have load bearing - footings, slabs, etc.)
To gain an appreciation of how little 70 kPa bearing is - take a look at a chart of SPT-"N" value vs large 'footing'. Divide by 5, say to keep "settlement" to 5mm or so - and you will see that the "N" value would only need to be 20 or so - and this would be achievable under compaction noted above (and, I do realize this is for "extensive" depth - but to gain the appreciation it is an analogy that can be studied).