What is it about a slab on grade you want to know?   Is it for pavement? Warehouse floor?  Commercial floor?  Residential floor?  Industrial?

Please provide more info so we can help.

NOt much to a slab-on-grade.  Mostly depends on your application.  Commercial/induatrial vs. residential.  Typically a 5" slab reinf'd w/6x6-8x8 WWM is more than adequate for slab-on-grade.  However, make sure your soil is compacted properly.  A vapor barrier over crushed stone wouldn't be a bad idea, either.

nonso, my friend

This subject has been extensively received attention in these forums and Ron,JAE etc friends once gave me very good inputs

So let me direct you to thread 592-4955  which I posted in Concrete engineering forum asking about the subject

You will find the responses there very helpful.

When it comes to software(I am against blind use of) I know that slabs on grade can be modelled by plates on springs (where necessary) as a method accepted by many institutions. You are not likely to need this complication though. As for books, get anything from PCA.

Good luck
IJR

Hi nonso,
For grade slab of water retaining structure the minimum thickness should be ((Height of water(in mm)/40 + 50 mm))
i.e. if the water height 5000 mm then minimum thickness should be 5000/40+50 = 175 mm. (considering no ground water table)

For grade slab of basement, the thickness will based on the ground water table .

Please give details for specific condition.

There are some great resources from the US Army
Corps of Engineers.  Everything from concrete pavement design manuals, to slabs subject to heavy loads.  Most of their manuals are available for download straight from the site.  An excellent reference area for a lot of civil engineering topics.  

I believe the site is www.usace.mil, navigate to technical publications.