How do you determine the thickness of concrete for slab on grade construction?
How would you determine the thickness for a new construction of a slab on grade that will have only liquid forces acting down on it?
Not sure what you mean by liquid forces, but a slab will perform differently depending many issues such as soil quality and bearing capacity. Slabs are most often edge loaded (where the load is carried by footings), but if you have a lot of weight in the center of the slab you may be bettter with a raft slab that spreads the weight evenly over the whole surface. But for your general knowledge, here is our guide on slab foundations -
Technical guide on how to build a slab on grade foundation
It is more than the thickness of concrete that will determine its structural integrity, it requires carefull planning of reinforcement steel, which would need to be done by an engineer.