If it is reinforced and/or prestressed it probably does not require any ground bearing, as it probably is designed to span between supports. As for code references, you should refer to your local governing code.
Needless to say, you will likely have some sort of issue with the bearing capacity of the soil before any sort of bearing issue with allowable bearing on the concrete. You will need to have a geotech involved.
Has anyone bothered to think or ask, what the hell is this? What’s it used for, what’s it made out of, how many rebar or PT rods would even fit in it? Span lengths, spacings of these members, loadings, etc. might be of interest too. But, these days we don’t bother to give any of these important engineering design details, we just ask some dumb generic questions which could apply to a space ship or a lump of molded clay. A shape which is 6" high, 4" wide at the base, has a 2" stem and a 2-2.5" wide head, it almost looks like a crude rail for a crane rail or railroad track. But, never mind, a cantilever is a cantilever, whether it is a 1.5' long, 4' deep, and 2' wide corbel or whether it is a 150' high flag pole. They are both cantilevers, so what BEARING do the details have one the solution?
I am not confident you will find such a reference.
My limited experience with a similar precast product from AU was several decades ago for residential applications where bearing of these beams were 110mm to match the thickness of 1 skin of brick/masonry wall, sometimes 230mm if there was an engaged brick pier, or an isolated brick pier. But again, these were residential loadings, not commercial.
From a code prescribed minimum, I think you will be out of luck - and given that these products don't have shear reinforcement AND the prestressing strands have zero development at the ends, I assume that any the precast manufacturers (or one of their collective trade organisations, maybe) have done testing-to-failure of their product/s to arrive at an 'acceptable minimum'.
Did you ever 'fix' the longitudinal cracking to your other 'ground beams' of this: thread507-423137 ?