I have a basement which does not have a concrete floor. i would like to add concrete floor but part of the basement has the building foundation exposed and it is higher than the floor height i would like, I can drill holes into the foundation but i do not want to compromise the exist foundation.
Without seeing the condition I can’t answer your question and be 100% certain that my answer will solve your problem, however I think I am imagining the condition correctly.
First you’ll want to establish the top of your form so that you can center your new dowels or keep your dowels below center and they don’t come out of the top of the slab. You’ll probably want to prep your soil first as well, i.e. place plastic & sand.
Where I am, we will drill into the foundation horizontally every 16" with a bit that is 1/8" larger than the selected rebar. Conditions dictate how deep to send the drill bit but I would say a 6" embedment will do the job for you. For a slab you’ll use #3 or #4 bar. Then we will clean the holes with a wire brush and air compressor to expel all of the dust from the hole. (Use a dust mask). Then you will squeeze a steel/concrete epoxy into the holes (we use Simpson or Hilti brands here.) While the epoxy is still wet you will install your rebar dowels into the holes. You want at least 16" of bar on the outside of the hole so precut your pieces to a minimum of 24". The more rebar outside the of the hole, the more material you have to tie your cage to. You will then tie the rest of your slab’s cage to the dowels in the foundation.
A structural engineer should be hired to make these type of determinations.