[Chaz301]

I have a 2 inch" hole through granite,  ledge, rocks and dirt with a core bore drill with two 3' extensions stuck 6 feet down! The drill i have can't go in reverse because it could unscrew and lose the core bit,I hv a hole in a cement floor under a stairwell, with limited space The chemicals i have access to are hydrochloric acid sulfuric acid muriatic acid,  also vinegar and water what would be the best combination to solve my problem please help me I've been working on this hole for 8 months thanks

[Enthalpy]

Welcome and compassion, Chaz301!

Muriatic acid is the same as hydrochloric.

Nearly no acid will do something to rocks, especially granite. Not the ones you cite. Anyway, an acid would destroy you drilling bit well before widening the hole.

Unless this is what you want: destroy the metal, keep the hole. Then hydrochloric+sulphuric is a good start. Though, you need acid amounts much bigger than the metal amount, the reaction will produce hydrogen waiting to detonate in the building, and the bubbles will let hot acid splat around. Too dangerous to my opinion. I'd prefer to destroy the drilling bit using an acetylene+oxygen torch, even with some extension to operate 2m down.

The drill bit has probably teeth of hard material that may stay at the bottom once the shaft is destroyed. To be removed before further drilling.

Did you already try a good lubricant like molybdenum bisulfide grease, to help the bit rotate ? Or a much stronger torque, if the shaft resists it? Hammer?

An other option would be to cool the bit a lot, hoping that it retracts and gets play in the bore. Dry ice (=frozen carbon dioxide) achieves −78.5 °C = −109.3 °F. Cold and carbonic gas would be the hazards.