Am I liable for one expiation or multiple expiations if I repeatedly swear with different formulations to abandon a single act, then break my oath, and have not offered expiation for the previous oaths?

The Shari'ah has forbidden excessive oath-taking, and your situation will not fall outside of two possibilities:

First: The oaths are successive, and the sworn-upon action has not been performed in between them. In this case, a single expiation (kaffarah) becomes obligatory upon you when you break the oath.

Second: You swear an oath, then break it, then swear another oath. If you have already paid the expiation for the first oath, then another expiation becomes obligatory for the subsequent oath by consensus. If you have not paid it, then the soundest opinion is that an expiation is obligatory for each oath.

Jurists have differed regarding the multiplicity of expiations due to the multiplicity of oaths. Some have held that an expiation is obligatory for each oath, while others have held that only a single expiation is required.