All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
It is not permissible to dig graves of dead people in order to study ancient civilizations and search for their remnants because it is not permissible to dig graves except for a necessity. What you mentioned in the question is not a necessity at all.
For more benefit, please refer to Fatwa 89731.
Allaah Knows best.