As far as i know, most JioFiber related OFC is on poles. The ones that are laid underground are mainly meant for connecting towers to fiber network. It might be possible that they will use the same underground OFC to provide JioFiber connectivity in areas where they have towers. In my locality, Jio laid underground fiber 2 years back for connecting their tower. But JioFiber still isn't available in my locality.
Meanwhile, they laid underground OFC in my friend's college campus to boost signal strength inside buildings and provide WiFi connectivity as well through indoor LTE & WiFi small cells.