The project will see the launch of new electric intercity trains on routes serving Bath from 2017.
Works under the project includes lowering the track in Box Tunnel and installing electrification equipment and canopy works at Bath Spa station.
Network Rail route managing director Patrick Hallgate said: "The work that we will be undertaking at Bath is part of our wider electrification project, delivering not only a greener and quieter railway but a better service for passengers across the south-west."
"We realise that this work will cause disruption to rail users, but we are working closely with all the relevant parties to minimise that disruption, and when the work is complete, it will pave the way for a massively improved rail service."
Scheduled to begin in 2015, the electrification work on Bath railway will be carried out in two phases.
Phase I of the project includes work on Box Tunnel area near Corsham, while Phase II covers the railway immediately east of Bath station and the direct route to Trowbridge.