Work on a £50m scheme to protect homes from falling into the Combe Down stone mines near Bath begins on Monday.
The mines will be filled with foam concrete and steel supports
The work will take about three months to complete, and is starting a year earlier than expected.
The first priority is to stabilise some of the main highways through Combe Down and motorists are being asked to be patient during the disruption.
Local residents, environmental groups and English Nature have campaigned to make the mines stable for more than 10 years.
Many homeowners are reported to have experienced problems selling their houses, and even getting insurance, due to the threat posed by the old stone mines.
The city of Bath was built from the mined stone, but they were abandoned 100 years ago and are now home to a community of rare bats.
Emergency work has been carried out to shore up the caverns in the short term, with the interests of both the bats and local residents taken into account.