
Fort Regent Tunnel in St Helier is closed for overnight work between Monday and Friday until 21 February, the government has said.
Work will remove the steel panelling within the tunnel so structural engineers can complete a routine survey of the concrete lining. The government said the work last took place a decade ago.
Earlier in January, the tunnel was closed for one night for a smole test so emergency services could prepare themselves in the event of a fire.
The government said the results of the survey would help Infrastructure and Environment to "fully understand the requirements for future improvements".
It said the work would take place overnight to "minimise disruption" between 19:00 and 06:00 GMT until Friday, 21 February.