It is seeking early contractor involvement (ECI) for the scheme, which also includes work to the Malpas Viaduct and Usk River Bridge.
The estimated value of the 20-month project is between 拢30m and 拢40m.
This project involves the delivery of significant structural protection and major improvements to life safety engineering systems in the tunnels.
The tunnels were damaged by a major lorry fire in 2011.
Further details of the tender in .
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