The Highways Network Manager for Amey, Eddie Fellows, said the A38 tunnels "really are in need of general maintenance".
Speaking to ITV News Central, he explained the work which will take place over the next seven weeks whilst the tunnels are closed 24 hours a day.
He said: "We'll be doing some structural repairs and some structural maintenance, essentially to infill the central wall through the tunnel so the northbound and southbound carriage ways are completely separate, and those will be linked only by emergency doors."
"We'll also be putting brand new lighting in the tunnels, " he added, " and we will be coating all the walls and the surfaces in the tunnels with a fire protection and that will all then be painted."
Cameras from ITV News Central went inside the St Chad's and Queensway tunnels to see the work going on there.
The A38 St Chad's and Queensway tunnels through Birmingham are now closed - and will stay closed for six weeks until September 2nd.
The ITV News Central guide to alternative transport during the Birmingham A38 tunnel closures.