There's no recovering a tunnel. Once the water comes in, you can't pump it out again. One possible solution to the spalling problem is to include tiny plastic fibers in the concrete mixture. When heated, the plastic would melt and reduce the risk of spalling. Another answer could be to use certain paints or coatings on the concrete.
Concrete buildings receive ratings indicating how long the structure can withstand fire.
Tunnel fires are an animal of a different color, with very hot temperatures lasting much, much longer. The tunnel itself sometimes works like a convection oven, drawing air in to fuel the fire. The air temperature during the Chunnel fire reached more than 1,000 degrees, heating the concrete to nearly 1,300 degrees. Professor Ulm pointed out that the United States hasn't seen a big tunnel fire like those two in Europe, but it's not impossible. Subway tunnels generally include sprinkler systems, giving them a tremendous advantage over long underground or underwater traffic and rail tunnels.