If you are talking about industrial facility service tunnels, then heavy concrete construction is the preferred way to go. These often carry substantial fork lift truck loads above, and serve as rated storm shelters during extreme weather events. They almost always have to be constructed by the open-cut method, so be prepared for some large excavations to accommodate them (unless you use sheet piles along the sides). Don't forget to slope the tunnel floor to a sump, and provide for automatic drainage. It's best to leave these open for ventilation, so they don't get too musty. If they must be enclosed, provide for natural and forced fan draft ventilation.
Dave
thaidavid's got it... and if you have pipe and cable trays, it's best to have 'free standing' frame supports rather than try to cast brackets into the wall... Ventilation really important... for health as well as corrosion.
