I remember Tunnel from my teenage years. I liked that one too. I think it was from Heinlein's juvenile series, but I'm not sure. Another one I always associate with Tunnel (because I read one after the other!) was Andre Norton's "Here Abide Monsters". Another juvenile oriented book (I think that's mostly what Norton wrote). Neither was really an "end of the world" scenario. More like, "people thrown into new worlds where they had to learn to survive". In Tunnel, it was a planned class exercise IIRC, in Monsters it was more of an impromptu, "oops, what happened, where the hell are we now?"