The Silo series. First one was okay though the protagonist could be a bit of an idiot at times (I'm freezing, I should light these small tires on fire. That'll keep me warm for 2 minutes while I choke on the smoke), but as a hard scifi, the series never answered enough critical questions (how do they get clean air?, is there really an oil deposit under Atlanta?). Also, the entire premise of how "wool" enters the story is so contrived, I failed to catch why it was necessary both in-universe and from a storytelling standpoint.

The second book was a prequel and the back stories of one of the characters was so fucking boring and predictable I just started skipping his chapters.

I read Wikipedia for the third book.