A mining shaft would be an option for a base in a Zombie Apocalypse. Since they will be at the beginning of the outbreak it is unlikely that they will be any zombies inside, also they won't be a target for Bandits because they have no resources in them. However, despite being secure they have no food or water. You would have to go out in the day to hunt or scavenge for food. While doing this you could get killed by zombies or bandits could follow you back to your base. Another con would be that always being in the dark could cause physiological problems for people that live in them. In conclusion, the cons outweigh the pros so they are not recommended. If you do decide to got to a mining shaft know that they only work for small groups (less than 20 members), because of lack of food.