China has a great tradition of tunnel warfare. Her adept North Korea for example built incursion tunnels that have been detected by South Korea:
Even during Napoleon's days a tunnel for invading Britain was considered among other things:
The Swiss for example have a dual use of their mountain tunnels as civilian bunkers.
I think it possible that the Chinese military rethinks the construction of bunkers and turns them rather into a network of tunnels over a large area connected by fast railways to give them the safest interior lines possible for redeploying important assets without enemy knowledge. Such tunnels could provide safety against nuclear and bunker buster attacks if they are concealed enough. They aren't just one local complex. So you could build nuclear shelters at a much shallower depths(less expensive) than currently considered if you make them a more delocalised network. Any strong explosion that would kill a local bunker complex losses much of the energy in labyrinth of tunnels.
From an economic perspective there are some great settlement agglomerations in China that would profit from such fast underground connections and would pay off as much as the Swiss idea while dual use benefits the investing and developing military.