https://www.youtube.com/watch?v=ONdPkKocbpQ

The Yinjiangbuhan Tunnel is 150 miles long, and parts will go as deep as   3,300 feet underground. This is allegedly why China had to build the tunnel :

https://thebl.com/china/china-building-worlds-largest-tunnel-to-boost-food-production-or-conceal-the-three-gorges-dam-failure.html