There are many bunkers and facilities that are very deep underground.
Iran has its Furdow Nuclear Facility which is 80 meters under hard rock and special hardened cement. Iran claims to have built a military base that is under 500 meters of dirt and rock in a mountain range.
A facility 500 meters underground has entrances, air vents, radio antenna and other vital infrastructure that have ground level portions. Destroy them and you could isolate a bunker or even suffocate its inhabitants.
China has a massive nuclear bunker system that can hold 1 million people. The nuclear shelter system is up to 2000 meters deep and was built within a deep natural cave system.
Electric Tunneling Machines for Getting Out of Underground Complexes
Elon Musk’s Boring Company recently completed a 1.25 mile tunnel in Los Angeles. In 2019, Elon Musk will start building a third generation all-electric tunneling machine which should be fifteen times faster. Currently, tunneling machines have about 20 meters per day speed. The third generation tunneling machine, Prufrock, will have a digging speed of about 300 meters per day.
The all-electric digging machine does not need to have air vents for the emissions. The Prufrock Machine would only need a week to dig new exits from even China’s 2000 meter deep nuclear shelter cave system.
If entrances are collapsed then electric digging machines would be able to dig new entrances and exits. The all-electric digging machine does not need to have air vents for the emissions.
Conversely, underground facilities could be attacked by digging machines.
Massive Underground Cities and Tunnel Systems
Elon Musk wants to make tunnels all across cities like Los Angeles. He wants to make many underground tunnels instead of roads or overpasses. He sees perhaps hundreds of layers of tunnels.
Boring company has a contract to the empty Chicago Block37 train station and O’Hare International Airport. Travel time would drop to 12 minutes instead of 50 minutes. People would either travel in their own electric self-driving Tesla’s at 150 miles per hour or in Tesla built electric tunnel vehicles.
Underground cities and complexes would enable another dimension to civilization.