Before you begin to dig, lay out your tunnel plan and get a building permit from your state or local government. Building codes can vary tremendously among the states and even among cities, so be sure to finish the required paperwork, pay any fees and get required licenses in order.
I was involved in building an addition to the deep underground military base at Dulce, which is probably the deepest base. It goes down seven levels and over 2.5 miles deep. I helped hollow out more than 13 deep underground military bases in the United States.
DOWNTOWN'S "underground" is a system of tunnels 20 feet below Houston's downtown streets and more than 6 miles long.Having started out years ago as a tunnel between two downtown movie theaters, today it includes restaurants and service retail and connects 95 city blocks.
So building a bunker under a shack could be potentially useless unless you decide to build a tunnel leading from your home to the underground bunker, which requires more planning and more work although it is a fairly good idea and an interesting project.
The method of tunnel construction depends on such factors as the ground conditions, the ground water conditions, the length and diameter of the tunnel drive, the depth of the tunnel, the logistics of supporting the tunnel excavation, the final use and shape of the tunnel and appropriate risk management.