Shipping containers (Connexes) are being used by people for underground shelters and hidden homes. These are only a few feet under the surface. Corrugated steel vertically can be used to reinforce the container roof. Weld or bolt some horizontal pieces across the roof and weld or bolt the corrugated support pieces every so often (48" or 36"). The corrugated pieces can be one foot or any length. Cover with a layer of sheet metal or plate metal and you have a good roof for under ground, deep underground.
Make sure to use a good adhesive primer and tow coats of paint before covering with earth.
Or use a honey comb mesh with corrugated steel for the reinforcement.
Approach with a calm resolve, attack with reckless indifference. Gladius Republicae!
"...use Gold like it's gunpowder..."