To prevent the ceiling from collapsing on the miners as the machine eats its way through the earth, powerful, earsplitting pneumatic drills bore deep holes in the ceiling rock, into which expansion bolts are screwed to prevent cave-ins.
ON Saturday, June 11, 1983, villagers on the Indonesian island of Java could be seen rushing to their houses, frantically sealing all cracks in ceilings, windows, and doors.
IN A 160-acre (65-ha) underground vault in Missouri, U.S.A., there is a wall-to-wall and floor-to-ceiling stockpile of 2.6 billion pounds (1.2 billion kg) of butter, cheese, and dried milk.