History
Room and pillar mining is one of the oldest mining methods. Early room and pillar mines were developed more or less at random, with pillar sizes determined empirically and headings driven in whatever direction was convenient.
Random mine layout makes ventilation planning difficult, and if the pillars are too small, there is the risk of pillar failure. In coal mines, pillar failures are known as squeezes because the roof squeezes down, crushing the pillars. Once one pillar fails, the weight on the adjacent pillars increases, and the result is a chain reaction of pillar failures. Once started, such chain reactions can be extremely difficult to stop, even if they spread slowly.
Read more about this topic: Room And Pillar
Famous quotes containing the word history:
“The history of men’s opposition to women’s emancipation is more interesting perhaps than the story of that emancipation itself.”
—Virginia Woolf (1882–1941)
“Most events recorded in history are more remarkable than important, like eclipses of the sun and moon, by which all are attracted, but whose effects no one takes the trouble to calculate.”
—Henry David Thoreau (1817–1862)
“I believe that history has shape, order, and meaning; that exceptional men, as much as economic forces, produce change; and that passé abstractions like beauty, nobility, and greatness have a shifting but continuing validity.”
—Camille Paglia (b. 1947)