An Elementary Textbook on Coal Mining Volume 1

An Elementary Textbook on Coal Mining Volume 1

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1897 edition. Excerpt: ...the bottom by the enormous weight of the roof, and a consequent upheaval of the bottom, or creep c, on both sides of the packs is produced. The degree of creep is greater in the road than on the far sides of the packwalls, because it is due to the combined effect of both packwalls. The shaded portion of the roof in the longitudinal sectionA shows the amount of roof that has been taken down in the road to secure height, also the way in which the creep has affected the roof. 1790. It is a very difficult matter, if not impossible, to stop a creep when it gets a start. Therefore, it is imperative to guard against accident by building the packwalls, in the first place, sufficiently wide and strong to be on the safe side. ' i TESTING THE ROOF. 1791. It is one of the important duties of a mine official to see that the roof in hauling roads, traveling roads, and even in working places is in a safe condition. The safety of the roof is judged by general appearances and the sound produced on tapping it with a small hammer m or other tool. If it looks solid and the sound indicates that it is so, the roof is usually safe; but this alone should not be implicitly relied on. The lamp should be held up to the roof, and a careful scrutiny be made for joints, or cracks. The sound may sometimes indicate that a stone is solid when it is not. This deceptive indication is generally due to the large size of the stone. Bell-shaped, wedge-shaped, and other loose pieces in an otherwise solid rock roof also emit a solid sound when struck with a pick or hammer. If a hollow sound is emitted when the roof is struck, the stone is unsafe and should be taken down, or timber set up under it. The sides must also be examined; this is usually done by carefully examining...show more

Product details

  • Paperback | 106 pages
  • 189 x 246 x 6mm | 204g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 1236907671
  • 9781236907677