A Treatise on Mine-Surveying (Paperback)

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. 1891 edition. Excerpt: ... as nearly as possible in the continuation of the base-line. By means of two plumb-lines, the connection between the underground-and surface-surveys has been effected with considerable success by Mr. E. Clark in the brown haematite mines belonging to the Glendon Iron Co. of Pennsylvania. The shafts are usually 4 feet square, but, where an extensive plant of pumping machinery is required, the size is increased to 8 feet by 6 feet. The depth of the shafts varies from 75 to 200 feet. The principal difficulty in the survey of these mines has always been the trouble experienced in connecting the underground-survey with the surface-survey, on account of the small size of the shafts, and the gradual movement of the ground pushing the shaft out of the perpendicular. The method adopted by Mr. Clark has been to establish a line at the surface, and, by means of a straight-edge, wire, and plumbbob, to project that line to the bottom of the shaft, and there use it as a base-line for the underground-survey. The line across the shaft is marked in the timbers by nails, which may be permanent and used in future surveys, if the earth about the shaft is sufficiently firm. A straight-edge is placed against the nails, and the assistant above lowers the plumb-bob by means of a reel and annealed-iron wire of sufficient strength to hold the plumb-bob, which is of cast-iron, and weighs 10 lbs. The two plumb-bobs are each received into a bucket filled with water at the bottom of the shaft. Vibration may be lessened by mud thrown into the bucket. When the plummets have become nearly stationary, a theodolite is set up in line with the wires. This is done by moving the instrument until the nearer wire coincides with the vertical hair, and the second wire is concealed...