Page 488 - Moving the Earth_ The Workbook of Excavation
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BLASTING AND TUNNELING
9.88 THE WORK
FIGURE 9.75 Draw point.
FIGURE 9.76 Drag scraper installations.
largest dimension being vertical. As each block is removed, a squared timber frame is erected in
the space and roofed with planks. The stability of the material will determine whether the blocks
must be dug and shored one at a time, or if a number can be opened and then shored at one time.
This work may be started at the bottom of the ore body or of the section being worked, and the
bottom level (or slice) is followed in sequence two or three sets behind by higher slices, so that the
cross section of the front resembles the underside of stairs. The roof of each frame serves as the floor
of the one above it. The line of advance may assume any one of a number of patterns, the straight
wall from side to side of the ore or section, or a center advance followed by stepped backsides.
The strength of the timbering in a large stope depends largely on keeping the sets in exact
alignment in all three directions. If any part starts to move, diagonals and bracing plates are
installed, sections are rebuilt, or the worked-out sections may be filled with waste rock.
