International Correspondence Schools · Scranton, Pa. : The Colliery engineer co. · leaf 367
timbered sec-tion should be enough larger than the standard section toadmit of a masonry lining. When the material is such thatthe side walls will stand of themselves for a time, hitchesA and B are excavated near the springing line and sets oftimbers placed as shown in Fig. 450. Iron clamps shoAvn… … [Fig. 450. between the lagging and the roof are filled with dry rubbleor cordwood. Roof timbers should be either 12 in. x 12 in. or 12 in.X 14 in. in cross-section, and placed with 2 to 4 feet clearspace between each set. Where the ground is very softwith a tendency to expand, larger timbers may be…
Railroad engineering
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