International Correspondence Schools · Scranton, Pa. : The Colliery engineer co. · leaf 362
ed. The timbers are put in place as the shaft is sunk. RAILROAD CONSTRUCTION. 951 Frames {sets, they are commonly called) of timber, shownat A in Fig. 447, are placed about 4 feet apart, and behindthese frames, lagging/), of either sawed timber or half roundpoles split from young trees, is placed… … Fig. 447 until another set is required, when timber struts C, mortisedinto the frames, form the permanent support. These strutsare placed one above the other, .and, together with theframes into which they are mortised, form continuous tim-ber columns extending from the bottom to the top of…
Railroad engineering
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