International Correspondence Schools · Scranton, Pa. : The Colliery engineer co. · leaf 369
re removed and the gaps filledwith masonry, the joints being thoroughly grouted. Allother timbers are left in place. The spaces A, /., etc., Fig.450, between the arch and roof timbers, are usually filledwith concrete. When the material through which the tunnel passes isvery soft, with slight… … Fig. 452. the heading is driven the ground composing the remainderof the section will have become thoroughly drained, and maybe taken out with much greater safety and less expensethan with a top heading. The mode of driving a headingthrough such material is illustrated in Fig. 452, in whichA…
Railroad engineering
Internet Archive · California Digital Library · Public Domain Mark 1.0. Free to use for anything.
