. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools . Fig. 66. inapphcable for inclined holes or even for vertical holes in con-fined places, such as tunnel-headings. For such places the onlypractical hand method is to use hammers. This may be doneby light drills and light hammers (one-man work), or by heavierdrills held by one man and struck by one or two men with heavyhammers. The conclusion of an exhaustive investigation as tothe relative economy of light or heavy hammers is that the light-hammer method is more economical for t
. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools . Fig. 66. inapphcable for inclined holes or even for vertical holes in con-fined places, such as tunnel-headings. For such places the onlypractical hand method is to use hammers. This may be doneby light drills and light hammers (one-man work), or by heavierdrills held by one man and struck by one or two men with heavyhammers. The conclusion of an exhaustive investigation as tothe relative economy of light or heavy hammers is that the light-hammer method is more economical for the softer rocks, theheavy-hammer method is more economical for the harder rocks,but that the light-hammer method is always more expeditiousand hence to be preferred when time is important. The subject of machine rock-drills is too vast to be treatedhere. The method is only practicable when the amount ofwork to be done is large, and especially when time is machines are generally operated by compressed air for tun-nel-work, thus doing the additional service of supplying freshair to the tunnel-headings
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