In 1862 Mr. Rziha employed old iron railway rails for strutting the Naensen tunnel, and his example was successfully followed in several tunnels built later where timber was scarce and expensive. The advantages which iron strutting is claimed to possess over the more common wooden structure are: its greater strength; the smaller amount of space which it takes up; and the fact that it does not wear out, and may, therefore, be used over and over again.
Fig. 28.—Strutting of Timber Posts and Railway Rail Caps.
Fig. 29.—Strutting made entirely of Railway Rails.
Iron Strutting in Headings.
—In strutting the headings the cross frames have a crown bar consisting of a section of old railway rail carried either by wood or iron side posts. When wooden side posts are used their upper ends have a dovetail mortise, and are bound with an iron band, as shown by [Fig. 28]. The base of the rail crown bar is set into the dovetail mortise and fastened by wedges. When iron side posts are employed they usually consist of sections of railway rails, and the crown bar is attached to them by fish-plate connections, as shown by [Fig. 29]. The iron cross frames are set up as the heading advances, and carry the plank lagging or poling-boards, exactly in the same manner as the timber cross frames previously described.
Fig. 30.—Rziha’s Combined Strutting and Centering of Cast Iron.
