. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. THE GREAT ALPINE TTTNNELS. 621 When the heading is driven .sufficiently forward to justify the commencement of the main tunnel, a fresh difficulty presents itself. This main tunnel has to ])c driven down hill, and consequently the water collects at the working face A; the bottom can not therefore l)e removed until a bore-hole is put down from A to a. When this is done the remaining- excavation can be taken out, and a further length of tunne
. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. THE GREAT ALPINE TTTNNELS. 621 When the heading is driven .sufficiently forward to justify the commencement of the main tunnel, a fresh difficulty presents itself. This main tunnel has to ])c driven down hill, and consequently the water collects at the working face A; the bottom can not therefore l)e removed until a bore-hole is put down from A to a. When this is done the remaining- excavation can be taken out, and a further length of tunnel driven to B. A l)ore hole is now sunk from B to />, whilst that from A to a can be plugged up; and thus the tunnel is gradually advanced. B}' the adoption of the (iri-eathead shi(dd nuich of this difficulty can be avoided; but one su))a(iueous tunnel through water-bearing strata, at considerable depth, is sufficient for a lifetime. As an illustration of th(^ danger to which men are exposed in such work, it is stated, with nuich regret, that in a certain tunnel, notwith- f. ^^^ ^^^^^1^~ U^dr: 7'(yA^/\/£:^ ^^^^^^^. W Wa(e' Ic'-ci {-'jr Dratnage) / 600 Jn> (Not to ScaCc) Fli;. \.—Diagrammatic section to illustrate method of cDnstructint; tiiniiel helow river lied. standing every precaution l)cing taken, all the men engaged in driving the drainage heading by means of a tunneling machine have died; and in the case of the iirst Vyrnwy tunnel crossing of the River Mersey—driving by Greathead shield under pressure—the mortalit}^ was great. Having explained in very general terms some of the difficulties of tunnel construction, we will proceed to the case of the great tunnels through the Alps, and for the purpose of rendering the subject more easih^ intelligible, the following particulars may be given: Length of tunnel in miles North or east portal above sea level South or west portal above sea level. do Highest level Maximum grade in tunnel per 1,(H)0 Maximum h
Size: 960px × 2603px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorsmithsonianinstitutio, bookcentury1800, bookdecade1840
