. Railroad construction. Theory and practice. A textbook for the use of students in colleges and technical schools. By Walter Loring Webb . Fig. 88.—Hoosac Tunnel Section through Soft Ground, 192 RAILROAD CONSTRUCTION. 165. absolutely required for clearance are objectionable, because anyslight settlement of the lining which would otherwise be harm-less would then become troublesome and even dangerous. , 88, and 89 ^ show some typical Fig. 89.—St. Cloud Tunnel. 165. Grade. A grade of at least ^ is needed for the tunnel is at the summit of two grades, the t
. Railroad construction. Theory and practice. A textbook for the use of students in colleges and technical schools. By Walter Loring Webb . Fig. 88.—Hoosac Tunnel Section through Soft Ground, 192 RAILROAD CONSTRUCTION. 165. absolutely required for clearance are objectionable, because anyslight settlement of the lining which would otherwise be harm-less would then become troublesome and even dangerous. , 88, and 89 ^ show some typical Fig. 89.—St. Cloud Tunnel. 165. Grade. A grade of at least ^ is needed for the tunnel is at the summit of two grades, the tunnel gradeshould be practically level, with an allowance for drainage, theactual summit being perhaps in the center so as to drain bothways. When the tunnel forms part of a long ascending grade,it is advisable to reduce the grade through the tunnel unless thetunnel is very short. The additional atmospheric resistance andthe decreased adhesion of the driver wheels on the damp rails ina tunnel will cause an engine to work very hard and still morerapidly vitiate the atmosphere until the accumulation of poison-ous gases becomes a source of actual danger to the engineer andfireman of the locomotive and of extreme discomfort to thepassengers. If the nominal ruling grade of the road weremaintained through a tunnel, the maximum resistance would be * Drinkers Tunneling. PLATE 11.
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