. Elements of railroad track and construction . ade is formed sloping from the center the sameas in fills. Rock cuts are usually excavated with a level 294 RAILROAD TRACK AND CONSTRUCTION. subgrade. The roadbed in tunnels may be shaped thesame as in open cuts if the volume of water to handle issmall, but if there is considerable water it is too expen-sive to make a wide tunnel and the drainage must beprovided for in some other way. One method is shownin Fig. 168. The subgrade is sloped toward the center, and a trench is excavated asshown. A tile drain of sufficientsize is laid in the trench an
. Elements of railroad track and construction . ade is formed sloping from the center the sameas in fills. Rock cuts are usually excavated with a level 294 RAILROAD TRACK AND CONSTRUCTION. subgrade. The roadbed in tunnels may be shaped thesame as in open cuts if the volume of water to handle issmall, but if there is considerable water it is too expen-sive to make a wide tunnel and the drainage must beprovided for in some other way. One method is shownin Fig. 168. The subgrade is sloped toward the center, and a trench is excavated asshown. A tile drain of sufficientsize is laid in the trench and sur-rounded by broken stone of ballastFig. 168. size. The size of the trench and the tile will be governed by localconditions. If the grade of the tunnel is not as great asdesired for the drain, the pipe can be given a greaterslope b)^ making the trench deeper toward the lower Cross-section of Cuts.—^The width of roadbedin cuts varies from 18 to 24 feet for single-track, andfrom 30 to 36 feet for double-track. In Fig. 169 is shown. Fig. 169. the shape of cross-sections in cut in use on some roads,the dimensions to the right being for double-track, andthe left for single-track. The main part of the roadbedhas a slope of J inch in one foot and then a slope oi Hinches in 1 foot into the ditch. The side slopes of the cutshould be the same as the angle of repose of the material. THE SUBGRADE. 295
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