. Railroad construction. Theory and practice . es for 4 feet span. The side walls should be carried downdeep enough to prevent their being undermined by scour orheaved by frost. The use of cement mortar is also an importantfeature of first-class work, especially when there is a rapid scour-ing current or a liability that the culvert will run under a Figs. 100 and 100a are shown standard plans for single anddouble^stone box culverts as used on the Xorfolkand Vrestern R Old-rail culverts. It sometimes happens (although veryrarely) that it is necessary to bring the grade line withi
. Railroad construction. Theory and practice . es for 4 feet span. The side walls should be carried downdeep enough to prevent their being undermined by scour orheaved by frost. The use of cement mortar is also an importantfeature of first-class work, especially when there is a rapid scour-ing current or a liability that the culvert will run under a Figs. 100 and 100a are shown standard plans for single anddouble^stone box culverts as used on the Xorfolkand Vrestern R Old-rail culverts. It sometimes happens (although veryrarely) that it is necessary to bring the grade line within 3 or 4feet of the bottom of a stream and yet allow an area of 10 or 12square feet. A single large pipe of sufficient area could not beused in this case. The use of several smaller pipes side by sidewould be both expensive and inefficient. For similar reasonsneither wooden nor stone box culverts could be used. In suchcases, as well as in many others where the head-room is not solimited, the plan illustrated in Fig. 101 is a very satisfactory. Fig. 101.—Standard Old-rail Culvert. N. & W. (1895.) solution of the problem. The old rails, having a length of 8 or9 feet, are laid close together across a 6-foot opening. Some-times the rails are held together by long bolts passing through J 210 RAILROAD CONSTRUCTION. § 191. the webs of the rails. In the plan shown the rails are confinedby low end walls on each abutment. This plan requires only 15inches between the base of the rail and the top of the culvertchannel. It also gives a continuous ballasted roadbed. ARCH CULVERTS. 191. Influence of design on flow. The variations in the designof arch culverts have a very marked influence on the cost andefficiency. To combine the least cost with the greatest effi-ciency, due weight should be given to the following elements:(a) amount of masonry, (b) the simplicity of the constructivework, (c) the design of the wing walls, (d) the design of thejunction of the wing walls with the barrel
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