. Text-book on roads & pavements . ll and adds much to the securityof the culvert. Care should be taken that the culvert have sufficient 44 A TEXT-BOOK ON ROADS AND PAVEMENTS. slope and be so placed that water may not stand init, in order to prevent injury from freezing. When thisis not feasible, iron pipe should be used. The top ofthe culvert pipe should be at least 18 inches below theroad surface to avoid crushing, and for the larger sizesof pipe (24 to 36 inches), at least two feet. The ends of pipe culverts should be set in masonrywalls to give protection against the washing of theface of
. Text-book on roads & pavements . ll and adds much to the securityof the culvert. Care should be taken that the culvert have sufficient 44 A TEXT-BOOK ON ROADS AND PAVEMENTS. slope and be so placed that water may not stand init, in order to prevent injury from freezing. When thisis not feasible, iron pipe should be used. The top ofthe culvert pipe should be at least 18 inches below theroad surface to avoid crushing, and for the larger sizesof pipe (24 to 36 inches), at least two feet. The ends of pipe culverts should be set in masonrywalls to give protection against the washing of theface of the embankment, hold the ends firmly in place,and prevent the entrance of water into the earth onthe outside of the pipe. These walls to give efficient protection must be construction, going down to a solid founda-tion below the bed of the stream. They may be builtof rubble masonry, and should be laid up in hydrauliccement mortar. Such construction is represented inFig. 9. The wall must extend far enough on the side. Fig. 9. to sustain the earth of the embankment from thewaterway, or wing walls may be used extending upstream for this purpose. The waterway should bepaved above the culvert far enough to prevent scour-ing at the base of the wall. DRAINAGE OF ROADS AND STREETS. 45 For quite small streams the walls may sometimesbe onjitted if the face of the embankment about theentrance to the pipe and the waterway for some dis-tance above and below be riprapped. Where it isnecessary to economize in the cost of construction,this method is preferable to the use of very light endwalls. On streams too large for a single pipe it is ofteneconomical to lay two or three pipes side by side,rather than to construct an arch or the open way of abridge. In laying large pipes it is usually advisableto place a broken-stone or concrete foundation underthe pipes throughout their lengths to insure imiformsupport. Art. 15. Concrete Culverts. Where the waterway required is too large to
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