. Economic Papers. ut it will usually be found that the saving in length of pipewill very nearly offset the cost of the headwalls and the culvert is moresubstantial with headwalls. The types of headwalls generally used are shown in Fig. 9, p. 26. The wall type, Fig 9 (c), will generally be found cheapest and mostsatisfactory when the diameter of the pipe is less than 36 inches. Fordiameters greater than 36 inches the straight or flared wing type, (a), (b), contain less material and the parapet wall is much shorter,lessening the liability of wash around the ends. The straight wing typeis
. Economic Papers. ut it will usually be found that the saving in length of pipewill very nearly offset the cost of the headwalls and the culvert is moresubstantial with headwalls. The types of headwalls generally used are shown in Fig. 9, p. 26. The wall type, Fig 9 (c), will generally be found cheapest and mostsatisfactory when the diameter of the pipe is less than 36 inches. Fordiameters greater than 36 inches the straight or flared wing type, (a), (b), contain less material and the parapet wall is much shorter,lessening the liability of wash around the ends. The straight wing typeis usually used at the outlet end of the pipe and the flared wing type atthe inlet end. Headwalls may be built of concrete, as shown in Plate II, stone orbrick. VITRIFIED PIPE. The use of vitrified clay sewer pipe for culverts is limited to placeswhere at least 12 inches of earth may be secured above the top of thepipe, where a solid bed may be obtained and (in the western part of the 26 CULVERTS AND SMALL BRIDGES FOR. (b) Flared W/na (c) Wajj M Fig. 9.—Types of end walls. State) the fall is sufficient to prevent the possibility of water standingand freezing in it. Manyfailures have resulted from attempting to usethis type of culvert when these conditions did not exist. If conditionsare favorable, however, the culvert will be very durable. Plate IIillustrates a good method of laying culverts of this type. The relative advantages and disadvantages of vitrified pipe for cul-verts may be briefly summarized. Advantages Disadvantages (1) Low in first cost. (1) Requires heavy earth protection. (2) Desirable in that it will not rust or (2) Has little supporting strength. decay. (3) Requires a headwall under all con- (3) Quickly laid. ditions. (4) Requires care in handling and laying. Vitrified sewer pipe is made in joints 2 to 3 feet in length and intwo thicknesses of shell known as single strength and double strengthjjipe. If conditions are such that vitrified pipe may be used at all,
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