. Economic Papers. (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. (
. Economic Papers. (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,. COUNTRY ROADS IN NORTH CAROLINA 27 single strength pipe is usually as satisfactory as double strengthand is much more economical. The joints should be filled with a 1: 3 cement mortar and tapered offwith a cone-shaped collar of mortar, as shown in Fig. 9, to prevent waterleaking through the joints, but if there is much danger of the pipesagging at the center under the weight of this fill a stiff clay may be usedin place of the cement mortar. TABLE IV—SIZES AND COSTS OF VITRIFIED PIPES Inside Diameteiof Pipes inInches 10121518 202430 3336 Areain Sq. Ft. Single Strength per Foot of Length Weightin Pounds 32436586100131270320365 List Price* Price F. O. , N. G. $ $ ApproximateCost per LinealFt. in Place $ ?Discounts on list prices f. o. b. cars at factory vary from 70% to 75%. CAST IRON PIPE. The chief use of cast iron pipe for culverts is in those places wherethe ea
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