Example. Fig. 154 shows the standard for vitrified and cast-iron pipe culverts of the New York 'Central and Hud son River R. R.* Table 83 gives the dimensions for the various diameters of pipe. Fig. 154 shows a head wall perpendicular to the barrel of the culvert; but this road also builds pipe culverts with wings splayed at an angle of 30° with the axis of the culvert.
The following notes are from the official drawing for Fig. 154.
"1. The grade of the pipe not to be less than 3 inches in 12 feet, if conditions permit. 2. Old rails 10 to 12 inches center to center to be used where soft material is found; and, where splicing of rails is necessary, they are to be fully bolted with two angle bars, and the splices in adjoining rails are to break joint. 3. Pipe joints to be made water-tight with neat portland cement and oakum. 4. The back filling in rear of pipe ends to consist of stone or other porous material. 5. All exposed corners and edges to be rounded to a 1-inch radius." Formerly, steam railroads sometimes laid vitrified culvert pipe upon a bed of concrete; but such a practice is no longer wise, since the cost of concrete has so decreased as to make it cheaper and better to construct a concrete pipe culvert or a monolithic concrete culvert (see * 1140, and also Art. 3—Box Culverts—and Art. 4—
Arch Culverts). However, if the vitrified pipe is to be used, and it can not be bedded firmly, then it may be necessary to lay a founda tion of concrete, in which case the concrete should envelop the lower third, or even the whole lower half, of the pipe so as to distribute the pressure and thus to diminish the possibility of longitudinal cracks.
Cost. Prices of vitrified pipe vary greatly with the con ditions of trade, and with competition and freight. Current (1909) prices for ordinary culvert pipe, in car-load lots f.o.b. at the factory, are about as in Table 84. Sewer pipe usually cost about 20 per cent less than culvert pipe. The standard length is 2 ft. for 24-inch pipe and less, and 2# ft. for 27-inch pipe and over.