CAST-IRON PIPE CULVERTS. Formerly cast-iron pipes were considerably used for culverts in localities where there was no stone suitable for masonry, when a waterway was required greater than could be obtained with a vitrified pipe. Cast-iron pipe from 12 to 48 inches in diameter, in sections 6, 8, and 12 feet long, was used by all the railroads of the Mississippi Valley. Some cast their own pipe, while others bought water pipe. In recent years most roads make a pipe which is heavier than the ordinary water pipe. The dimensions differ on different roads, but the following seem to be the heaviest in common use.
At present there is a tendency to discontinue the use of cast-iron pipe culverts for two reasons, viz.: (1) The larger sizes of cast-iron pipe frequently crack under either comparatively low or very high embankments; and (2) concrete culverts can usually be made which are stronger and cheaper. But in localities where materials for making concrete are scarce, cast-iron pipe will doubtless continue to be used.
Construction. In constructing a cast-iron culvert, the points requiring particular attention are: 1. Form a depression for the socket, so the pipe may not be supported at its two' ends and possibly break as a beam. 2. Shape the soil to fit the bottom of the pipe, so that it may have a uniform support on the bottom. 3. Since the pipe is nearly certain to settle more under the middle of the roadway than at tha ends, the center of the pipe should be laid a little above a straight line joining the two ends. 4. Tamp the soil in tightly under and along the sides of the pipe to give a firm lateral support. 5. Protect the two ends by a suitable head wall. 6. If necessary lay riprap or construct an apron at the lower end to prevent scour at the outfall.
Ordinary cast-iron pipes are strong enough to support any ordi nary embankment, if the pipe is properly bedded and if the earth is thoroughly tamped against the side; but breakages do sometimes occur where the pipe is not carefully bedded, or where the earth is dumped on one side and allowed to slide down against the pipe.*
Some railroads limit the larger sizes of cast-iron pipe culverts to banks more than 8 or 10 ft. high and less than 25 or 30 ft.
The amount of masonry required for the end walls depends upon the relative width of the embankment and the number of sections of pipe used. For example, if the embankment is, say, 40 feet wide at the base, the culvert may consist of three 12-foot lengths of pipe and a light end wall near the toe of the bank; but if the embankment is, say, 32 feet wide, the culvert may consist of two 12-foot lengths of pipe and a comparatively heavy end wall well back from the toe of the bank. The smaller sizes of pipe usually come. in 12-foot lengths, but sometimes a few 6-foot lengths are included for use in adjusting the length of culvert to the width of the bank. The larger sizes are generally 6 feet long.
Fig. 154, page 573, shows the standard cast-iron pipe culvert of the New York Central and Hudson River Railroad.
Cost. The price of cast-iron pipe varies with the con dition of trade, but is about 1 J2 cents per pound, f.o.b. at the foundry. In constructing a branch railroad in Southern Illinois, on which 590 tons of cast-iron pipe were used, the average cost of unloading was 33 cents per ton, of wagon haul was 44 cents per ton per mile, and of laying was 55 cents per ton, the cost of laying being more per ton for the smaller sizes than for the larger.