. The elements of railroad engineering . , and truss bridges occasionally lessthan 75 feet. When a cattle pass is to be built under a railroad the usual formis a stringer opening. When a highway is carried across a railroad at grade a road- 58 WOOD BOX CULVERTS 59 crossing is required; and if the highway is in the country wherestock is hkely to be driven, cattle guards are required. Cattleguards and road crossings will be used for a number of years tocome, but will eventually disappear with the abolition of allgrade crossings. CULVERTS Blind Drains. — A blind drain consists of cobble or large
. The elements of railroad engineering . , and truss bridges occasionally lessthan 75 feet. When a cattle pass is to be built under a railroad the usual formis a stringer opening. When a highway is carried across a railroad at grade a road- 58 WOOD BOX CULVERTS 59 crossing is required; and if the highway is in the country wherestock is hkely to be driven, cattle guards are required. Cattleguards and road crossings will be used for a number of years tocome, but will eventually disappear with the abolition of allgrade crossings. CULVERTS Blind Drains. — A blind drain consists of cobble or large brokenstones, carefully laid so that water in small quantities can find itsway between them and thus under the bank. A better construc-tion for the same purpose is a line of vitrified earthen pipe orcast-iron pipe, from 4 inches to i foot in diameter, laid withhead walls of rough masonry or concrete at the ends. Wood Box Culverts. — Box culverts are built of wood or stone;of wood in new construction under low embankments where stone. Fig. 21 is very expensive, wood cheap, and the item of first cost an im-portant one. Wood culverts consist of rectangular boxes as longas the width of the bottom of the embankment, and are usuallybuilt of heavy timbers, as shown in the plan. Fig. 21. A portionof the cover timbers are notched dowTi to hold the sides apart, orplanks are nailed to the under side of some of the cover timbers are fastened together with drift bolts or boat bolts are simply long pieces of round or square iron, some- 60 CULVERTS, BRIDGES, AND MINOR STRUCTURES times pointed, and with or without heads. Boat spikes are square-sectioned, long, chisel-pointed nails, forged rather than bolts are usually driven into holes bored for them. Boatspikes may be driven without boring, but the boruig is sometimesdone. Very cheap, small box culverts of i or 2 square feet in section,may be built of 2- to 3-inch plank, the sides being planks on edgeand
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectrailroadengineering
