. The elements of railroad engineering . n the fall is greater than 0 inches, RAILROAD CONSTRUCTION. 879 make a sufficient numberof drops of 9 inches eachto equal the difference inthe elevation of the twoends of the drain. At each drop, place across-sill 2 feet in culverts are not madeof greater span than 3 a wider opening isrequired, a double-box cul-vert is built with a divisionwall 2 feet in thickness. A general plan for asingle-box culvert is shownin Fig. 384. The distancemarked 10 ft. is termedthe heiglit of the embank-incnt at center line. Box culverts are gen-erally
. The elements of railroad engineering . n the fall is greater than 0 inches, RAILROAD CONSTRUCTION. 879 make a sufficient numberof drops of 9 inches eachto equal the difference inthe elevation of the twoends of the drain. At each drop, place across-sill 2 feet in culverts are not madeof greater span than 3 a wider opening isrequired, a double-box cul-vert is built with a divisionwall 2 feet in thickness. A general plan for asingle-box culvert is shownin Fig. 384. The distancemarked 10 ft. is termedthe heiglit of the embank-incnt at center line. Box culverts are gen-erally constructed of dryrubble masonry. Thestones in the abutments(also called side zualls, andhaving a height of 3 ft., inFig. 384) should be ofgood size, faced with bedsroughly dressed and laidwith joints well reaching throughfrom face to face of wallmust be used in sufficientnumbers to insure a com-pact and stable flags (4 ft. G and 1 ft. thick, inFig. 384) must be of com-pact stone free from seams. 880 RAILROAD CONSTRUCTION. and with faces dressed so as to insure a complete cov-ering. Mortar is used at the discretion of the engineerin charge. The parapet, 1 ft. thick, is laid on the coveringflags. In soft, marshy soils, a 1-foot paving will not afford a se-cure foundation, especially if quicksand be present. A pit3 feet in depth and filled with stone, leaving only sufficientdepth for the 1-foot paving, and well rammed, will, togetherwith the paving, bear any ordinary box culvert. In wet,boggy soils, a secure foundation may be obtained by exca-vating a pit of double the area of the superstructure to thedepth of 2 feet and laying a course of logs of uniform sizeover the entire bottom of the pit. A layer of broken stoneis then spread over the logs of sufficient depth to secure auniformly level surface. The paving is laid upon thissurface, and the foundation is then in readiness for theabutments. Rule I.—To Lay Out a Box Culvert on the Grou
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectrailroadengineering
