. The elements of railroad engineering . firm and secure, such as hard clay, sand, gravel,or rock, a deep trench must be dug to receive the founda-tion. If the soil is soft or marshy, it may be necessary todrive piles and cut them off at a uniform elevation belowthe water-line, and fill betAveen and to the depth of one footabove tops of piles with concrete made with hydraulic cement. 800 RAILROAD CONSTRUCTION. Tlie trench should extend outside the lines of the founda-tion at least Ii inches, in order that the pressure of thesuperstructure may be sufficiently distributed. The firstcourse of mas
. The elements of railroad engineering . firm and secure, such as hard clay, sand, gravel,or rock, a deep trench must be dug to receive the founda-tion. If the soil is soft or marshy, it may be necessary todrive piles and cut them off at a uniform elevation belowthe water-line, and fill betAveen and to the depth of one footabove tops of piles with concrete made with hydraulic cement. 800 RAILROAD CONSTRUCTION. Tlie trench should extend outside the lines of the founda-tion at least Ii inches, in order that the pressure of thesuperstructure may be sufficiently distributed. The firstcourse of masonry should project at least G inches outsidethe body of the abutment for the same reason, andshould be composed of much larger stones than those whichform the main body of the superstructure. The paving be-tween the abutments and curl)ing- at ends of arch should beof the same dimensions as adopted for box culverts. Apartial section of arch culvert with concrete foundation isshown in Fig. 390. The stones forming the impost course. at A, in a culvert of IG feet span, should be from 0 inches to12 inches thick. 1472. Concrete.—The concrete for the foundationsshould be composed of the following ingredients: Cement,1 part; sand, 3 parts; broken stone, 5 parts. If the con-crete is to be deposited below the water level, Portlandcement should invariably be used. If the pit is free fromwater at the time of construction, though ordinarily belowwater level, Rosendale or any other good American cementmay be used. The value of concrete depends much uponthe quality of the sand and broken stone used and the man-ner of mixing. Sand containing loam should never be used, RAILROAD CONSTRUCTION. 891 and if none other is available, the sand should be washed ina slight current of water, which will remove all the stone should be broken to a fairly uniform size, and con-tain no piece which will not pass through a 2^-inch suitable stone is not available, hard-burned brickbats,b
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectrailroadengineering
