. Field-book for railroad engineers. Containing formulas for laying out curves, determining frog angles, levelling, calculating earth-work, etc., etc., together with tables of radii, ordinates deflections, long chords, magnetic variation, logarithms, logarithmic and natural sines, tangents, etc., etc . Fig. 55. an excavation, EFG being the centre line, AL and Cil/the extremeside lines, and 0 the centre of the curve. Then the calculation of tlieQrst section would include all between the lines .41 Ci and B^Di\^-hile the true section lies between A C and B D. In like manner, thecalculation of the
. Field-book for railroad engineers. Containing formulas for laying out curves, determining frog angles, levelling, calculating earth-work, etc., etc., together with tables of radii, ordinates deflections, long chords, magnetic variation, logarithms, logarithmic and natural sines, tangents, etc., etc . Fig. 55. an excavation, EFG being the centre line, AL and Cil/the extremeside lines, and 0 the centre of the curve. Then the calculation of tlieQrst section would include all between the lines .41 Ci and B^Di\^-hile the true section lies between A C and B D. In like manner, thecalculation of the second section would include all between HK andNP, while the true section lies between BD and L M. It is evident,therefore, that at each station on the curve, as at jP, the calculation istoo great by the wedge-shaped mass represented hy KFD^, and too Fig. 56. ^n ■mull by the mass represented by BiFB These masses balance 112 EARTH-WORK. each other, when the distances out on each side of the centre line areequal, that is. when the cross-section may be represented hy ADFRE(fig. 56). But if the excavation is on the side of a hill, so that thedistances out differ very much, and the cross-section is of the shapeAD FEE, the difference of the wedge-shaped masses may requireconsideration. 130. Problem. Given the centre height c, the greatest side height h,the least side height h, the greatest distance out d, the least distance out d,and the ividlh of the road-bed b, to find the correction in excavation C, atany station on a curve of radius R or defection angle D. Solution. The correction, from what has been said above, is a trian-gular prism of which B FR (fig. 56) is a cross-section. The height ofthis prism at B (fig. 55) is Bi H, the height at A is R^ S, and the heightat F is 0. Bi 11 and R^ S, being veiy short, are here consideredstraight line
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectrailroadengineering
