. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools . of roadbed 18 feet; slope IJ to 1. 120 RAILROAD CONSTRUCTION. §104, The products in the fifth column may be obtained veryreadily and with sufficient accuracy by the use of the slide-ruledescribed in § 106. The products should be considered as (a-\-d){a-\-d) -^—. In this problem s = lj, — = .6667. To applys s the rule to the first case above, place 6667 on scale B over 89 on scale A, then opposite 89 on scale B will be found on scale A. The position of the decimal point wi
. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools . of roadbed 18 feet; slope IJ to 1. 120 RAILROAD CONSTRUCTION. §104, The products in the fifth column may be obtained veryreadily and with sufficient accuracy by the use of the slide-ruledescribed in § 106. The products should be considered as (a-\-d){a-\-d) -^—. In this problem s = lj, — = .6667. To applys s the rule to the first case above, place 6667 on scale B over 89 on scale A, then opposite 89 on scale B will be found on scale A. The position of the decimal point will be evident from an approximate mental solution of the problem. Sta. CenterHeight. a-^d (a+rf)2 (a+dys Areas. 171819202122 ( vo_ J ^^ ab 6X182 ~ 2 54 10X54 = 3245 cub. yards : 540 vol. 104. Equivalent sections. When sections are very irregularthe following method may be used, especially if great accuracy. Fig. 51.—Equivalent Section. is not required. The sections are plotted to scale and then auniform slope line is obtained by stretching a thread so that theundulations are averaged and an equivalent section is the distances {xi and Xr) from the center. The area § 105. EARTHWORK. 121 may then be obtained independent of the center depth as follows: hLet s = the slope ratio of the side slopes = cot /3 =—. (See Fig. 50.) Then the l/xi-{-Xr\ . , , XrXr XiXi, db XiXr ah (48) These approximate methods are particularly useful for rapidlymaking up monthly estimates, realizing that the inaccuracies,plus and minus, will be wiped out when the final computationis made by a more accurate method. 105. Three-level sections. The next method of cross-section-ing in the order of complexity, and therefore in the order of Fig. 52. accuracy, is the method of three-level
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