. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools, and a hand-book for the use of engineers in field and office . Fig. 51.—Equivalent Section. is not required. The sections are plotted to scale and then auniform slope linfe 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:Let s = the slope ratio of the side slopes = cot /3 =—.
. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools, and a hand-book for the use of engineers in field and office . Fig. 51.—Equivalent Section. is not required. The sections are plotted to scale and then auniform slope linfe 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:Let s = the slope ratio of the side slopes = cot /3 =—. (See Fig. 51.) Then the 1 (Xi + Xr Area = — . xiXr ah {xi-\-Xr) 2a Xr Xr XI Xi ob s 2~ s 2~2 (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 cornputationis made by a more accurate method. 105. Three-level sections. The next method of cross-section-ing in the prder of complexity, and therefore in the order of. Fig. 52. accuracy, is the method of three-level sections. The area ofthe section is ^{a-^d){wr-\-w{) , which may be written \{a-\-d)w , in which w = Wr+wi. If the volume is com- puted by averaging end areas, it will equal -\{si\d)w -a})^{a^d)w -ah\. (49) 122 RAILROAD CONSTRUCTION. §i05. _o UID (Ht-l oO c3>u o d .2+3 u ou ^ -ao a * ID a _3o ou o. o > * ■* 3^ + ^0 ^-s. ki. i I-l CO CO + + v.^ t^ .4 u I + Pi 1-1 ao 03. + + + + 1> GO CO OJ o CO I + 00 + CO CO + 3 CO O1—1C<J o -1 00 1^ 00 CD 00 O OS + + o6 K) + (M OS O TTl CO Tf 05 CO 00 k M fc, »-( fc< iM fe, 1—1 &. V) GO TtH (N 00 TfH rH O (N d CO T-l rj< l-l IM r—( O fe. 3S fc,r^ fe, CO 6^ o fe, ct 00 • Ol o or, (M • o r^ 00 o (N »0 CO c CO ■<f c r-t rH 1 CM I—1 ci CO T-l + T(4 l^ OS Tj f , n M (■5 O ft in ft o o Ti .2 0) -♦J -I3 3ft o O u (4 3-p > 3o O 03>
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Keywords: ., bookauthorwebbwalt, bookcentury1900, bookdecade1920, bookyear1922
