\fdO'^ - Old Forge Coal Mines

RAILROAD CONSTRUCTION. 283
Art. 1462. The height of top of the covering flags is
5 feet. 1^ times 5 feet =7.5 feet. Adding 2 feet, we have
length of the wing walls, i. e. , the distance from inside face
of the side walls to the end of the wing walls, 7.5 + 2 = 9
feet G inches. Ans.
(824) The span of a box culvert should not exceed
3 feet. When a larger opening is required, a double box cul-
vert with a division wall 2 feet in thickness is substituted,
(825)
(826)
(827)
(828)
See Art. 1 462.
See- Art. 1462.
See Art. 1463.
See Art. 1465.
(829) The thickness of the base should be -j^ of the
height. The height is 16 feet and the thickness of the base
should be t*^ of 16 feet, or 6.4 feet. Ans.
(830)
(831)
See Art. 1468.
See Art. 1468.
(832) Trautwine's formula for finding the depth of
keystone (see formula 103, Art. 1469), is as follows:
J .1 ri . • r 4/radius of arch +A^ span ,
depth of keystone m feet=^^
j
!-^—^-
, , ,
\-0.2 foot.
In this example the arch being semicircular, the radius and
half-span are the same. Substituting known values in the
given formula, we have
4/T5 + 15
depth of keystone =
j 1-
0.2 foot =1.57 feet. Ans.
Applying Rankine's formula (formula 104), depth of
keystone = -/. 12 radius, we have depth of keystone =
y. 12 X 15= 1.34 feet. Ans.