\fdO'^ - Old Forge Coal Mines

294 RAILROAD CONSTRUCTION.
(902) The rod reading for grade will be the difference
between the height of instrument and the elevation of the
grade for the given station ;
(903)
(904)
See Art. 1547.
See Art. 1548.
i. e., 125.5 — 118.7 =6.8 ft.
Ans.
(905) The skew of abridge is the angle which its center
line makes with the general direction of the channel spanned
by the bridge.
(906)
See Art. 1549.
(907) The length of A ^ is determined by the principles
of trigonometry stated in Art. 1243, from the following
proportion A
: sin 46° 55' : sin 43° 22' :: 421.532 :
^^=396.31 ft. Ans.
(908)
(909)
See Art. 1551.
See Art. 1553.
(91 0) See Art. 1554 and Figs. 465 and 466.
B; whence,
(91 1) The depth of the center of gravity of the water
below the surface is — = 5 ft. Applying the law for lateral
pressure, given in Art. 1554, we have
{a) Total water pressure = 10 X 5x40x62.5 = 125,000 lb.
Ans.
{b) Taking a section of the dam 1 ft. in length, we have
lateral pressure = 10 X 5 X 62.5 = 3,125 lb.
The center of water pressure is at — the depth of the
o
water above the bottom, i. e., at 10 -^ 3 = 3- ft.
The moment of water pressure about the inner toe of
the dam will, therefore, be 3,125 X 3-= 10,417 ft. -lb. Ans.
6
(912)
The volume of a section of the cofferdam 1 ft. in
length is 11 X 1 X 5 = 55 cu. ft., which, at 130 lb. per cubic
foot, will weigh 55 X 130 = 7,150 lb.