\fdO'^ - Old Forge Coal Mines

RAILROAD CONSTRUCTION. 295
(a) The moment of resistance of the cofferdam is the product
of its weight, viz., 7,150 lb. multiplied by the perpendicular
distance from the inner toe of the dam to the vertical
line drawn through the center of gravity of the dam. This
perpendicular distance is 2.5 ft. The moment of resistance
is, therefore, 7,150 X 2.5 = 17,875 ft. -lb. Ans.
(d) The factor of safety of the cofferdam is the quotient
of the moment of resistance of the dam divided by the
moment of water pressure. Hence, 17,875 -r- 10,417 = 1.71.
This calculation does not include the additional weight and
resistance of the piles and timber enclosing the puddled wall,
which will greatly increase the factor of safety.
(913)
(914)
(915)
(916)
(917)
(918)
(919)
See Art. 1565.
See Art. 1555.
See Art. 1556.
See Art. 1557.
See Art. 1559.
See Arts. 1560 and 1561.
See Arts. 1563 and 1564.
(920) As the sides of the bridge piers are always, and
the ends often, battered, the deeper the foundation the
greater will be the dimensions of the caisson plan. The
thickness of the walls and deck of the caisson will depend
upon the weight of the masonry and the bridge which they
must support.
(921) To reduce the friction of the earth against its sides
while sinking.
(922)