Rods 1-1/8 inches in diameter tie the side walls,
passing through angle columns in the walls and the bulb-angle columns
in the center. Layers of concrete are laid over the roof rods to a
thickness of from eighteen to thirty inches, and carried two inches
below the rods, imbedding them. For the sides similar square rods and
concrete are used and angle columns five feet apart. The concrete of
the side walls is from fifteen to eighteen inches thick. This type is
shown by photographs on page 41. The rods used are of both square
and twisted form.
[Illustration: LAYING SHEET WATERPROOFING IN BOTTOM]
[Illustration: SPECIAL BRICK AND ASPHALT WATERPROOFING]
[Sidenote: _Methods of
Construction
Typical
Subway_]
The construction of the typical subway has been carried on by a great
variety of methods, partly adopted on account of the conditions under
which the work had to be prosecuted and partly due to the personal
views of the different sub-contractors. The work was all done by open
excavation, the so-called "cut and cover" system, but the conditions
varied widely along different parts of the line, and different means
were adopted to overcome local difficulties. The distance of the rock
surface below the street level had a marked influence on the manner in
which the excavation of the open trenches could be made. In some
places this rock rose nearly to the pavement, as between 14th and 18th
Streets. At other places the subway is located in water-bearing loam
and sand, as in the stretch between Pearl and Grand Streets, where it
was necessary to employ a special design for the bottom, which is
illustrated by drawing on page 42.
Pages:
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53