The blasting was done early in the morning and the day gang
removed the spoil, which was hauled to the shafts and the portal in
cars drawn by mules. A large part of the rock was crushed for
concrete. The concrete floor was the first part of the lining to be
put in place. Rails were laid on it for a traveler having moulds
attached to its sides, against which the walls were built. A similar
traveler followed with the centering for the arch roof, a length of
about 50 feet being completed at one operation.
[Illustration: FOUR COLUMN (TOWER) VIADUCT CONSTRUCTION]
[Illustration: MANHATTAN VALLEY VIADUCT, LOOKING NORTH]
[Illustration: ERECTION OF ARCH, MANHATTAN VALLEY VIADUCT]
On the Park Avenue section from 34th Street to 41st Street two
separate double-track tunnels were driven below a double-track
electric railway tunnel, one on each side. The work was done from four
shafts, one at each end of each tunnel. At first, top headings were
employed at the north ends of both tunnels and at the south end of the
west tunnel; at the south end of the east tunnel a bottom heading was
used. Later, a bottom heading was also used at the south end of the
west tunnel. The rock was very irregular and treacherous in character,
and the strata inclined so as to make the danger of slips a serious
one. The two headings of the west tunnel met in February and those of
the east tunnel in March, 1902, and the widening of the tunnels to the
full section was immediately begun.
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