removal of girders "C."

[Illustration: FIG. 6. (Full page image)

GENERAL ARRANGEMENT OF TEMPORARY AND PERMANENT STRUCTURES]

During the latter part of 1908 a 48-in. cast-iron water main was laid by
the city on a cradle built by the Railroad Company on girders "C" on the
east side of the avenue. This is part of the high-pressure system, and the
location and elevation of this water main were taken into consideration
when the underpinning was designed. This main, and the 48-in. cast-iron
sewer bracketed to girders "C," are shown on Fig. 4, Plate XLVIII.

Elevations had been taken on marks on the elevated railway columns
between 30th and 34th Streets at the time the original surveys were made,
in 1902, and these marks were used to test the level of the structure
during the progress of the excavation.

At the extreme south end of the work the procedure was changed. The east
side was excavated down to sub-grade, the east portion of the south
abutment was constructed, and six rows of the permanent steel viaduct were
erected. Very little excavation had been done on the west side of the
avenue at the south end of the work, and it would have delayed the
completion of the work to have waited for the excavation for and the
construction of the west portion of the south abutment and the erection of
the steel; therefore, instead of supporting the girders "C" on the central
rock core, the east ends were taken up on the permanent viaduct girders,
and the west ends were supported on a concrete pier on the rock. The
central portion of the avenue was excavated in advance of the west portion.
The permanent viaduct girders were put in place from east to west across
the avenue, and the girders "C" were supported on the deck of the permanent
viaduct approximately under the west elevated railway columns before the
west portion of the avenue was excavated, the central portion of the south
abutment having been constructed before the west portion. This procedure
was adopted only at the north girders "C" at elevated railway column No.
488, the south set of girders "C" being on the rock immediately south of
the south abutment. Figs. 2 and 4, Plate XLIX, and Fig. 2, Plate LII, show
various stages of the work at the south end.

[Illustration: PLATE XLIX, FIG. 1.--TW 60, P.T. & T.R.R. Co. Terminal
Station West. Under Ninth Ave., looking South from North abutment, showing
underpinning and excavation of rock core. Aug. 13, 08.]

[Illustration: