Transactions of the American Society of Civil Engineers, vol. LXVIII, Sept. 1910 | Page 7

the piers. Elevations were taken on each set of girders during each operation, and careful observations were made on the elevated railway columns. Where the rock was very close to these bents, the open space between the posts was filled with blocking so that there would be less danger of the bent shifting if struck by blasted materials. Fig. 3, Plate XLVIII, shows one of these bents filled with blocking.
All structures being carried on girders "C," which, in turn, were carried on the sides of the permanent viaduct, the central core was excavated. Fig. 4, Plate XLVIII, and Figs. 1, 2, 3, and 4, Plate XLIX, show various views of the work at this stage.
The central portion of the viaduct was then erected, and, using concrete piers and timber bents, all structures were placed on its deck. Fig. 3, Plate XLIX, shows the piers under the elevated railway columns prior to the 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: PLATE XLIX, FIG. 2.--TW 84, P.T. & T.R.R. Co. Terminal Station West. View looking toward Ninth Ave. from South side of 31st St., 200 feet West of Ninth Ave. Jan. 28, 09.]
[Illustration: PLATE XLIX, FIG. 3.--TW 88, P.T. & T.R.R. Co. N.R. Div. Terminal Station West. Center line of 32nd St., looking East from Sta. 183+50, showing excavation under Ninth Avenue, permanent concrete piers under Elevated Railway Columns and removal of temporary shoring girders "C". April 8, 09.]
[Illustration: PLATE XLIX, FIG. 4.--TW 95, P.T. & T.R.R. Co. N.R. Div. Terminal Station West. View under Ninth Avenue looking Southward from 100 feet South of center line, showing underpinning of Ninth Avenue structure taken at sub-grade. May 25, 09.]
It was made a practice all through the work to transfer the weight of the structures very positively from one support to another by lifting them bodily by jacks, and putting in filler pieces before releasing the jacks, not trusting to wedging to transfer the loads. In fact, apart from the boxing-in of the surface railway concrete, no wedges whatever were used. This appears to have been a decided advantage, for, with the constant pounding of trains on the elevated railway and the jarring due to heavy trucks on the pavement blocks, it is very likely that wedging would have become loosened and displaced, whereas, with blocking, there was little or no tendency toward displacement