Forty-eight-Inch Brick Sewer.—This sewer was in the center of Ninth Avenue, with the invert about 12 ft. below the surface, and manholes about 100 ft. apart, and had to be abandoned in this position to allow the transverse girders to be put in place to carry all structures while the excavation was being done.
Twenty-four-Inch Cast-Iron Water Main.—This water main was laid under the west elevated railway columns, with its top about 3 ft. below the surface, a space being left for it in the brick foundations, and a large column base casting being used to span it. Valves were installed, one north of 33d Street and one south of 31st Street, prior to excavating near the pipe, so that if it was broken the water could be shut off promptly.
Street Surface.—It was the original intention to close and excavate the east side of the avenue and to erect there a street-traffic trestle before closing the west side, but, at the contractor's request, both sides were closed, and all vehicular traffic was turned into the center. A light trestle on the west side of the avenue provided for pedestrian traffic.
Other Sub-surface Structures.—There were various gas mains, water mains, electric conduits, manholes, hydrants, etc., in the avenue, and most of these were cut out temporarily, at the contractor's request, to be replaced subsequently.
Supports for Elevated Railway Structure.—As stated previously, the central track had to be supported independently.
The overhead girders, known as girders "B", were therefore designed as shown on [Fig. 1], and put in place as shown on [Figs. 2] and [3]. The outside tracks were blocked directly on these girders, and the central track was supported by blocking up the transverse girders on I-beams placed between the girders "B"; and no blocking was placed between the girders "B" and the longitudinal girders carrying the central track. The weight on each column was assumed to be 172,000 lb.
Fig. 1. (full page image)
DETAILS OF STEEL GIRDERS, ETC. SUPPORTING NINTH AVENUE STRUCTURES
Supports for Surface Railway Structure.—A uniform load of 3,000 lb. per lin. ft. of single track, with the weight of a car at 39,000 lb., was assumed. Several feet of earth, between the structure and the rock, were mined out, and the structure was supported on I-beams and posts, and ultimately on the transverse girders by using timber bents under the I-beams, as shown on [Fig. 3].