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.

[Illustration: FIG. 1. (Full page image)