3, Plate LX. The
bench was then excavated in two lifts, leaving the wall-plates supported
on narrow longitudinal berms, which were removed in short sections to
permit the placing of posts under the wall-plates.
_Thirty-second Street Open-Cut Work._--Before actual open-cut excavation
was started, all buildings facing it were underpinned to rock. For this
purpose, a trench was dug along the face of the buildings and of the
same depth as their cellars. Holes were cut in the front foundation
walls through which long needle-beams (Fig. 4, Plate LX) were inserted
and jacked up on blocking placed on the cellar floor and in the trench,
until the weight of the building had been taken off its foundations. A
close-sheeted trench was then sunk to rock under the front building
walls, and a light rubble masonry retaining wall was built in it to
support the building permanently. Frequently, the excavation for the
underpinning wall, which was taken out in sections from 30 to 40 ft.
long, and in places was carried to a depth of 40 ft., was very
troublesome on account of the large quantity of water encountered and
the fineness of the sand, which exhibited a tendency to flow when
saturated.
The Elevated Railroad columns in Sixth Avenue, near the north and south
lines of 32d Street, were underpinned in a manner similar to the
building foundations, while those on the center line of the street were
supported by girders riveted to them close under the track level.
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