2, Plate LX, before
placing the remainder of the lining.
In 32d Street the normal progress of the excavation was frequently
interrupted by encountering soft and unsound rock. In the excavation
between the East River and the Intermediate Shafts it was possible to
overcome these conditions by temporarily narrowing the excavation on one
side and supporting the roof on 16 by 16-in. transverse timbers caught
in niches in the rock at the sides, leaving sufficient room for the
steam shovel to work through. In order to save time, the height of the
excavation was not increased before placing these timbers, so that,
previous to the concreting, they all required to be raised to clear the
masonry lining and were then supported on posts on the center line
between the tunnels. This permitted the remainder of the excavation to
be made, and such additional timbering as was required was placed. At
most of these sections a brick arch and water-proofing were used, on
account of the presence of water. In certain places the center line
posts were buried in the core-wall, and, in order to permit the placing
of the water-proofing, were then cut off one by one flush with its top
as the load was transferred to the completed masonry. In other cases the
load was transferred to posts clear of the masonry and the center line
posts were entirely removed.
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