It was finally decided to support the tracks on
screw-piles carried through the lining of the tunnels, as originally
proposed by the writer.

In order to know something of the capacity of screw-piles in the actual
material to be passed through, it was resolved to test them. A caisson
was sunk at the end of one of the Erie Railroad piers on the New Jersey
side near the line of the tunnels, and, to obtain parallel conditions as
much as possible, the excavation was carried down to the proposed grade
of the tunnel. Various types of screw-piles were sunk therein and tests
were made, not only of the dead load carrying capacity, but also with
the addition of impact, when it was found that screw-piles could be sunk
to hard ground and carry the required load. The final part of the test
was the loading. The screw-pile, having a shaft 30 in. in diameter and a
blade 5 ft. in diameter, was loaded with 600,000 lb., with the result
that, for a month--the duration of this loaded test--there was no
subsidence.

Again, and after the iron tunnel lining had been constructed across the
river, tests were made of two types of supports: One a screw-pile 29-1/2
in. in diameter with a blade 4 ft. 8 in. in diameter and the other a
wrought-iron pipe 16 in. in external diameter. Tests were made, not only
for their carrying capacity, but also for their value as anchorages, and
it was found that the screw-pile was more satisfactory in every way; it
could be put down much more rapidly, it was more easily maintained in a
vertical position, and it could carry satisfactorily any load which
could be placed on it as a support for the track. The 16-in. pipe did
not prove efficient either as a carrier or as an anchorage. These tests
will be mentioned in the detailed description of the work to follow.
Figs. 2 and 3 illustrate the general arrangement and details of the
machine designed by the writer and used for sinking the test piles in
the tunnels. This machine had been used originally on the New Jersey
side on the test pile at Pier C, and the adaption was not exactly as
shown on these drawings, but if the screw-piles had been placed in the
tunnels, the arrangement shown would have been used.

Surveys, soundings, and borings were commenced in the latter part of
1901 on an assumed center line of tunnels which was the center line of
32d Street extended westward.

The soundings were made from a float stage fastened to a tugboat, the
location being determine