The rubble masonry
foundation is 45 feet square and rests on a 2-foot course of concrete.
The subway passes under its east side within 3 feet of its center,
thus cutting out about three-tenths of the original support. At this
place the footing was on dry sand of considerable depth, but on the
other side of the monument rock rose within 3 feet of the surface. The
steep slope of the rock surface toward the subway necessitated
particular care in underpinning the footings. The work was done by
first driving a tunnel 6 feet wide and 7 feet high under the monument
just outside the wall line of the subway. The tunnel was given a
2-foot bottom of concrete as a support for a row of wood posts a foot
square, which were put in every 5 feet to carry the footing above.
When these posts were securely wedged in place the tunnel was filled
with rubble masonry. This wall was strong enough to carry the weight
of the portion of the monument over the subway, but the monument had
to be supported to prevent its breaking off when undermined. To
support it thus a small tunnel was driven through the rubble masonry
foundation just below the street level and a pair of plate girders run
through it. A trestle bent was then built under each end of the
girders in the finished excavation for the subway. The girders were
wedged up against the top of the tunnel in the masonry and the
excavation was carried out under the monument without any injury to
that structure.

[Illustration: THREE PIPES SUBSTITUTED FOR LARGE BRICK SEWER AT 110TH
STREET AND LENOX AVENUE]

[Illustration: SEWER SIPHON AT 149TH STREET AND RAILROAD AVENUE]

[Illustration: CONCRETE SEWER BACK OF ELECTRIC DUCT MANHOLE--BROADWAY
AND 58TH STREET]

At 134th Street and Broadway a two-track structure of the steel beam
type about 200 feet long was completed. Approaching it from the south,
leading from Manhattan Valley Viaduct, was an open cut with retaining
walls 300 feet long and from 3 to 13 feet in height. After all this
work was finished (and it happened to be the first finished on the
subway), it was decided to widen the road to three tracks, and a
unique piece of work was successfully accomplished. The retaining
walls were moved bodily on slides, by means of jacks, to a line 6-1/4
feet on each side, widening the roadbed 12-1/2 feet, without a break
in either wall. The method of widening the steel-beam typical subway
portion was equally novel. The west wall was moved bodily by jack