or the upper face wall
could be braced against it. The top of this form was tied by cables
attached to rods in the rock and by rods with turnbuckles running from back
to front of the form; braces were also put in from the back of the
retaining wall form to the walls of buildings along the property lines,
when this could be done. The middle section of the form was held by rods
with turnbuckles which passed through the form and were fastened to each of
the tie-rods drilled into the rock, as was also done in the case of the
lower face wall. It was generally possible to hold the form to true
position in this manner, but occasionally it had a tendency to bulge; when
this occurred, the rods leading through the form and fastened to the
tie-rods were tightened up, the placing of the concrete was slowed up, and
no serious bulging occurred.

Bulkheads at the ends of the sections were built of rough planking securely
braced to the rock, except that a planed board was laid up against the face
of the form to make a straight joint. At the end of each section a V was
formed, as shown by Fig. 1, Plate LI. At all corners, a "return," or
portion of the wall running at right angles, was built, and no section of
wall was stopped at a corner.

_Filling Forms of Lower Face Walls._--A temporary trestle was erected above
the elevation of the bridge seat, and a track, leading from the mixer to
the form to be filled, was laid on it. At the commencement of each section
a layer of mortar (1 part of cement to 2-1/2 parts of sand) was deposited
on the bottom. A 1:3:6 mixture of concrete was used; it was run from the
mixer into dump-cars and deposited in the form through chutes, three of
which were provided for each 50-ft. section, the average length. The
concrete was mixed wet, and was not rammed; the stone was spaded back from
the face, and no facing mixture or facing diaphragms were used. Work on
each section was continued day and night without any intermission from the
time of commencement to the time of completion. At frequent intervals the
box drains were washed out thoroughly with a hose, in order to prevent them
from clogging up with grout.

[Illustration: PLATE LI, FIG. 1.--TW 66, P.N.Y. & L.I.R.R. Terminal Station
West. Box drains and tie rods, South side, Sta. 184+80 to 185+14. Sept. 17,
08.]

[Illustration: PLATE LI, FIG. 2.]

[Illustration: PLATE LI, FIG. 3.--P 46. P.R.R. Tunnels, N.R. Div. Sect. Gy.
West. Disposal trestle just befo