The sections of concrete built in trench varied in height from 13 to
59 ft. from the base to the top of the back wall. With the exception of
the Seventh Avenue wall, 50 ft. in height, and the Ninth Avenue wall,
62 ft. in height, none of those sections constructed by the bench
method was more than 14 ft. The forms and bracing for these walls were
substantially the same, except that the low walls were built in lengths
of approximately 50 ft., while the forms for the Seventh and Ninth
Avenue walls were only 20 ft. long.

The forms and bracing for the Ninth Avenue walls are shown on Fig. 8.
These forms were built in one piece and moved ahead from section to
section, and they were firmly braced from the bottom with raker braces
to a point 36 ft. above the base, the upper part being held in place by
¾-in. bolts passed through the forms and anchored by cables to bolts
grouted into the rock behind.

After the forms had been set and braced, an 8-in. brick wall was laid
up the face of the rock, containing a vertical line of three-cell hollow
tile block every 5 ft. of length, and laid to conform as nearly as
possible to the face of the rock, all voids being filled with broken
stone. Water-proofing, similar to that described for the walls in the
trench, was then applied to the brick and tile wall for the full height,
and firmly braced to the front forms, the braces being removed as the
concrete reached them. The concrete was mixed at the street level and
deposited through chutes, as described previously.

Tables 1, 2, and 3 show the quantity of cement used in each section of
retaining wall, and give figures by which the quantities of other
materials may be determined.