4-in. brick wall was built
simultaneously on line with the back of the wall to the height of
the first step. Where the bottom strut was below that elevation, the
brickwork was left low at that immediate point and built up when the
strut was removed. The brick wall was then water-proofed on the side
toward the concrete, and loose laps of the water-proofing were allowed
to hang over the brickwork and at least 8 in. down the back. A 6-in.
vitrified pipe drain was then laid along the surface of the rock just
outside of the brick wall, the joints in the pipe being caulked with
oakum saturated in cement, and pointed with cement mortar above a line
1 in. below the horizontal diameter, the remainder of each joint being
left open. Cross-drains were laid from tees in the back drain to the
face of the wall at all low points in the rock and at least for every
25 ft. of wall length, the joints of these discharge pipes being caulked
and cemented throughout. The surface of the rock was then washed and
scraped clean, and was covered with about 1 in. of mortar, after which
the section was ready for concrete.

The building of monolithic sections in trenches required that the thrust
from one set of struts be taken by the concrete before the set above
could be removed, and necessarily caused slow progress, the rate at
which concrete was deposited being just sufficient to prevent one layer
from setting before the next layer above could be placed.

The concrete used was mixed in the proportions of 1 part of cement to
3 parts of sand and 6 parts of stone, in 2-bag batches, in 3/4-yd. and
1-yd. Ransome portable mixers mounted with air-driven engines on the same
frame. These mixers were placed at the surface, and were charged with
barrows, the correct quantities of sand and stone for each batch being
measured in rectangular boxes previous to loading the barrows. The
concrete was discharged from the mixer into a hopper which divided into
two chutes, only one of which was used at a time, the concrete being
shoveled from the bottom of the chutes to its final position. Facing
mortar, 2 in. thick, was deposited simultaneously with the concrete, and
was kept separate from it by a steel diaphragm until both were in place,
when the diaphragm was removed and the two were spaded together. The
bottoms of the guide-planks were cut off just above the concrete as it
progressed, and, as soon as the wall had reached a strut at one end of
the section, that str