ould determine the
effective room to be occupied by the wall, it was determined to make the
back vertical below the top of rail and gain the necessary increase in
width below that point by making a heavy batter on the face.

The type of wall having been thus determined, calculations were made
of the width of base required for each 1/4-in. batter from 2 to 3 in.,
inclusive, first for a depth of 13 ft. below the top of the curb and
then for each 5 ft. below that elevation, to a depth corresponding to
the distance between the top of the curb and the top of the rail at the
point of greatest variation. These widths of wall were determined for
the two pressures previously decided on, and curves were then plotted
showing the thickness of wall required for each batter calculated and
for each pressure. They are shown on Plate LIV. The curves in broken
lines represent the widths required for saturated material, and the
curves in dotted lines for hydraulic pressure. Mean curves were then
drawn between each broken and its corresponding dotted curve. These are
shown in solid lines, and represent the widths of wall which were used
in the construction. Typical sections of the wall and pipes back of it
are shown on Fig. 3.

The extreme positions of the back of the wall on the two streets having
been determined, as previously stated, the width of base required at
those points fixed the toe of the wall at the top of rail as 254.5 ft.
south of the center line of the Terminal in 31st Street, and 258.5 ft.
north of the center line in 33d Street.

[Illustration:
Fig. 3.
TYPICAL SECTIONS OF RETAINING WALL IN THIRTY-FIRST STREET]

CONTRACTS.

The construction was done under the following contracts:

_1._--The principal contract, dated June 21st, 1904, was with the New
York Contracting and Trucking Company, later assigned by that company
to the New York Contracting Company-Pennsylvania Terminal, for the
performance of the following works:

(_a_).--The excavation for and construction of a retaining wall in
Seventh Avenue, 31st Street, Ninth Avenue, and 33d Street.

(_b_).--Excavation over the area enclosed by the retaining wall.

(_c_).--The building of sewers and the laying of water and gas pipes.

(_d_).--The building of a timber trestle to support the surface of
Eighth Avenue between the south side of 31st Street and the north
side of 33d Street, and also the surface of 31st and 33d Streets
between