facing for the rock
on the sides in order to prevent disintegration, due to exposure, and give
a finished appearance to the work. Above the rock surface a retaining wall
of gravity section was designed, the top being slightly higher than the
yards of the adjoining properties. The face wall was designed to be as thin
as possible, in order to allow the maximum space for tracks.

The excavation, therefore, was laid out so that the back of the retaining
wall would not encroach on the adjoining property, but would practically
coincide with the property line at positions of maximum depth.

The batter on the face of the wall was 2 in. per ft., and a bridge seat
3-1/2 ft. wide was formed at an elevation of 22 ft., minimum clearance,
above the top of the rail. This bridge seat was made level. The maximum
height of the south wall is 49 ft., and of the north wall 65 ft.

The face walls were classed as "Upper Face Walls," extending from the base
of the retaining wall to the bridge seat, and as "Lower Face Walls,"
extending from the bridge seat to the base of the wall. The general design
is shown on Fig. 8.

In considering the design of the face wall it was felt that, the wall being
so thin, ample provision should be made to prevent any accumulation of
water and consequent pressure back of the wall; therefore, no attempt was
made to water-proof it, but provision was made to carry off any water which
might appear in the rock. Box drains, 2 ft. wide and 6 ft. from center to
center, were placed against the rock, so that, there being but 4 ft.
between the drains, and the wall having a minimum thickness of 2 ft., any
water in the rock would not have to go more than 2 ft. to reach a drain,
and would probably pass along the face of the rock to a drain rather than
through 2 ft. of concrete. These drains were connected with pipes leading
through the wall at its base.

[Illustration: FIG. 8. (Full page image)

RETAINING AND FACE WALLS NORTH SIDE]

These box drains occurred so frequently, and decreased the section of the
wall so materially, that it was thought desirable to tie the wall to the
rock. This was done by drilling into the rock holes from 6 to 15 ft. in
depth, and grouting into each hole a 1-1/2-in. rod having a split end and a
steel wedge. The outer end of each rod was fitted with a 12 by 12 by
1/2-in. plate and a nut, and extended into the wall, thus tying the
concrete securely to the rock. The drains being 6 ft. from center