ith 3-in. plank tops, were laid
on it to form the ditch and the shoulders for the flagstone covers. The
track, which had previously been blocked up on the rock between the
ditches, was raised and supported on the ditch boxes above the finished
floor level. At the same time, light forms were braced from the ditch
boxes to the grade of the base of the low-tension and telephone-duct
bank. After depositing the concrete to this level, the telephone ducts
were laid.

The forms for the water-proofing or sand-wall up to the 15 deg. line and for
the main side-walls and core-walls were built in 30-ft. panels and were
supported on carriages, which, traveling on a broad-gauge track above
the ditches, moved along the tunnel, section by section, as the work
advanced. The panels were hung loosely from joists carrying a platform
on the top chord of the carriage trusses, and were adjusted
transversely by bracing and wedging them out from the carriage. The
small forms for the refuge niches, ladders, etc., were collapsible, and
were spiked to the main panel forms just previous to the deposition of
the concrete. The concrete was deposited from the platform on top of the
carriage, to which the cars were elevated in various ways. Plate LXI
shows the details of the carriages, and is self-explanatory.

The concrete for the sand-walls and the core-wall, to the level of the
sidewalk, was deposited at the same time; two carriages in each tunnel,
placed opposite each other, forming a 60-ft. length, were used at each
setting. The floor section of the 4-in. tile drains had been laid with
the floor concrete, and, as the sand-wall concrete was deposited, the
drains were brought up simultaneously, broken stone being deposited
between the tile and the rock to form a blind drain and afford access to
the open joints of the tile for the water entering the tunnel through
seams in the rock. The drains were spaced at intervals not exceeding 25
ft., depending on the wetness of the rock, and were placed at similar
intervals in the core-wall under the lowest projecting points of the
rock on the center line between the tunnels. A small ditch lined with
loose 6-in. vitrified half pipe was provided in the top of the sand-wall
to collect the water from the extrados of the arch and lead it to the
top of the drains. Great difficulty was experienced in maintaining these
drains clear, and, on completion of the work, a large amount of labor
was expended in removing obst