The sinking of the Intermediate Shafts was the first work undertaken by
the contractor.
The 33d Street Shaft was 34.5 ft. long, 21 ft. wide, and 83 ft. deep.
The rock surface averaged 5 ft. below the ground surface. Sinking was
started on July 10th, 1905, and was completed on October 3d, 1905, the
rock being hard and dry. The average daily rate was 0.73 ft. and an
average of 17.1 cu. yd. were excavated per day, with two shifts of 8 hr.
each. The first shift started at 6 A. M. and the second at 2.30 P. M.,
ending at 11 P. M. These hours were adopted in order to avoid undue
disturbance during the night.
[Illustration: PLATE LIX, FIG. 1.--AIR-OPERATED STEAM SHOVEL USED IN
TUNNEL.]
[Illustration: PLATE LIX, FIG. 2.--TIMBERING IN TOP HEADINGS ABOVE
I-BEAMS.]
[Illustration: PLATE LIX, FIG. 3.--FIRST SECTION OF CONCRETE LINING AT
FIFTH AVENUE.]
[Illustration: PLATE LIX, FIG. 4.--TIMBERING AND RUBBLE MASONRY OVER
I-BEAMS.]
Before blasting the first lift of rock, channel cuts 5 or 6 ft. deep
were made along the sides of the shaft, in order to avoid damage to the
walls of neighboring buildings. Timbering was required for a depth of
only 10 ft. below the surface of the ground.
A drift, 30.6 ft. long, 17 ft. wide, and 27 ft. high, connected the
south end of the shaft with the tunnels. The drift was excavated in
three stages, a top heading and a bench in two lifts. While blasting the
cut in the top heading, there was enough concussion to break glass in
the neighboring buildings. The use of a radialax machine reduced the
concussion somewhat, but it was very quickly abandoned on account of the
length of time required for the drilling.
The construction of the 32d Street Shaft was quite similar to the one on
33d Street. It was 31.5 ft. long, 20.5 ft. wide, and 71 ft. deep. The
depth of earth excavation averaged 19.5 ft. The rock in this shaft was
seamy and not quite as hard or dry as that in 33d Street, and timbering
was required for practically the full depth to the crown of the drift.
Sinking was started on May 15th, 1905, and was completed on October
26th, 1905. The daily average rate was 0.30 ft. in earth and 0.52 ft. in
rock. The drift was excavated in much the same manner as the one in 33d
Street, but the rock being softer the radialax machine was not used.