Excavation in rock was made by sinking a pit to sub-grade for the full
width of the tunnel and advancing the face of the pit in several lifts,
the muck being blown over the slope and loaded into buckets at its foot.
The work was attacked at several places simultaneously, and the spoil
was hoisted by derricks located at convenient points along the side of
the cut.
_Thirty-third Street Work in Tunnel and Open Cut._--The West 33d Street
Shaft was similar to the one in 32d Street, and was sunk during
February, March, and April, 1907, through 10 ft. of earth, 21 ft. of
soft rock, and 29 ft. of fairly hard rock. It was necessary to timber
heavily the upper 30 ft. of the shaft. The timber later showed evidences
of severe strain, and had to be reinforced.
[Illustration: Plate LXI.--EXCAVATION AND TIMBERING IN HEAVY GROUND
OF THREE-TRACK TUNNEL OF 33D ST.]
As soon as the shaft excavation was deep enough, a drift was driven
part way across the tunnels, and top headings were started both east and
west to explore the rock. The heading to the west was divided into two
drifts, as shown on Plate LXI. These two drifts were continued to the
west end of the contract, and were then enlarged to a full-sized heading
and timbered, as shown on Plate LXI and Fig. 3, Plate LX.
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