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. The rock near
the shaft contained many wet rusty seams, and settlement was detected in
the segmental tunnel timbering soon after the widening of the heading
was completed. Short props were placed under the timbers, and the street
surface was opened with a view of stripping the earth down to the rock
and thus lightening the load on the timbering. Street traffic was
maintained on a timber structure with posts eventually carried down to
the rock surface, and the walls of the buildings on the north side of
the street were underpinned to rock. The settlement of the tunnel
timbering was checked for a time, and the bench was excavated as shown
on Plate LXI. In this work the cut in the center was first made, and the
short props were replaced by struts, as shown; after this the berms were
removed and the side posts were placed. While building the brick arches,
holes were left in the masonry around the struts. After the masonry had
hardened, piers were built on the arches to support the segmental
timbers. The struts were then removed and the openings filled with
masonry. The voids above the arch were packed with rock and afterward
thoroughly grouted.

The timbers near the shaft continued to settle, and, although they had
been placed