There was a moderate flow
of water through the cracks, and, in spite of every effort, some of the
fine sand was constantly carried into the heading.
In one or two instances considerable ground was lost at the face. On the
evening of December 14th, 1906, as a heavy coal wagon was passing along
33d Street above the heading, the rear wheels dropped through the
asphalt pavement. An examination disclosed a cavity under the pavement
about 14 ft. long, 12 ft. wide and 14 ft. deep. Evidently, the fine sand
had gradually settled into the voids caused by the loss of material at
the face, and the settlement broke the brick sewer over the heading. The
sewer was temporarily repaired, and the hole in the street was filled
before morning. A tight bulkhead was built across the heading, and work
was abandoned at that point. The north drift was advanced to a point
108 ft. west of Fifth Avenue where sand was also encountered and a
considerable run occurred. After that time all work on the three-track
section was discontinued.
The Company then took up the consideration of changes in plan. To
determine the difficulties of driving a Twin Tunnel at a lower
elevation, an exploration drift, 8 ft. high and 12 ft. wide, was driven
on the center line of the street as a top heading on the proposed new
grade.
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