New-York tribune., 1907-07-02
TUNNELS NOT ON LEVEL
MR.. LEWISS REPORT.
North Brooklyn Tube Tsrenty-eight
Inches Too LoaC IN One Place.

Nelson P Lewis, chief engineer of the Board
Of Estimate and Apportionment. has made a re-
port TO the Mayor on the condition of the tunnels
between Manhattan and Brooklyn. This report
the result of the complaint made by the
Brooklyn League. in which it was said the
shafts settling and that they had to be
supported by steel piles
Mr.. Lewis admitted there were obstacles TO be
overcome but he said he convinced they
were being overcome hut he said the experiment
tai operation of trains which will precede the
opening of the tunnel to public travel will de-
monstrate its entire safety" Those portions of
the tubes in rock are in excellent condition. he
saws Both Castiron tubes have been completed
At the Brooklyn end of the north tunnel the
engineer says. the bottom of the tube is four
inches below the theoretical grade. this variation
decreasing toward the west 10 a point just east
Of Garden Place, where the tube suddenly
to nine inches above grade. then gradually ap-
preached true grade, crossed il about 100 feet
west of Hicks street. and dropped TO twenty
eight inches below grade, this being the greatest
departure" In the next hundred feet true
grade" was recovered
From that point TO the bukhead line the tube
bottom was mostly above grade the maximum
distance being 10I2 inches. while at one place
81 fell nine inches below the grade After cross
ing the buIkhead line the tube continued above
the theoretical grade for more than five hundred
feet the maximum variation being seventeen
inches
The south tube. the engineer reports from IT'S
easterly end shows slight variation from the true
grade, with a maximum of about five inches
above and below. From the Brooklyn end Of the
tunnel 10 points about five hundred feet west of
the bulkhead line both tubes rest upon coarse
sand OF excellent supporting power. From this
point 10 the rock reef and between the reef and
the rock through which the west end of the tun-
mel is driven they rest upon a very fine sand and
river silt. The parts of the tubes resting upon
this soft material have settled somewhat since
they were put into position. Statements as 70
the time and causes of this settlement are con-
ficting 1t has been claimed that this settle
nent may have occurred gradually during some
months after the tunnel was driven. The eng-
neers of the Rapid Transit Commission and Of
the Rapid Transit Subway Construction Com
pany assure that the settlement which
reached maximum of twelve inches in the north
tube and nine inches in the south tube oc-
CURED when air pressure was reduced before the
joints had been caulked, and the fine material
coming into the tubes left spaces onto which they
settled. So far as can learn there has been no
perceptibe settlement during the last year"
To obviate further settlement piles are now be- /,
ing placed under those parts of both tubes which
rest in the soft material Mr.. Lewis reports that
in some places these piles being driven every
thirty-fve feet AS a rule, the piles are placed |
fifty feet apart They are in pairs. seven feet 4
apart between centres, each pile consisting of a |
steel tube twenty inches in diameter flied with |
concrete and reinforced with steel rods and |
hoops.
Flattening occurred in both tubes" the ensi- |
neer reports and was noticeable where there |
were sharp edges in the grade lines. This fiat |
tenIng is most noticeable in the land section, |
reaching its maximum in grade variation about |
"heTe the tubes became entirely submerged, |
Where II was about ten inches in the north and |
about seven inches in the south tube"
IN reporting on the broken plates, Mr.. Lewis
says: By far the greatest number occurred on |
the Brooklyn land section of both tubes. where
the material was coarse sand and gravel |
and the tubes were wholly or in part abve water.
ana, as IN the case of the fiattening they are !
most noticeable where there are sharp changes |
iTcfn the true grade line This would appear to |
indicate that the cracking was not due TO the
inability Of the tubes 10 retain their proper
functions after they were IN position but TO the
stresses to which they were subjected by the |
Irregular course Of the shield when il desarted |
from the proper grade and the efforts TO bring
il back TO grade after such departure. There
especially in the south tube, and I am informed
that nearly If not all, the cracking occurred |
immemdiately behind the shield during the |
progress OF the work More of the cracked tubes
appear TO be leaking in that part of the tubes
Of the F>urman street shaft although for
about 600 feet the tubes are entirely below mean
high tide. In the portions which still under
air pressure I could no leaks at either joints
from cracked plates, but some may develop
when the air pressure is again removed"
Mr.. Lewis reports that the ability Of the tubes
70 retain their shape when trains pass through |
them depends upon the character of the ma
terial in which they lie. AS the tubes lie in
soft sand in some places, 4 is absolutely neces-
sary for them to have supporting piles, he says.
THIRD RAIL on C. r. R. OF N. ].