--------------+-----------------+-------------------+-------------------------+
| | Station: | Date: |
| |---------+---------+------------+------------+
| | | | | |
Material. | Method. | From | To | From | To |
--------------+-----------------+---------+---------+------------+------------+
{|Top heading |107+79.03|107+69 |Dec. 20, '04|Dec. 27, '04|
{|Top heading |107+69 |107+23 |Jan. 1, '05|Jan. 15, '05|
Rock {|Excavating bench |107+79 |107+23 |Jan. 21, '05|Feb. 28, '05|
{|Bottom heading |107+23 |106+72 |Mar. 1, '05|Mar. 11, '05|
{|Bottom heading |107+23 |107+15 |Oct. 12, '05|Oct. 27, '05|
{| | | | | |
| | | | | |
Rock |Bottom heading |107+15 |106+62 |Nov. 6, '05|Dec. 2, '05|
| | | | | |
| | | | | |
Mixed |Bottom heading |106+62 |106+55 |Dec. 2, '05|Dec. 23, '05|
| | | | | |
| | | | | |
Mixed |Bottom heading |106+55 |106+17 |Feb. 12, '06|Mar. 22, '06|
| | | | | |
Mixed |Rock cut |106+17 |105+85 |Apr. 2, '06|Apr. 20, '06|
| | | | | |
Mixed |Rock cut |105+85 |105+55 |July 27, '06|Aug. 26, '06|
| | | | | |
| | | | | |
Earth |Breasting and |105+55 | 99+40 |Aug. 26, '06|Jan. 2, '07|
| poling | | | | |
| | | | | |
Mixed |Rock cut | 99+40 | 98+70 |Jan. 2, '07|Feb. 6, '07|
| | | | | |
Rock |Full face | 98+70 | 98+60 |Feb. 6, '07|Feb. 12, '07|
| | | | | |
Mixed |Bottom heading | 98+60 | 98+39 |Feb. 12, '07|Mar. 6, '07|
| | | | | |
Rock |Bottom heading | 98+39 | 98+17 |Mar. 6, '07|Mar. 15, '07|
| | | | | |
Mixed |Rock cut | 98+17 | 95+68 |Mar. 15, '07|July 30, '07|
| | | | | |
Rock |Middle heading | 95+68 | 94+61 |July 30, '07|Aug. 21, '07|
| | | | | |
Mixed |Rock cut | 94+61 | 93+56 |Aug. 21, '07|Oct. 3, '07|
| | | | | |
Rock |Middle heading | 93+56 | 92+73 |Oct. 3, '07|Nov. 11, '07|
| | | | | |
Mixed |Rock cut | 92+73 | 90+55 |Nov. 11, '07|Feb. 13, '08|
| | | | | |
Mixed |Rock cut | 90+55 | 90+44.4 |Feb. 25, '08|Mar. 3, '08|
--------------+-----------------+---------+---------+------------+------------+
--------------+------+--------+--------+--------------------------------------+
| | |Rate of | |
|Number| |progress| |
| of | Linear |in feet | |
Material. | days.| feet. |per day.| Remarks |
--------------+------+--------+--------+--------------------------------------+
{| 7} | | {|Stopped to brace portal. No work done |
{| 14} | | {|from March 12th to October 11th, 1905,|
Rock {| 38} | 54 | 0.77 {|except a little trimming in September.|
{| 10} | | {|All work up to this date done in |
{| 15} | | {|normal air. Heading advanced to 106+70|
{| } | | {|and bulkheaded. |
| | | | |
Rock | 26 | 53 | 2.04 | |
| | | | |
| | | {|Heading advanced to 106 + 40. Shut |
Mixed | 21 | 7 | 0.33 {|down in order that Line D might have a|
| | | {|lead. |
| | | | |
Mixed | 38 | 38 | 1.00 {|Shut down on account of air shortage. |
| | | | |
Mixed | 18 | 32 | 1.78 |Shut down on account of air shortage. |
| | | | |
Mixed | 30 | 30 | 1.00 |Shut down April 20th to July 27th, |
| | | |1906. |
| | | | |
Earth |127 | 615 | 4.84 | |
| | | | |
| | | | |
Mixed | 35 | 70 | 2.00 | |
| | | | |
Rock | 6 | 10 | 1.66 | |
| | | | |
Mixed | 22 | 21 | 0.95 | |
| | | | |
Rock | 9 | 22 | 2.44 | |
| | | | |
Mixed |110 | 249 | 2.26 |Heading advanced to 97+82. |
| | | | |
Rock | 49 | 107 | 2.18 | " " " 94+35. |
| | | | |
Mixed | 43 | 106 | 2.46 | |
| | | | |
Rock | 39 | 83 | 2.13 | |
| | | | |
Mixed | 94 | 218 | 2.32 |Shut down until Line D shields met. |
| | | | |
Mixed | 6 | 11 | 1.83 | |
--------------+------+--------+--------+--------------------------------------+
LINE D, MANHATTAN.
--------------+-----------------+---------+---------+------------+------------+
{|Top heading |107+70.49|107+16 |Dec. 9, '04|Jan. 31, '05|}
{|Removing bench |107+70.49|107+35 |Jan. 1, '05|Jan. 27, '05|}
Rock {|Bottom heading |107+35 |106+80 |Jan. 30, '05|Feb. 10, '05|}
{|Trimming |107+70 |106+80 |Mar. 29, '05|Apr. 12, '05|}
{|Trimming |107+70 |106+80 |Aug. 31, '05|Sept 19, '05|}
| | | | | |
Rock |Bottom heading |106+80 |106+67 |Oct. 5, '05|Nov. 8, '05|
| | | | | |
Mixed |Bottom heading |106+67 |106+39 |Nov. 8, '05|Dec. 23, '05|
| | | | | |
|Sliding hood and | | | | |
Mixed |breasting. Rock |106+29 |105+70 |Dec. 23, '05|Jan. 24, '06|
|bench | | | | |
| | | | | |
Earth |Poling and |105+70 |104+61 |Jan. 24, '06|Feb. 27, '06|
|breasting | | | | |
| | | | | |
| | | | | |
Earth |Poling, breasting|104+61 |103+90 |Mar. 2, '06|Mar. 31, '06|
| and shutters | | | | |
| | | | | |
| | | | | |
Earth |Shutters |103+90 | 99+41 |Apr. 20, '06|Sept 3, '06|
| | | | | |
| | | | | |
Mixed |Bottom bench | 99+41 | 99+17 |Sept 3, '06|Sept 23, '06|
| | | | | |
Mixed |Bottom heading | 99+17 | 98+50 |Oct. 2, '06|Nov. 24, '06|
| | | | | |
| | | | | |
Rock |Bottom heading | 98+50 | 97+72 |Nov. 24, '06|Jan. 16, '07|
| | | | | |
Mixed |Bottom heading | 97+72 | 97+27 |Jan. 16, '07|Feb. 10, '07|
| | | | | |
Mixed |Rock cut | 97+27 | 95+72 |Feb. 10, '07|Apr. 23, '07|
| | | | | |
Rock |Middle heading | 95+72 | 95+57 |Apr. 23, '07|May 11, '07|
| | | | | |
Rock |Middle heading | 95+57 | 94+65 |May 23, '07|June 17, '07|
| | | | | |
| | | | | |
Mixed |Middle heading | 94+65 | 94+41 |June 17, '07|June 25, '07|
| | | | | |
Mixed |Rock cut | 94+41 | 94+03 |June 25, '07|July 13, '07|
| | | | | |
Rock |Middle heading | 94+03 | 92+64 |July 13, '07|Sept 12, '07|
| | | | | |
Mixed |Middle heading | 92+64 | 92+54 |Sept 12, '07|Sept 20, '07|
| | | | | |
Rock |Middle heading | 92+54 | 92+50 |Sept 20, '07|Sept 21, '07|
| | | | | |
Mixed |Rock cut | 92+50 | 90+38.66|Sept 21, '07|Jan. 8, '08|
--------------+-----------------+---------+---------+------------+------------+
--------------+------+--------+--------+--------------------------------------+
| | |Rate of | |
|Number| |progress| |
| of | Linear |in feet | |
Material. | days.| feet. |per day.| Remarks |
--------------+------+--------+--------+--------------------------------------+
{| | | | |
{| | | | |
Rock {|123 | 90 | 0.73 |In normal air. |
{| | | | |
{| | | | |
| | | | |
Rock | 34 | 13 | 0.40 |Bottom heading timbered. |
| | | | |
Mixed | 45 | 38 | 0.84 | |
| | | | |
| | | | |
Mixed | 32 | 59 | 1.84 | |
| | | | |
| | | | |
Earth | 31 | 109 | 3.41 | |
| | | | |
| | | | |
| | | |Three days' delay to set shutters in |
Earth | 29 | 71 | 2.45 |top. Shut down 20 days to permit |
| | | |consolidation of the river bed and to |
| | | |repair broken plates. |
| | | | |
Earth |136 | 449 | 3.40 |Four days of 136, delay account of |
| | | |flood. |
| | | | |
Mixed | 20 | 24 | 1.20 | |
| | | | |
Mixed | 53 | 67 | 1.27 |Thirteen days' shut-down to put on |
| | | |hood. |
| | | | |
Rock | 53 | 78 | 1.47 | |
| | | | |
Mixed | 25 | 45 | 1.40 | |
| | | | |
Mixed | 72 | 155 | 2.15 | |
| | | | |
Rock | 18 | 15 | 0.83 | |
| | | | |
Rock | 25 | 92 | 3.68 |Twelve days' delay to repair cutting |
| | | |edge. |
| | | | |
Mixed | 8 | 24 | 3.00 | |
| | | | |
Mixed | 18 | 38 | 2.11 | |
| | | | |
Rock | 61 | 139 | 2.28 | |
| | | | |
Mixed | 8 | 10 | 1.25 | |
| | | | |
Rock | 1 | 4 | 4.00 | |
| | | | |
Mixed |109 | 211.34| 1.94 | |
--------------+------+--------+--------+--------------------------------------+
Openings were made between the headings as follows:
Tunnel _D_, February 20th, 1908;
Tunnel _B_, March 3d, 1908;
Tunnel _C_, March 5th, 1908;
Tunnel _A_, March 18th, 1908.
It was necessary to cut away the projecting floors of the working
compartments before the cutting edges could be shoved together.
_Contractor's Organization._--Tunnel operations were carried on
continuously for thirteen days out of fourteen, regular work being shut
down for repairs on alternate Sundays. When the required pressure was
more than 32 lb., four gangs of laborers were employed, each gang
working two shifts of 3 hours each, with an intermission of 3 hours
between the shifts. When the pressure was less than 32 lb., three gangs
were employed, each gang covering 8 hours, but with an intermission of
about 1/2 hour in low pressure for lunch.
_Air Pressures Required._--During the greater portion of the work in
soft ground, pressure was maintained which would about balance the
hydrostatic head at the axis of the tunnel. This required a pressure
varying from 30 to 34 lb. per sq. in. above that of the atmosphere. In
Tunnels _B_ and _D_, at Manhattan, during the work in soft ground,
pressures as high as 37 lb. were maintained for considerable periods of
time; in the firm material near the reef 28 lb. was often sufficient.
While removing the broken plates, the pressure was raised for a short
time to 42 lb., and was maintained between 37-1/2 and 40 lb. for a
little more than one month.
_Air Supply._--For regular operation the contractor furnished four
compressors on each side of the river, each having a rated capacity of
5,000 cu. ft. of free air per minute delivered at 50 lb. above normal,
when running at the rate of 100 rev. per min. An additional compressor
of the same capacity was supplied on each side of the river, in
compliance with the requirement for 25% excess capacity; the additional
compressors had also high-pressure air cylinders which could be
connected at will, and in which the pressure could be increased to 150
lb., and the air used to supply rock drills, grouting machines, etc. The
entire combination on each side of the river, therefore, was rated at
25,000 cu. ft. of free air per minute, or a mean of 6,250 cu. ft. per
heading. Its safe working capacity was not far from 20,000 cu. ft. per
min.
The shields broke through rock surface in Tunnels _B_, _C_, and _D_, at
Manhattan, in November and December, 1905. The consumption of air in the
four tunnels soon exceeded 15,000 cu. ft. for 24 hours, and in Tunnel
_D_, on several occasions, it exceeded 7,000 cu. ft. for a like period.
Blows had become frequent, and it was evident that the air plant was
inadequate for driving four tunnels at once in the open material east of
the Manhattan rock. Work in Tunnel _A_, therefore, was not resumed,
after the suspension on December 29th, for about ten months, and Tunnel
_C_ was also closed down for more than four months of the time between
December, 1905, and July, 1906. During this period the capacity of the
plant was increased from the rated 25,000 cu. ft. of free air per
minute, to 35,000. In Tunnel _D_ the material had gradually become
firmer, with more clay and less escape of air, as the Blackwell's Island
Reef was approached, and, at the end of the period, the rock surface was
within 3 ft. of the top of the shield; in Tunnel _B_, the rock of the
reef was still a little below the shield, but the overlying material
contained a large proportion of clay and held air very well. Tunnel _C_
was still in open material, but, with two lines safe and with the
increased air plant, it was deemed best to resume work in Tunnel _A_,
which was done on October 23d, 1906. Thenceforward work was continuous
in all headings until the meeting points with the Long Island shields
were reached.
This period, January to October, 1906, inclusive, was the most strenuous
of the entire work, particularly the first six months. With one and, at
times, two tunnels closed down, the consumption of air in the headings
from Manhattan was an average of more than 20,000 cu. ft. per min. for
periods of from 30 to 60 days; it was often more than 25,000 cu. ft. for
24 hours, with a maximum of nearly 29,000 cu. ft., and doubtless this
was exceeded considerably for shorter periods. On several occasions the
quantity supplied to a single tunnel averaged more than 15,000 cu. ft.
per min. for 24 hours. The greatest averages for 24 hours were obtained
later in Tunnel _A_, after the resumption of work there, and exceeded
19,000 cu. ft., but the conditions in the headings of the other lines
were then so favorable that the work was carried on continuously in all.
The deficiency in the original plant at Manhattan was so marked, and the
need of driving all headings from Long Island simultaneously so clear,
that it was decided to increase the rated capacity of the Long Island
compressor plant to 45,400 cu. ft. of free air per minute, which was
10,400 cu. ft. greater than the capacity of the Manhattan plant after
the latter had been augmented.
[Illustration: PLATE LXXII]
The earth encountered on emerging from rock, when driving westward from
Long Island, was far more compact and less permeable to air than on the
Manhattan side, but for a distance of from 400 to 600 ft. immediately
east of the reef, it was a clean open sand, and, while the shields were
passing through this, the quantity of air supplied to the four headings
seldom fell below 20,000 cu. ft. per min.; it was usually more than
25,000 cu. ft., with a recorded maximum of 33,400 cu. ft. Although this
was greater than ever used on the Manhattan side, it was more uniformly
distributed among the several headings, and in none equalled the maximum
observed on the Manhattan side, the largest having been 12,700 cu. ft.
per min. for 24 hours; it must be remembered, however, that at one time
only two tunnels were in progress in the bad material in the tunnels
from Manhattan.
From the foregoing experience, it would seem that the plant finally
furnished at Long Island, having a rated capacity of 45,400 cu. ft. of
free air per minute, would have been a reasonable compliance with the
original actual needs on the Manhattan side and _vice versa_; the plant
finally developed on the Manhattan side, having a rated capacity of
35,000 cu. ft. of free air per minute, would have sufficed for the Long
Island side.
The total quantity of free air compressed for the supply of the working
chambers of the tunnels and the Long Island caissons was 34,109,000,000
cu. ft., and, in addition, 10,615,000,000 cu. ft. were compressed to
between 80 and 125 lb. for power purposes, of which at least 80% was
exhausted in the compressed-air working chambers. The total supply of
free air to each heading while under pressure, therefore, averaged about
3,550 cu. ft. per min.
The quantity of air escaping during a sudden blow-out is apparently much
smaller than might be supposed. Investigation of a number of cases,
showing large pressure losses combined with a long stretch of tunnel
supplying a relatively large reservoir of air, disclosed that a maximum
loss of about 220,000 cu. ft. of free air occurred in 10 min. This
averages only a little more than 19,000 cu. ft. per min., the maximum
recorded supply to one tunnel for a period of 24 hours. Of this
quantity, however, probably from 30 to 40% escaped in the first 45
seconds, while the remainder was a more or less steady loss up to the
time when the supply could be increased sufficiently to maintain the
lowered pressure. Very few blows showed losses approaching this in
quantity, but the inherent inaccuracy of the observations make the
foregoing figures only roughly approximate.
[Footnote C: _Minutes of Proceedings_, Inst. C. E., Vol. CXXX, p. 50.]