Excavation.
Work was started on the New York side on April 18th, 1904, the Weehawken shaft being at that date still under construction. As will have been noted in the description of the shafts, the contractor found a shaft already prepared for his use, and cross-drifts at grade and at right angles to the future tunnels, and extending across their entire width. The first essential was to get access to the shield chambers, which were to lie about 330 ft. to the west of the shaft, so that the construction of these enlargements in which the shields for the subaqueous tunnels were to be built might be finished as soon as possible and thus allow the earliest possible start to be made with the shield-driven tunnels.
PLATE XXXII.
TRANS. AM. SOC. CIV. ENGRS.
VOL. LXVIII, No. 1155.
HEWETT AND BROWN ON
PENNSYLVANIA R. R. TUNNELS: NORTH RIVER TUNNELS.
With this in view, two bottom headings, on the center line of each of the two tracks, were driven westward from the western cross-heading at the foot of the shaft. When about 138 ft. had been made in this way, the two headings were brought together and a break-up was made to the crown level of the tunnel, as the depth of rock cover was doubtful. From this break-up a top heading was driven westward to Station 200 + 30. While widening the heading out at Station 200 + 20 the rock was penetrated on the south side. The exposed wet sand and gravel started to run, and, as a consequence, a change in design was made, the shield chambers (and consequently the start of the shield-driven tunnels) being moved eastward from their original location 133 ft. to their present location. A certain amount of time was necessarily spent in making these changes of design, which involved a rearrangement of the whole layout from the Terminal Station to the start of the River Tunnels. On July 5th, 1904, however, the new design was formally approved. No sooner had this been decided than a strike arose on the work, and this was not settled until August 1st, 1904, but from that time the work progressed without delay. No further reference will be made to the work in the shield chambers, as that will come under the heading of "River Tunnels," being of the segmental, cast-iron lined type.
A top heading was now driven over the original bottom heading west of the shaft, and at the same time the original cross-drifts from the shaft were amalgamated with and broken down by a heading driven at the crown level of the "Intercepting Arch" which here cuts across the ordinary run of tunnel at right angles and affords access to the tunnels from the shafts.
The excavation of the upper portion of the intercepting arch at its southern end gave some trouble, and caused some anxiety, as the rock cover was penetrated and the wet sand and gravel were exposed. This made it necessary to timber all this section heavily, and the tracks of the New York Central Railroad directly above were successfully supported. The general way in which this timbering was carried out will be described under the head of "Timbering."
Meanwhile, the excavation of the tunnels west of the intercepting arch was continued until the North and South Tunnels were taken out to their full outlines, leaving a core of rock between them. This core was gradually removed, and timbering supporting the rock above the middle wall was put in as excavation went on. The ground, which was entirely of micaceous schist, typical of this part of Manhattan, seamed with veins of granite, was rather heavy at the west end, or adjacent to the shield chambers, and required complete segmental timbering across the whole span. One heavy fall of rock in the corewall between the North and South Tunnels took place on November 2d, but fortunately did not extend beyond the limits of the permanent work. On November 7th, 1904, the excavation east of the intercepting arch was begun by driving a bottom heading in the South Tunnel. This was continued to Station 197 + 14 and then was taken up to the crown level and worked as a top heading with the view of keeping track, by making exploratory borings upward from the roof at frequent intervals, of the rock surface, which was here irregular and not known with any degree of certainty. The work was not pressed with any vigor, because all efforts were then being bent toward excavating from the River Tunnels as much rock as possible. In Section Gy-East the conditions were exceptionally variable, as the rock was subject to sudden changes from a soft crumbling mica schist to broad bands of hard granite, and, in addition, the rock surface was very irregular, and, for a good length of this section, was below the crown of the tunnel, a condition which led to the adoption of the cut-and-cover method for part of the work.
The irregularity in conditions called for varying methods of procedure, but in general the methods were as shown on [Plate XXXIII], and described as follows:
In Solid Rock.—Where there was plenty of good rock cover, a top middle heading was driven, which was afterward widened out to the full cross-section of the twin tunnel arches. If necessary, a few lengths of segmental timbering were put in before taking down the bench, which was generally kept some 40 or 50 ft. behind the breast of the heading. After the bench was down, the middle conduit trench was excavated and the trimming done.
In Soft Rock.—Where there was not enough rock cover, or where there was actual soft ground in the roof, wall-plate headings at the springing line level were driven ahead of the remainder of the work. The wall-plates were laid in these, the roof was taken out in short lengths, and segmental timbering spanning from wall-plate to wall-plate was put in. The roof being thus held, the bench excavation proceeded without trouble. Where the rock was penetrated and soft ground showed in the roof, poling boards were driven ahead over the crown-bars, as shown in [Fig. 4].
PLATE XXXIII.
TRANS. AM. SOC. CIV. ENGRS.
VOL. LXVIII, No. 1155.
HEWETT AND BROWN ON
PENNSYLVANIA R. R. TUNNELS: NORTH RIVER TUNNELS.
Cut-and-Cover Work.—After some 225 ft. had been driven from the intercepting arch, it was found that the crown of the tunnel was continually in soft ground. To ascertain the extent of this condition the contractor decided to make soundings as far as Tenth Avenue, which was done by sinking trial pits and making wash-borings in the street. These soundings showed that there would be soft ground in the crown from Station 194 + 75 to Station 194 + 25 (at one point to a depth of 12 ft. below the crown), and on each side of this section the cover was insufficient from Station 193 + 58 to Station 195 + 30. This condition being known, it was decided to adopt cut-and-cover work for this length, the principal reasons being that repairs to sewers, streets, and drains would be no more, and probably less, expensive than with the tunnel method; the underpinning of a heavy brick brewery building adjoining the works on the north side would be facilitated, and the opening in the street, through which muck and materials could be handled, would relieve the congested shaft, through which the large volume of muck from the River Tunnels was then being conveyed. On the other hand, the cut-and-cover method was adversely affected by the presence of a heavy timber trestle built down the south side of the street and over which passed all the excavation from the Terminal Station, amounting to a very heavy traffic. As this trestle had to be supported, it complicated the situation considerably. Very little active progress was made between June, 1905, and April, 1906, as the contractor's energies during that time were much taken up with the progress of the shield-driven tunnels. In April, 1906, preparations were made to start a 50-ft. length of open cut, rangers being fixed and sheathing driven; and the sewer which ran down the middle of this street was diverted to the outside of the open-cut length.
April and May were occupied in driving the sheathing down to rock, supporting the trestle, underpinning the adjoining brewery, and excavating the soft material above the rock. On June 2d, 1906, rock was reached, and, by July 31st, the excavation was down to subgrade over nearly the whole 50 ft. in the first length. In the meantime another length was opened up, and eventually a third.
The surface of the rock now seemed to be rising, and the heavy buildings had been passed, so that tunneling was reverted to for the rest of the work, though many difficulties were caused by soft rock in the roof from time to time.
When the excavation for the open-cut work of the Terminal Station had advanced to the line of Tenth Avenue, the contractor started a heading from this point and drove westward under Tenth Avenue until the headings driven eastward from the cut-and-cover portion, were met.
This was done to expedite the work under Tenth Avenue, where the ground was not very good, where there were several important gas and water mains in the street, and where, moreover, the tunnels were of exceptionally large span (24 ft. 6 in.), making a total width of some 60 ft. for the excavation. The excavation for the New York Tunnels was practically finished in January, 1908.
Drilling and Blasting.—The foregoing short description will serve to show in a general way the scheme adopted in making the excavation. A few details on drilling and blasting methods may not be out of place.
Percussive drills run by air pressure were used. They were Ingersoll-Sergeant, Nos. 3½, A-86, C-24, and F-24. The air came from the high-pressure compressor previously described. This compressor, without assistance, could supply air for nine drills, but, when fed by compressed air from the lower pressure, its capacity was increased three or four times.
The air was compressed to 100 lb. per sq. in. in the power-house, and was delivered at about 80 lb. per sq. in. at the drills. A 3-in. air line was used. The drill steel was 1⅛-to 1⅜-in. octagonal. The holes were about 3¼ in. in diameter at starting and 2⅝ in. at the full depth of 10 ft. The powder used on the New York side was 40% Forcite, the near presence of heavy buildings and lack of much rock cover necessitating light charges and many holes spaced close together.
To compensate the contractor for the inevitable excavation done outside the neat lines of the masonry lining, the excavation was paid for to the "Standard Section Line" which was 12 in. outside the neat lines on top and sides and 6 in. outside at the bottom of the cross-section. The actual amount of excavation done was about 11% greater than that paid for. The distance excavated beyond the neat line, because of the very heavy timbering necessary, was about 2.1 ft. instead of the 1 ft. allowed, and at the bottom about 0.85 ft. instead of the 0.50 ft. paid for.
For a period of 5 months detailed records were kept of the drilling and blasting. About 12,900 cu. yd. of excavation are included. A sketch and table showing the method of driving the heading, the number and location of the holes drilled, and the amount of powder used, is given in [Fig. 5]. From this and similar figures the information in [Table 5] is derived.
| Portion of excavation. | Feet of Hole drilled per cubic Yard of Execavation | Pounds of Power Used per Cubic Yard of Excavation | ||||
|---|---|---|---|---|---|---|
| 15-ft. 4-in. span-- twin tunnel | 19-ft. 6-in. span-- twin tunnel | 24-ft. 6-in. span-- twin tunnel | 15-ft. 4-in. | 19-ft. 6-in. | 24-ft. 6-in. | |
| Wall-plate heading[C] | 13.00 | 10.97 | 10.97 | 3.77 | 2.85 | 2.85 |
| Total heading[C] | 7.87 | 8.17 | 7.81 | 2.31 | 2.02 | 1.78 |
| Bench and raker bench[C] | 5.97 | 6.15 | 7.56 | 0.94 | 0.93 | 1.13 |
| Trench[C] | 9.82 | 15.96 | 18.10 | 1.84 | 2.49 | 2.73 |
| Average for section[C] | 6.69 | 7.43 | 8.95 | 1.28 | 1.30 | 1.45 |
| Actual amount[D] | 6.82 | 7.27 | 8.95 | 1.22 | 1.24 | 1.27 |
[C] ]Figures taken from typical cross-sections.
[D] This gives the actual amount of drilling done and powder used per cubic yard for the whole period of 5 months of observation, but as this length included 280 ft. of heading and only 220 ft. of bench, the average figures (for powder especially) are too low.
[Table 6] gives the rate and cost of drilling, and the cost of powder. It will be seen that the average rate of drilling was 2.71 ft. per hour per drill or 27.1 ft. per drill per shift.
[Table 7] shows the result of observation as to the time taken in various subdivisions of the drilling operations. These observations were not carried on for a long enough period to give correct results, but the percentages of time spent on each division of the operation are believed to be about right. The headings of this table are self-explanatory. The necessary delays include all time spent in changing bits, making air-line connections, etc. The unnecessary delays are stoppages caused by lack of supplies or insufficient air pressure.
By [Table 6] it will be noticed that the cost of labor for drilling and sharpening steels was about $0.29 per lin. ft. of hole drilled. The total cost, including repairs, supply of air, etc., came to about $0.38, as will be seen from [Table 8].
Timbering.—On the New York side nearly the whole length of the excavation needed timbering, to a greater or less extent, and for the most part required timbering of quite a heavy type.
TABLE 6.—Rock Tunnel Excavation under 32d Street, East of Cut-and-Cover Section. Drilling and Blasting.—Detailed Cost of Labor in Drilling, also Quantity and Cost of Powder Used.
| Drilling and Blasting. | Powder Used. | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Type. | Date. | Total feet drilled. | No. of drill shifts (10-hour.) | Feet drilled per man per hour. | Quantity of excavation, in cubic yards. | Cost of labor only. Drilling and sharpening. | Total Quantity. | Cost per cubic Yard at 11 cents per pound. | |||||||||||
| Total. | Per linear feet. | Per cubic yard | |||||||||||||||||
| Actual. | Paid for. | Actual. | Paid for | ||||||||||||||||
| 1907 | Heading | Bench | Total | Heading | Bench | Total | Heading | Bench | Total | Actual.[E] | Paid for[F] | Pounds. | |||||||
| $ | $ | $ | $ | $ | $ | ||||||||||||||
| Ke. | May | 2,971 | 5,578 | 8,549 | 98 | 204 | 302 | 3.031 | 2.734 | 2.831 | 1,736 | 1,664 | 2,331 | 0.27 | 1.34 | 1.40 | 1,595 | 0.10 | 0.10 |
| June | 2,093 | 6,194 | 8,287 | 85 | 223 | 308 | 2.462 | 2.777 | 2.691 | 809 | 698 | 2,440 | 0.29 | 3.01 | 3.49 | 1,960 | 0.27 | 0.31 | |
| July | 7,627 | 7,627 | 268 | 268 | 2.845 | 2.845 | 1,022 | 960 | 2,031 | 0.26 | 1.98 | 2.11 | 966 | 0.10 | 0.11 | ||||
| Aug. | 2,552 | 2,552 | 95 | 95 | 2.688 | 2.688 | 743 | 716 | 640 | 0.25 | 0.86 | 0.89 | 430 | 0.06 | 0.07 | ||||
| Sept. | 2,133 | 2,133 | 79 | 79 | 2.700 | 2.700 | 238 | 238 | 533 | 0.25 | 2.24 | 2.24 | 280 | 0.13 | 0.13 | ||||
| Total | 5,064 | 24,084 | 29,148 | 183 | 869 | 1,052 | 2.767 | 2.770 | 2.770 | 4,548 | 4,276 | 7,975 | 0.27 | 1.75 | 1.87 | 5,231 | 0.13 | 0.13 | |
| Ki. | May | 6,976 | 6,976 | 216 | 216 | 3.229 | 3.229 | 614 | 527 | 1,604 | 0.23 | 2.61 | 3.04 | 1,230 | 0.22 | 0.26 | |||
| June | 4,089 | 4,089 | 135 | 135 | 3.029 | 3.029 | 357 | 259 | 1,234 | 0.30 | 3.45 | 4.76 | 1,036 | 0.32 | 0.44 | ||||
| July | 3,733 | 3,733 | 140 | 140 | 2.666 | 2.666 | 530 | 404 | 1,084 | 0.29 | 2.04 | 2.68 | 550 | 0.11 | 0.15 | ||||
| Aug. | 6,715 | 6,715 | 249 | 249 | 2.769 | 2.769 | 925 | 890 | 1,901 | 0.28 | 2.05 | 2.13 | 905 | 0.10 | 0.11 | ||||
| Estim | 14,742 | 14,742 | 46 | 546 | 2.700 | 2.700 | 3,254 | 2,908 | 4,570 | 0.31 | 1.40 | 1.57 | 2,470 | 0.08 | 0.09 | ||||
| Total | 11,065 | 25,190 | 36,255 | 351 | 935 | 1,286 | 3.152 | 2.694 | 2.819 | 5,680 | 4,988 | 10,393 | 0.29 | 1.83 | 2.08 | 6,191 | 0.12 | 0.14 | |
| Ko. | May | 1,617 | 1,617 | 55 | 55 | 2.921 | 2.921 | 250 | 188 | 471 | 0.29 | 1.88 | 2.50 | 376 | 0.17 | 0.22 | |||
| June | 2,948 | 2,948 | 107 | 107 | 2.755 | 2.755 | 496 | 347 | 883 | 0.29 | 1.78 | 2.54 | 357 | 0.08 | 0.11 | ||||
| July | 3,734 | 3,734 | 131 | 131 | 2.850 | 2.850 | 626 | 606 | 1,003 | 0.27 | 1.60 | 1.65 | 609 | 0.11 | 0.11 | ||||
| Aug. | 8,260 | 8,260 | 290 | 290 | 2.848 | 2.848 | 709 | 2,161 | 0.26 | 3.00 | 3.04 | 918 | 0.14 | 0.14 | |||||
| Estim | 4,787 | 4,787 | 285 | 285 | 1.180 | 1.680 | 605 | 535 | 2,397 | 0.50 | 3.96 | 4.48 | 762 | 0.14 | 0.16 | ||||
| Total | 21,346 | 21,346 | 868 | 868 | 2.460 | 2.460 | 2,695 | 2,385 | 6,915 | 0.32 | 2.57 | 2.90 | 3,022 | 0.12 | 0.14 | ||||
| Grand Total | 16,129 | 70,620 | 86,749 | 534 | 2,672 | 3,206 | 3.020 | 2.710 | 2.710 | 12,923 | 11,649 | 25,283 | 0.29 | 1.96 | 2.17 | 14,444 | 0.12 | 0.14 | |
The work done during the 5 months when these analyzed cost figures were kept includes 280 ft. of bench and 220 ft. of heading. This excess of bench over heading causes the general average amounts per cubic yard to be too low.
[E]Actual amount of excavation.
[F] ]Amount of excavation paid for.
| Drilling and Firing Data for Each Sub-division of Section | Drilling and Firing Data for Total Sections | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sub- divisions | Volume of each sub- division paid for | No. of sets | No. of holes in set | No. times fired | Total lbs. of power per hole fired | Linear feet of tunnel broken | Total length drilled | Total length of similar headings | Length drilled per linear foot of tunnel | Cu yds per linear foot of tunnel | Total feet drilled per cubic yard | Total lbs. of power per linear foot of tunnel | Total lbs. of power per foot drilled | Total lbs. of power per cubic yard |
| a | b | c | d | e | f | g | h | i | j | k | l | m | n | o |
| A | 17.775 | [G]1 | 6 | 3 | 4.50 | Σ(c + d) ÷ g | (b + i) ÷ g | j ÷ k | (c + d + f) ÷ g | m ÷ j | m ÷ k | |||
| [H]1 | 9 | 1 | 1.50 | |||||||||||
| [I]1 | 6 | 1 | 1.00 | |||||||||||
| [J]1 | 6 | 1 | 0.75 | 6.0 | 195 | 2 | 65.00 | 5.925 | 10.97 | 17.00 | 0.261 | 2.848 | ||
| A' | 1.00 | 2 | 3-4 | 1 | 0.25 | 5.0 | 21 | 2 | 8.40 | 0.400 | 21.00 | 0.70 | 0.166 | 1.750 |
| B | 5.925 | [G]2 | 3-4 | 1 | 1.00 | 4.0 | 35 | 2 | 17.50 | 2.962 | 5.90 | 3.50 | 0.200 | 1.181 |
| C | [K]1 | 3 | 2 | 1.125 | ||||||||||
| 33.33 | 4 | 7 | 1 | 1.125 | 5.0 | 186 | 1 | 37.20 | 6.666 | 5.58 | 6.975 | 0.187 | 1.046 | |
| D | 6.665 | 2 | 5-6 | 1 | 0.75 | 3.0 | 33 | 2 | 22.00 | 4.444 | 4.95 | 5.500 | 0.250 | 1.237 |
| Total for Heading | 150.10 | 20.397 | 7.81 | 33.675 | 0.227 | 1.778 | ||||||||
| E | 50.00 | 9 | 5 | 1 | 1.50 | 5.0 | 405 | 1 | 81.00 | 10.000 | 8.10 | 13.500 | 0.167 | 1.350 |
| F | 88.88 | 10.5 | 4 | 2 | 1.50 | |||||||||
| [L]5.0 | 4 | 1 | 1.50 | 4.0 | 682 | 1 | 170.50 | 22.222 | 7.67 | 23.230 | 0.136 | 1.046 | ||
| G | 22.22 | 5.5 | 4 | 2 | 1.00 | 5.0 | 132 | 1 | 26.40 | 4.444 | 5.94 | 4.400 | 0.166 | 0.990 |
| Total for Bench | 277.90 | 36.666 | 7.56 | 41.150 | 0.150 | 1.133 | ||||||||
| H | 9.77 | 5 | 3 | 1 | 0.50 | |||||||||
| 4 | 6 | 1 | 0.50 | 6.0 | 156 | 1 | 26.00 | 1.628 | 15.96 | 3.250 | 0.125 | 1.995 | ||
| I | 26.66 | 8 | 5 | 1 | 1.00 | 6.0 | 252 | 2 | 84.00 | 4.444 | 18.90 | 13.333 | 0.158 | 3.000 |
| Total of Trench | 110.00 | 6.072 | 18.10 | 16.583 | 0.151 | 2.731 | ||||||||
| Total for Whole Section | 548.00 | 63.135 | 8.95 | 91.408 | 0.172 | 1.446 | ||||||||
| Powder taken at 0.5 lb. per stick | ||||||||||||||
[G] ]6 Cut Holes-8 feet (Black circle)
[H] ]9 First Side Rd. and Bottom-7 feet (Circle with dot in it)
[I] ]6 Back Round-7 feet (Circle with line in it)
[J] ]6 Top Back Round-7 feet (Circle with x in it)
[K] ]A' 7 Holes-3 feet (Open circle)
[L] ]line holes (Plus sign)
TABLE 7.—Analysis of Drilling Time on Section Gy-East.
| Position in Section. | Nature of Rock. | No. of Drill Shifts observed for average. | Average Time Taken: | Feet Drilled. | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Setting up. | Drilling. | Necessary delays. | Unnecessary delays. | Taking down machine. | Loading and firing. | Total drilling. | Mucking. | Total. | Per shift. | Per working hour. | |||
| h. m. | h. m. | h. m. | h. m. | h. m. | h. m. | h. m. | h. m. | h. m. | |||||
| Heading | Quartz | 8 | 0:38 | 4:52 | 1:40 | 0:05 | 0:04 | 7:19 | 2:41 | 10:00 | 22:00 | 2.86 | |
| Heading | Hard mica schist | 1 | 0:15 | 8:00 | 1:45 | 10:00 | 10:00 | 42.0 | 4.20 | ||||
| Bench | Quartz | 23 | 1:23 | 5:57 | 2:23 | 0:05 | 0:05 | 0:07 | 10:00 | 10:00 | 25.9 | 2.59 | |
| Bench | Medium mica schist | 16 | 1:10 | 6:08 | 1:50 | 0:12 | 0:07 | 0:07 | 9:34 | 0:26 | 10:00 | 22.22 | 2.32 |
| Center trench | Medium mica schist | 10 | 0:58 | 5:53 | 1:33 | 0:06 | 0:12 | 0:30 | 9:12 | 0:48 | 10:00 | 22.0 | 2.39 |
| Center trench | Soft mica schist | 9 | 1:10 | 6:40 | 1:17 | 0:10 | 0:20 | 0:23 | 10:00 | 10:00 | 26.44 | 2.64 | |
| General average | 67 | 1:08 | 5:58 | 1:53 | 0:07 | 0:09 | 0:12 | 9:27 | 0:33 | 10:00 | 24.1 | 2.54 | |
| Percentage | 11.3% | 59.7% | 18.9% | 1.1% | 1.5% | 2% | 94.5% | 5.5% | 100% | ||||
TABLE 8.--Analyzed Cost of Drilling.
| Item of Cost. | Cost per Foot of Hole Drilled | Cost per drill shift | ||||||
|---|---|---|---|---|---|---|---|---|
| 15 ft. 4 in. | 19 ft. 6 in. | 24 ft. 6 in. | Average. | 15 ft. 4 in. | 19 ft. 6 in. | 24 ft. 6 in. | Average. | |
| Drilling labor | $0.25 | $0.28 | $0.31 | $0.28 | $6.95 | $7.75 | $7.60 | $7.45 |
| Sharpening | 0.02 | 0.02 | 0.01 | 0.016 | 0.58 | 0.42 | 0.34 | 0.43 |
| Drill steel (5 in. per drill shift) | 0.007 | 0.007 | 0.006 | 0.007 | 0.19 | 0.20 | 0.15 | 0.19 |
| Drill repairs | 0.02 | 0.02 | 0.02 | 0.02 | 0.61 | 0.59 | 0.42 | 0.54 |
| High-pressure air | [M]0.05 | 0.04 | 0.07 | 0.07 | 1.39 | 1.86 | 1.67 | 1.82 |
| Totals | $0.35 | $0.38 | $0.41 | $0.385 | $9.67 | $10.82 | $10.18 | $10.43 |
[M] This is an estimated figure, ascertained by taking a proportion of the whole charge for plant running.
General Methods.—Whenever any considerable support was needed for the ground, segmental timbering was used. In most cases, this was supported by wall-plates at the springing line, and was set with an allowance for settlement, so that it would be clear of the work when the masonry lining was put in. As the twin-tunnel section involved the excavation of the North and South Tunnels at the same time, the cross-section of the upper part of the excavation consisted of two quadrants rising from the springing line and connected at the top by a horizontal piece from 19 to 28 ft. in length. This made a rather flat arch to support by timbering.
The timber for the segmental work was 12 by 12-in. yellow pine. In light ground the bents were spaced at 5-ft. centers, in heavy ground 2-ft. 6-in. centers.
When the soft ground in the roof was struck, posts had to be used in the heading to support the caps. When the bench was removed, the posts were replaced by others down to the bottom of the excavation. These long posts were a great hindrance to all the work, and each replacement of short posts by long ones meant a settlement of the caps; consequently, it was decided to use in the section east of the cut-and-cover, where all the ground was heavy, a temporary inner bent of segmental timber, within and reinforcing the permanent bent, and resting on separate wall-plates. This is shown by [Fig. 6]. These temporary bents were inside the work, and were removed as the arch was built. However, the caps settled considerably in some cases, so that it was not possible to do away with posting entirely.
In heavy ground the caps were set about 1 ft. above the neat line of the crown of the brick arch, in some cases they were set only 6 in. above, but the settlement was often more than this, causing great trouble in cutting out the encroaching timber when the arch had to be built.
In the tunnels east of the cut-and-cover portion, wall-plate headings were driven (shown by areas marked Aon [Fig. 5]), and, when a length of wall-plate had been set, the full-width heading was advanced a foot or two at a time, the timber segmental bents being set up as soon as possible; lagging was then driven over the cap into the soft ground. [Fig. 6] shows the double set of segmental bents adopted in the 15-ft. 4-in. twin tunnels east of the cut-and-cover section.
When the soft ground came down so low as to interfere with the excavation of the wall-plate headings, a small heading was driven into the soft ground on the line of the ends of the caps, and lagging was driven down from this to the wall-plate heading, as illustrated in [Fig. 4].
In the 19-ft. 6-in. tunnels the wall-plate for the inner bent was supported by a side-bench, termed the "Raker" bench. This was left in position until the rest of the bench and the middle subgrade conduit trench had been excavated; it was then possible to support the caps by two rows of posts from subgrade level, take out the inner bents, and excavate the raker bench.
The 24-ft. 6-in. twin tunnels, which are at the extreme eastern end of this section, adjoining the open-cut work of the Terminal Station, and under Tenth Avenue, were driven from the Terminal Station-West, and the timbering had to be made very secure on account of the pipes and sewers in the street above. Detailed records were kept of the amount of timber used and the cost of labor and material expended in timbering. These records cover the same portion of tunnel as that for which the detailed records of drilling costs, previously referred to, were kept. These records are shown in [Tables 9] and [10]. It will be noted that the timber used in blocking, that is, filling up voids outside the main timbering, amounted to more than two-thirds of the total timber, and that the cost of labor in erecting the timbering exceeds the prime cost of the timber by about one-third. The following distinction is made between permanent and temporary timbering: The permanent timbering is that which is concreted in when the masonry is built; the temporary consists of the lower bents and posts, which have to be removed when the masonry is built.
Force Employed in Excavation.—A typical day's working force for drilling, blasting, mucking, and timbering is shown in [Table 11].
Where there was any large quantity of soft ground in the roof, the timber gang was much larger than shown in [Table 11], and was helped by the mucking gang. The drillers did most of the mucking out of the heading before setting up the drills.
Excavation of Weehawken Rock Tunnels.—This subject may be dismissed in a few words, as very few features of interest were called into play. The rock was of good quality, being the sandstone typical of this part of the country. Little or no timbering was needed, there were no buildings above the tunnel to be taken care of, and large charges of powder could be used.
TABLE 9.— Supplementary Analysis of Timbering, Rock Tunnel Excavation Under 32d Street, East of Cut-and-Cover Section. Analyzed Cost of Timbering, per Foot Run and per Bent.
| Ke | |||
|---|---|---|---|
| Per foot run of tunnel | Per bent, 3 ft, 6 in., center to center | Per cubic yard excavation | |
| PERMANENT TIMBERING. | |||
| Lumber in feet, B. M. | |||
| Upper Bent. | 274 | 685 | 7.8 |
| Blocking. | 294 | 735 | 8.3 |
| Total. | 568 | 1,420 | 16.1 |
| Cost, in dollars. | |||
| Lumber. | 23.75 | 59.38 | 0.67 |
| Labor. | 37.50 | 93.75 | 1.06 |
| Total. | 61.25 | 153.13 | 1.73 |
| TEMPORARY TIMBERING. | |||
| Lumber in feet, B. M. | |||
| Lower Bent. | 479 | 11.97 | 13.6 |
| Blocking. | 193 | 483 | 5.5 |
| Total. | 672 | 16.80 | 19.1 |
| Cost, in dollars. | |||
| Lumber. | 29.13 | 72.81 | 0.82 |
| Erection labor. | 28.85 | 72.13 | 0.82 |
| Removal labor. | 8.29 | 20.73 | 0.23 |
| Total labor. | 37.14 | 92.86 | 1.05 |
| Total. | 66.27 | 165.67 | 1.87 |
| GRAND TOTAL. | |||
| Lumber in feet, B. M. | 1,240 | 3,100 | 35.2 |
| Cost, in dollars. | |||
| Lumber. | 52.88 | 132.19 | 1.49 |
| Labor. | 74.64 | 186.61 | 3.60 |
| Total. | 127.52 | 318.80 | |
| Ki | |||
| Per foot run of tunnel | Per bent, 3 ft, 6 in., center to center | Per cubic yard excavation | |
| PERMANENT TIMBERING. | |||
| Lumber in feet, B. M. | |||
| Upper Bent. | 227 | 830 | 5.3 |
| Blocking. | 164 | 601 | 3.8 |
| Total. | 391 | 1,431 | 9.1 |
| Cost, in dollars. | |||
| Lumber. | 16.84 | 61.56 | 0.39 |
| Labor. | 12.82 | 46.88 | 0.30 |
| Total. | 29.66 | 108.44 | 0.69 |
| TEMPORARY TIMBERING. | |||
| Lumber in feet, B. M. | |||
| Lower Bent. | 186.33 | 681.25 | 4.33 |
| Blocking. | 42.80 | 156.50 | 0.99 |
| Total. | 229.13 | 837.75 | 5.32 |
| Cost, in dollars. | |||
| Lumber. | 9.65 | 35.31 | 0.22 |
| Erection labor. | 10.38 | 37.97 | 0.24 |
| Removal labor. | 9.74 | 34.09 | 0.23 |
| Total labor. | 20.12 | 72.06 | 0.47 |
| Total. | 29.77 | 107.37 | 0.69 |
| GRAND TOTAL. | |||
| Lumber in feet, B. M. | 6.20 | 22.69 | 14.4 |
| Cost, in dollars. | |||
| Lumber. | 26.49 | 96.87 | 0.61 |
| Labor. | 32.94 | 118.94 | 0.77 |
| Total. | 59.43 | 215.81 | 1.38 |
| Ko | |||
| Per foot run of tunnel | Per bent, 3 ft, 6 in., center to center | Per cubic yard excavation | |
| PERMANENT TIMBERING. | |||
| Lumber in feet, B. M. | |||
| Upper Bent. | 261 | 962 | 4.1 |
| Blocking. | 408 | 1,508 | 6.5 |
| Total. | 669 | 24.70 | 10.5 |
| Cost, in dollars. | |||
| Lumber. | 28.00 | 103.38 | 0.44 |
| Labor. | 29.79 | 110.00 | 0.47 |
| Total. | 57.79 | 213.38 | 0.91 |
| TEMPORARY TIMBERING. | |||
| Lumber in feet, B. M. | |||
| Lower Bent. | 350 | 1,291 | 5.5 |
| Blocking. | 61 | 227 | 1.0 |
| Total. | 411 | 1,518 | 6.5 |
| Cost, in dollars. | |||
| Lumber. | 18.45 | 68.16 | 0.29 |
| Erection labor. | 20.83 | 76.92 | 0.33 |
| Removal labor. | 12.16 | 44.59 | 0.19 |
| Total labor. | 32.99 | 121.51 | 0.52 |
| Total. | 51.44 | 189.67 | 0.81 |
| GRAND TOTAL. | |||
| Lumber in feet, B. M. | 1,080 | 3,988 | 17.1 |
| Cost, in dollars. | |||
| Lumber. | 46.45 | 171.54 | 0.73 |
| Labor. | 62.78 | 231.50 | 0.99 |
| Total. | 109.23 | 403.04 | 1.72 |
TABLE 10.—Timbering:—Detailed Cost of Timber, Labor, and Superintendence. Rock Tunnel Excavation under 32d Street, East of Cut-and-Cover Section.
| Date. | Timber Used, in Feet, B. M. | Excavation in Cubic Yards. | Cost of Timber. | Cost of Labor. | Total Cost. | Cost per Cubic Yard (Actual). | Cost per Cubic Yard (Paid for). | Cost, per 1,000 Ft., B. M., of Total Timber. | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Main timber. | Blocking timber. | Total timber. | Actual. | Paid for. | Main. | Block. | Total. | Timber. | Labor. | Total. | Timber. | Labor. | Total. | Total timber. | Labor. | Total. | ||||
| 1907 | a | b | c | d | e | f | g | h | i | j | h / d | i / d | j / d | h / e | i / e | j / e | h / c | i / c | j / c | |
| Ke | May | 18,016 | 15,234 | 33,250 | 1,736 | 1,664 | $810 | $565 | $1,375 | $1,792 | $3,167 | $0.79 | $1.03 | $1.82 | $0.82 | $1.07 | $1.90 | $41.35 | $53.89 | $95.24 |
| June | 14,048 | 11,528 | 25,576 | 809 | 698 | 680 | 457 | 1,087 | 1,576 | 2,663 | 1.34 | 1.95 | 3.29 | 1.55 | 2.25 | 3.81 | 42.50 | 61.62 | 104.12 | |
| July | 20,092 | 7,339 | 27,431 | 1,022 | 960 | 900 | 300 | 1,200 | 1,580 | 2,780 | 1.16 | 1.55 | 2.72 | 1.25 | 1.64 | 2.89 | 43.74 | 57.60 | 101.34 | |
| August | 6,485 | 2,632 | 9,117 | 743 | 716 | 290 | 110 | 400 | 300 | 700 | 0.53 | 0.40 | 0.94 | 0.57 | 0.41 | 0.98 | 43.87 | 32.90 | 76.77 | |
| Sept. | 1,632 | 2,224 | 3,856 | 238 | 238 | 73 | 94 | 167 | 60 | 227 | 0.70 | 0.25 | 0.95 | 0.70 | 0.25 | 0.95 | 43.31 | 15.56 | 58.87 | |
| Removal | 663 | 663 | ||||||||||||||||||
| Total | 60,273 | 38,957 | 99,230 | 4,548 | 4,276 | $2,703 | $1,526 | $4,229 | $5,971 | $10,200 | $0.91 | $1.51 | $2.22 | $1.00 | $1.40 | $2.40 | $42.62 | $60.19 | $102.81 | |
| Ki | May | 3,537 | 3,537 | 614 | 527 | $150 | $150 | $100 | $250 | $0.24 | $0.16 | $0.40 | $0.28 | $0.19 | $0.47 | $42.41 | $28.27 | $70.68 | ||
| June | 300 | 300 | 357 | 259 | $14 | 14 | 44 | 58 | 0.04 | 0.12 | 0.16 | 0.05 | 0.17 | 0.22 | 46.66 | 146.33 | 193.33 | |||
| July | 7,776 | 5,811 | 13,587 | 530 | 404 | 350 | 233 | 583 | 525 | 7,108 | 1.10 | 0.99 | 2.09 | 1.44 | 1.30 | 2.74 | 42.91 | 38.64 | 81.54 | |
| August | 19,712 | 5,702 | 25,414 | 925 | 890 | 887 | 220 | 1,107 | 1,018 | 2,125 | 1.20 | 1.10 | 2.30 | 1.24 | 1.14 | 2.38 | 43.56 | 40.06 | 83.61 | |
| Sept. | 20,556 | 9,218 | 29,774 | 1,585 | 1,501 | 925 | 325 | 1,250 | 1,028 | 2,278 | 0.79 | 0.65 | 1.44 | 0.83 | 0.68 | 1.51 | 41.98 | 34.53 | 76.51 | |
| Removal | 1,669 | 1,407 | 1,139 | 1,139 | 0.68 | 0.68 | 0.81 | 0.81 | ||||||||||||
| Total | 48,344 | 24,268 | 72,612 | 5,680 | 4,988 | $2,176 | $928 | $3,104 | $3,854 | $6,958 | $0.55 | $0.68 | $1.23 | $0.63 | $0.77 | $1.40 | $42.75 | $53.09 | $95.84 | |
| Ko | May | 4,332 | 8,788 | 13,120 | 250 | 188 | $175 | $366 | $561 | $303 | $864 | $2.24 | $1.21 | $3.45 | $3.00 | $1.61 | $4.61 | $42.76 | $23.10 | $65.86 |
| June | 7,132 | 10,017 | 17,149 | 496 | 347 | 324 | 396 | 720 | 562 | 1,282 | 1.45 | 1.18 | 2.58 | 2.07 | 1.61 | 3.68 | 41.98 | 32.77 | 74.75 | |
| July | 3,070 | 200 | 3,270 | 626 | 606 | 134 | 10 | 144 | 156 | 300 | 0.23 | 0.25 | 0.48 | 0.23 | 0.26 | 0.49 | 44.04 | 47.70 | 91.74 | |
| August | 10,704 | 2,102 | 12,806 | 718 | 709 | 481 | 80 | 561 | 727 | 1,288 | 0.78 | 1.01 | 1.79 | 0.80 | 1.02 | 1.82 | 43.80 | 56.77 | 100.57 | |
| Sept. | 2,400 | 245 | 2,645 | 396 | 324 | 108 | 8 | 116 | 400 | 516 | 0.29 | 1.01 | 1.30 | 0.36 | 1.23 | 1.59 | 43.85 | 151.23 | 195.08 | |
| Removal | 209 | 211 | 535 | 535 | 2.56 | 2.56 | 2.54 | 2.54 | ||||||||||||
| Total | 27,638 | 21,352 | 48,990 | 2,695 | 2,385 | $1,242 | $860 | $2,102 | $2,683 | $4,785 | $0.78 | $1.00 | $1.78 | $0.88 | $1.12 | $2.00 | $42.91 | $54.75 | $97.65 | |
| Grand total | 136,255 | 84,577 | 220,832 | 12,923 | 11,649 | $6,121 | $3,314 | $9,435 | $12,508 | $21,943 | $0.73 | $0.97 | $1.70 | $0.81 | $1.07 | $1.88 | $42.73 | $56.65 | $99.38 | |
Work was begun on September 1st, 1904, immediately on the completion of the work on the shaft. The North and South Tunnels in this case are completely independent, as will be seen from [Plate XXXIV]. The procedure adopted was to drive a top heading on the center line of each tunnel and to break down the bench from this. The drilling was at first supplied with steam power from a temporary plant, as the contractor was at that time installing his permanent plant, which was finished at the end of November, 1904. At this time the rate of advance averaged 3½ lin. ft. of full section per day of 24 hours. By the end of January the Weehawken rock tunnels were completely excavated, and by the middle of April, 1905, the excavation for the shield chambers was finished; the erection of the shields was started at the end of that month.
| Grade. | Total No. | Rate per day. | Drilling and blasting: No. | Mucking: No. | Timbering: No. |
|---|---|---|---|---|---|
| Superintendent | 1 | $7.70 | ½ | ⅛ | ⅜ |
| Assistant engineer | 1 | 5.80 | ½ | ⅛ | ⅜ |
| Electrician | 1 | 3.50 | ½ | ⅛ | ⅜ |
| Engineer | 1 | 3.50 | 1 | ||
| Signalman | 1 | 2.00 | 1 | ||
| Foreman | 3 | 4.00 | 1 | 1 | 1 |
| Driller | 5 | 3.00 | 5 | ||
| Driller's helper | 5 | 2.00 | 5 | ||
| Laborers | 14 | 2.00 | 14 | ||
| Timbermen | 3 | 3.00 | 3 | ||
| Timbermen's helpers | 4 | 2.00 | 4 | ||
| Machinist | 1 | 4.00 | 1 | ||
| Blacksmith | 2 | 3.50 | 2 | ||
| Blacksmith's helper | 2 | 2.00 | 2 | ||
| Nipper | 2 | 2.00 | 2 | ||
| Waterboy | 1 | 2.00 | 1 | ||
| Total | 47 | 20½ | 17⅜ | 9⅛ |
The general scheme of excavation is shown by Plate [XXXIII]. The bench was kept 50 or 60 ft. behind the face of the heading. The powder used was 60% Forcite. The general system of drilling was as shown in [Fig. 7]. The average length of hole drilled per cubic yard of excavation was 2.9 ft., as against 7.70 ft. at Manhattan; and the amount of powder used was 1.96 lb. per cu. yd., as against 1.24 lb. at Manhattan. There was little timbering. A length of about 30 or 40 ft. adjoining the Weehawken shaft was timbered, and also a shattered seam of about 17 ft. in width between Stations 262 + 10 and 262 + 27.
The two entirely separate tunnels gave a cross-section which was much more easily timbered than the wide flat span at Manhattan, and the segmental timbering was amply strong without posts or other reinforcement.
[Table 12] is a summary of the cost of excavating the Land Tunnels, based on actual records carefully kept throughout the work.
TABLE 12.—Cost of Excavation of Land Tunnels, in Dollars per Cubic Yard.
| Manhattan. | Weehawken. | Total yardage and average cost. | |
|---|---|---|---|
| Cubic yards excavated | 43,289 | 8,311 | 51,600 |
| Labor. | |||
| Surface transport | $0.49 | $0.87 | $0.55 |
| Drilling and blasting | 2.37 | 1.55 | 2.24 |
| Mucking | 2.49 | 2.08 | 2.42 |
| Timbering | 0.87 | 0.18 | 0.76 |
| Total labor | $6.22 | $4.68 | $5.97 |
| Material. | |||
| Drilling | $0.15 | $0.15 | $0.15 |
| Blasting | 0.21 | 0.21 | 0.21 |
| Timber | 0.39 | 0.20 | 0.36 |
| Total material | $0.75 | $0.56 | $0.72 |
| Plant running | $0.76 | $0.65 | $0.74 |
| Surface labor, repairs and maintenance | 0.15 | 0.08 | 0.14 |
| Field office administration | 1.05 | 1.18 | 1.07 |
| Total field charges | $8.96 | $7.15 | $8.64 |
| Chief office administration | $0.34 | $0.38 | $0.34 |
| Plant depreciation | 0.66 | 1.01 | 0.72 |
| Street and building repairs | 0.27 | 0.23 | |
| Total average cost per cubic yard | $10.23 | $8.54 | $9.93 |