Transactions Of The American Society Of Civil Engineers Vol Lxv

Chapter 2

Chapter 23,411 wordsPublic domain

The average quantity of powder used on the whole work was about 2.9 lb. per cu. yd. The tables on the diagrams, Figs. 1, 2, 3, and 4, show that the quantity actually used in making the advance at the main working faces was about 2.5 lb. The difference is accounted for by the larger percentage of powder used for trimming the sides, breaking out the cross-passages between the tunnels, and the excavation of the ditches, the latter operation not being done until the concrete lining was about to be put in.

There was some time, too, during the earlier stages of the work, when it is believed that an excessive quantity of powder was used; for one or two months it ran up to 4 lb. per cu. yd.

The dynamite used was "Forcite." At first, both 40% and 60% were used, the 60% generally only for blasting the cut in the headings; during the latter part of the work, however, the 60% was used exclusively.

The rock as a rule broke very well, and only a comparatively small quantity could not be handled by the shovels without being broken up further by block-holing. In the sandstone the quantity of powder per cubic yard was much more than for any of the trap.

In drilling the Central Shaft, a 6-hole cut was made approximately on the center line, east and west, the enlargement requiring about 18 more holes, which were generally about 6 ft. deep, the average advance being about 4 ft. per day of 24 hours.

The drills were run by steam until a depth of about 150 ft. had been reached, air from the plant at Hackensack being available after that time. Four drills were used most of the time, and six later when air was available. This work was done entirely by the John Shields Construction Company, and a depth of 205 ft. was sunk in 6 months (from July 15th, 1905, to January 15th, 1906). A derrick was used for hoisting and lowering men and tools during the sinking, elevators being put in later.

_Drilling Data._--During the progress of the work, both general and detailed observations were made of the drilling, the results of which are shown in the tables. Table 1 has been compiled from the records as platted daily on the chart from the inspectors' reports, as shown by Plate XXIII, and described on page 113. Table 2 contains some data relating to the drilling in the headings.

The general results of these observations show that the average time the drills were "actually working" was 5.2 hours per shift, and that they were actually "hitting the rock" about half of this time, or about 2.5 hours per shift. The average depth drilled per hour, during the time the drills were "actually working," was 2.66 ft.

The "actual working time," as noted above, covers the period from the time the drills were first set up in the heading after blasting until they were taken down for the next blast; it does not include the time occupied in setting up or taking down, which would probably average 30 min. more per shift. It is believed that this figure will also apply very closely to drills working on the bench, though no actual observations were taken to determine this, on account of the irregularity with which they were worked.

The actual working time of the drills in the 736 shifts (7,360 hours) covered by Table 1, was 3,826 hours, or 5.2 hours per shift. The average depth drilled per yard, as shown in the last column of Table 1, agrees fairly well with the figures on the diagrams, Figs. 1, 2, 3, and 4.

Table 2 has been compiled from detailed timed observations of individual drilling of down holes in the bench, for periods of 7 or 8 hours each, in January, 1907. The work at that time was in fairly normal condition at all points.

The figures in the third column of Table 2 include the time required for moving from one hole to another, when this occurred during the observation, the time required for changing bits, oiling drills, etc., and all delays of all kinds. A close record of the delays was kept, and it was considered that, of the 93 hours, 48 min., in Table 2, the unnecessary delays amounted to 5 hours, 7 min., or about 5½ per cent.

TABLE 1.

#S. Number of shifts covered by observations. #Hrs Average number of hours worked per shift. D/Hr Average depth drilled per hour per drill. D/Yd Average depth drilled per yard. Hack. Hackensack Whk. Weehawken CS Central Shaft

+-----------+----+-----------+------+------+------ Method. | Date. | #S | Place. | #Hrs | D/Hr | D/Yd ----------------+-----------+----+-----------+------+------+------ {| Aug. '06 | 44 | Hack., N. | 5.69 | 2.78 | 10.1 {| Sept. '06 | 38 | " N. | 5.80 | 3.77 | 11.1 No. 1-- {| Aug. '06 | 43 | " S. | 5.60 | 2.89 | 9.1 4-drill {| Sept. '06 | 36 | " S. | 6.18 | 2.65 | 8.7 {| Jan. '07 | 16 | CS E. N. | 5.99 | 2.99 | 8.2 {| Jan. '07 | 20 | " S. | 6.05 | 2.9 | 7.1 {| Apr. '07 | 48 | CS W. N. | 4.92 | 3.3 | 6.7 {| Apr. '07 | 48 | " S. | 5.00 | 3.2 | 7.7 | | | | | | {| Dec. '06 | 54 | Whk., N. | 4.95 | 2.16 | 4.52 Nos. 2 and 3-- {| Dec. '06 | 54 | " S. | 5.23 | 2.14 | 4.54 5-drill {| Dec. '06 | 52 | Hack., N. | 5.03 | 2.2 | 5.77 {| Dec. '06 | 54 | " S. | 5.90 | 1.82 | 5.67 | | | | | | No. 4-- {| June '07 | 56 | Whk., N. | 4.77 | 2.55 | 4.23 7-drill {| June '07 | 58 | " S. | 4.82 | 2.26 | 3.88 | | | | | | 8-drill {| May '07 | 60 | Hack., N. | 4.67 | 2.44 | 5.00 {| May '07 | 60 | " S. | 4.54 | 2.57 | 4.80 ----------------+-----------+----+-----------+------+------+------

TABLE 2.

Hrs. _Hours._ Min. _Minutes._

+----------+---------------+---------------- Date. | Place. | Total | Number of feet | | working time. | drilled. ----------------+----------+---------------+---------------- | | Hrs. Min. | Jan. 14th, 1907 | Whk. N. | 8 0 | 15 " 15th, 1907 | " N. | 7 32 | 12 | " N. | 7 22 | 14 " 12th, 1907 | " S. | 8 0 | 20 | " S. | 8 0 | 11 | " S. | 8 0 | 10 " 11th, 1907 | Hack. N. | 8 0 | 13 " 17th, 1907 | " N. | 7 10 | 10 | " N. | 7 5 | 11 | " N. | 7 10 | 10 " 16th, 1907 | " S. | 4 20 | 10 | " S. | 6 9 | 10 | " S. | 7 ... | 8 ----------------+----------+---------------+--------------- Totals. | | 93 48 | 154 ----------------+----------+---------------+--------------- Average: 36.6 min. per ft. drilled, or 1.64 ft. drilled per hour.

As a check on the average figures obtained from various sources, the following estimate of the cost of drilling per cubic yard was made up from these average figures, for comparison with the actual average cost on the whole work. The cost records show this to be about $2.25 per yd., exclusive of power for running the drills, almost exactly what the following estimates give for theoretical average conditions, although no effort was made to have this latter compare so closely.

_Estimated Cost per Drill per Day._

Drill Runner 1 at $3.50 per day, $3.50 Helper 1 " 2.00 " " 2.00 Nipper 1/5 " 1.75 " " 0.35 Heading foreman 1/12 " 5.00 " " 0.42 Walking boss 1/50 " 7.50 " " 0.15 Blacksmith 1/12 " 4.00 " " 0.34 Blacksmith helper 1/12 " 2.00 " " 0.16 Machinist 1/12 " 3.00 " " 0.25 Machinist helper 1/24 " 1.75 " " 0.07 Pipe fitter and helper 1/50 " 5.00 " " 0.10 Oil, waste, blacksmith coal, etc. 0.24 Drill steel, 6 in. per shift 0.20 ----- $7.78

Average number of feet drilled per cubic yard 3 to 3.5 Number of feet drilled per drill, per shift 10.5 to 12 Number of yards per drill, per shift 3.5± Cost of drilling, per yard, $7.78/3.5 $2.22±

In all the foregoing tables and computations, the quantities used have been those paid for. The quantity taken out, however, has been 10% more than that paid for, and 28% more than the contractor was actually required to take out.

The specifications required that the excavation should be taken entirely outside of the neat line, as shown on Plate VIII of the paper by Mr. Jacobs, but not necessarily beyond this line, but that the contractor would be paid for rock out to the standard section line, which is 1 ft. larger on the sides and top and 6 in. deeper in the bottom than the neat line.

A great deal of the extra quantity was due to rock falling from the core-wall side whenever one working face was behind the other. Blasting at the face behind generally loosened more or less rock on the core-wall side of the tunnel which was ahead, in one or two instances breaking entirely through, as shown in Fig. 2, Plate XXVI, the hole in the core-wall in this case being utilized by building a storage chamber in it.

Table 3 gives some of the statistics of drilling in the Simplon Tunnel, as compared with the drilling on this work, the figures for the Simplon being taken from papers read before the Institution of Civil Engineers of Great Britain.

TABLE 3. -------------------------------------------+--------------+---------- | | | Bergen Hill. | Simplon. -------------------------------------------+--------------+---------- Drills set up in heading, percentage of | | total elapsed time | 50% | 60% Actually drilling the rock, percentage of | | total elapsed time | 25% | 50% Average advance per round (attack) | 8.5 ft. | 3.8 ft. Average time for each attack | 36 hours. | 5 hours. Average advance per day of 24 hours | 5 ft. | 18 ft.** Depth of holes | 10 ft. | 4.6 ft. Diameter of holes | 2¾ in. | 2¾ in. Linear feet drilled per hour, per drill | 2.7 | 7.0 Linear feet drilled per cubic yard | 5.0 | 6.0 Pounds of dynamite per cubic yard | 3.4 to 5.7 | 8½ Average depth drilled with one sharpening | 12 in. | 6½ in. Total number of men per day of 24 hours* | 450 | 3,300 -------------------------------------------+--------------+----------

[* On Bergen Hill Tunnels, for two full working faces at the Hackensack end, about 3,000 ft. in from portal (March, 1908). At Simplon, two full faces and two headings, at a distance of about 5,000 ft. in from the portal (January, 1900). These both include lining as well as excavation. The lining of the Bergen Hill Tunnels progressed about twice as fast as the excavation; it is inferred that on the Simplon it progressed at about the same rate as the excavation.]

[** At the Italian end, in Antigoric gneiss, which is stated to be very hard rock.]

The figures in Table 3 are for "heading only" in both cases, except for the last item (number of men), the heading in the Simplon Tunnels being about 60 sq. ft., as compared with the heading of Method No 4 (which has been used for comparison), of 210 sq. ft.

_Mucking and Disposal._--The conditions affecting the disposal of the muck, after blasting, were quite different at the two ends, the grade descending in the direction of the loads at Weehawken and ascending at the Hackensack end. At the Weehawken end the mouth of the tunnels was at the bottom of a shaft some 80 ft. deep, Fig. 2, Plate XXII, the muck in the tunnel cars being hoisted by elevators to a platform at the top from which it was dumped into standard-gauge cars supplied by the Erie Railroad, as shown by Fig. 7; or later hauled to the crusher or storage pile, some 500 ft. distant, on the north side of Baldwin Avenue. At the western end, the cars were hauled directly to the surface through the approach cut, and the material, except that required for concrete and rock packing, was deposited in the embankment across the Hackensack Meadows, a haul of from 1,000 to 3,000 ft. beyond the portal.

All disposal tracks were of 3-ft. gauge, the main running tracks being generally laid with 60-lb. second-hand rails, although some of lighter weight were used.

Except for about 1,000 ft. in each tunnel at the Weehawken end, where the muck was loaded by hand, four steam shovels, operated by compressed air, were used, one at each working face. One of these was a "Marion, Model No. 20," weighing 38 tons, the others were "Vulcan Little Giant," of about 30 tons each. All these shovels were on standard-gauge track, and were moved back from 300 to 500 ft. from the working face during blasting.

At Weehawken, previous to the time the shovels were installed, the muck was shoveled by hand into the cars from the bottom of the bench, and the heading muck was dumped into them from the movable platform (Jumbo) shown by Fig. 1, Plate XXII. There were three loading tracks at the face. The cars used at that time were similar to that shown by Fig. 5, but were about two-thirds the size and had no end door; stop-planks were supposed to be placed in the ends but seldom were. The loads averaged about ½ cu. yd. (measured in place). After the shovel was installed the cars shown by Fig. 5 were used, and the loads averaged nearly 1 cu. yd.

The empty cars were pushed up to the shovel by hand from the storage track. When loaded, they were given a start with the bucket of the shovel, and were then allowed to coast by gravity out to the storage track near the shaft, where they were stopped by placing rolls of cement bags or burlap on the rails. After the lining was started, the loaded cars were stopped on the inside of the lining and only sent out over the single track through this latter at stated intervals, when several cars followed in close succession, with a long interval which permitted the concrete to be brought in. The empty cars were hauled back to the storage track near the working face by mules, one mule usually hauling two cars at a time.

Up to the time the trap rock was reached, about 1,100 ft. from the shaft, the excavated material was disposed of by loading it on flat cars. All the trap, however, was stored to be used later for concrete and ballast.

When the tunnels were in full working order, sixty muck cars of the type shown by Fig. 5, were in use, about evenly divided between the two tunnels. For some time the work was greatly hampered by lack of cars, and even with the sixty finally obtained, there were many times when extra cars could have been used to advantage to keep the shovel working.

When mucking by hand, the mucking gangs consisted of from 15 to 20 men. The maximum output was 50 cu. yd., and averaged about 35 cu. yd. per shift; there was a great deal of trouble in keeping the gangs full, as labor at that time was very scarce, and the tunnels were quite wet. The maximum output of either of the shovels was 159 cu. yd. in one shift, and the best average in any month--which was between July and December, 1907, during which time only the enlargement and bench of the Central Shaft headings was being taken out from the western end--was 60 cu. yd. per shift. As the shovels were generally idle for one shift out of three, the quantity actually handled averaged 90 cu. yd. per shift during the shifts the shovel worked. All these quantities were "measured in place," and, as previously noted, would be about equal to twice as much measured loose in the cars.

The shovels at both ends were usually worked with three crews for the two tunnels; two day crews, one at each shovel, and a night crew which was used in either tunnel as occasion required. The day crews generally averaged from 45 to 60 hours overtime during the month, one of them working during the early part of the evenings in the opposite tunnel to the night crew. For a short time, when the ventilation at the western end was very bad, four crews were worked, day and night crews in each tunnel; but, as a general rule, the method of working three crews was preferred by the men, and was less expensive for the contractor.

At the Hackensack end, 4-yd., Allison, one-way, dump cars were used, being handled by "dinky" locomotives, of which there were three in use up to October, 1907, and four after that. One 15-ton Porter engine, with 10 by 16-in. cylinders, was used outside the tunnels for handling the trains (from 6 to 8 cars) on the dumps and to the crusher; the other three, 12-ton Vulcans, 9 by 14-in., were used in the tunnels. About 30 dump cars were in use, and of these there were generally from 3 to 6 under repair.

Generally, 4 cars were hauled out together, although 5 and occasionally 6 were handled. The work was generally arranged so that the heavy mucking shift alternated in the two tunnels, the two engines being worked there and a single engine in the other tunnel.

The tunnel engines left the cars on a track just outside the portal, from which they were made up into trains of from 6 to 8 cars and taken to the dump or crusher by the large "dinky."

The muck from the Central Shaft headings was loaded by hand into cars similar to that shown by Fig. 5, but smaller and having no door at the forward end. A double elevator took the cars to a platform about 20 ft. above the surface, where they were dumped by revolving platforms, similar to those at Weehawken, into storage bins or directly into wagons. The muck was all hauled away in wagons; part of it was used to fill some vacant lots, and part was hauled to the crusher at the Western Portal.

The method under which the best results were obtained was that in which a full round was blasted every 36 hours, securing an advance of practically 9 ft. of full section. During the first shift of the three, as soon as the blasting had been completed and lights strung, the shovel was moved forward, and cleaned up the floor to the main pile of muck, the material from the blast being scattered from 150 to 300 ft. back from the face; during this shift, also, the drillers mucked the heading and set up their drills, the muckers helping to carry in the columns and drills. During the second shift the main pile of muck was disposed of, leaving not more than 2 or 3 hours' work for the shovel on the third shift. This left nearly the whole of the third shift for drilling the lift holes.

_Ventilation._--At Weehawken considerable difficulty was caused by fog and smoke accumulating in the tunnels after blasting. This was generally worse on days when the barometric pressure was low outside, and worse in the North than in the South Tunnel. A 6-ft. fan, driven by an electric motor, was installed in the cross-passage at Station 274, 900 ft. from the shaft, the headings at that time being about 300 ft. in advance of this point, to force the air from the South into the North Tunnel, drawing it in at the mouth of the South Tunnel and discharging it at the mouth of the North Tunnel, thus insuring a circulation in both tunnels, as shown in plan by Fig. 8.