Transactions of the American Society of Civil Engineers, vol. LXVIII, Sept. 1910 | Page 7

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 | 2? in. | 2? 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 | 8? Average depth drilled with one sharpening | 12 in. | 6? 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,