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 |