[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.