The average time taken for each operation at all the working faces is given in [Table 28]. The work has been subdivided into the different kinds of ground encountered.
The progress, as shown by the amount of work done each month by each shield, is given in [Table 29].
TABLE 28. —Shield-Driven Tunnel Work.—Total Number of Rings Erected and Shifts Worked by All Four Shields in Contracts Gy-West and Gj, and the Average Size of Gang, Amount of Excavation and Time Taken per Ring for the Various Operations Involved in Building Tunnel in Each of the Several Kinds of Ground Encountered; Also the Extent and Nature of All the Unavoidable Delays.
| Weight of iron. | Description of Material. | Total No. of rings. | Total No. of feet. | Total number of 8-hour shifts. | Average air pressure. | Ave. No. of Men in Gang. | Cu. yd. per ring. | Time per cu. yd. | Average Time per Ring. | Ave. Unavoidable Delay per Working Face. | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Shield. | Drilling. | Grouting. | Air trans. | Total. | Shoving and mucking. | Erecting. | Lost time. | Total. | Items not included in previous figures. | Time. | ||||||||
| Unit. | Unit. | Hrs. Min. | Hrs. Min. | Hrs. Min. | Hrs. Min. | Ave. unit. | ||||||||||||
| Unit. | Unit. | Unit. | Unit. | Unit. | K | L | M | Hrs. Min. | ||||||||||
| Ordinary | Rock. | 165 | 412.5 | 597 | 16 | 18 | 9 | 0.25 | 1 | 28 | 51 | 0-27 | 25 15 | 3 41 | 0 02 | 28 58 | 1st Bulkhead | 136 00 |
| Rock and earth and rock and gravel. | 177 | 442.5 | 500 | 14 | 22 | 5 | 0.3 | 2 | 30 | 45 | 0-26 | 19 31 | 2 55 | 0 11 | 22 37 | 2d " | 147 54 | |
| Sand and gravel (unobstructed), NJ | 188 | 470.0 | 241 | 13 | 24 | 0.6 | 3 | 27 | 39 | 0-12 | 7 31 | 2 24 | 0 20 | 10 15 | Grouting | 246 00 | ||
| Sand and silt (with piles.) | 171 | 427.5 | 199 | 22 | 23 | 1.0 | 3 | 27 | 43 | 0-09 | 6 46 | 2 24 | 0 09 | 9 19 | Blow-outs | 91 11 | ||
| Silt under R. R. tracks, NY | 396 | 990.0 | 355 | 19 | 27 | 3 | 30 | 42 | 0-06 | 4 09 | 2 51 | 0 10 | 7 10 | Miscellaneous | 230 33 | |||
| Rip-rap and silt under bulkhead. | 77 | 192.5 | 193 | 23 | 26 | 4 | 30 | 43 | 0-21 | 14 47 | 3 41 | 1 34 | 20 02 | Total | 851 38 | |||
| Total mixed and difficult ground. | 1,174 | 2,935.0 | 2,085 | 17 | 22 | 4 | 0.3 | 3 | 29 | 43 | 0-18 | 11 02 | 2 54 | 0 16 | 14 12 | |||
| Silt--ordinary iron | 1,302 | 3,255.0 | 676 | 25 | 22 | 4 | 26 | 12 | 0-07 | 1 20 | 2 35 | 0 14 | 4 12 | |||||
| Heavy | Silt--heavy iron. | 2,209 | 5,522.5 | 791 | 26 | 25 | 8 | 33 | 12 | 0-05 | 0 58 | 1 44 | 0 10 | 2 52 | ||||
| Silt--ord and heavy iron under river. | 3,511 | 8,777.5 | 1,467 | 26 | 24 | 6 | 30 | 12 | 0-06 | 1 09 | 2 05 | 0 12 | 3 26 | |||||
| Grand total. | 4,685 | 11,712.5 | 3,552 | 21 | 23 | 2 | 0.2 | 4 | 29 | 20 | 0-11 | 3 33 | 2 15 | 0 13 | 6 01 | |||
Average delay per ring—0 hrs. 44 min.
Average rings built by one shield = 1,146¼.
| Average time per ring. | 6 hr 01 min |
| Delays. | 44 min |
| ————— | |
| Total time per ring. | 6 hr 45 min |
Note.—The "unavoidable delays" included in this table do not embrace the periods during which the work was at complete or partial standstill due to experiments and observations, shortage of iron due to change of design, and holidays.
K-Including time for jacks.
L-Including time spent by the whole gang on bolting; in addition to this there was a small gang which spent its whole time bolting.
M-Chiefly due to breakdowns of hydraulic lines and erector.
Air Pressure.—The air pressure varied from 17 to 37 lb. Behind the river line it averaged 17 lb. and under the river 26 lb. Behind the river lines the pressure was generally kept about equal to the water head at the crown, except where at Weehawken, as previously described, this was impossible.