TABLE 30.— Average Time Taken for Various Operations Connected with Building Concrete Arches in Subaqueous Tunnels.
| Average time in hours, form stood after filing. | Type of reinforcement. | Length of section, in feet. | Time, in hours, moving and erecting forms. | Time, in hours, placing concrete in Arch. | Time, in hours, placing concrete in key. | Time, in hours, placing concrete in key and arch. | Total Time in hours, for moving, erecting, and filling. | Total time in hours, per linear foot, for moving, erecting, and filling. | Remarks. | |
|---|---|---|---|---|---|---|---|---|---|---|
| 70 | A day work | 50 | 20 | 15 | 15.40 | 30.40 | 50.40 | 1.01 | ||
| Moving | Erecting | |||||||||
| A day work | 20 | 2 | 3 | 8.30 | 2.40 | 11.10 | 16.10 | 0.80 | ||
| 53 | B day work | 20 | 2 | 3 | 10.40 | 11.20 | 22.10 | 27.00 | 1.35 | Includes placing rods |
| 58 | C day work | 20 | 2 | 3 | 11.00 | 7.20 | 18.20 | 23.20 | 1.16 | do. |
| 58 | D day work | 20 | 2 | 3 | 9.30 | 4.35 | 14.25 | 19.25 | 0.91 | do. |
| 53 | D day work | 20 | 2 | 3 | 6.15 | 2.05 | 8.20 | 13.20 | 0.05 | do. |
| 53 | Sub-Type No. 1 piece work | 20 | 2 | 3 | 6.00 | 3.00 | 9.00 | 14.00 | 0.70 | do. |
The only compressed air available was the high-pressure supply, at about 90 lb.; a reducing valve, to lower this pressure to 30 lb. was used between the air line and the grouting machine. This was thought to be about as high a pressure as the green concrete arch would stand, and, even as it was, at one point a section about 2 ft. by 1 ft. was blown out.
A rough traveling stage resting on the bottom step of the duct bench concrete was used as a working platform. In the earlier stages of the work the grouting was carried on in a rather haphazard manner, but, when the last system of grout and vent pipes was adopted; the work was undertaken systematically, and was carried out as follows:
Two 20-ft. lengths of arch were grouted at one time, and, in order to prevent the grout from flowing along the arch and blocking the pipes in the next lengths, a bulkhead of plaster was made at the end of every second length to confine the grout.
After a section had been grouted, test holes were drilled every 50 ft. along the crown to see that all the voids were filled; if not, holes were drilled in the arch, both for grouting and for vents, and the faulty section was re-grouted. An average of ¾ bbl. of cement and an equal quantity of sand was used per linear foot of tunnel. The average amount put in by one machine per shift was 15 bbl., and therefore the average length of tunnel grouted per machine per shift was 20 ft. The typical working force was: