METHOD AND COST OF LINING GUNNISON TUNNEL.—The costs are for concrete in place in the side walls and the arch of the tunnel, for a length of 440 lin. ft. The quantity of concrete considered in estimating the cost per cubic yard was 616 cu. yds. The material was mixed and placed in ½ cu. yd. batches, the proportion of the mixtures being 1-2.2-4.4. The final cost includes the labor of excavating and screening gravel and sand, the hauling of the same from the bins at the pit to the storage bins at the main shaft, the care of the chutes in the shaft and the mixing of the concrete in the tunnel at the bottom of the shaft, the transportation of the concrete from the mixer to the traveler, the deposition of the concrete, the setting up and taking down of forms and the cost of the cement. It does not include the construction of the gravel pit chutes that hold the screens, the building of the road from the gravel pit to the storage bins at the shaft, the concrete mixer and its installation, the traveler and its installation, the cost of material and labor in the construction of the concrete forms, the requisite power to run the machinery and other expenses of a similar nature.
The gravel used for the concrete was obtained from a pit situated on top of a hill not far from the main shaft leading down to the tunnel. This gravel bed contains very closely the proper proportions of sand and gravel for the concrete aggregates. The gravel was excavated and loaded by hand into side dump cars of 35 cu. ft. capacity. These cars were run to the edge of the hill where the gravel was dumped upon a screen from which it ran by gravity, passing thence into storage bins. From the storage bins the sand and gravel were drawn off into dump wagons having a capacity of 2 cu. yds. and hauled a distance of one-half mile to a second set of storage bins located at the top of the shaft leading into the tunnel. The road from the storage bins at the gravel pit to the storage bins at the head of the shaft was down grade. A two-horse team could readily haul 2 cu. yds. of gravel over this road. The storage bins at the top of the shaft leading into the tunnel communicated with the measuring boxes at the bottom of the shaft by means of chutes. The measuring boxes discharged directly into tram cars. The average length of haul from the mixer to the place of deposition of concrete was about 4,500 ft.
The concrete was placed in the side walls by means of a traveler, which was so operated in the tunnel as to allow the passage of the concrete trains beneath it. The traveler was 64 ft. long and was provided with a slow motion electric hoist, by which the cars containing the concrete were elevated to the top of the traveler and thence transferred to any desired position. The concrete was dumped from these cars into boxes where any remixing or tempering that was required was done, after which the concrete was shoveled directly into the forms. The entire operation of handling the materials of the concrete, it will be seen, utilized gravity to the greatest possible degree.
In order to get a good average cost per cubic yard for handling gravel and sand, this analysis has been based on five months' operation, from November, 1906, to March, 1907. In these five months there were 4,123 cu. yds. of sand and gravel handled. The concrete considered was placed during the month of March. Below is given the distribution of the cost of the concrete as to the specified divisions of the work and as to the class of work involved in each division. Measurements taken at the mixer show that each cubic yard of concrete contained 0.74 cu. yds. of gravel, 0.445 cu yds. of sand and 5.6 sacks of Portland cement. The total of the aggregates is, therefore, 1.185 cu. yds. per cubic yard of concrete. The cement costs $0.62 per sack on the work, making a cost of $3.472 per cubic yard of concrete.
Excavating and screening 4,123 cu. yds. gravel—
| Total cost. | Per cu. yd. gravel. | |
| Foreman, 66⅞ days at $3.04 | $ 203.30 | $0.049 |
| Labor, 397½ days at $2.56 | 1,017.60 | 0.247 |
| Labor, 116¼ days at $2.08 | 241.80 | 0.059 |
| ———— | ——— | |
| Total | $1,462.70 | $0.355 |
| Hauling 4,123 cu. yds. gravel and sand— | ||
| 2-horse team and driver, 210 days at $3.60 | $756.00 | $0.183 |
| 2-horse team and driver, 4½ days at $4 | 18.00 | 0.005 |
| ——— | ——— | |
| Total | $774.00 | $0.188 |
As there were 1.185 cu. yds. of gravel per cubic yard of concrete the cost of gravel per cubic yard of concrete was for—
| Excavating and screening (1.185 × $0.355) | $0.421 |
| Hauling (1.185 × $0.188) | 0.223 |
| ——— | |
| Total | $0.644 |
Adding to this the cost of cement $0.62 × 5.6 = $3.472, we have $0.644 + $3.472 = $4.116, as the cost of concrete materials per cubic yard of concrete. The cost of labor, mixing and placing was as follows for 616 cu. yds.: