| Excavation of heading | $8 | to | $10.00 | per | cu. | yd. |
| Tunnel in soft ground | 8 | to | 9.00 | „ | „ | „ |
| Tunnel in rock | 7 | to | 8.50 | „ | „ | „ |
| Brick masonry | 10.00 | „ | „ | „ | ||
| Timber in place | $40 per M. ft. B. M. | |||||
It is the practice in America to include the work of hauling under excavation, but not to include the strutting, which is paid for separately. In some cases only the market price of the timber is paid for separately, the cost of setting up being included in the price of excavation. The writer prefers the European practice of including the total cost of timbering under excavation, since the two operations are so closely connected, and since the contractor employs the same timber over and over again. Knowing the dimensions of the several members of the strutting, it is a simple, although somewhat tedious, process to calculate the total quantity required. An idea of the quantity of timber required for strutting in soft ground may be had from the data given on [page 55]. The quantity will decrease as the cohesion of the material penetrated increases, until it becomes so small in hard rock-tunnels as to cut very little figure in the total cost.
The cost of hoisting excavated materials through shafts depends upon the depth from which it is hoisted, and upon the character of hoisting apparatus employed. The following table, showing the cost of hoisting for different lifts and by different methods, is given by Rziha, the cost being in francs per cubic meter:—
| Height in Metres. | Windlass. | Horse Gins. | Steam Hoists. | |
|---|---|---|---|---|
| Francs per Cu. M. | One Horse. Francs per Cu. M. | Two Horses. Francs per Cu. M. | Francs per Cu. M. | |
| 15 | 0.172 | 0.077 | 0.062 | 0.035 |
| 30 | 0.212 | 0.087 | 0.070 | 0.045 |
| 45 | 0.257 | 0.100 | 0.080 | 0.050 |
| 60 | 0.305 | 0.112 | 0.092 | 0.082 |
| 90 | 0.410 | 0.152 | 0.110 | 0.087 |
| 120 | 0.535 | 0.195 | 0.135 | 0.092 |
| 150 | 0.722 | 0.240 | 0.157 | 0.112 |
Mr. Séjourné, a French engineer, who has been connected with the construction of numerous tunnels by the Belgian method where he was in position to secure comparative figures, has given the following rules for calculating the cost of tunnels. Assuming A to represent the cost of excavating a cu. yd. in the open air, the cost of excavating the same quantity underground in driving headings will be from 9 A to 11 A, and in enlarging the profile it will be about 5 A. The cost of constructing single-track tunnels varies with the thickness of the lining, and may be calculated by the following formulas:
| Without lining, | C = 5.5 A. |
| With roof arch only, | C = 6.4 + 6.4 A. |
| With lining 18 in. thick, | C = 9.4 + 7 A. |
| With lining 2 ft. thick, | C = 11 + 8 A. |
In these formulas C is the cost per cu. yd. of excavation, including the masonry. For double-track tunnels the amounts given by the above formulas may be used by reducing them about 71⁄2% or 8%.
The second method of estimating the cost of tunnel work consists in assuming as a unit the unit cost of tunnels previously excavated under similar conditions. Mr. La Dame gives the following unit prices for a number of tunnels driven through different materials:
| Nature of Soil. | Tunnels, No. of | Excav. per Cu. Yd. | Cost per Lin. Ft. | Max. and Min. per Lin. Ft. | ||||
|---|---|---|---|---|---|---|---|---|
| Granite-gneiss | 56 | $3.07 | @ | $3.85 | $100. | $61.46 | @ | $190.40 |
| Schist | 39 | 1.38 | @ | 1.53 | 75.42 | 43.11 | @ | 70.68 |
| Triassic | 3 | ... | 90.85 | 84.75 | @ | 93.33 | ||
| Jurassic | 69 | 1.23 | @ | 1.38 | 77.86 | 35.24 | @ | 157.2 |
| Cretaceous | 34 | 0.61 | @ | 0.77 | 59.60 | 27.37 | @ | 92.25 |
| Tertiary and modern | 39 | 0.33 | @ | 0.61 | 105.80 | 51.52 | @ | 188.36 |
In the following table is given a list of tunnels excavated through different soils, from the most compact to very loose materials, and driven according to the various methods which have been illustrated.