The cost of excavating the preliminary headings or drifts is greater per unit of material removed than that of excavating the enlargement of the section. The cost of bottom drifts is also always greater than that of top headings, the material penetrated remaining the same. Mr. Rziha gives the comparative unit costs of excavating drifts, headings, and enlargement of the profile as follows:—
| Bottom drifts | $9.20 | per | cu. | yd. |
| Top headings | 4.80 | „ | „ | „ |
| Enlargement of profile | 2.84 | „ | „ | „ |
The cost of hauling increases with the length of the tunnel. This fact and amount of this increase are indicated by the following actual prices for the Arlberg tunnel:—
| Top heading | $6.76 | per | cu. | yd., | increasing | 37 | cts. | per | mile |
| Bottom drift | 7.40 | „ | „ | „ | „ | 26 | „ | „ | „ |
| Enlargement of profile | 2.70 | „ | „ | „ | „ | 10 | „ | „ | „ |
In all the prices given above, the cost of strutting and hauling is included in the cost of excavation.
The cost of excavation is not always the same for the same character of materials in different tunnels. The following figures show the prices paid for the excavation of calcareous rock in four different German tunnels:—
| Berliner Nordhausen Wetzler R.R. | $1.24 | per | cu. | yd. |
| Ofen | 1.30 | „ | „ | „ |
| Stafflach | 2.76 | „ | „ | „ |
| Gries | 1.92 | „ | „ | „ |
The method of tunneling has little influence upon the cost of the work, as shown by the following figures from tunnels excavated through calcareous rock by different methods:—
| Ofen tunnel | Austrian method | $93.19 | per | lin. | ft. |
| Dorremberg tunnel | Belgian method | 86.08 | „ | „ | „ |
| Stafflach tunnel | English method | 91.69 | „ | „ | „ |
The Martha and Merten tunnels, excavated through soft ground by the Austrian and German methods respectively, cost $87.95 and $87.55 per lin. ft. respectively. In the excavation of the various sections of the tunnel for the new Croton Aqueduct in America, the following prices were paid:—