136. In taking out the rock, the expense will depend much upon the nature and stratification of the rock encountered.
SHAFTS.
137. In tunnels of considerable length, a long time would be consumed in working from the ends only. In such cases it is customary to sink shafts at the most convenient places (the shallowest when at the proper distance,) and to commence at the bottom of these to work both ways. This operation involves considerable expense, as all draining, ventilating, and removal of excavated materials must be effected through the shaft.
In leaving openings for the exit of smoke and for admission of light in artificial arches, regard must be had to their position. They should be at the springing rather than at the crown of the arch, as they will thus less affect the strength of the masonry.
The approaches of tunnels in cities and in other places where appearance is of importance, are finished with face coping and wings.
138. Tunnels, when conducted in the most expeditious manner, require for their completion a long time. The following table shows the rate of progress upon some of the most important tunnels of America.
| Name of Tunnel. | Length in feet. | Time in days. | Average daily advance, in feet. |
|---|---|---|---|
| *Penn Railroad, | 3,612 | 697 | 5.18 |
| *Kingwood B. & O. R. R. | 4,100 | 750 | 5.47 |
| Board Tree B. & O. R. R. | 2,250 | 675 | 3.32 |
| *Welling, B. & O. R. R. | 1,240 | 524 | 2.37 |
| Pacific Railroad, | 700 | 210 | 3.33 |
| Pittsburgh and Connelsville, (estimated) | 4,500 | 810 | 5.56 |
| General average daily advance, in feet, | 4.205 | ||
| Those marked * being for a double track. | |||
The following table also gives the time and cost of other tunnels in different parts of the world.
| Name and location of tunnel. | Material. | Length in feet. | Time in days. | Daily average in feet. | Section. | Cost per foot. |
|---|---|---|---|---|---|---|
| $ | ||||||
| Nerthe, France, | Hard limestone | 15,153 | 29½ × 26¼ | |||
| Riqueral, France, | Chalk | 18,623 | 2,139 | 8.7 | 26¼ × 26¼ | 39.89 |
| Pouilly, France, | Chalk & clay | 10,928 | 2,504 | 4.4 | 20⅓ × 20⅓ | 113.96 |
| Arscherville, France, | 7,348 | 1,878 | 3.9 | 26¼ × 26¼ | 68.38 | |
| Maurage, France, | 15,752 | 2,085 | 7.5 | 25½ × 25½ | 94.43 | |
| Rolleboise, France, | Chalk | 8,670 | 626 | 13.9 | 25 × 25 | 62.98 |
| Roule, France, | 5,645 | 522 | 10.8 | 25 × 25 | 62.98 | |
| Lioran, France, | 4,548 | 2,087 | 2.2 | 21⅓ × 21⅓ | 56.98 | |
| Kilsby, England, | Clay and sand | 7,233 | 1,252 | 5.8 | 27 × 23½ | 194.31 |
| Belchingly, England, | Blue clay | 3,972 | 626 | 6.3 | 24 × 25 | 102.86 |
| Thames & Medway, Eng’d, | Chalk | 11,880 | 939 | 12.6 | 30 × 38⅔ | 45.59 |
| Box, England, | Marble, freestone and marl | 9,680 | 1,252 | 7.7 | 35 × 39 | 148.15 |
| Harecastle, England, | Rock and sand | 8,778 | 939 | 9.3 | 14 × 16 | 57.05 |
| Nochistongo, Mexico, | Clay and marl | 21,659 | 287 | 75.4 | 13¾ × 11½ | |
| Blisworth, England, | Rock and clay | 9,240 | 2,191 | 4.2 | 16½ × 18 | 23.18 |
| Sapperton, England, | Rock | 12,900 | 1,878 | 6.9 | 15 × 15 | 12.44 |
| Black Rock, U. S. | Greywacke slate | 1,932 | 19 × 17¼ | 77.18 | ||
| Blaisy, France, | Chalk and clay | 13,455 | 1,043 | 12.9 | 26¼ × 26¼ | 136.06 |
| Edge Hill, England, | Clay & freestone | 6,600 | 22 × 16 | 30.15 | ||
| Littlebourg, England, | 8,607 | 590 | 14.6 | 27½ × 24 | 129.61 | |
| Woodhead, England, | Millstone | 15,840 | 1,800 | 8.8 |
The cost per cubic yard for excavating tunnels in some places has been as follows:—