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REPORT ON EUROPEAN TUNNELS.
TUNNEL OF THE NEETHE.
The tunnel of the Nerthe, on the railway between Marseilles andAvignon , is 4,639 metres, or very nearly three miles in length. Insection it is 26 feet 3 inches wide at the widest, and 24 feet 7 incheshigh above the rails. It has 24 shafts, which are not over the centreof the tunnel, but about 30 feet on one side. They communicatewith it by lateral galleries, 10 feet in width, and as high as the tun-nel itself. These shafts are circular, about 10 feet in diameter, andhave all been left open. The two ends of the tunnel are nearly at thesame level. From the Avignon entrance, the grade rises towards thecentre at the rate of 1 in 500, and from there descends towards theMarseilles entrance at the rate of 1 in 1,000. The highest point, inthe centre, is about fourteen feet above one entrance, and eight feetabove the other. It passes through marl, dolomite, lias, and variouslimestone formations. For 950 yards of its length it is in rock cut-ting, where arching is unnecessary. The remainder is lined withmasonry. The whole tunnel was completed in three years, and itscost was 2,254 francs per running metre, or $412 per running yard.The shafts vary in depth from 65 to 623 feet. The following tablewill show the cost of sinking them, and is interesting, as exhibitingthe increased cost per foot as they go deeper. It does not include thecost of the wooden curbs or of the masonry. [Plate X.]
COST OF SINKING SHAFTS.
Cost per Foot.
Shaft.
Depth.
Averagecost per Foot.
From 0to 1ST feetin depth.
$
$
1 to 5
67
8.88
8.88
6
200
10.97
10.97
7
178
12.80
12.80
8
252
13.72
13.47
9
345
16.46
15.06
10
292
. 15.85
15.24
11
387
16.77
15.24
12
482
16.77
15.55
13
552
16.77
13.05
14
623
16.77
11.58
16
519
18.29
13.60
16
472
15.85
13.05
17
469
15.85
13.29
18
375
15.24
13.78
19
396
12.19
10.42
20
489
13.41
10.97
21
467
18:29
15.73
22
361
15.24
13.78
23
299
15.85
14.94
24
258
13.41
13.41
From 328
From 4.59
to 328 feet
to 459 feet
to 810 feet
in depth.
in depth.
in depth.
$
$
$
14.70
18.41
17.31
18.29
19.81
18.60
21.34
16.10
19.76
22.70
14.63
18.29
24.06
16.64
25.91
16.10
19.81
16.34
19.69
16.83
18.29
13.47
14.02
15.24
18.78
16.83
16.02
17.51
13.41