For Spans between 25 and 70 feet. Rise, 1/5 of the Span. Depth of Arch, .055 of the Span. Thickness of Abutments, from ¼ to 1/5 of the Span. Batter, 1 inch per foot.

Cost Of Tunnels Prior To 1855

{Major McClellan, U.S.A.)

Location.

Per Cable Yard.

$ Cts.

Black Rock, U. S., greywacke slate............................

6 60

Blaisley, France, lined.........

3 18

Blisworth.Eng, blue clay, lined

1 55

Blue Ridge, U. S.....................

4 00

Location.

Per Cubic Yard.

3 Cts.

England, freestone, marble,) clay, etc. lined.............

3 46

Lehigh, U.S., hard granite.....

4 36

Schuylkill, U. S., slate............

2 00

Union, U.S. slate ..................

2 08

Railway Tunnels

In soft sandstone, U. S., without lining, per lineal yard... $88 00

In loose ground, thick lining, per lineal yard................. 710 00

Ordinary brick lining, including centring, per cubic yard. 8 60

Shafts

Blaisley Tunnel, clay, chalk, and loose earth, per yard in depth, $139.11. Deepest, 046 feet.

Black Rock, 7 feet in diameter and 139 in depth, hard slate, per yard in depth, $79.50, or per cubic yard, $18.72.

The time required to drive the heading of the Black Rock Tunnel for 1782.5 feet was 2387 turns of 12 hours each.