Weights of Various Types of Lining per Linear Foot of Tunnel.
| Reference No. | Type of Lining. | Weights of complete rings (segments only), in pounds. | Weights of bolts, nuts, and washers, in pounds. | Weights of segments and bolts in tunnel complete, in pounds. |
|---|---|---|---|---|
| 1 | Ordinary cast iron without pockets. | 9,273.0 | 336.3 | 9,609.6 |
| 2 | Ordinary cast iron with pockets. | 9,158.8 | 336.3 | 9,495.2 |
| 3 | Ordinary cast steel without pockets. | 10,099.6 | 336.3 | 10,436.0 |
| 4 | Heavy cast iron without pockets. | 11,594.0 | 533.4 | 12,127.6 |
The weights in [Table 18] are calculated by assuming cast iron to weigh 450 lb. per cu. ft., and cast steel 490 lb. In actual practice the "ordinary" iron was found to weigh a little more than the weights given, and the "heavy" a little less.
The silt in the sub-river portion averaged about 100 lb. per cu. ft., so that the weight of the silt displaced by the tunnel was about 41,548 lb. per lin. ft.
Taper Rings.—In order to pass around curves (whether horizontal or vertical), or to correct deviation from line or grade, taper rings were used; by this is meant rings which when in place in the tunnels were wider than the standard rings, either at one side (horizontal tapers or "Liners"), or at the top ("Depressors"), or at the bottom ("Elevators").
In the original design a ½-in. taper was called for, that is, the wide side of the ring was ½ in. wider than the narrow side, which was of the standard width of 2 ft. 6 in. As a matter of fact, during construction, not only ½-in., but ¾-in. and 1-in. tapers were often used.
These taper rings necessitated each plate having its own unalterable position in the ring, hence each plate of the taper ring was numbered, so that no mistake could be made during erection.
The taper rings were made by casting a ring with one circumferential flange much thicker than usual, and then machining off this flange to the taper. This was not only much cheaper than making a special pattern for each plate, but made it possible to see clearly where and what tapers were used in the tunnel.
Taper rings were provided for all kinds of lining (except the cast steel), and the lack of taper steel rings was felt when building the steel-lined parts of the tunnel, as nothing could be done to remedy deviations from line or grade until the steel section was over and cast iron could again be used. [Table 19] gives the weights of the different kinds of tapers used.