The web is not of uniform thickness. The middle part of each A and B segment is 1½ in. thick; at the distance of 6 in. from the root of each flange, the thickness of web begins to increase, so that at the root it is 2⅜ in. thick. The web of the key plate is 1¾ in. thick.
The bolts are of mild steel, and are 1½ in. in diameter; there are 67 in one circumferential joint and 5 in each radial joint. As there are 12 such radial joints, there are altogether 60 bolts in the cross-joints, making a total of 127 bolts per ring.
This original type of ordinary iron was modified for a special purpose as follows: It was known that for some distance on either side of the river, and especially at Weehawken, the tunnels would pass through a gravel formation, rather open, and containing a heavy head of water. It was thought that, by carrying the caulking groove around the bolt holes, it would be possible to make them more water-proof than by the simple use of the red-leaded grummets. Hence the "Pocket Iron" was adopted for this situation, the name being derived from the pocket-like recess which the caulking groove formed when extended around the bolt hole. The details of this lining are shown on [Fig. 11], and the iron (except for the pockets) is exactly like the pocketless type.
On the New York side, in both North and South Tunnels, two short lengths were built with cast-steel lining. This was done where unusual stresses were expected to come on the lining, namely, at the point where the invert passed from firm ground to soft, and also where the tunnels passed under the heavy river bulkhead wall.
The design was precisely the same as for the ordinary pocketless iron, and [Fig. 11] shows the details. After the tunnels had entered into the actual under-river portion, several phenomena (which will be described later) led to the fear that the tunnels, being lighter than the semi-liquid mud they displaced, might be subject to a buoyant action, and therefore a heavier type of lining was designed. The length of ring, number of bolts, etc., were just the same as for the lighter iron, but the thickness of the web was increased from 1½ to 2 in., the thickness of the flanges was proportionately increased, and the diameter of the bolts was increased from 1½ to 1¾ in. This iron was all of the pocketless type, shown in [Fig. 11]. [ Table 18] gives the weights of the various types of lining.
TABLE 18.—Weights of Tunnel Lining, Diameter and Weights of Bolts, etc.
| Reference No. | Type of Lining. | Weight of one "A" Segment, in pounds. | Weight of one "B" Segment, in pounds | Weight of one key, in pounds. | Weight of one complete ring, in pounds. | Diameter of bolts, in inches. | Weight of 1 bolt, nut, and 2 washers, in pounds. | Weight of bolts, nuts, and washers per ring, in pounds. | Total weight of one ring (segments and bolts), in pounds. |
|---|---|---|---|---|---|---|---|---|---|
| 1 | Ordinary cast iron without caulking pockets. | 2,063 | 2,068 | 480 | 23,183 | 1½ | 6.62 | 840.7 | 24,024 |
| 2 | Ordinary cast iron with caulking pockets. | 2,038 | 2,043 | 469 | 22,897 | 1½ | 6.62 | 840.7 | 23,738 |
| 3 | Ordinary cast steel without caulking pockets. | 2,247 | 2,252 | 522 | 25,249 | 1½ | 6.62 | 840.7 | 26,090 |
| 4 | Heavy cast iron without caulking pockets. | 2,579 | 2,584 | 606 | 28,985 | 1¾ | 10.50 | 1,333.5 | 30,319 |