Design of Metal Lining.
New York Shield Chambers.—The shield chambers may be seen on [Plate XXXII], previously referred to, which shows the junction of the iron-lined tunnels and the shield chambers. They consist of two iron-lined pieces of tunnel placed side by side, with semi-circular arches and straight side-walls. The segments of the arch are made to break joint with one another by making the side-wall or column castings of two different heights, as shown in [Fig. 9]. The length of each ring is 18 in.
The reason for the adoption of this type of construction was the necessity for keeping the width of the permanent structure within the 60-ft. width of the street. The length of this twin structure is 28.5 ft., and the weight of the metal in it is as follows:
| 19 long-column arch rings at 22,802 lb. | 433,238 | lb. |
| 19 short-column arch rings at 23,028 lb. | 437,532 | " |
| --------- | ||
| Total weight | 870,770 | lb. |
General Type of River Tunnel Lining.—The main ruling type adopted for the tunnels under the Hudson River, and in the soft water-bearing ground for some distance on the shoreward side of the river lines, consists of two parallel metal-lined tunnels, circular in cross-section, each tunnel being 23 ft. outside diameter, and the two tunnels 37 ft. apart from center to center, as shown on [Fig. 10]. The metal lining is of cast iron (except for a few short lengths of cast steel) and of the usual segmental type, consisting of "Rings" of iron, each ring being 2 ft. 6 in. in length, and divided by radial joints into eleven segments, or "Plates," with one "Key," or closing segment, having joints not radial but narrower at the outside circumference of the metal lining than at the inside. The whole structure is joined, segment to segment, and ring to ring, by mild-steel bolts passing through bolt holes in flanges of all four faces of each segment. The joints between the segments are made water-tight by a caulking of sal-ammoniac and iron borings driven into grooves formed for the purpose on the inner edges of the flanges. The clearances between the bolts and the bolt holes are also made water-tight by using grummets or rings of yarn smeared with red lead, having a snug fit over the shank of the bolt and placed below the washer on either end of each bolt. When passing through ground more or less self-sustaining, the space outside the iron lining (formed by the excavation being necessarily rather larger than the external diameter of the lining itself) was filled with grout of 1:1 Portland cement and sand forced by air pressure through grout holes in each segment. These holes were tapped, and were closed with a screw plug before and after grouting.
Having thus stated in a general way the main ruling features of the design, a detailed description of the various modifications of the ruling type will be given.
The two main divisions of the iron lining are the "ordinary" or lighter type and the heavy type. The details of the ordinary iron are shown in [Fig. 11], which shows all types of lining. It was on this design that the contract was let, and it was originally intended that this should be the only type of iron used. The dimensions of the iron are clearly shown on the drawing, and it will be seen that the external diameter is 23 ft., the interior diameter, 21 ft. 2 in., the length of each ring, 2 ft. 6 in., and the thickness of the iron skin or web, 1½ in. The bolt holes in the circumferential flanges are evenly spaced through the circle, so that adjacent rings may be bolted together in any relative position as regards the radial joints, and, as a matter of fact, in the erection of the tunnel lining, all the rings "break joint," with the exception of those at the bore segments, as will be described later. This type of iron, when the original type was modified, came to be known as the ordinary pocketless iron; that is, the weight is of the ordinary or lighter type, in contradistinction to the heavier one, which later supplanted it, and the caulking groove runs along the edges of the flanges and does not form pockets around the bolt holes, as did the groove in a later type.
Each ring is made up of eleven segments and a key piece. Of these, nine have radial joints at both ends, and are called "A" segments; two, called "B" segments, have a radial joint at one end and a non-radial joint at the other. The non-radial joint is placed next to the key, which is 12.25 in. wide at the outside circumference of the iron and 12.50 in. wide at the inside.
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 |
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.
TABLE 19.— Weights of Cast-Iron Taper Rings, in Pounds per Complete Ring.
| Classification. | Weight of cast iron per complete ring, in pounds. |
|---|---|
| Ordinary pocketless ½-in. taper | 23,767.7 |
| Ordinary pocketless 1-in. taper | 24,352.4 |
| Ordinary pocket ½-in. taper | 23,481.7 |
| Heavy pocketless ½-in. taper | 29,564.8 |
| Heavy pocketless ¾-in. taper | 29,854.7 |
| Heavy pocketless 1-in. taper | 30,144.6 |
Cast-Steel Bore Segments and Accessories.—The following feature of these tunnels is different from any hitherto built. It was the original intention to carry the rolling load independent of the tunnel, or to assist the support of the silt portion of the structure by a single row of screw-piles, under each tunnel, and extending down to firmer ground than that through which the tunnels were driven. Therefore, provision had to be made whereby these piles could be put down through the invert of the tunnel with no exposure of the ground.
This provision was afforded by the "Bore Segments," which are shown in detail in [Fig. 12]. There are two segments, called No. 1 and No. 2, respectively. These two segments are bolted together in the bottom of two adjacent rings, and thus form a "Pile Bore." As the piles were to be kept at 15-ft. centers, and as the tunnel rings were 2 ft. 6 in. in length, it will be seen that, between each pair of bore-segment rings, there came four "Plain" rings. The plain rings were built up so that the radial joints broke joint from ring to ring, but with the bore-segment rings this could not be done, without unnecessarily adding to the types of segments.
The bore segments were made of cast steel, and were quite complicated castings, the principle, however, was quite simple. The segments provided an opening just a little larger than the shaft of the pile, the orifice being 2 ft. 7 in. in diameter at the smallest (lowest) point, while the shaft of the pile was to be 2 ft. 5¼ in. In order to allow of the entry of the screw-blade or helix of the pile, a slot was formed in the depth of Bore Segment No. 1, so that, when a pile was put in position above the bore, the blade, when revolved, would enter the slot and thus pass under the metal lining, although the actual orifice was only slightly larger than the pile shaft.
The wall of the pile orifice in Segment No. 2 was made lower than that in No. 1 so as to allow the blade to enter the slot in Segment No. 1. When the pile is not actually in process of being sunk, this lower height in No. 2 is made up with the removable "distance piece." This had a tongue at one end which engaged in a recess cast to take it in Segment No. 2 and was held in place by a key piece at the other end of the distance piece. Details of the distance piece and key are shown in [Fig. 12].
The flanges around the pile bore were made flat and furnished with twelve tapped holes, six in Segment No. 1 and six in Segment No. 2, for the purpose of attaching the permanent arrangements in conjunction with which the pile was to be attached to the track system, independently of the tunnel shell, or directly to the tunnel. It was never decided which of these alternatives would be used, for, before this decision was reached, it was agreed that, at any rate for the present, it was better not to put down piles at all.
To close the bore, the "Bore Plug" was used. This is shown on [Fig. 12]. It was of cast steel, and was intended to act as a permanent point of the screw-pile, that is, the blade section was to be attached to the bore plug, the distance piece and key were to be removed, and the pile was to be rotated until the blade had cleared the slot; the distance piece and key were then to be replaced and sinking resumed.
The plug was held in place against the pressure of the silt by the two "dogs," while the dogs themselves were attached to the tunnel, as shown in [Fig. 12]. The ends of the dogs, which rested on the flanges of the metal lining of the tunnel, were prevented from being knocked off the flanges (and thus releasing the plug) by steel clips.
It was expected that it might be desirable to keep the lower end of the piles open during their sinking, so that the bore plugs were not made permanently closed, but a seating was formed on the inner circumference of the plug, and on the seating was placed the "Plug Cover," made of cast iron, 18¾ in. in diameter and 3 in. thick, furnished with a lug for lifting and a 3-in. tapped hole closed by a screw-plug, through which any soundings or samples of ground could be taken prior to sinking the piles. This plug cover was held in place by a heavy steel "Yoke" under it, which engaged on the under side of the flange, on top of which the cover was set. The yoke was attached to the cover by a 1¾-in. tap-bolt, screwed into the yoke and passing through a 2-in. hole bored in the center of the cover. This rather peculiar mode of attaching the cover was adopted so that the cover could be removed by taking off the nut of the yoke, in case it was desired to open the end of the pile during the process of sinking.
The plug was a fairly close fit at the bottom of the orifice, that is, at the outside circumference of the tunnel, where the bore was 2 ft. 7 in. in diameter and the plug 2 ft. 6¾ in., but at the top of the bore-segment there was more clearance, as the plug was cylindrical while the bore tapered outward. To fill this space, it was intended that steel wedges should be used while the shield was being driven, so that they would withstand the crushing action of the thrusting shield, and, when the shield was far enough ahead, that they should be removed and replaced by hardwood wedges. This method was only used in the early weeks of the work; the modification of not using the shield-jacks which thrust against the bore segments was then introduced, and the wooden wedges were put in, when the bore plugs were set in place, and driven down to the stage of splitting.
When it was resolved not to sink the screw-piles, the bores had to be closed before putting in the concrete lining. This was done by means of the covers shown in [Fig. 13]. The bore plug and all its attachments were removed, and the flat steel cover, 2 in. thick and with stiffening webs on the under side, was placed over the circular flanges of the pile bore. The cover was attached to the bore segments by twelve 1½-in. stud-bolts, 6 in. long, in the bolt holes already mentioned as provided on these flanges.
When these were in place, with lead grummets under the heads of the bolts, and the grooves caulked, the bore segments were water-tight tight, except in Bore Segment No. 2, at the joint of the distance piece; and, to keep water from entering here, this segment was filled to the level of the top of the flanges with 1:1 Portland cement mortar.
The weights of the various parts of the bore segments are given in [Table 20].
TABLE 20.— Weights of Bore Segments and Accessories, in Pounds.
| Part. | No. | Material. | Weight, in pounds. |
|---|---|---|---|
| Bore Segment No. 1 | 1 | Cast Steel | 3,004.0 |
| Bore Segment No. 2 | 1 | " " | 2,628.0 |
| Distance piece | 1 | " " | 423.5 |
| Key | 1 | " " | 34.3 |
| Plug | 1 | " " | 1,192.5 |
| Yoke | 1 | " " | 57.3 |
| Dogs | 2 | " " | 106.0 |
| Slot cover | 1 | Rolled steel | 6.4 |
| Plug cover | 1 | Cast iron | 162.0 |
| Dog holders | 2 | Rolled steel | 6.4 |
| Complete weight of one pair, without bolts | 7,620.4 | ||
Sump Segments.—In order to provide sumps to collect the drainage and leakage water in the subaqueous tunnels, special "sump segments" were installed in each tunnel at the lowest point—about Station 241 + 00. The details of the design are shown in [Fig. 14]. The segment was built into the tunnel invert as though it were an ordinary "A" segment. In building the sump, three lining castings were bolted, one on top of the other, and attached to the flat upper surface of the sump segment; meanwhile, the bolts attaching the sump segment to the adjacent tunnel plates were taken out and the plate and lining segments were forced through the soft mud by hydraulic jacks, the three 6-in. holes in the bottom of the sump segment being opened in order to minimize the resistance. The sump when built appeared as shown in [Fig. 14], the top connection being made with a special casting, as shown.
The capacity of each sump is 500 gal., which is about the quantity of water entering the whole length of each subaqueous tunnel in 24 hours.
Cross-Passages.—When the contract was let, provision was made for cross-passages between the tubular tunnels, in the form of special castings to be built into the tunnel lining at intervals. However, the idea was given up, and these castings were not made. Later, however, after tunnel building had started, the question was raised again, and it was thought that such cross-connections would be very useful to the maintenance forces, that it might be possible to build them safely, and that their subsequent construction would be made much easier if some provision were made for them while the shields were being driven. It was therefore arranged to build, at intervals of about 300 ft., two consecutive rings in each tunnel, at the same station in each tunnel, with their longitudinal flanges together, instead of breaking joint, as was usually done. The keys of these rings were displaced twelve bolt holes from their normal positions toward the other tunnel. This brought the keys about 6 ft. above the bench, so that if they were removed, together with the B plates below them, an opening of about 5 by 7 ft. would be left in a convenient position with regard to the bench.
Nothing more was done until after the tunnels were driven. It was then decided to limit the cross-passages between the tubular tunnels to the landward side of the bulkhead walls. They were arranged as follows: three on the New York side, at Stations 203 + 22, 206 + 80, and 209 + 80, and two on the New Jersey side, at Stations 255 + 46 and 260 + 14. The cross-passages are square in cross-section.
TABLE 21.—Weights of Sump Segments.
| Part. | No. | Material. | Weight, in pounds. |
|---|---|---|---|
| Middle top casting | 1 | Cast steel | 880 |
| End top castings | 2 | " " | 1,718 |
| Lining castings | 3 | " " | 18,232 |
| Sump segment | 1 | Cast iron | 3,560 |
| Total weight per sump, exclusive of bolts | 24,390 | ||
Turnbuckle Reinforcement for Cast-Iron Segments.—During the period of construction, a certain number of cast-iron segments, mostly in the roof, but in some cases at Manhattan in the invert, behind the river lines, became cracked owing to uneven pressures of the ground. Before the concrete lining was put in, considerable discussion occurred as to the wisest course to pursue with regard to these broken plates. It was finally thought best not to take the plates out, as more harm than good might be done, but to reinforce them with turnbuckles, as shown in [Fig. 15]. The number of broken segments was distributed as follows:
North Manhattan Tunnel 87, chiefly in silt (not under the river),
South Manhattan Tunnel 7, chiefly in silt (not under the river),
North Weehawken Tunnel 24, chiefly in sand (not under the river),
South Weehawken Tunnel 48, chiefly in silt, under the Fowler Warehouse.
The chief features of the tunnel lining have now been described, and, before giving any account of the methods of work, it will be well to mention briefly the salient features of the concrete lining which is placed within the actual lining.