Part 9

The greatest deviations between the lines and grades in the subaqueous tunnels as determined by these means and those as originally laid out in the contract drawings are on the Weehawken side, and were caused by the unexpected behavior of the tunnel when the shields were driven "blind" into the silt, causing a rise which could not be overcome, and the thrusting aside of one tunnel by the passage of the neighboring one. Had this unfortunate incident not occurred, it is clear that it would have been possible to adhere very closely indeed to the contract lines and grades, although the deviation is small, considering all things.

The internal outline of the concrete cross-section is uniform throughout, and is built on the lines and grades thus described.

_Steel Rod Reinforcement of Concrete._--The original intention had been to line the metal lining of the tube tunnels with plain concrete, but, as the discussion on the foundation question continued, it was felt advisable, while still it was intended to put in the foundations, to guard against any stresses which were likely to come on the structure, by using a system of steel rods embedded circumferentially within the concrete. Designs were made on this basis, and even the necessary material prepared, before the decision to omit the piles altogether was reached. However, in order to provide a safeguard for the structure where it is partly or wholly beyond the solid rock, it was decided to use reinforcement, even with the piles omitted.

For this purpose the tunnel was considered as a girder, and longitudinal reinforcement was provided at the top and bottom. The top reinforcement extends from a point 25 ft. behind the point where the crown of the tunnel passes out of rock on the New York side to where the crown passes into rock on the New Jersey side. The bottom reinforcement extends from where the invert of the tunnel passes out of rock on the New York side to where it passes into rock on the New Jersey side.

The reinforcement both at top and bottom consists of twenty 1-in. square twisted rods, ten placed symmetrically on either side of the vertical axis, 9 in. apart from center to center and set 4 in. (to their centers) back from the face of the concrete.

As a further precaution, circumferentially-placed rods were used on the landward side of the river lines, mainly to assist in preventing the distortion of shape which might occur here, either under present conditions, such as under the Fowler Warehouse at Weehawken, or under any possible different future conditions, such as might be brought about by building some new structure in the vicinity of the tunnels.

For purposes of classification of the circumferential reinforcement, the tunnel was divided into two types, "_B_" and "_C_"; (Type "_A_" covering the portion which, being wholly in solid rock, was not reinforced at all).

Type "_B_" covers the part of the tunnels on both sides of the river lying between the point where the top of the tunnel passes out of rock and the point where the invert passes out of rock on the Manhattan side, or out of gravel on the Weehawken side. The reinforcement consists of twenty 1-in. square longitudinal rods in the crown of the tunnel, as described for the general longitudinal reinforcement, together with 1-in. square circumferential rods at 10-in. centers, and extending over the arch to 2 ft. 3 in. below the horizontal axis.

Type "_C_" extends from the latter limit of Type "_B_" to the river line on each side, and consists of longitudinal reinforcement in both top and bottom, as described before, together with circumferential reinforcement entirely around the tunnel, and formed of 1-in. square twisted rods at 15-in. centers.

Type "_D_" consists of longitudinal reinforcement only, and extends from river line to river line, thus occupying 72.5% of the length in which concrete is used. The reinforcement consists of twenty 1-in. twisted rods at 9-in. centers in the crown, and twenty 1-in. rods at 9-in. centers in the invert. In addition to the three standard types, "_B_," "_C_," and "_D_," there were two sub-types which were used in Type "_D_," and in conjunction with it wherever the thickness of the center of the concrete arch became less than 1 ft. 6 in., measuring to the outside of the metal lining. This thickness was one of the limits used in laying out the lines and grades, and in general the arch was not less than this. There were one or two short lengths, however, where it was less, for, if the arch thickness requirement had been adhered to, it would have resulted in a break of line or grade for the sake of perhaps only a few feet of thin arch, and it was here that the sub-types came into play.

Sub-type 1 was used where the arch was less than 1 ft. 6 in. thick at the top. The extra reinforcement here consisted of 1-in. square twisted rods, 16 ft. long, laid circumferentially in the crown at 10-in. centers.

Sub-type 2 was used where the arch was less than 1 ft. 6 in. thick at the side. The extra reinforcement here consisted of 1-in. square twisted rods, 16 ft. long, laid circumferentially, at the side on which the concrete was thin, at 10-in. centers. Very little of either of these two sub-types was used. The entire scheme is shown graphically and clearly on Plate XXXVII.

_Cross-Passage Lining._--There are two main types of cross-passages: Lined with steel plates, and unlined.

There is only one example of lining with steel plates, namely, the most western one at Weehawken. This is built in rock which carried so much water that, in order to keep the tunnels and the passage dry, it was decided to build a concrete-lined passage, without attempting to stop the flow of water, and within this to place a riveted steel lining, not in contact with the concrete, but with a space between the two. This space was drained and the water led back to the shield chamber and thence to the Weehawken Shaft sump. The interior of the steel lining is covered with concrete.

In the passages not lined with steel plates the square concrete lining is rendered on the inside with a water-proof plaster. Each of the passages is provided with a steel door.

_Provisions in Concrete Lining for Surveys and Observations._--The long protracted discussion as to the provision for foundations in these tunnels led to many surveys, tests, and observations, which were carried out during the constructive period, and, as it was desired to continue as many of these observations as possible up to and after the time when traffic started, certain provisions were made in the concrete lining whereby these requirements might be fulfilled. The chief points on which information was desired were as follows:

The change in elevation of the tunnel, The change in lateral position of the tunnel, The change in shape of the tunnel, The tidal oscillation of the tunnel.

A detailed account of these observations will be found in another paper on this work, but it may be said now that it was very desirable to be able to get this information independently of the traffic as far as possible, and therefore provision was made for carrying on the observations from the side benches.

For studying the changes in level of the tunnel, a permanent bench-mark is established in each tunnel where it is in the solid rock and therefore not subject to changes of elevation; throughout the tunnel, brass studs are set in the bench at intervals of about 300 ft. A series of levels is run every month from the stable bench-mark on each of these brass plugs, thus obtaining an indication of the change of elevation that the tunnels have undergone during the month.

These results are checked on permanent bench-marks in the subaqueous portion of the tunnels. These consist of rods, encased in pipes of larger diameter, which extend down through the tunnel invert into the bed-rock below the tunnel. Leakage is kept out by a stuffing-box in the invert. By measuring between a point on these rods where they pass through the invert and the tunnel itself a direct reading of the change of elevation of the tunnel is obtained. These measurements are taken at weekly intervals, and, as the tunnels are subject to tidal influences, being lower at high tide than at low tide, are always taken under the same conditions as to height of water in the river. These permanent bench-marks are at Stations 209 + 05 and 256 + 02 (about 100 ft. on the shoreward side of the river line in each case) in the South Tunnel, at Stations 220 + 00 and 243 + 86, also in the South Tunnel, and at Station 231 + 78 in the North Tunnel. In order to study the lateral change of position, a base line was established on the side bench at each end of each tunnel in the portion built through the solid rock.

At intervals of about 300 ft. throughout each tunnel, alignment pockets are formed in the concrete arch, also above the bench, on the south bench of the North Tunnel and the north bench of the South Tunnel. In each pocket is placed a graduated and verniered brass bar, so that, when the base line is projected on these bars, the lateral movement of the tunnel can be read directly. As it was desirable to have as much cross-connection as possible between the tunnels at the points where the instruments were to be set up, five of the main survey stations were set opposite each of the five cross-passages. Then, for the purpose of increasing the cross-connection still further, pipes 6 in. in diameter were put through from one tunnel to the other at axis level at Stations 220 + 60, 231 + 78, 234 + 64, 241 + 99, and 251 + 13, and a survey station was put in opposite each one.

Points were established at Station 220 + 00, which is the point of intersection for the curve on the original center line of the tunnel, and also at Station 220 + 23, where the intersection of the track center line comes in the North Tunnel. As it was desirable to have the survey stations not much more than 300 ft. apart, so as to obtain clear sights, other stations were established so that the distances between survey stations were at about that interval.

For studying changes of shape in the tunnel, brass "diameter markers" were inserted at each survey station in the concrete lining at the extremities of the vertical and horizontal axes. These were pieces of brass bar, 3/8 in. in diameter and 6 in. long, set in the concrete and projecting 5/8 in. into the tunnel, so that a tape could be easily held against the marker and read.

For obtaining the tidal oscillation of elevation of the tunnel, recording gauges are attached to the invert of the tunnel at each of the five permanent bench-marks referred to above in such a way that the recording pencil of the gauge is actuated by the rod of the permanent bench-mark. A roll of graduated paper is driven by clock-work below the recording pencil which thus marks automatically the relative movement between the moving tunnel and the stable rods. These have shown that in the subaqueous part of the tunnel there is a regular tidal fluctuation of elevation, the tunnel moving down as the tide rises, and rising again when the tide falls. For an average tide of about 5 ft. the tunnel oscillation would be about 1/8 in. Before the concrete lining was placed, there was a tidal change in the shape of the tunnel, which flattened about 1/64 in. at high tide. After the concrete lining was placed, this distortion seemed to cease.

The general design and plan of the work have been described, and before giving any account of the contractor's methods in carrying it out, Table 22, showing the chief quantities of work in the river tunnels, is presented.

Methods of Construction.

The following is an account of the methods used by the contractor in carrying out the plans which have already been described. First, it may be well to point out the sequence of events as they developed in this work. These events may be divided into six periods.

_1._--Excavation and Iron Lining: June, 1903, to November, 1906;

_2._--Caulking and grummeting the iron lining: November, 1906, to June, 1907;

_3._--Surveys, tests and observations: April, 1907, to April, 1908;

_4._--Building cross-passages and capping pile bores: April, 1908, to November, 1908;

_5._--Placing the concrete lining: November, 1908, to June, 1909;

_6._--Cleaning up and various small works: June, 1909, to November, 1909.

The tunnels were under an average air pressure of 25 lb. per sq. in. above normal for all except Periods 5 and 6, during which times there was no air pressure in the tunnels.

All the work will be described in this paper except that under Period 3 which will be found in another paper.

_Period 1.--Excavation and Iron Lining, June, 1903, to November, 1906._--Table 23 gives the chief dates in connection with this period.

_Manhattan Shield Chambers._--The Manhattan shield chamber construction will be first described. The Weehawken shield chambers have been described under the Land Tunnel Section, as they are of the regular masonry-lined Land Tunnels type, whereas the Manhattan chambers are of segmental iron lining with a concrete inner lining.

During the progress of excavation, the location of the New York shield chambers was moved back 133 ft., as previously described in the "Land Tunnel" Section, and when the location had been finally decided, there was a middle top heading driven all through the length now occupied by the shield chamber. Narrow cross-drifts were taken out at right angles to the top heading, and from the ends of these the wall-plate headings were taken out. Heavy timbering was used, as the rock cover was only about 6 ft., and the whole span to be covered was 60 ft. The process adopted was to excavate and timber the north side first, place the iron lining, and then excavate the south side, using the iron of the north side as the supports for the north ends of the segmental timbering of the south. The only incident of note was that at 2:00 A.M., on October 20th, 1904, the rock at the west end of the south wall-plate heading was pierced. Water soon flooded the workings, and considerable disturbance was caused in the New York Central Railroad yard above. The cavity on the surface was soon filled in, but to stop the flow of mud and water was quite a troublesome job.

TABLE 22.--QUANTITIES OF WORK IN SUBAQUEOUS TUNNELS.

============================+========================================= | TYPE. |----------+--------------+--------------+ DESCRIPTION, QUANTITY, |MANHATTAN | CAST IRON, | CAST IRON, | LENGTH, ETC. |shield | ordinary | ordinary | |chambers. | pocketless. | pocket. | ----------------------------+----------+--------------+--------------+ Length, in feet. | 59.00| 4,374.99 | 2,146.3 | ----------------------------+----------+--------------+--------------+ Excavation, in cubic yards. | | | | Total. | 1,884 | 67,344 | 33,038 | Per linear foot. | 31.9 | 15.4 | 15.4 | Cast-iron tunnel lining, | | | | in pounds. | | | | Total. |847,042 |39,643,120 |19,715,405 | Per linear foot. | 14,357 | 9,061 | 9,186 | Cast-steel tunnel lining, | | | | in pounds. | | | | Total. | | 1,544,962 | 757,938 | Per linear foot. | | 353.1 | 353.1 | Steel bolts and washers, | | | | in pounds. | | | | Total. | 23,627 | 1,475,991 | 724,095 | Per linear foot. | 400.46| 337.37 | 397.00 | Rust joints, in linear feet.| | | | Total. | 3,376 | 170,755 | 83,935 | Per linear foot. | 57.2 | 39.0 | 39.1 | Concrete, in cubic yards. | | | | Total. | 766 | 20,030 | 9,827 | Per linear foot. | 12.98| 4.58 | 4.58 | Steel beams, plates, etc., | | | | in pounds. | | | | Total. | 12,346 | 83,774 | 41,098 | Per linear foot. | 2,092.5 | 19.1 | 19.1 | Steel bolts, hooks, etc., | | | | in pounds. | | | | Total. | 1,328 | 36,980 | 18,142 | Per linear foot. | 22.5 | 84.5 | 84.5 | Expanded metal, in pounds. | | | | Total. | 594 | 2,215 | 1,086 | Per linear foot. | 10.07| 0.506| 0.506| Vitrified conduits, in | | | | duct feet. | | | | Total. | 2,560 | 235,903 | 115,728 | Per linear foot. | 43.49| 53.92 | 53.92 | ============================+==========+==============+==============+

============================+========================================== | |--------------+-------------+------------- DESCRIPTION, QUANTITY, | CAST IRON, | CAST STEEL, | LENGTH, ETC. | heavy | ordinary | Total. | pocketless. | pocketless. | ----------------------------+--------------+-------------+------------- Length, in feet. | 5,522.05 | 152.66 |12,255.00 ft. ----------------------------+--------------+-------------+------------- Excavation, in cubic yards. | | | Total. | 85,001 | 2,349 | 189,616 Per linear foot. | 15.4 | 15.4 | cu. yd. Cast-iron tunnel lining, | | | in pounds. | | | Total. |61,559,845 | | 121,765,412 Per linear foot. | 11,148 | | lb. Cast-steel tunnel lining, | | | in pounds. | | | Total. | 2,730,905 |1,549,711 | 6,583,516 Per linear foot. | 494.5 | 10,151.4 | lb. Steel bolts and washers, | | | in pounds. | | | Total. | 2,935,455 | 51,266 | 5,210,434 Per linear foot. | 581.59 | 335.82 | lb. Rust joints, in linear feet.| | | Total. | 218,656 | 5,996 | 482,718 Per linear foot. | 39.6 | 39.3 | ft. Concrete, in cubic yards. | | | Total. | 25,282 | 713 | 56,618 Per linear foot. | 4.58 | 4.58 | cu. yd. Steel beams, plates, etc., | | | in pounds. | | | Total. | 105,738 | 7,432 | 250,388 Per linear foot. | 19.1 | 48.7 | lb. Steel bolts, hooks, etc., | | | in pounds. | | | Total. | 46,675 | 1,471 | 104,596 Per linear foot. | 84.5 | 96.4 | lb. Expanded metal, in pounds. | | | Total. | 2,795 | 62 | 6,752 Per linear foot. | 0.506| 0.406| lb. Vitrified conduits, in | | | duct feet. | | | Total. | 297,752 | 7,757 | 659,700 Per linear foot. | 53.92 | 50.81 | duct ft. ============================+==============+=============+============

TABLE 23.--EXCAVATION AND IRON LINING.