Masonry Lining of Land Tunnels.
[Plates XXXII] and [XXXIV] show in detail the tunnels as they were actually built. It will be seen that in all work, except in the Gy-East contract, there was a bench at each side of each tunnel in which the cable conduits were embedded. In Gy-East the bank of ducts which came next to the middle wall was carried below subgrade, and the inner benches were omitted.
The side-walls and subgrade electric conduits were water-proofed with felt and pitch. The water-proofing was placed on the outside of the side-walls (that is, on the neat line), and the space between the rock and the water-proofing was filled with concrete. This concrete was called the "Sand-Wall."
The general sequence of building the masonry lining is shown in [Fig. 8]. The operations were as follows:
1.—Laying concrete for the whole height of the sand-walls, and for the floor and foundations for walls and benches up to the level of the base of the conduits;
2.—Water-proofing the side-walls, and, where there was a middle trench containing subgrade conduits, laying and water-proofing these conduits;
3.—Building concrete wall for conduits to be laid against, and, where there was a middle trench, filling up with concrete between the conduits;
4.—Laying conduits;
5.—Laying concrete for benches and middle-wall;
6.—Building haunches from top of bench to springing of brick arch;
7.—Building brick arch and part of concrete back-filling;
8.—Finishing back-filling.
The whole work will be generally described under the headings of Concrete, Brickwork, Water-proofing, and Electric Conduits.
Concrete.—The number of types and the obstructions caused by the heavy posting of the timbering made it inadvisable to use built-up traveling forms at the Manhattan side, though they were used in the Weehawken Rock Tunnels.
The specifications required a facing mixture of mortar to be deposited against the forms simultaneously with the placing of the concrete. This facing mixture was dry, about 2 in. thick, and was kept separate from the concrete during the placing by a steel diaphragm. The diaphragm was removed when the concrete reached the top of each successive layer, and the facing mixture and concrete were then tamped down together. This method was at first followed and gave good results, which was indeed a foregone conclusion, as the Weehawken shaft had been built in this way. However, it was found that as good results, in the way of smooth finish, were to be obtained without the facing mixture by spading the concrete back from the forms, so that the stone was forced back and the finer portion of the mixture came against the forms; this method was followed for the rest of the work. All corners were rounded off on a 1-in. radius by mouldings tacked to the forms. The side-bench forms were used about four times, and were carefully scraped, planed, filled at open joints, and oiled with soap grease each time they were set up. When too rough for face work they were used for sand-wall and other rough work.
PLATE XXXIV.
TRANS. AM. SOC. CIV. ENGRS.
VOL. LXVIII, No. 1155.
HEWETT AND BROWN ON
PENNSYLVANIA R. R. TUNNELS: NORTH RIVER TUNNELS.
The mixing was done by a No. 4 Ransome mixer, driven by 30-h.p. electric motors. The mixer at Manhattan was set on an elevated platform at the north end of the intercepting arch; that at Weehawken was placed at the entrance to the tunnels. The sand and stone were stored in bins above the mixers, and were led to the hoppers of the mixers through chutes. The hoppers were divided into two sections, which gave the correct quantities of sand and stone, respectively, for one batch. The water was measured in a small tank alongside. A "four-bag" batch was the amount mixed at one time, that is, it consisted of 4 bags of cement, 8¾ cu. ft. of sand, and 17½ cu. ft. of broken stone, and was called a 1 : 2½ : 5 mixture. It measured when mixed about ¾ cu. yd.
The cement was furnished to the contractor by the Railroad Company, which undertook all the purchasing from the manufacturer, as well as the sampling, testing, and storing until the contractor needed it. The Railroad Company charged the contractor $2 a barrel for this material.
The sand was required by the specifications to be coarse, sharp, and silicious, and to contain not more than 0.5% of mica, loam, dirt, or clay. All sand was carefully tested before being used. The stone was to be a sound trap or limestone, passing a 1½-in. mesh and being retained on ⅜-in. mesh. The contractor was allowed to use a coarser stone than this, namely, one that had passed a 2-in. and was retained on a 1½-in. mesh.
The concrete was to be machine-mixed, except in cases of local necessity. The quantity of water used in the mixture was to be such that the concrete would quake on being deposited, but the engineer was to use his discretion on this point. Concrete was to be deposited in such a manner that the aggregates would not separate. It was to be laid in layers, not exceeding 9 in. in thickness, and thoroughly rammed. When placing was suspended, a joint was to be formed in a manner satisfactory to the engineer. Before depositing fresh concrete, the entire surface on which it was to be laid was to be cleaned, washed and brushed, and slushed over with neat cement grout. Concrete which had begun to set was not to be used, and retempering was not to be allowed.
The forms were to be substantial and hold their shape until the concrete had set. The face forms were to be of matched and dressed planking, finished to true lines and surfaces; adequate measures were to be taken to prevent concrete from adhering to the forms. Warped or distorted forms were to be replaced. Plastering the face was not allowed. Rock surfaces were to be thoroughly washed and cleaned before the concrete was deposited.
These specifications were followed quite closely.
A typical working gang, as divided among the various operations, is shown below:
| Superintendence. | ||||||
| ½ | Superintendent | @ | $250 | per | month | |
| ½ | Assistant engineer | " | 150 | " | " | |
| 1 | Assistant superintendent | " | 150 | " | " | |
| Surface Transport. | ||||||
| 1 | Foreman | @ | $2.50 | per | day | |
| 1 | Engineer | " | 3.00 | " | " | |
| 1 | Signalman | " | 2.00 | " | " | |
| 16 | Laborers | " | 1.75 | " | " | |
| 3 | Teams | " | 7.50 | " | " | |
| Laying. | ||||||
| 1 | Foreman | @ | $4.00 | per | day | |
| 8 | Laborers | " | 2.00 | " | " | |
| Forms. | ||||||
| 1 | Foreman | @ | $4.50 | per | day | |
| 4 | Carpenters | " | 3.25 | " | " | |
| 5 | Helpers | " | 2.25 | " | " | |
| Tunnel Transport. | ||||||
| ¼ | Foreman | @ | $3.25 | per | day | |
| ¼ | Engineer | " | 3.00 | " | " | |
| ¼ | Signalman | " | 2.00 | " | " | |
| 4 | Laborers | " | 1.75 | " | " | |
| Mixers. | ||||||
| ¼ | Foreman | @ | $3.25 | per | day | |
| 2 | Laborers | " | 1.75 | " | " | |
The superintendent and assistant engineer looked after the brickwork and other work as well as the concrete. The surface transport gang handled all the materials on the surface, including the fetching of the cement from the cement warehouses.
The tunnel transport gang handled all materials in the tunnel, but, when the haul became too long, the gang was reinforced with laborers from the laying gang. Of the laying gang, two generally did the spading, two the spreading and tamping, and the remaining force dumped the concrete. The general cost of this part of the work is shown in [Table 13].
The figures in [Table 13] include the various items built into the concrete and some that are certificate extras in connection with the concrete, such as drains, ironwork and iron materials, rods and bars, expanded metal, doors, frames and fittings, etc.
Water-proofing.—According to the specifications, the water-proofing was to consist of seven layers of pitch and six layers of felt on the side-walls and a ½-in. layer of mastic, composed of coal-tar and Portland cement, to be plastered over the outside of the arches.
By the time the work was in hand, some distrust had arisen as to the efficiency of this mastic coating, and a great deal of study was devoted to the problem of how to apply a felt and pitch water-proofing to the arches. The difficulty was that there was no room between the rock and the arch or between the timber and the arch (as the case might be) in which to work. Several ingenious schemes of putting the felt on in layers, or in small pieces like shingles, were proposed and discussed, and a full-sized model of the tunnel arch was even built on which to try experiments, but it was finally decided to overcome the difficulty by leaving out the arch water-proofing altogether, and simply building in pipes for grouting through under pressure, in case it was found that the arch was wet.
As to the arch built through the length excavated by cut-and-cover on the New York side, it was resolved to water-proof that with felt and pitch exactly as the side-walls were done, the spandrel filling between the arches being raised in a slight ridge along the concrete line between tunnels in order to throw the water over to the sides. The portions of arch not water-proofed were rather wet, and grouting with a 1:1 mixture was done, but only with the effect of stopping large local leaks and distributing a general dampness over the whole surface of the arch.
TABLE 13.—Cost of Concrete in Land Tunnels, in Dollars per Cubic Yard.
| Manhattan. | Weehawken. | Total yardage. | |
|---|---|---|---|
| Cubic yards placed | 14,706½ | 3,723 | 18,429½ |
| Labor. | Average Cost per Cubic Yard. | ||
| Surface transport | $0.31 | $1.43 | $0.54 |
| Superintendence and general labor at point of work | 0.31 | 1.31 | 0.51 |
| Mixing | 0.52 | 0.56 | 0.53 |
| Laying | 1.38 | 1.45 | 1.39 |
| Tunnel transport | 1.30 | 1.47 | 1.34 |
| Cleaning | 0.21 | 0.17 | |
| Forms: erecting and removal | 1.58 | 1.51 | 1.56 |
| Total labor | $5.61 | $7.73 | $6.04 |
| Material. | |||
| Cement | $2.30 | $2.22 | $2.28 |
| Sand | 0.34 | 0.40 | 0.36 |
| Stone | 0.91 | 0.61 | 0.85 |
| Lumber for forms | 0.47 | 0.45 | 0.47 |
| Sundry tunnel supplies | 0.16 | 0.17 | 0.16 |
| Total materials | $4.18 | $3.85 | $4.12 |
| Plant running | $0.44 | $0.44 | $0.44 |
| Surface labor, repairs and maintenance | 0.25 | 1.24 | 0.44 |
| Field office administration | 0.50 | 1.72 | 0.75 |
| Total field charges | $10.98 | $14.98 | $11.79 |
| Plant depreciation | $0.62 | $1.57 | $0.81 |
| Chief office administration | 0.24 | 0.31 | 0.25 |
| Total average cost per cubic yard | $11.84 | $16.86 | $12.85 |
| Cost of Miscellaneous Items in Concrete. | |||
| Manhattan. | Weehawken. | Average. | |
| Cubic yards | 14,706½ | 3,723 | 18,429½ |
| Amount, in dollars | $6,184.83 | $1,756.79 | $7,941.62 |
| Unit cost | 0.42 | 0.47 | 0.43 |
The 24-ft. 6-in. tunnel adjoining the Terminal Station-West was water-proofed by a surface-rendering method which, up to the present time, has been satisfactory. Generally speaking, the arches of the Land Tunnels, though not dripping with water, are the dampest parts of the whole structure from Tenth Avenue to Weehawken, and it would seem as if some form of water-proofing over these arches would have been a distinct advantage.
There was no difficulty in applying the water-proofing on the side-walls, after a little experience had been gained as to the best methods. The specifications required the sand-wall to be covered with alternate layers of coal-tar pitch and felt, seven layers of the former and six layers of the latter, the felt to be of Hydrex brand or other equally satisfactory to the engineer. The pitch was to be straight-run, coal-tar pitch which would soften at 60° Fahr., and melt at 100° Fahr., being a grade in which distillate oils, distilled from it, should have a specified gravity of 1.105. The pitch was to be mopped on the surface to a uniform thickness of 1/16 in., and a covering of felt, previously mopped with pitch, was to be applied immediately. The sheets were to lap not less than 4 in. on cross-joints and 12 in. on longitudinal joints, and had to adhere firmly to the pitch-covered surface. This layer was then to be mopped, and another layer placed, and so on until all the layers were in place. This water-proofing was to extend from the bottom of the cable conduits to the springing of the brick arch. Where sub-track conduits were used, these were to be surrounded with their own water-proofing. The work was carried out as specified; the sand-walls were not rendered, but were built smooth enough to apply the water-proofing directly to them. They were dried with gasoline torches before the application of the pitch, and in very wet sections grooves were cut to lead the water away.
The first attempts were with the felt laid in horizontal strips. This ended very disastrously, as the pitch could not sustain the weight of the felt, and the whole arrangement slipped down the wall. The felt was then laid vertically, being tacked to a piece of horizontal scantling at the top of the sand-wall and also held by a row of planks braced against it at about half its height. A layer of porous brick was laid as a drain along the base of the water-proofing, covered by a single layer of felt to prevent it from becoming choked with concrete.
The water-proofing of the sub-track conduits was troublesome, as the numerous layers and the necessity for preserving the proper laps in both directions between adjacent layers made the whole thing a kind of Chinese puzzle. Various modifications, to suit local conditions, were made from time to time. Conduits outside the general outline of the tunnel are difficult to excavate, to lay, and to water-proof, and should be avoided wherever possible.
The usual force in water-proofing consisted of a foreman, at $3.50 per day, and nine laborers at $1.75 per day. These men not only laid the water-proofing, but transported the materials, heated the pitch, and cut up the rolls of felt. In general, two men transported material, one tended the heater, and the other six worked in pairs, two preparing the surface of the concrete sand-wall, two laying pitch, and two laying felt.
The cost of the water-proofing operation was about as shown in [Table 14].
TABLE 14.— Cost of Water-Proofing, in Dollars per Square Foot.
| Manhattan. | Weehawken. | Total. | |
|---|---|---|---|
| Square feet covered | 47,042 | 13,964 | 60,736 |
| Average cost per square foot. | |||
| Labor | $0.07 | $0.07 | $0.07 |
| Material | 0.12 | 0.09 | 0.11 |
| Total field charges | $0.19 | $0.16 | $0.18 |
| Chief office and plant depreciation | 0.01 | 0.03 | 0.02 |
| Total average cost | $0.20 | $0.19 | $0.20 |
Brickwork in Arches.—Owing to the heavy timbering, the brickwork at Manhattan was interfered with to a considerable extent, and the gang was always kept at work at two or more places. The work was carried up to a point where it was necessary to back-fill, or prop or cut away encroaching timbers, and then the men were moved to another place while this was being done.
The centers were set up in sets of seven, spaced 4 ft. apart. Two 14-ft. lengths of 3 by 4-in. yellow pine lagging were used with each set of ribs, with 24 by 8-in. block lagging in the crown.
All centers were set ¼ in. high, to allow for settlement, except in the 24-ft. 6-in. span, in which they were set ½ in. high. This proved ample, the average settlement of the ribs being 0.01 ft. and of the masonry, 0.003 ft. In the 24-ft. 6-in. span the ribs were strengthened with 6 by 6-in. blocking and 12 by 12-in. posts to subgrade. Great trouble was here encountered with encroaching timbering, due to the settlement of the wide flat span. Grout pipes were built in, as previously mentioned.
Each mason laid an average of 0.535 cu. yd. of brickwork per hour, or 4.28 cu. yd. per day. The number of bricks laid per mason per hour was 218, or 1,744 per day.
The bricks were of the best quality of vitrified paving brick, and were obtained from the Jamestown Brick Company, of Jamestown, N. Y. The average size was 8¾ by 3-15/16 by 2-7/16 in.; the average number per cubic yard of masonry was 408, the arches being from 19 ft. to 24 ft. 6 in. in span and from 22 to 27 in. thick. The joints were 3/16 in. at the face and averaged 9/16 in. through the arch.
The proportions for mortar were 1 of cement and 2½ of sand. One cubic yard of masonry was composed of 73.5% brick and 26.5% mortar. The volume of the ingredients in a four-bag batch was 12.12 cu. ft., and the resulting mixture was 9.54 cu. ft. The number of barrels of cement was 0.915 per cu. yd. of masonry, and about 17.7% of the mortar made was wasted. The average force employed was:
| Laying. | ||||||
|---|---|---|---|---|---|---|
| 1 | Foreman | @ | $8.00 | per | day | |
| 4 | Layers | " | 6.00 | " | " | |
| 8 | Tenders | " | 2.00 | " | " | |
| 2 | Mixers | " | 2.00 | " | " | |
| Forms. | ||||||
| 1 | Foreman | @ | $4.50 | per | day | |
| 4 | Carpenters | " | 3.50 | " | " | |
| 5 | Helpers | " | 2.25 | " | " | |
| Transport. | ||||||
| ¼ | Hoist engineer | @ | $3.00 | per | day | |
| ¼ | Signalman | " | 2.00 | " | " | |
| 4 | Laborers | " | 2.00 | " | " | |
For materials, the following prices prevailed:
Cement, $2.00 per bbl.,
Sand, $0.90 to $1.00 per cu. yd.,
Brick, $16.00 per thousand, delivered at yard,
Centers, $26.00 each,
Lagging, $45.00 per 1,000 ft. B. M.
The cost of the brickwork is given in Table 15.
TABLE 15.—Cost of Brickwork.
| Manhattan. | Weehawken. | Total. | |
|---|---|---|---|
| Cubic yards placed | 4,137 | 790 | 4,927 |
| Labor. | Average Cost per Cubic Yard. | ||
| Surface transport | $0.35 | $1.19 | $0.48 |
| Superintendent and general labor at point of work | 0.17 | 0.04 | 0.16 |
| Laying and mixing | 2.58 | 3.20 | 2.60 |
| Forms: erection and removal | 2.62 | 0.32 | 2.25 |
| Tunnel transport | 1.19 | 1.12 | 1.18 |
| Total labor | $6.91 | $5.87 | $6.75 |
| Material. | |||
| Brick | $6.56 | $6.56 | $6.56 |
| Cement | 1.76 | 1.75 | 1.76 |
| Sand | 0.20 | 0.28 | 0.22 |
| Forms | 0.92 | 0.98 | 0.98 |
| Overhead conductor pockets | 0.15 | 0.09 | 0.13 |
| Total material | $9.59 | $9.66 | $9.60 |
| Plant running | $0.55 | $0.30 | $0.51 |
| Surface labor, repairs and maintenance | 0.36 | 1.30 | 0.51 |
| Field office administration | 0.55 | 0.88 | 0.60 |
| Total field charges | $17.96 | $18.01 | $17.97 |
| Chief office administration | $0.60 | $0.66 | $0.61 |
| Plant depreciation | 0.35 | 0.64 | 0.39 |
| Total average cost per cubic yard | $18.91 | $19.31 | $18.97 |
In [Table 16] the cost of grout is expressed in terms of barrels of cement used, because in the schedule of prices attached to the contract, that was the unit of payment for grout.
TABLE 16.—Cost of Grout Over Arches in Land Tunnels.
Cost, in Dollars per Barrel of Cement Used.
| Manhattan. (Gy-East only.) | Weehawken. | Total. | |
|---|---|---|---|
| Barrels used | 3,000½ | 261½ | 3,262 |
| Average Cost per Barrel of Cement Used. | |||
| Labor | $0.55 | $0.46 | $0.53 |
| Material | 2.30 | 2.25 | 2.28 |
| Field office administration | 0.08 | 0.06 | 0.08 |
| Plant and supplies | 0.10 | 0.07 | 0.09 |
| Total field charges | $3.03 | $2.84 | $2.98 |
| Chief office and plant depreciation | 0.21 | 0.22 | 0.28 |
| Total average cost | $3.24 | $3.06 | $3.20 |
Vitrified Earthenware Conduits for Electric Cables.—The general drawings will show how the ducts were arranged, and that manholes were provided at intervals. They were water-proofed, in the case of those embedded in the bench, by the general water-proofing of the tunnels, which was carried down to the level of the bottom of the banks of ducts; and in the case of those below subgrade, by a special water-proofing of felt and pitch wrapped around the ducts themselves.
The portion of wall in front of the ducts was bonded to that behind by bonds, mostly of expanded metal, passing between the ducts. Examples of the bonding will be seen in the drawings.
The joints between successive lengths of 4-way and 2-way ducts were wrapped with two thicknesses of cotton duck, 6 in. wide, those of single-way ducts were not wrapped, but plastered with cement mortar. The ducts were laid on beds of mortar, and were made to break joints at top and bottom and side to side with the adjacent ducts. They were laid with a wooden mandrel; a square leather washer at the near end acted as a cleanser when the mandrel was pulled through.
The specifications required the ducts to be laid at the same time as the concrete and be carried up with it, but this was found to be a very awkward operation, as the tamping of the concrete and the walking of men disturbed the ducts, especially as the bonds lay across them. It was resolved, therefore, to build the portion of the wall behind the ducts first, with the bonds embedded in it at the proper heights and projecting from it, then to lay up the banks of ducts against this wall, bending the bonds down as they were reached, and finally, after all the ducts were in, to lay the concrete in front of and over the top of the ducts. Several detailed modifications of this general scheme were followed at one time or another when necessary or advisable.
The laying of ducts below subgrade was not complicated by the presence of bonds, the water-proofing caused the trouble here, as before described.
The specifications called for a final rodding after completion. A group of the apparatus used in this process is shown in [ Fig. 1, Plate XXXV]; the various parts are identified by the following key:
| 1.—4-way duct, for telephone and telegraph cables, |
| 2.—2-way duct, for telephone and telegraph cables, |
| 3.—1-way duct, for high- and low-tension cables, |
| 4.—Plug for closing open ends of ducts, |
| 5.—Plug for closing open ends of ducts in position, |
| 6, 7, and 8.—Cutters for removing obstructions, |
| 9.—Hedgehog cutter for removing grout in ducts, |
| 10.—Rodding mandrel for multiple ducts, |
| 11.—Laying mandrel, |
| 12.—Rodding mandrel, with jar-link attached, |
| 13.—Laying mandrel, |
| 14 and 15.—Rubber-disk cleaners, used after final rodding, |
| 16 and 17.—Sectional wooden rods used for rodding, |
| 18.—Section of iron rods used for rodding, |
| 19.—Jar-link, |
| 20.—Cotton duck for wrapping joints of multiple ducts, |
| 21.—Hook for pulling forward laying mandrel, |
| 22.—Top view of trap for recovering lost or broken rods left in ducts. |
Ordinary ¾-in. gas pipe was used for the rod, and a cutter with rectangular cross-section and rounded corners was run through ahead of the mandrel: following the cutter came a scraper consisting of several square leather washers, of the size of the ducts, spaced at intervals on a short rod. The mandrel itself was next put through, three or four men being used on the rods. All the ducts in a bank were thus rodded from manhole to manhole. When a duct was rodded it was plugged at each end with a wooden plug. A solid wooden paraffined plug was used at first, but afterward an expansion plug was used.
Very little trouble was met in rodding the power conduits, except for a few misplaced ducts, or a small mound of mortar or a laying mandrel left in. At such points a cut was made in the concrete and the duct replaced.
In the subgrade telephone and telegraph ducts east of the Manhattan Shaft, much trouble was caused by grout in the ducts. The mandrel and cutters were deflected and broke through the web of the ducts rather than remove this hard grout. Trenches had to be cut from the floor to the top of the water-proofing, the latter was then cut and folded back, and the ducts replaced. To do this, a number of ducts had to be taken out to replace the broken ones and get the proper laps. The water-proofing was then patched and the concrete replaced. This grout had not penetrated the water-proofing, but had got in through the ends of the ducts where they had not been properly plugged and protected. The duct gang, both for laying and rodding, generally consisted of
1 Foreman, at $3.50 per day,
and 9 laborers, at $1.75 per day.
When laying: 4 men were laying, 2 men mixing and carrying mortar, and 3 were transporting material. When rodding: 4 men were rodding, 2 men at adjacent manholes were connecting and disconnecting cutters and mandrels, 1 was joining up rods, and 2 men assisting generally.
The cost of this work is shown in [Table 17].