[Ill.u.s.tration: Fig. 136.--General Plan of Centers for Roof Arch, Hodges"

Pa.s.s Tunnel.]

The construction of the centering for the roof arch is shown by Figs.

136 and 137, Fig. 137 giving detail dimensions of the ribs and lagging.

The center, as shown by Fig. 136, consisted of four ribs s.p.a.ced 3 ft. on centers. Each rib consists of two side posts and an arch piece. The side posts on each side are connected at the bottoms by a sill and at the top by a cap. Jacks between the sill and a mud sill laid on the concrete invert or in the ditch held the center in place during arch construction. Lowering these jacks dropped the center onto trucks traveling on the mud sills. Thus the center was moved along as the work progressed. As will be noted from Figs. 134 and 135, the side wall forms carried the work only to the bottoms of the old caps. The arch center completed the concrete wall work and the roof arch. Only about one-third of the new lining had the brick arch, as shown by the drawings; in the remaining two-thirds the concrete was carried up much further on each side; in fact, the brickwork const.i.tuted only the top third of the arch.

[Ill.u.s.tration: Fig. 137.--Details of Centers for Roof Arch, Hodges" Pa.s.s Tunnel.]

In describing the forms and centers we have left much of the explanation to the drawings. These show all dimensions and details, and indicate in a measure the mode of procedure. The work done consisted of excavation enlarging the section, of removing the old timber lining and of the form work, concreting and bricklaying for the new lining. All of it above convenient reach from the ground was done from a movable staging formed by a deck fixed on a flat car so as to be adjustable in height. The concrete was mixed by hand on this car platform and shoveled directly into the forms, the platform being raised as the work increased in height. The concrete used was a 1-3-5 mixture of 2-in. broken stone.

The organization of the working force is not easily stated since the work was done as the traffic permitted and varied with the conditions.

Generally from 12 to 16 men were all that could be employed to advantage. Complete records of cost were kept, but they were destroyed by fire, so that the only figures available on this point are the totals. These are as follows:

Item. Totals. Per lin. ft.

Labor $21,129 $14.81 Materials 13,939 9.77 ------- ------- Total $35,068 $24.58

These amounts average the cost of the invert, which was required for about one-third of the length, over the whole tunnel.

~RELINING A SHORT TUNNEL.~--The following figures show the cost of relining with concrete a timber lined railway tunnel. The concrete side walls were 14 ft. high and had an average thickness of 2 ft. Therefore each side wall averaged nearly 1.3 cu. yds. per lin. ft., and the two walls averaged 2.59 cu. yds. per lin. ft. of tunnel. The concrete was mixed 1-3-5, being, we believe, unnecessarily rich in cement. The average amount of concrete placed in the walls per day was 50 cu. yds.

Cost of Side Walls.

Materials-- Per cu. yd.

1.33 bbl. cement at $2.00 $2.66 0.5 cu. yd. sand at 0.18 0.09 0.75 cu. yd. stone at 0.55 0.41 ------- Total $3.16

Labor on concrete-- 0.01 day foreman at $5.00 $0.05 0.03 day foreman at $3.00 0.09 0.03 day engineman at $3.00 0.09 0.35 day laborer at $1.75 0.61 ------- ------- 0.42 Total $0.84

Labor, removing timber, building forms, excavating, etc.-- 0.02 day foreman at $5.00 $0.10 0.05 day foreman at $3.00 0.15 0.40 day laborer at $1.75 0.70 ------- ------- 0.47 Total $0.95

Miscellaneous-- 0.02 day engineer and superintendent at $5.00 $0.10 Falsework and forms, timber and iron 0.07 Tools, light, etc. 0.10 Interest and depreciation of $1,800 plant at 20% per annum 0.09 Train service, 0.03 day work train at $25 0.75

Summary concrete side walls-- Per cu. yd.

Materials $3.16 Labor on concrete 0.84 Labor removing timber, etc. 0.95 Train service 0.75 Miscellaneous 0.34 ------- Total $6.04

In the two side walls there were 2.59 cu. yds. of concrete per lin. ft.

of tunnel, hence the cost of the side walls was $6.04 $2.59 = $15.64 per lin. ft. of tunnel. The concrete arch varied in thickness, averaging from 14 to 20 ins. at the springing line to 8 to 14 ins. at the crown. The arch averaged 1.2 cu. yds. per lin. ft. of tunnel. About 20 cu. yds. of arch were placed per day. The arch concrete was mixed 1-3-5 and the cost was as follows:

Cost of Concrete Arch.

Materials-- Per cu. yd.

1.36 bbls. cement, $2.00 $2.72 0.05 cu. yd. sand, 0.18 0.09 0.75 cu. yd. stone, 0.55 0.41 ------- Total $3.22 1.8 cu. yds. dry rock backing at 0.55 $0.99 Labor on concrete-- 0.02 day foreman at $5.00 $0.10 0.12 day foreman at 3.00 0.36 0.88 day laborer at 1.75 1.54 ------- ------- ------ 1.02 Total $1.96 $2.00 Labor placing 1.08 cu. yds. rock backing-- 0.01 day foreman at $5.00 $0.05 0.51 day foreman at 3.00 0.15 0.55 day laborer at 1.75 0.96 ------- ------- ------- 0.61 Total $1.90 $1.16 Labor removing timbers, forms, excavations, etc.-- 0.02 day foreman at $5.00 $0.10 0.04 day foreman at 3.00 0.12 0.06 day carpenter at 2.50 0.15 0.40 day laborer at 1.75 0.70 ------- ------- ------- 0.52 Total $2.06 $1.07 Train service-- 0.06 day at $25 $1.50 Miscellaneous-- Engineering and superintendence. .07 Falsework, timber and iron .13 Tools, light, etc .12 Interest and depreciation, $1,800 plant, 20% per annum 0.09

Summary concrete arch-- Concrete materials $3.22 Dry rock backing (1.8 c. y.) 0.99 Labor and concrete 2.00 Labor placing 1.8 cu. yds. rock backing 1.16 Labor removing timber, etc 1.07 Train service hauling materials 1.50 Engineering and superintendence 0.07 Falsework, timber and iron 0.13 Tools, light, etc. 0.12 Interest and depreciation plant 0.09 ------ Grand total $10.35

It will be noted that the "train service" is an item that really should be considered as a part of the cost of the materials, for the cost of the sand and stone is the cost f. o. b. cars at the sand pit and at the quarry, to which should be added the cost of hauling them to the tunnel--to-wit, the "train service."

Summing up, we have the following as the cost per lineal foot for lining this single-track tunnel with concrete: Per lin. ft.

2.59 cu. yds. side walls at $6.04 $15.64 1.20 cu. yds. arch at 10.33 12.40 ------- ------ ------- 3.79 cu. yds. Total $9.38 $28.04

It should be remembered that the higher cost of the arch concrete is due in large measure to the fact that 1.8 cu. yds. of dry rock packing above the arch are included in the cost of the concrete. Strictly speaking, this dry rock packing should not be charged against the arch concrete, and, segregating it, we have the following:

Per lin. ft.

2.59 cu. yds. concrete side walls at $6.04 $15.64 1.20 cu. yds. concrete arch at 8.18 9.82 2.16 cu. yds. dry rock at 0.55 1.19 Labor placing 2.16 cu. yds. at 0.64 1.39 ------ Total $28.04

This is a much more rational a.n.a.lysis of the cost and a still further reduction in the cost of the arch concrete might be made by prorating the train service item ($1.50 per cu. yd. concrete). At least half of this train service should be charged to the dry rock backing, for there are 1.25 cu. yds. of sand and broken stone to 1.80 cu. yds. of dry rock backing.

The amount of this dry rock backing, or packing, varies greatly in different parts of a tunnel. In the first half of this tunnel it averaged 1.8 cu. yds. per lin. ft., while in the second half it averaged nearly 2.4 cu. yds. per lin. ft.

~METHOD OF MIXING AND PLACING CONCRETE FOR A TUNNEL LINING.~--The tunnel known as the Burton tunnel is located on the Jasper-French Lick extension of the Southern Ry., and about 4 miles from French Lick, Ind.

It is a single track tunnel 2,200 ft. long with 300 ft. at one end on a 4-30" curve and 1,900 ft. on tangent. The material penetrated was slate and loose rock, requiring solid timbering throughout. This timbering is shown by Fig. 138, which also shows the concrete lining; the timbering was embedded in the concrete lining.

[Ill.u.s.tration: Fig. 138.--Sections Showing Concrete Lining for Burton Tunnel.]

The original timber lining was composed as follows: Posts 1012 ins. and s.p.a.ced 3 ft. apart were set on 312-in. sills and carried 1012-in.

wall plates which supported 1012-in. segmental arch ribs s.p.a.ced 3 ft.

apart. The lagging behind the posts was 36-in. stuff and the lagging over the arch ribs was 46-in. stuff. The section of the concrete lining is shown by Fig. 138, it required 4,132 cu. yds. of concrete and 161.43 lbs. of reinforcement per lin. ft. The concrete was a 1-2-5 crushed stone--between 2 in. and in. size--mixture; it required 1.16 bbls. of cement, 0.52 cu. yds. sand and 0.92 cu. yds. of stone per cubic yard of concrete. The amount of reinforcement per cubic yard of concrete was 39.1 lbs.

[Ill.u.s.tration: Fig. 139.--View of Mixer Plant Showing Car Tracks, Burton Tunnel.]

[Ill.u.s.tration: Fig. 140.--View of Mixer Plant Showing Method of Unloading Materials, Burton Tunnel.]

All the concrete was mixed and handled from one end of the tunnel. The mixing plant was located in the approach cut at one end. A standard gage main track ran through the cut. About 20 ft. in the clear to one side of this track a trestle 500 ft. long was built, carrying an 18-ft. gage derrick track and a narrow gage 3-cu. yd. dump car track. A stiff leg derrick operating a 1 cu. yd. orange peel or a 1 cu. yd. clam-sh.e.l.l Hayward bucket was mounted on a carriage traveling on the 18-ft. gage track. The side of the trestle nearest the railway track was sheeted vertically and the s.p.a.ce between this sheeting and the track was floored over at track level for stock piles. Near the end of the trestle toward the tunnel and on the same side of the track was the mixer plant. This consisted of two 85 cu. yd. bins, one for sand and one for stone, carried by a tower so that their bottoms were 25 ft. above track level.

Below the bins was a charging platform pierced by a measuring hopper.

Below the measuring hopper was a 1 cu. yd. cubical mixer and below the mixer was a 3-ft. gage track for 1 cu. yd. Koppel side dump cars. To the rear of the tower at ground level there was a 20-cu. yd. sand bin and a 20-cu. yd. stone bin set side by side with a continuous bucket elevator leading from each to the corresponding bin on the tower. The cement house was located directly across the railway track from the tower. At the side of the cement house nearest the track there was an inclined bag elevator leading up to a bridge spanning the railway track at the level of the charging floor of the mixer plant. On this bridge ran a car for carrying bags of cement. The plant as described is shown by Figs. 139 and 140.

In operation the derrick unloaded the stone and sand cars by means of the Hayward buckets either into the bins at the feet of the bucket elevators or onto stock piles on the flooring beside the trestle. When put into stock piles the materials had to be reloaded by derrick into the 3 cu. yd. cars on the trestle narrow gage track and carried by these cars to the elevator boots. The sand and stone were chuted from the tower bins directly into the charging hopper below. Here the cement bags, brought across the bridge on the car into which they were loaded directly by the bag elevator, were opened and the cement added to the sand and stone. The charge was then dropped into the mixer and from the mixer the batch dropped into the Koppel concrete cars.

In the tunnel a traveling platform was constructed on two standard gage flat cars so coupled that a platform 100 ft. long and slightly narrower than the clear s.p.a.ce between side wall forms was obtained. Connecting the end of the platform toward the mixing plant was a rampe or inclined platform mounted on wheels. The Koppel car tracks from the mixer were carried up the incline and the full length of the level platform. The cars were hauled to the foot of the incline by a light locomotive. A cable was then hooked to them; this cable was run through a block on the level platform, its free end coming back to the locomotive, which thus pulled the cars up the incline by moving back toward the mixer. On the level platform the cars were pushed by hand and dumped on the floor, whence the concrete was shoveled into the forms.

The platform construction deserves mention in the particular that it provided for adjusting the platform vertically. At each corner of the car a vertical post some 7 or 8 ft. high was set up. The side stringers of the platform carried two vertical posts at each end; these two posts were s.p.a.ced just far enough apart to slide over the corner post, one on each side of it. A block at the top of the corner posts with the hoist line connected to the bottoms of the platform posts and the lead line going to a winch head, thus made it possible to lift the platform any distance within the height of the vertical post guide and hold it there by blocking under the posts. The arrangement is shown roughly by the sketch, Fig. 141. There was block and tackle for each corner post and a winch at each end of the car. The vertical movement of the platform was between 6 and 7 ft.

The floor was cemented first, then the side walls and finally the roof arch. Floor construction was begun at the portal farthest from the mixing plant. Koppel car tracks were laid through the tunnel and the concrete was dumped from them directly on the ground. The cars were hauled by a light locomotive. As the concreting advanced the dump car track was raised and suspended from timbers across tunnel so that the concrete could be placed under it. As fast as the floor hardened the permanent standard gage track was laid and a temporary third rail placed to give also a dump car track.

[Ill.u.s.tration: Fig. 141.--Sketch Showing Telescopic Support for Concreting Platform, Burton Tunnel.]

When the floor had been finished the side walls were constructed, using the traveling platform and beginning at the far portal. The wall forms consisted of 46-in. studs, s.p.a.ced 3 ft. apart and carrying 212-in.

lagging. A 66-in. waling outside the studs at about mid-height held the studs to the timbering by lag bolts reaching through the wall to the 1012-in. posts. A strip of plank nailed across wall between stud and post held the form at the top. Wall forms were erected for 100 ft. of wall at a time. These forms required about 45 ft. B. M. lumber per lineal foot of form on one side or 90 ft. B. M. for both sides. Two sets of side wall forms or 200 ft. of wall forming were built, and used over and over again. The concrete was shoveled into the wall forms from the traveling platform, the lagging being placed a board at a time as the work progressed upward and the platform being elevated as required, its final position being at about springing line level. When 100 ft. of side walls had been completed the traveling platform was moved ahead for another 100-ft. section.

[Ill.u.s.tration: Fig. 142.--Sketch Showing Device for Removing Centering Ribs, Burton Tunnel.]

The centers consisted of 612-in. ribs, made up of 312-in. plank. The feet of the ribs rested on folding wedges on 612-in. wall plates, supported by 66-in. posts setting close against the finished wall.

The ends of the ribs were held from closing in by 66-in. walings, one on each side, lag-bolted through the lining to the timbering. The centering required about 315 ft. B. M. of lumber per lineal foot of center. The method of removing the centers was novel. A flat car had erected on it a narrow working platform high enough to reach well up into the arch. Along this platform at the center was erected a sort of "horse," which could be elevated and lowered by jacks. The sketch, Fig.

142, shows the arrangement. At each end and at the middle of the platform two guide posts a a were erected and braced upright. Between these guide posts set plunger posts which were raised and lowered by screw jacks. The three plunger posts carried a longitudinal timber c.

The car was run under the ribs of centering to be removed and the timber c raised by working the jacks until it came to close bearing under the ribs d. The railings and the wedges at the foot of the ribs were then removed, leaving the ribs hanging on the timber c. This timber was then jacked down to clear the lining and the ribs rotated horizontally on the point of suspension as a pivot until their ends swung in over the platform. The car was then moved ahead to where the centers were to be used again; the ribs were rotated back to their normal position across tunnel; the timber c was jacked up, and the wedges and railings placed at the first of the ribs.

The concreting on the roof arch was begun at the portal. Two shifts were worked and 42 ft. of arch were concreted each shift.

~METHOD AND COST OF LINING GUNNISON TUNNEL.~--The costs are for concrete in place in the side walls and the arch of the tunnel, for a length of 440 lin. ft. The quant.i.ty of concrete considered in estimating the cost per cubic yard was 616 cu. yds. The material was mixed and placed in cu. yd. batches, the proportion of the mixtures being 1-2.2-4.4. The final cost includes the labor of excavating and screening gravel and sand, the hauling of the same from the bins at the pit to the storage bins at the main shaft, the care of the chutes in the shaft and the mixing of the concrete in the tunnel at the bottom of the shaft, the transportation of the concrete from the mixer to the traveler, the deposition of the concrete, the setting up and taking down of forms and the cost of the cement. It does not include the construction of the gravel pit chutes that hold the screens, the building of the road from the gravel pit to the storage bins at the shaft, the concrete mixer and its installation, the traveler and its installation, the cost of material and labor in the construction of the concrete forms, the requisite power to run the machinery and other expenses of a similar nature.