Fig. 136.—General Plan of Centers for Roof Arch, Hodges' Pass 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 spaced 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 constituted only the top third of the arch.
Fig. 137.—Details of Centers for Roof Arch, Hodges' Pass 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 2½-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 2½ 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.