The concrete for the sand-walls and lower part of side-walls was handled on tracks and platforms laid on cantilever beams at mid-height of the trestle, as shown by [Fig. 3, Plate LXII]. For the walls above the springing line, the tracks were laid on top of the I-beam ties, and some of the arch concrete, also, was delivered from the mixer at that level and hauled up an incline to the level of the top of the arch. By far the greater part, however, was turned out from mixers set on the completed arch, and was transported on tracks hung in part from the street timbering.
Completion.—Except in the heavily-timbered portions, such as at Fifth Avenue, where the load had to be transferred from posts to the completed masonry section by section, the lining of the tunnels presented no special difficulty. The large number of small forms to be set, and the mutual interference of the concreting and duct-laying operations proved to be the most troublesome features of the work.
The restoration of the streets, public utilities, etc., at the open-cut sections was a slow and tedious operation, but the tunnels themselves were completed in March, 1909, 3 years and 10 months after the inception of the work. The finished tunnels are shown by the photograph, [Fig. 4, Plate LXII], taken at the junction of the twin and three-track types.
FOOTNOTES:
[A] Presented at the meeting of December 1st, 1909.
[B] Of the paper by Mr. Noble.
[C] Of the paper by Mr. Noble.
[D] Of the paper by Mr. Noble.