DETAILS OF WATER-PROOFING One layer of felt with 4" overlap to be nailed to lagging of inch boards, using tin washers on nails over the whole of the intrados of the arch before starting any concrete or placing any of the permanent felt and pitch water-proofing. The water-proofing over the arch can be laid in mats of three thicknesses of felt properly joined together with pitch made as shown diagrammatically at “x”
Each of these mats of three-ply felt will be overlapped half the width of the mat, as shown diagrammatically at “y”

The third method provided for water-proofing the whole of the arch, and was the same as B except for the addition of the water-proofing inside the back lagging. In placing this water-proofing, the felt was cut in strips about 11 ft. long (about 1 ft. longer than the length of a section of arch), and six thicknesses were cemented together with hot pitch. These mats were then laid shingle-fashion, as shown at D, [Fig. 18], up the sides of the arch until a space about 5 ft. wide remained at the crown; shorter mats were then brought out over this, laying them perpendicular to the axis of the tunnel. Care was taken in making all laps, irrespective of the direction in which the arch was built, so that they would lay with the grade, that is, so that the water would tend to flow over the edges of the laps rather than against them.

Most of the wet sections of the tunnel were at the ends, where sand-walls had been built for the purpose of providing a smooth surface against which the water-proofing was to be placed; there were several wet places at isolated points in the tunnels, however, and, in order to avoid building sand-walls at these points, the method shown at E, [Fig. 18], was adopted. This involved a slightly larger excavation, 2 ft. outside of the neat line, up to the height of the top of the bench, where there was not already that much room. The bench-wall was built with a back form on the neat line, the water-proofing was placed as shown, protected by an armor course of brick, and then continued over the arch when this latter was built. The excavation and refilling with rock packing were done at the contractor’s expense, which he was willing to assume rather than build these short sections of sand-wall.

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PLATE XXVII.
TRANS. AM. SOC. CIV. ENGRS.
VOL. LXVIII, No. 1154.
LAVIS ON
PENNSYLVANIA R.R. TUNNELS: BERGEN HILL TUNNELS.

Fig. 1. K 181. P.R.R. Tunnels, N. R. Div. Sect. K. (Bergen Hill Tunnels.) Timbered section near Weehawken Shaft, showing method of placing waterproofing and keying arch. Dec. 8, 08.