The approach cut at the western end is 300 ft. long, the alignment being
a 2° curve, as shown in Fig. 19. The bench-walls and conduit lines built
throughout the length of the tunnels are extended through the approach
cut, the top of the former gradually sloping from the portal to the
mouth of the cut, where they are just level with the top of the rail,
the conduits also being depressed to the same relative position with the
tops of the benches.
[Illustration: Fig. 19. [Full Page]
BERGEN HILLS TUNNELS.
Hackensack Portal and Approach.
SECTIONS AND ELEVATIONS.
PLAN OF APPROACH.
PROFILE THROUGH APPROACH.
SECTION SHOWING METHOD OF MAKING JOINT BETWEEN COPING AND WALL.
PLAN SHOWING METHOD OF MAKING JOINT BETWEEN ADJOINING SECTIONS.
SECTION OF BENCH AND RETAINING WALLS AND HALF ELEVATION OF PORTAL.]
The top of the rock at the mouth of the cut, Station 327, was from 4 to
6 ft. below the top of the rail, and gradually rose through the approach
until at the portal it was about 6 or 8 ft. above the roof of the
tunnel. The rock was covered with hardpan. A profile of this part of the
work is shown on Fig. 19. The rock throughout the approach was
water-bearing to a considerable extent, and a face-wall was built at the
sides with free drainage, through rock packing and vitrified and
cast-iron drains behind it, to keep this water from flowing over the
tops of the bench-walls, and also to keep the lines of conduits dry.
The retaining walls were built in 25-ft. sections, the joints
corresponding to those in the benches, being at the even stations, +08,
+33, +58, and +83. =V=-shaped joints were made down the face, and the
ends of the sections were made as shown by Fig. 19. The back part of the
joint was mopped with hot pitch before the next section was built, so
that there was practically no bond between any two adjoining sections.
The concrete in these walls was placed late in the season, and the
expansion cracks, which were entirely confined to the =V=-shaped joints,
were quite small even in the coldest weather of the following winter,
nor were there any indications during the past summer of any stresses
due to expansion. The coping and drain at the top of the wall were built
together, but separate from the rest of the wall, the joint being made
as shown in the sketch on Fig. 19. Thus far, there has seemed to be no
seepage through either the vertical or horizontal joints.
The portal is built of granite, a half elevation being shown on Fig. 19,
the stone being supplied by the Millstone Granite Company, Millstone
Point, Conn. Fig. 3, Plate XXVII, shows the portal and the cut-and-cover
section after the arches were completed but not covered.
The forms for the concrete in the approach were made of ordinary dressed
lumber, and the surface was rubbed twice after the forms were removed,
which was as soon as possible after the concrete had set. The surface
was first very lightly rubbed with a piece of soft, light-colored,
sandstone to remove any irregularities, being wetted slightly if
necessary while being rubbed. After the concrete had become fairly hard
and dry, it was rubbed a second time and a uniform texture and color
obtained. The completion of this work was delayed until the second week
in January, and considerable difficulty was encountered in obtaining a
good finish of that part which was built after cold weather set in, when
it was necessary to protect it from frost. Unless extreme care was taken
to prevent freezing after the rubbing, the entire surface was likely to
scale off, although no cement or other material was added to it after
the removal of the forms. A general view of the completed approach is
shown by Fig. 4, Plate XXVII.