Transactions of the American Society of Civil Engineers, vol. LXVIII, Sept. 1910 | Page 2

Avenue a
cut which came to the grade of 32d Street about midway between Ninth
and Tenth Avenues, and a trestle was constructed from this point over
Tenth Avenue and thence to the disposal pier at the foot of West 32d
Street.
On May 11th, 1906, the work of excavation was commenced on the
east side of Ninth Avenue, and on July 9th, 1906, on the south side of
31st Street, between Ninth and Tenth Avenues. From the beginning, the
excavation was carried on by day and night shifts, except on Sundays
and holidays, until January, 1909, except that during the period from
November, 1907, to October, 1908, the night shift was discontinued.
_Geology._--The rock encountered may be classed as "gneiss"; its
character varied from granite to mica schist. It was made up of quartz,
feldspar, and mica, and there were also some isolated specimens of
pyrites, hornblend, tourmaline, and serpentine. On the south side of the
work, just west of Ninth Avenue, there were excellent examples of
"contortions" of veins of quartz in the darker rock. On the east side of
Ninth Avenue, near the north end of the work, glacial marks were
found on the rock surface. The general direction of the stratification
was north 5° west, and the general incline about 60° with the horizontal.
As a rule, the rock broke sharply along the line of stratification. On the
south side it broke better than on the north side, where it was usually
softer and more likely to slide; and this, together with the fact that in
winter it was subject to alternate freezing and thawing and in summer
to the direct rays of the sun, made it rather difficult to get a good
foundation for the retaining walls.
WORK IN AND UNDER NINTH AVENUE.
_General Description._--The work involved the excavation of about

375 ft. of the full width of Ninth Avenue to an average depth of about
58 ft., and the construction over this area of a steel viaduct, the deck of
which was about 24 ft. below the surface, for the ultimate support of
the Ninth Avenue structures.
The following estimated quantities appear in the contract: Excavation
of rock, 72,600 cu. yd.; excavation of all materials except rock, 9,300
cu. yd.; concrete (1:3:6) in abutments, etc., 1,680 cu. yd.; timber,
504,000 ft., B.M.; structural steel, 1,320,000 lb., etc.
While this excavation was being done it was necessary to support and
maintain the three-track elevated railway structure of the Interborough
Rapid Transit Company, of which 18 columns, or a length of about 340
ft., were affected, the two-track surface railway structure of the New
York City Railway Company, and various pipes, sewers, and conduits,
and to maintain all surface vehicular and pedestrian traffic. All
structures were left in place with the exception of the pipes, most of
which were temporarily cut out. The 48-in. brick sewer in the center of
Ninth Avenue was broken, and the sewage was pumped across the
excavation through a smaller pipe.
The general method adopted was as follows: The east and west sides of
the avenue were closed, vehicular traffic was turned into the center, and
a trestle for pedestrians was constructed west of the westerly elevated
railway columns. All structures were then supported on transverse
girders, running across the avenue, below the surface, and these rested
on concrete piers on the central rock core. The sides of the avenue were
then excavated to sub-grade, and the permanent steel viaduct was
erected on both sides of the avenue as close as possible to the central
rock core. The weight of all structures was then transferred to the
permanent steel viaduct, erected on the sides of the avenue, by timber
bents under the transverse girders resting on the permanent steel
viaduct, and all weight was thus taken off the central rock core. This
core was then excavated to sub-grade, the permanent viaduct was
completed, and all structures were placed on its deck, using concrete
piers and timber bents.
The design and erection of the permanent steel viaduct and the

permanent foundations on its deck were done under another contract,
apart from the North River Division work, and are not described in this
paper.
_Elevated Railway Structure of the Interborough Rapid Transit
Company._--The Ninth Avenue Elevated Railway was built between
1877 and 1880 as a two-track structure, the design being such as to
permit a third or central track to be added later, and this was built in
1894. It is supported on columns under the outside tracks, about 43 ft.
from center to center longitudinally and 22 ft. 3 in. from center to
center transversely, the central track being carried by transverse girders
between the columns.
The columns carrying the structure are of fan top design, with the
points of bearing near the extremities