After the piles in each pier have been cleaned out they must be cut off
at exactly the same height--sometimes a very difficult task when there
is little room. The oxy-acetylene torch is used for the purpose, the
intensely hot flame cutting off the steel almost like butter.]
[Illustration: A CLUSTER OF PILES, CLEANED OUT, FILLED WITH CONCRETE
AND CUT OFF FLUSH BY MEANS OF THE OXY-ACETYLENE FLAME.]
~PILES ARE NEXT FILLED WITH CONCRETE~
The hollow shell is next filled with concrete reinforced by means of
long two-inch steel rods, sometimes fifty feet in length. On clusters
of these concrete-filled piles, the weight of the building is supported.
That this method of constructing foundations is indeed rapid, the
story of the work at 145-147 West Twenty-eighth Street, New York City,
proves. Rock was located 38 feet below the curb. The material above
it was clay and water-bearing sand. Structural steel was due in three
weeks, but the completion of the cellar was still ten days off. The
steel pile foundation method offered the only solution of the problem.
Specifications were drawn which called for eighty-five 12-inch steel
piles, driven to rock, blown clean by compressed air, and filled with
concrete, reinforced with 2-inch rods. Despite various obstructions on
the ground (shoring of neighboring buildings and the like) the driving
was started on June 30th. The excavator was still taking out his runway
while the rear half of the lot was completely driven. After he had left
the ground a compressor was set up, and the first pipe was blown on
July 7th. Three days later all driving and cleaning had been completed.
During the following two days all the piles were filled and capped. In
a word, the entire foundation had been completed three days before the
expected arrival of the steel.
[Illustration: CONCRETE PILES WHICH HAVE BEEN SUNK TO ROCK BOTTOM AND
IN WHICH TWO-INCH STEEL RODS HAVE BEEN INSERTED TO ACT AS REINFORCEMENT
FOR THE CONCRETE WHICH WILL EVENTUALLY BE POURED IN.]
Such rapid work is not unusual with the steel foundation method.
On another contract, work was completed not in the three months
stipulated, but in exactly one month and a half, during which brief
time all the excavation had been done, including sheeting, shoring,
pile-driving, the mounting of concrete girders to carry the wall and
capping of the piles ready to receive the grillage.
[Illustration: THE STEEL PILE IS EASILY FORCED EVEN THROUGH THE SOFT
UPPER LAYERS OF BED ROCK. SOMETIMES VERY LARGE PIECES ARE BLOWN UP INTO
THE AIR BY THE BLAST OF COMPRESSED AIR.]
Sometimes difficulties are encountered which would prove all but
insurmountable and certainly hopelessly expensive with other methods.
Thus in carrying out the one contract, water was found 12 feet from the
curb. Two running streams had intersected at that point. The piles were
simply sunk through the stream to rock bottom without any difficulty.
The excessive cost of open-pit work has sometimes made it impossible
to build twelve or fourteen-story buildings in many sections of the
city of New York. The steel pile has, however, made steel building
construction profitable.
The carrying capacity of a steel pile is enormous. On a single 12-inch
steel pile one hundred tons can be safely maintained. Piers containing
sixteen piles have been used, and loadings up to 1300 tons are not
unusual.
Naturally the question arises: Do the steel piles deteriorate in
time? The question has been answered over and over again by the piles
themselves. After a service of fifteen years the steel foundation
piles were removed from the site of a building which now stands at the
northwest corner of Wall and Nassau streets, in New York City. They
showed practically no deterioration. The oxidation on the outside was
almost negligible.
[Illustration: BLOWING OUT MUD AND ROCK WITH COMPRESSED AIR
CLEANING OUT A HOLLOW STEEL PILE BY MEANS OF COMPRESSED AIR A GEYSER OF
MUD ALWAYS APPEARS.]
[Illustration: A DRIVEWAY ALONG THE TOP OF THE OLIVE BRIDGE DAM.]