How Hollow Steel Piles, Compressed and Concrete Are Employed to Make a
Foundation
Rapidity of building construction is of primary importance in every
city of metropolitan size. When real estate is sold at the rate of
several hundred dollars a square foot it is self-evident that time is
indeed money. The delay of a few days in completing a structure may
deprive the owner of the chance of earning thousands in rental money.
Because of the excessive depth of an open caisson, the completion of
a foundation may be delayed for months. Hence the building may not
be completed until the renting period has passed and the owner must
wait an entire year before he can expect any financial return on his
investment.
Because rapidity is so essential in city building construction the
method of first sinking an open pit to rock in providing a foundation
has been displaced to a large extent by a system in which heavy hollow
steel piles are employed in clusters to support a building. The hollow
piles are driven through quicksand to rock, cleaned out and ultimately
filled with concrete.
~PILES ARE DRIVEN DOWN TO SOLID ROCK~
In this method of constructing foundations, which is illustrated,
hollow steel piles are driven in the well-known manner down to solid
rock. The steel pile sections vary in length from 20 feet to 22 feet,
and in diameter from 12 inches to 24 inches. If the ground is to be
penetrated to a depth greater than 22 feet, the sections of piling
are connected by means of a sleeve in such manner that a watertight
joint is formed. Under a pressure of 150 pounds to the square inch a
jet of compressed air is then employed to blow out the earth and water
contained within the shell. A spouting geyser of mud rising sometimes
to a height of 150 feet, and occasional large pieces of rock blown
up from a depth of 40 feet below the ground, bear testimony to the
terrific force of the air blast.
[Illustration: THE PILES ARE ABOUT TWENTY-TWO FEET LONG. IF GREAT
DEPTHS ARE TO BE REACHED SECTIONS OF PILING ARE JOINED TOGETHER BY
MEANS OF A SLEEVE.]
When the shell has been completely cleaned out by means of the blast
of compressed air, the exposed rock can be examined by lowering an
electric light. Steel sounding rods are employed to test the hardness
of the rock and to detect the difference between soft and hard bed
rock. After the piles in each pier have been cleaned out, they must
be cut off at absolutely 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 at the exact elevation desired.
[Illustration: CUTTING STEEL PILES WITH A HOT FLAME