The Portland daily press., 1893-10-19
THE cAlssoN IN PLACE.
Completion of a Notable Work on the New
Pier of Cape Elizabeth Bridge-A Forty
Ton Tube Planted in the Water.

A notable piece of work was completed
at the Cape Elizabeth bridge yesterday
afternoon. In building the new iron
draw demanded by the United States
government, the county commissioners
found it necessary to make some radical
changes in the old method of construc-
ton. The old wooden draw was upheld
by pier of piling. AS this pier had to
reach forty-five feet above the bottom OF
the harbor at this point piles about
sixty feet in length had been used
When it.came to putting in the stone pier
required for the new iron draw, the COM
missioners found that they had on their
hands an engineering problem quite new
in this region. To build. a stone pier
forty-five feet high IN the strong and
deep current of the harbor at this point
was impossible without some special en-
cheering device, such as the caisson. 1t
was determined to use the device. First,
it was necessary to obtain a sure founda-
ton for the new pier, and this could be
obtained only by driving piles into the
harbor mud. The location of the pier
having been determined, piles were
driven as thickly as possible in a circu
lar space about twenty-five feet in diane
ter. Then diver went down below the
surface and sawed them off even with the
bottom of the harbor. This was slow
and difficult task, but when once done
it left firm and even base. This base
obtained, the next thing was to build
the pier on top Of it. To do this it was
necessary to keep the water away, and it
is for this that the caisson was devised.
The county commissioners contracted
with the Portland company to furnish it
for $500, and it has been put in under
the superintendent of ex-City Civil
Engineer Goodwin. The caisson is a
great cylindrical steel funnel twenty-five
feet in diameter, fifty feet high and
weighing forty tons. This funnel is put
down into the water, it's lower end going
around the base of piles just as the ferule
goes on cane or the biscuit cutter over
the biscuit. The caisson is there forced
down into the mud around the pile for
a distance of about five feet-enough to
make it's connection with the piling firm.
It would have been impracticable to
have put this great caisson down all at
once. So it was built in sections each
six feet long. When one section had
been rivetted on. the caisson would be
lowered and another added. The Port
land company had devices for holding
and lowering it, which enabled it to- be
handled readily. The work was success
fully completed yesterday, and the great
caisson was in place. The next step will
be to put in the bottom Of it, and on top
of the piling base ten feet of concrete
AS the caisson is full of water this con-
crete must be of kind to harden under
water. After it has hardened the caisson
will be water tight, and will then be
pumped out. This will leave the place
for building up the stone and cement
pier, which will be constructed to the
top of the caisson. Then nthe steel shell
will be peeled away as low as low water
line, leaving the stonework bare. Below
low water line the steel will be left to
hold the stone work solidly in place.