New-York tribune., 1909-10-24
TO FIX LOCK FLOOR
ENGINEERS' PUZZLE
IN CANAL ZONE.
To AUoid Pressure Which
Might Burst 1OO,0OO-Ton
Concrete Mass.

The magnitude OF the problems con-
fronting the engineers who are building
the huge locks at Panama, by far the
largest work OF the kind yet attempted, Is
shown by the nature of recent experiments
which have been carried on at the site of
the lock foundations. The object OF these
experiments is to determine the best way
TO anchor down the floors of the lock, and
prevent 1t from being lifted bodily by the
pressure OF the water.
Now, to the average reader the state
ment that the floor of this huge concrete
structure has to be anchored down to the
mother rock below will come very much as
a surprise, for 1t has a uniform thickness
of thirteen feet. Moreover. since the locks,
when in operation. will be filed with not
less than forty-fve feet of water, one
would imagine that the pressures on the
floor would be altogether downward. Yet.
as matter OF fact provision has to be
made for maximum upward bending
stresses upon the floor which will occur
not when the locks are full, but when
they are unwatered for inspection. This
upward thrust might become so great
that the weight Of the thirteen-foot thick
ness OF concrete. plus it's own strength to
resist bending and breaking stresses, would
NON 1NNA%~N
from below and wrecked.
Now, since the floor of a single lock
would weigh over 10000 tons, It can be
understood that this upward pressure tend
ing to burst in the floor when the lock is
empty must be Of enormous proportions
The question will naturally be asked.
What is the character of force which is
capable OF lifting up and breaking apart
mass OF concrete 1000 feet long. 11O feet
wide and weighing 10000 tons?
The answer Is that water seeping through
the surrounding ground. and possibly fol-
lowing along the sides OF the lock from the
Gatun Lake. and collecting below the
floor Of the lock. might expose the latter,
when the lock was emptied, to an hydraulic
pressure equivalent to that exerted by a
column of water eighty-seven feet In
height that being the vertical distance or
head" from the under side Of the floor of
the lock to the level of the water of the
Gatun Lake. Those OF our readers who are
familiar with the principles Of hydraulics
Will understand that should such seepage
occur and a film of water gather be-
meath the lock when II was empty, and
should there be a clear connection between
this film of water and the body Of water In
| the lake. hydrostatic pressure acting YER
tically against the under side OF the fool
OF the lock would be established
The engineers have guarded against suct
| seepage OF water by sinking q deep curtain
wall through the ground beneath the en-
trance to the locks. extending this wal
down the full length of the locks agains
the outside wall. and sinking it everywher,
to the impervious underlying rock. TIL,
| possibility OF seepago past this wall Is veri
remote; but such is the extraordinary car
which has been taken to render the Pan
anna Canal absolutely secure against disas
ter that IL has been decided to consider tn
| floor of the locks as liable to this seepag
| and this upward pressure and TO take spe
| cial steps for anchoring the floor down t
1 the rock below. Experiments have beel
| made to determine the effect OF anchorinl
steel bars In the rock underlying the floor
for the purpose OF ascertaining to what ex
tent they could be trusted to hold the foo
down against upward pressure. A numbe
OF old French steel rails were sunk In tn
rock to depths of from five to fifteen feet
and secured therein by concrete. In tn
test, on q rail put down five feet, the roc
began to crack under a pull of $3.50 pound
and finally gave way under pull of 1865
pounds. The second rail, anchored ten fee
deep, resisted all efforts to pull 1t up, tn
apparatus breaking under a pull of 237,7(
pounds.
The board OF engineers having the ir
vestigation in hand found that the max
mum thrust to be resisted above the inter
mediate gate sill is that due to eighty-seve
feet of water. This thrust would occur
case the lock and forebay should be pumpe
dry for examination and a full head shoul
develop under the entire area of the floor
1t has been decided that this can be resist
ed by a floor thirteen feet in thickness: