essure stronger than
anticipated. Quicksands ran through the sheet piling as through a
sieve. The walls of the excavation began to slough and cave. The gas
pressure became alarming when the weight of earth and water was taken
off; sand boils began to develop at the bottom; the floor of the cut
was blowing up.

The fate of the Industrial Canal hung in the scale.

To meet the situation the engineers pumped a great volume of water into
the excavation. Its weight counterbalanced the earth pressure of the
side and the gas pressure of the bottom.

Then another ring of sheet piling was driven inside the other two. This
one was of steel, and the walls were braced apart by wooden beams ten
inches square and fifteen feet apart in both directions. This is one of
the largest cofferdams of steel ever driven. As an added precaution
against the danger of a blowout by the third stratum of quicksand,
which had a static head of 75 feet, 130 ten-inch artesian wells were
driven inside the steel cofferdam. Fifty-six similar wells were driven
between the steel and the wooden cofferdams to dry out the second
stratum of quicksand, as much as possible, and lessen its flowing
character.

In November, 1919, the work of unwatering the lock site again began.
Only one foot every other day was taken off. Engineers watched every
timber. It was not until January 4, 1920, that the unwatering was
complete. The plan had worked. Only in one place had there been any
movement--a section of the wooden sheet piling about 300 feet long
bulged forward a maximum distance of three inches, when the bracing
caught and stopped it.

Then began the work of driving the 24,000 piles on which the lock was
to be floated. They are 60 feet long and their tips are 100 feet below
the surface of the ground.

In March, 1920, the work of laying the concrete began. The work was
done in 15-foot sections, for only a few of the braces could be moved
at one time. When it was finished in April, 1921, the lock was in one
piece, a solid mass of steel and stone, 1,020 feet long, 150 feet wide,
and 68 feet high, weighing, with its gates and machinery, 225,000 tons,
and filled with water, 350,000 tons.

The concrete floor of the lock is 9 to 12 feet thick, the walls 13 feet
wide at the bottom, decreasing to a two foot width at the top. Six
thousand tons of reinforcing steel were used in the construction, and
125,000 barrels of cement. There are 90,000 cubic yards of concrete in
th