Transactions of the American Society of Civil Engineers, vol. LXX, Dec. 1910 | Page 3

The sand and gravel were from the nearby Cow Bay
supply, and screened and washed. None of the gravel was larger than
1/2 in., grading down from that to very coarse sand. The sand was also
run-of-bank, and very well graded.
The caissons, after being placed, were filled with sand and gravel from
the adjoining beach up to about mean high-water mark, and the edges
outside all around were protected from tidal and wave scour by rip-rap
of "one man" stone.
The trusses were constructed on a radius of 34 ft., with 8 by 8-in.
chords, 6 by 6-in. posts, and 1-in. rods. The loading was figured as a
loaded coal cart plus 100 lb. per ft. All lumber was clear yellow pine,
except the floor, which was clear white oak. The pipe rail and all bolts
below the roadway level, and thus subject to frequent wettings by salt
water, were of galvanized iron. The trusses were set 9 ft. 9 in. apart on
centers, giving a clear opening of 8 ft. between the wheel guards under
the hand-rails. The fender piles were creosoted. The float was 18 ft.
long and 12 ft. wide.
A contract was let to the Snare and Triest Company, and work was
commenced early in August, 1909. The first caisson was poured early
in September, and the last about the beginning of October.
The caissons were all cast standing on parallel skids at about mean high
water. It was first intended to construct a small marine railroad and

launch the caissons in that manner, rolling them along the skids to the
head of the marine railway. This plan was abandoned, however, and by
sending in at high tide a powerful derrick scow, many of the caissons
were lifted bodily from their position and set down in the water, towed
to place and sunk in position, while the others, mostly the upper
sections, were lifted to the deck of the scow and placed directly from
there in their final position. There was not much difficulty in getting
them to settle down to a proper bearing. Provision had been made for
jetting, if necessary, but it was not used. In setting Caisson No. 2 a nest
of boulders was encountered, and a diver was employed to clear away
and level up the foundation. The spacing was accomplished by a float
consisting of two 12 by 12-in. timbers, latticed apart, and of just
sufficient length to cover the clear distance between the caissons. The
first caissons being properly set inshore, the float was sent out, guyed
back to the shore, and brought up against the outer edge of the set
caisson. The next caisson was then towed out, set against the floating
spacer, and sunk in position. There was some little trouble in plumbing
the caissons, but, by excavating with an orange-peel bucket close to the
high side and depositing the material against the low side, they were all
readily brought to a sufficiently vertical and level position to be
unnoticed by sighting along the edge from the shore.
The trusses were all constructed in the contractor's yard at Bridgeport,
and were towed across the Sound on a scow. They were set up and
braced temporarily by the derrick boat, and then the floor and deck
were constructed in place.
On December 26th, 1909, a storm of unusual violence--unequaled in
fact for many years--swept over the Sound from the northeast; the
waves beat over the pier and broke loose some floor planks which had
been only tacked in position, but otherwise did no damage, and did not
shift the caissons in the least. The same storm partly destroyed a pier of
substantial construction less than a mile from the one in question.
Unfortunately, the work was let so late in the summer, and the
restrictions as to seasoning the concrete were enforced so rigidly, that
the work of setting the caissons could not be commenced until

November 11th, thus the entire construction was forced into the very
bad weather of the late fall and early winter. As this involved very
rough water and much snow and wind, the work was greatly delayed,
and was not completed until the middle of January. The cost of the
entire dock was about $14,000.
The writer believes that the cost was much less than for masonry piers
by any other method of construction, under the existing circumstances
of wind, tide, and exposure.
It would seem that for many highway bridges of short span, causeways,
and similar structures, the use of similar caissons would prove
economical and permanent, and that they might be used very largely to
the exclusion of cribwork, which, after a decade or so, becomes a
source of constant maintenance charges, besides never presenting an
attractive appearance. Finally, in bridges requiring the