During the erection of the viaduct at Douarnenez--Department of
Finistêre--over the river Pouldavid, one end of one of the heavy
latticework girders dropped into the river, as shown in the upper
one of the annexed cuts taken from _L'Illustration_. The difficult
problem to be solved was to remove the obstruction in as short a time
as possible, and at the least expense; and the engineers came to the
conclusion that it would be best to raise the fallen end, as the girder
was intact, with the exception of those parts that struck the bottom of
the river, and which could easily be replaced by others.
[Illustration: THE VIADUCT OF DOUARNENEZ.--THE POSITION OF THE FALLEN
GIRDER.]
[Illustration: THE VIADUCT OF DOUARNENEZ.--THE GIRDER RAISED.]
The viaduct has three spans of 190 ft. each, and is 88 ft. above the
surface of the water. While rolling the girders upon the piers, the
pivot of one of the rollers broke, and a projecting length of 183 ft.
of the girder dropped a vertical distance of 72 ft. That part of the
girder that had to be raised was 183 ft. long, and weighed 145 tons,
and the free end had to be moved a distance of 72 ft. in an arc the
radius of which was 183 ft. Suitable scaffoldings were erected on the
piers and below the fallen end of the girder; four strong and heavy
double chains were connected with the lower end of the girder and
passed over a scaffolding erected for this purpose, and the opposite
ends of the chains were connected with a heavy box weighted with rails,
and containing 2,700 cubic ft. of water. The upper end of the fallen
girder was disconnected from the other parts of the structure, and a
heavy steel pivot bar inserted, upon which the girder could turn. The
box was so weighted that the fallen girder was somewhat heavier than
the box, and then windlass chains were connected with the lower end
of the girder, and wound upon windlass drums operated on top of the
scaffolding. The weighted box thus merely acted as a counterbalancing
weight, the raising being accomplished by means of the windlass. On
the 1st of August the lower end of the girder was raised 17 inches,
and remained in this position for twenty-four hours, during which time
examinations were made which proved that the calculations were correct,
and that all the parts worked perfectly. The operation was completed
the next day with perfect success, and was witnessed by a great
multitude, attracted by the novel sight.