The railroad from Montlucon to Eygurande, which is being constructed by
the state engineers, crosses the valley of the Tardes in the environs of
Evaux (Creuse).
At the spot selected for the establishment of the viaduct the gauge is
deep and steep. The line passes at 300 feet above the river, and the total
length of the metallic superstructure had to be 822 feet. To support this
there was built upon the right bank a pier 158 feet in height, and, upon
the left, another one of 196 feet. The superstructure had been completed,
and a portion of it had already been swung into position, when a violent,
gale occurred and blew it to the bottom of the gorge. At the time of the
accident the superstructure projected 174 feet beyond the pier on the
right bank, and had to advance but 121 feet to reach the 33 foot
scaffolding that had been established upon the other pier.
It blows often and violently in this region. For example, a gale on the
20th of February, 1879, caused great damage, and, among other things, blew
the rear cars of a hay train from the top of the Louvoux viaduct to the
Bouble.
The superstructure of the Tardes viaduct had already withstood the tempest
of the 23d and the 24th of January, 1884, and neither any alteration in
its direction nor any change in the parts that held it upon the pile could
be perceived. But on the night of January 26-27 the storm doubled in
violence, and the work was precipitated into the ravine. No one was
witness of the fall, and the noise was perceived only by the occupants of
the mill located below the viaduct.
The workmen of the enterprise, who lived about 325 feet above this mill
and about 650 feet from the south abutment, heard nothing of it, the wind
having carried the noise in an opposite direction. It was not until
morning that they learned of the destruction of their work and the extent
of the disaster.
One hundred and sixty-nine feet of the superstructure, weighing 450 tons,
had been precipitated from a height of nearly 200 feet and been broken up
on the rock at 45 feet from the axis of the pier. The breakage had
occurred upon the abutment, and the part 195 feet in length that remained
in position in the cutting was strongly wedged between walls of rock,
which had kept this portion in place and prevented its following the other
into the ravine.
Upon the pier there remained a few broken pieces and a portion of the
apparatus used in swinging the superstructure into place.
Below, in the debris of the superstructure, the up-stream girder lay upon
the down-stream one. The annexed engraving shows the state of things after
the disaster.
Several opinions have been expressed in regard to the cause of the fall.
According to one of these, the superstructure was suddenly wrenched from
its bearings upon the pier, and was horizontally displaced by an impulse
such that, when it touched the masonry, its up-stream girder struck the
center of the pier, upon which it divided, while the down-stream one was
already in space. The fall would have afterward continued without the
superstructure meeting the face of the pier.
[Illustration: DESTRUCTION OF THE TARDES VIADUCT.]
Upon taking as a basis the horizontal displacement of the superstructure,
which was 45 meters to the right of the pier, and upon combining the
horizontal stress that produced it with that of the loads, the stress
exerted upon the body may he deduced. But this hypothesis seems to us
scarcely tenable, especially by reason of the great stress that it would
have taken to lift the superstructure. On another hand, it was possible
for the latter to slide over one edge of the pier, and this explains the
horizontal distance of 45 feet by which its center of gravity was
displaced. It is probable, moreover, that the superstructure, before
going over, moved laterally upon its temporary supports.
The girders were, in fact, resting upon rollers, and the roller apparatus
themselves were renting upon wedges, and there was no anchorage to prevent
a transverse sliding.
Under the prolonged thrust of a very high wind, the superstructure, by
reason of its considerable projection, must have begun to swing like a
pendulum. These oscillations acquired sufficient amplitude to cause the
superstructure to gradually move upon its rollers until the latter no
longer bore beneath the webs. The flanges therefore finally bent upward
where they rested upon the rollers, through the action of the weight which
they had to support, and the entire superstructure slid off into space.
An examination of the bent pieces seems to give great value to this
hypothesis.--_Le Genie Civil_.
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