Geotechnical News September 2011
41
BOOK REVIEWS
The Story of the Vaiont
By Eduardo Semenza
(1927 – 2002)
Told by the geologist who discovered
the slide
Published in Italian in 2001
English edition published in 2010
On 12 February 2008, while
launching the
,
cited the Vaiont Dam
as one of five
“cautionary tales”, caused by
“the failure of engineers and
geologists (Wikipedia).
The Vaiont concrete arch dam was
constructed in 1960 near Longarone in
northeastern Italy, about 100 km north
of Venice. The dam and reservoir were
to form part of a hydropower project to
provide power to Italy’s’ northern cities
The Vaiont slide occurred in Octo-
ber 1963 during the third filling of the
Vaiont reservoir. The axis of the slide
mass was less than 1 km upstream of
the 300 m high concrete arch dam. The
water displaced by the slide overtopped
the dam, which caused considerable
damage downstream and the death of
almost 2000 persons. The maximum
height of the wave was about 210 m,
above the top of the concrete arch dam.
Initial engineering studies for the
Vaiont dam started in 1926 under the
direction of Carlo Semenza (father of
the author) and continued up to 1940.
World War II intervened but studies
recommenced in 1948 and excavations
for the foundation of the concrete arch
dam started in 1957. During these pe-
riods site investigations and studies
concentrated on the permeability and
stability of the abutments for the dam.
Studies of slope stability within the res-
ervoir were not made. Up to that time,
it was not general practice to request
geological studies for projects.
In March 1959 the Pontesi landslide
occurred near Fagare, about 80 km
south of Vaiont dam site. This prompt-
ed the need to verify the possible risks
of landslides in the Vaiont reservoir.
Edoardo Semenza, a recent geology
graduate was commissioned in July
1959 to make the study. By the end
of August 1959 he verbally commu-
nicated his findings concerning slope
stability to the project managers. He
notes that there are sites of various pa-
leoslides, only one of which is poten-
tially dangerous – the “Colle Isolato”
on the right side of the valley. Edoardo
Semenza hypothesizes that new move-
ments of the slide mass could be pro-
duced by filling the reservoir. The story
of Vaiont begins.
Alfred J Hendron and Franklin D
Patton in their preface to the English
version note: “In some ways the story
can be compared to a Greek tragedy.
The project engineer, Carlo Semenza,
was told at various times by one or
more of his experienced consultants
(Dal Piaz, Caloi, Penta and Muller) and
others that a it was unlikely: 1), there
was significant previous landslide, 2),
the moving rock could be stabilized by
drainage, and 3) further movements of
the slide would be fatal to the project.
On the other hand his son, Edoardo, a
recent geology graduate, was telling
him: 1), there was a very large pre-
existing slide just upstream from the
dam, 2) the slide had previously moved
across the valley, 3) the slide was rest-
ing on weak materials, and 4) the old
slide could be reactivated by rising the
reservoir. As we now know Edoardo
was correct. We think that these con-
flicting technical opinions provided the
real drama prior to the slide, not the
contrived plots of the reporters and au-
thors of the play and movie”.
