Malpasset Dam in France
After 5 years of the completion in 1954 of construction work in southeast
France, Malpasset Dam was destroyed in Dec. 1959. Over 400 people were
killed.The dam was an arch type concrete dam and was 61m high and 222m
long, 1.5m to 6.8m in breadth.Its bedrock is consisted of Hercynian metamorphic
rocks mainly of gneiss and schist.
The cause of the destruction of this dam was considered the existence of the weak planes in the bedrock on the left bank. At that time, any detailed geological investigation such as core drilling and trench investigation had not been performed.
From this tragic accident, the geological condition of the bedrock and the existence of weak planes such as faults has been recognized to be important in the design stage of dam construction.
The dam site has been well preserved until now and investigations are possible. We, IAEG Japan National Group members visited this dam site on 16 Sep. in 2014, just 55 years after this tragic and important incident for engineering geology in the world.
Vaiont Dam in Italy
Vaiont Dam was constructed in 1960 in the north-east region of Italy, but
it’s reservoir was completely buried by the huge landslide of the slope
of Mt. Toc(1921m) in Oct. 1963. 2125 people were killed by terrible large
water wave that overflowed the dam. The volume of overflow water was estimated
Vaiont dam is a concrete arch dam and is 264.2m high, 191m long and 3.4m to 22.7m in breadth. The height of 264.2m is still the second one in the world. Volume of the reservoir was 168×106m3. The bedrock of the dam site is consisted of calcareous sedimentary rocks of Cretaceous to Jurassic Formation. The landslide occurred on the slope of Mt. Toc that is composed of Cretaceous calcareous sedimentary rocks dipping parallel with the slope direction. Geological investigation had been performed during dam construction mainly in 1959 to 1960 and the existence of the old (about 20 thousands years ago) huge landslide which had buried old Vaiont canyon was reported. Monitoring of landslide had been continued from 1959 after the start of impounding the reservoir, however, the ruinous landslide of huge volume occurred on 9 Oct. in 1963. The sliding mass was estimated to be 2.7×108m3 in volume, 1500m long, 1800m in breadth and the maximum thickness was 250m.
After this terrible and tragic accident, the geological condition and stability of reservoir slope were recognized to be important in design stage of dam construction projects.
Vaiont Dam was completely abandoned, but was not destroyed by the landslide. We can walk on dam crest now and can observe the shiny planes of the sliding failure on the mountain slopes. The huge landslide mass burying the Vaiont valley are seen from downstream and road.
We, IAEG Japan National Group members visited this dam and reservoir area on 20 Sep. in 2014, just 50 years after this tragic and important incident for engineering geology in the world.