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.

View of the dam site from downstream of the right bank	Wedge shaped planes of bedrock in the left bank.Fallen large concrete blocks are seen
Members investigating on the crest of remained dam on right bank(1)	Members investigating on the crest of remained dam on right bank(2)
Outcrops of gneiss in the downstream of the dam site. Hard rocks, but many complicated joints or foliation are seen	Investigation team members of IAEG Japan National Group
Large wall outcrops of calcareous sedimentary rocks, near to Nice. Big eroded caves are seen

 

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 about 25×106m3.

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.

View of Vaiont valley and dam from Longarone. 1190 people were killed by the incident	Extremely steep slope of Vaiont canyon, view from dam crest
Over view of failure plane of the landslide on the slope and movement mass (This photo is presented by Dr. Nakasuji)
View of the upstream portion of the landslide and movement mass	Landslide mass burying the reservoir. Structure of the sedimentary rocks are observed
Alternation of calcareous silt stone and limestone of Cretaceous to Jurassic formation at the dam site	Investigation team members of IAEG Japan National Group
Over view of mountains in the Dolomites area at Cortina d’Ampezzo