1. Malpasset Dam Disaster
By Martin Coulthurst
Robert Williams

2. Malpasset Dam
Constructed on the Reyran River approximately 7km north of Fréjus, Southern France
Built to supply water for irrigation and storage of drinking water
Construction was completed in 1954
The Malpasset Dam was a doubly curved equal angled arched dam
The dam was approximately 60m high above the river bed, 102m above sea level

3. Malpasset Dam
Diagrams showing the Malpasset Dam before failure

4. Site Geology Underlying the dam is the metamorphic rock Gneiss
Gneiss is an impermeable rock, thought to be watertight, with fine fissuration.
The types of Gneiss present are Massive Augen Gneiss and Schistose Gneiss
Downstream plunging strata was present, 30°-50° SW.

5. Site Geology Gneiss Schist Malpasset Dam Mined Coal Deposits Dolerite
Rhyolite

6. Site Geology
Before construction, fissuration of the Gneiss in the foundation area was identified.
Extensive grouting of the foundation area was highly recommended by geologists, but consultants and the commission then thought it unnecessary

7. Failure of the Dam
The dam failure occurred at 9.10 p.m. on December 2nd, 1959.
The breach created a water flood wall 40 meters high and moving at 70 km/h, destroying two small villages - Malpasset and Bozon, in the process
Over 400 people died in this disaster

8. Failure of the Dam Failure occurred in two phases:
Slow progressive deformations of the rock foundations and straining of the dam shell
Instantaneous failure of the dam and foundations
Causes => Combination of:
Pressure build-up under the dam
Pore pressures and state of rock on the left bank
Tectonic fault on downstream side of dam

9. Malpasset Dam after Failure

10. Malpasset Dam after Failure

11. Alternative Solutions
Fissuration of the rock should have been investigated
More thorough geological study of the region needed before construction
The original design of a gravity dam could have been implemented
Installation of curtain grouting and drainage

12. Solution Solution Curtain Grouting and Drainage
A system of boreholes filled with grout at the abutments.
Will stop the infill of water into the gneiss fissures
Drainage channels drilled further downstream.
Will stop the build up of any water pressure

13. Should span whole length of the dam
Grout curtain should be perpendicular to the angle of fissuration
Drainage curtain should be downstream of the grout curtain

14. Conclusion
As a result of the Malpasset Dam failure, lessons have been learnt for future arch dam construction
The need for testing the dam foundations for different traits was recognised
The need for safety monitoring of arch dams was also recognised
The design itself was not to blame for the failure