Malpasset Dam Disaster By Martin Coulthurst Robert Williams

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

Malpasset Dam Diagrams showing the Malpasset Dam before failure

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.

Site Geology Gneiss Schist Malpasset Dam Mined Coal Deposits Dolerite Rhyolite

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

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

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

Malpasset Dam after Failure

Malpasset Dam after Failure

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

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

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

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