Malpasset dAm Failure

1
Malpasset dAm Failure

• December 2, 1959, France

Manh Tung Nguyen, James Neville

• Introduction to The Dam
• Geology Profile
• The Failure
• Engineering Solution

2
Malpasset Dam

• Southeast of France in the Var Region, the dam
  was founded on the River Reyran, 7km NE of Frejus

• Designed by Andre Coyne, the God of arch dam
  designs

• A double curvature arch dam with a height of 60 m
  and a crest length of 223 m

• Began construction in April 1952 and finished in
  1954

3
Site Geology

• The dam is situated in the crystalline Tanneron
  Massif.

• Mainly metamorphic gneissic rock
• Massive Augen Gneiss
• Schistose Gneiss

Gneiss

• General trend of foliation lies between 30o and
  50o to SW

Schist

• Two set of faults form a wedge failure at the
  left abutment.

• Geological foliation at left abutment almost
  parallel to the arch thrust of the dam.

Mined Coal Deposits
4
The Failure

• Exceptional rainfall levels, Autumn 1959
• 9.30pm 2nd Dec, 1959. Sudden failure without
  warning

• 50,000,000 m3 of water released
• Water wall of 40m height, moving at 20m/s

• Causes flooding in Frejus , 7km downstream
• Over 400 people was killed instantly and rising
  to 700.

5
Causes of Failure

• Concentrated arch thrust at left abutment

• Deformation and crack forming at the bottom of
  the left abutment.

• Seepage under the dam, hence uplift force

• Separation of right abutment from foundation rock

• Evidence of uplift below right abutment

15m
6
Engineering Solutions

• Engineering solutions at the time were, TO DO
  NOTHING!
• Nothing was done which has caused the uplifting
  of the a dam section due to the hydrostatic
  pressure.
• Only FOS designed for the dam was mass shear and
  relatively weak rock has a large margin.
• A vibratory wire extensometer was embedded in the
  concrete, this was deemed efficient.
• This failure radicalized dam design bringing
  design attention to
• - Mechanical effects of water seeping into the
  foundation.
• - Normal practice to make a methodical
  inventory of the rock structure in depth.

7
Overcoming Seepage

• Little work can to increase the friction of the
  fault line in the in rock due to the hydrostatic
  pressure, a more applicable dam design would have
  been more appropriate for the insitu case.
• However another method would be to reduce the
  Hydrostatic pressure to prevent the uplifting of
  the wedge of rock.
• Method 1)
• Grout the foundation rock of concrete gravity
  dams.
• Grouting will reduce seepage through the rocks
  and disclose
• the presence of any unsuspected weaknesses in
  the foundations

8
Overcoming Seepage

• Most Common Design- Grout Curtain.
• Single line of grout holes located near the
  upstream face of the dam at 5 foot centre's.
• A corresponding line of drainage is drilled a few
  feet downstream from the grout curtain.
• Essential to control the grouting pressures so
  that splitting and lifting of rock will occur.