The Teton Dam in Idaho failed in 1976, 11 years after construction began. The failure resulted in 11 deaths and $400 million in property damage. The dam was built on volcanic rock formations with high permeability and instability. The soil used for the dam core was aeolian silt, or loess soil, which has lower plasticity and cohesion than ideal materials. Hydraulic fracturing during construction and a piping failure along the core led to vertical fractures in the soil, weakening the structure until it ultimately collapsed.

1. An Analysis of Teton Dam
Failure, USA

2. Teton Dam Facts
• constructed from February 1972 to June 1976.
• Bureau of Reclamation designed Teton Dam.
• Construction contract awarded to Morrison-Knudsen Company, Inc.
• located in southeastern Idaho, 12 miles northeast of Rexburg.

4. Dam Design and
Construction

6. Teton Dam Failure
• Failed on June 5th , 1976.
• 11 deaths resulted from the disaster.
• $400 million in property damage.
• The towns of Sugar City and Rexburg were struck the hardest.

9. Geology of Teton Dam’s Site
• Volcanic Plateau known as Rexburg Bench.
• Composed of Basalt and Rhyolite Tuff.
 High permeability
• Consisted of highly fissured and unstable rock.
• Seismically active area.
Basalt Rock
(https://flexiblelearning.a
uckland.ac.nz/rocks_min
erals/rocks/basalt.html)
Rhyolite Tuff
(http://markstein
metz.photoshelte
r.com/image/I000
0.T6UG4upcSw)

10. Analysis of Soil Material of Dam Core
• Required properties for large dam core
High Plasticity Index
Impermeability
Plasticity Properties
Relatively Deformable
Suitable Material – Clay Mineral

11. Soil Material used in Teton Dam
• Aeolian Silt, also called Idaho Loess Soil.
Classically Silty Soil
Lower plasticity index (PI) value
Slightly cohesive or even cohesionless
Sensitive to water content
Loess Soil
(https://commons.wikimedia.org/wiki/
File:LoessVicksburg.jpg)
Fig. The R/size diagram; the relation of bond/weight ratio to particle size for
ideal engineering soils (Smalley and Dijkstra, 1991).

12. Hydraulic Fracturing
• Finite element analyses
• Distribution of stress at the embankment
• Used to construct stress-strain parameter
• Water pressure is higher than soil’s tensile strength and total
transverse normal stress
• Pressure applied with wet condition, volume at key trench fill
decreases. Wetted fill reduce the stress of the soil.

13. Piping Failure
• Water leaking under the grout
cap due to erosion
• Piping failure along the key
trench fill

14. Field hydro-fracturing test
• Dye water is used to test the flows of fracture
• Vertical fracture is shown
• Soil at the key trenches and soil within the embankments
• Decrease in stress due to arching in the soil

15. Cubical soil sample test
• Borehole
• Water pressure increases, flow rate in the hole increases
• Fracturing pressure leads to rapid increase of flow rate, with or
without water pressure increase
• Fracturing happens along vertical planes
• Backfill compact
• Water penetrated to loess soil zone when water pressure is
applied.
• Soil wedge apart

16. Conclusion
• Stability of dams to protect Lives and property.
• Assessment of risks and liabilities with environmental considerations.
• Proper civil and geotechnical engineering design.

17. Thank you