Paper: OSP-17 V.S. Pillai & B. Muhunthan THE FAILURE OF TETON DAM – A NEW THEORY BASED ON "STATE BASED SOIL MECHANICS"

OUTLINE Background Aspects Post failure investigations Focus of our investigations State dependent behavior of Teton core – Silt Analysis Conclusions

Background Aspects

Location of Teton Dam 64 km Northeast of Idaho falls 64 km Northeast of Idaho falls Across Teton river Across Teton river Near Wyoming- Idaho border in the Teton mountain range Near Wyoming- Idaho border in the Teton mountain range

Design cross section of the dam at river valley section ( after IP, 1976)

A typical cross section of the dam at the right abutment (after IP, 1976) El.5200 El.5300

Teton Dam-Zoned earth fill dam-405 ft. high Teton Dam-Zoned earth fill dam-405 ft. high Part of a multi-purpose Irrigation and Power project ( , USBR) Part of a multi-purpose Irrigation and Power project ( , USBR) Construction of the dam completed and first filling started in November 1975 Construction of the dam completed and first filling started in November 1975 Dam failed suddenly on June 5, 1976 when the reservoir level rose to El ft. Dam failed suddenly on June 5, 1976 when the reservoir level rose to El ft.

Dam Failure – First Leakage Around 7:00 am on June 5, 1976 dam personnel discovered a leak about 30 m from the top of the dam Around 7:00 am on June 5, 1976 dam personnel discovered a leak about 30 m from the top of the dam Leak

The Dam Breaks (11:59 AM)

Senator Frank Church (Idaho) The anguished Senator Frank Church, flying over the disaster area, stated that: The anguished Senator Frank Church, flying over the disaster area, stated that: “This dam was built according to the latest state-of- the-art” “Nothing like this should have happened....Nothing like this could have happened, except for a fatal flaw either in the siting of the dam or in the design”

Post Failure Investigations Independent Panel (IP) Independent Panel (IP) Interior Review Group (IRG) Interior Review Group (IRG) Documented well in literatureDocumented well in literature General conclusions: Seepage piping and internal erosion Hydraulic fracture Wet seams Differential settlement and cracking Settlement in bedrock Seepage through rock openings

Focus of Our Investigations Low plasticity of the impervious core Low plasticity of the impervious core Low placement liquidity index (LI) of the core Low placement liquidity index (LI) of the core High compaction/Constrained modulus of the core High compaction/Constrained modulus of the core Crack potential of the core under low confining stresses/upper portion of the dam Crack potential of the core under low confining stresses/upper portion of the dam

25 Some properties of the impervious core – Zone I Teton core

STATE BASED SOIL MECHANICS State of soil is defined in a 3-D space (p, q, e or v) State of soil is defined in a 3-D space (p, q, e or v) p‘-mean effective stress - (  ’ 1 +2  ’ 3 )/3 q - shear stress - (  1 -  3 ) e - void ratio or v=(1+e) - specific volume Limits to stable states of soil behavior – SBS (p,q,e) 2-D representation of the normalized state boundary surface Soils state in liquidity index-confining stress space

CSL FL Soil states in normalized stress-space

Possible soil states in v-lnp’ space X1 X2 X3 Dense (Hvorslev regime) Soft Cam-clay regime

LI-lnp ' diagram & q/p ' -Equivalent liquidity diagram (after Schofield, 1980) A B LI 5 =LI+0.5log(p‘/5)

Family of critical state lines (Modified after Schofield and Wroth, 1968)

Longitudinal section of the dam –(Schematic) (Modified after IP, 1976) A1A1 A4A4 Typical element AnAn

p' - – Unstable (Fracture) CSL NCL Stable dense Stable soft (Yield) Crack line A1A1 A2A2 A3A3 A4A4 p' q A1A1 A2A2 A3A3 A4A4 Cam-clay yield surface Crack Surface CSL q/p'~2 q/p'~0.7 q/p' = 3 Stress path during construction - Conceptual q/p'= 2 q/p' = 3 q/p' = 0 q/p' = M v

Soil elements at different depths Cross section of dam near right abutment El El. 5300

lnp' v - – Unstable (Fracture) CSL NCL Stable dense Stable soft (Yield) Crack line A1A1 A2A2 A3A3 A4A4 p' q A1A1 A2A2 A3A3 A4A4 Cam-clay yield surface Crack Surface CSL q/p'~2 q/p'~0.7 q/p' = 3 Stress path of a soil element during construction

Soil States in 3-D Space

Material parameters Critical State ParameterValue   1.95  G (psf) p' c (psf)12000

FINITE ELEMENT ANALYSIS ABAQUS – FE software developed by Hibbitt, Karlsson and Sorenson Inc. Critical state plastic material model and Porous elastic material model *MODEL CHANGE option was used to simulate the construction of dam SURFACE was used to draw the contours of q/p‘ ratio as well as LI 5 variation

FE Analysis technique

Contours of q/p‘ ratio El.5301 Reservoir level

3 Details of q/p ratio at the right abutment ( for q/p>3, Zone 1 cracked) CRACKED

Contours of equivalent liquidity LI 5 Prone for cracking

Conclusions A transverse (s) or large opening(s) had developed in the core (Zone-1) to a maximum depth of 32 feet below the crest at the right abutment near Sta A transverse crack(s) or large opening(s) had developed in the core (Zone-1) to a maximum depth of 32 feet below the crest at the right abutment near Sta When the reservoir level to the level of the deepest crack, water flowed freely barreling downstream into the chimney drain (Zone- 2) When the reservoir level rose to the level of the deepest crack, water flowed freely barreling downstream into the chimney drain (Zone- 2) A combination of low plasticity, low LI, its variation under the subsequent confining stress condition, played a key role in the cracking of the core A combination of low plasticity, low LI, its variation under the subsequent confining stress condition, played a key role in the cracking of the core State based soil mechanics also explains the flaws of the findings by others and are provided in the Paper State based soil mechanics also explains the flaws of the findings by others and are provided in the Paper

Flooded City of Rexburg Thank you for your patience !