geotechnical aspects of dam safety.pptx
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Corps of Engineers
BUILDING STRONG
Geotechnical Aspects of Dam Safety
William Empson, PE, PMPSenior Levee Safety Program Risk ManagerU.S. Army Corps of EngineersRisk Management CenterWilliam.B.Empson@usace.army.mil
Dam Safety WorkshopBraslia, Brazil20-24 May 2013
mailto:William.B.Empson@usace.army.milmailto:William.B.Empson@usace.army.mil -
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Geotechnical Aspects of Dam SafetyTopics
Concrete Dams To be presented by Structural Instructor
Earth and Rock Fill Dams Failure modes Seepage Filters Stability
Emergency Spillways Erosion
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Geotechnical Aspects of Concrete DamsFailure Modes
Foundation Leakage, Piping 11Overtopping 9
Deterioration 6Flow Erosion 3Gate Failure 3
Sliding 2Deformation 2Faulty Construction 2
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Geotechnical Aspects of Concrete Dams-Foundation Piping
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Geotechnical Aspects of Concrete Dams-Uplift Pressure
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Geotechnical Aspects of Concrete Dams-Flow Erosion
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Geotechnical Aspects of Concrete Dams-Sliding
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Geotechnical Aspects of Concrete Dams-Foundation Improvements
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Geotechnical Aspects of Concrete Dams- Arch Dam Abutments
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Geotechnical Aspects of Dam SafetyTypes of Embankment Dams
Earth FillHydraulic FillHomogenous Rolled FillZoned Rolled Fill
Rock fillDiaphragm Rock FillCentral Core Rock Fill
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Geotechnical Aspects of Dam SafetyTypes of Embankment Dams
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Geotechnical Aspects of Earth Dams-Hydraulic Fill Dam
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Geotechnical Aspects of Earth DamsFailure Modes
Cause Failures Incidents Total
Embankment Piping 23 14 37Foundation Piping 11 43 54Overtopping 18 7 25Flow Erosion 14 17 31Sliding 5 28 33Deformation 3 29 32Slope Protection Damage 0 13 13Deterioration 2 3 5
Gate Failure 1 3 4Earthquake Instability 0 3 3Faulty Construction 0 3 3
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Geotechnical Aspects of Earth DamsFailure Modes (Cont.)
Piping Along outlet conduits Through cracks across the impervious core
Inadequately compacted core material at contactwith uneven surfaces In zones susceptible to erosion within the
foundation
Overtopping Inadequate spillway capacity Large, rapid landslides in the reservoir Too little freeboard
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Geotechnical Aspects of Earth DamsFailure Modes (Cont.)
Slope Failure Design deficiencies Neglected remedial actions
Instability Excessive deformations Excessive stresses
Excessive loss of materials due to erosion
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Geotechnical Aspects of Earth DamsFailure Modes (Cont.)
Earthquake conditions Excessive deformation
Excessive pore pressure buildup Sudden densification of loose, saturated, non-
cohesive soils that causes rapid build-up of pore fluidpressures
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Geotechnical Aspects of Earth Dams
Technical Requirements
Dam and foundation must be sufficientlywatertight and have adequate seepagecontrol for safe operationMust have sufficient spillway and outletcapacity as well as adequate freeboardto prevent over topping by the reservoir
Must be stable under all loading conditions
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Geotechnical Aspects of Earth DamsSeepage
Seepage through the foundation orabutments causing piping orsolutioning of rockSeepage through embankments,along conduits, or along abutmentcontacts causing piping or internalerosion
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Geotechnical Aspects of Earth DamsThrough Seepage
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Geotechnical Aspects of Earth Dams MilfordDam, KS
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Geotechnical Aspects of Earth DamsFoundation Seepage
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Geotechnical Aspects of Earth Dams-Hodges Village Dam - Seepage
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Geotechnical Aspects of Earth DamsPiping Into Voids
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Geotechnical Aspects of Earth DamsSink Hole, Clearwater Dam, MO
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Geotechnical Aspects of Earth DamsInternal Drains
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Geotechnical Aspects of Earth DamsBlanket Drain Exit
Embankment
Foundation
Blanket Drain
Gravel swale
Proper configuration facilitates free drainage
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Geotechnical Aspects of Earth DamsBlocked Drain Exit
Embankment
Foundation
Blanket Drain
Swale
Improper configuration blocks drainage
G h i l A f E h D
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Geotechnical Aspects of Earth Dams-
Uplift in Rock and Seepage
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Geotechnical Aspects of Earth DamsSeepage Reduction Measures
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Geotechnical Aspects of Earth DamsToe Drains and Relief Wells
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Geotechnical Aspects of Earth DamsEmergency Repairs
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Geotechnical Aspects of Earth DamsEmergency Repair for Boils
i = h / l
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Geotechnical Aspects of Earth DamsConduits
Seepage collars designers thought they would stop seepage
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Geotechnical Aspects of Earth DamsFilter Design
Facilitates the controlled flow of water andprevents movement of soil particles Collection and control Adequate carrying capacity Prevents migration of fines
Criteria Permeability Stability
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Geotechnical Aspects of Earth DamsSlope Stability
Type slopes Embankment slopes Cut slopes Reservoir rim slopes
Failure modes Shallow Slide Deep Slide Wedge (Block) Slide
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Geotechnical Aspects of Earth DamsShallow Slide
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Geotechnical Aspects of Earth DamsShallow Slide
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Geotechnical Aspects of Earth DamsDeep Slide
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Geotechnical Aspects of Earth DamsWaco Dam, TX
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Geotechnical Aspects of Earth Dams Abutment Slide, Libby Dam, MT
Reservoir Rim Slides
G t h i l A t f E th D
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Geotechnical Aspects of Earth DamSpillway Erosion
Painted Rock Dam, AZ
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Earthquakes & Dams
162 COE dams in high
seismic areas (2 andabove) subject todamage
Most built in 1940s and1950s with no seismicdesign
Seismic design forliquefaction came intopractice in the late 1970searly 1980s
43210
Seismic ZonesLocation of Embankment Dams
Low hazard to life & property
High hazard to life & property
E th k E i i
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Earthquake Engineering
Near failure of Lower San Fernando DamSan Fernando Earthquake - 1971
Seismic dam safetybecomes a priority
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Earthquake SizeIntensity Scale Damage based
Modified Mercalli I-XII
Magnitude Scales (Instrumental) Energy basedRichter M 1-9Local MLSurface Wave MsMoment Mw
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Comparison of earthquake energy release to the seismic energy yield ofquantities of the explosive TNT
Magnitude Energy Yield (approximate)
-1.5 6 ounces Breaking a rock on a lab table 1.0 30 pounds Large Blast at a Construction Site 1.5 320 pounds 2.0 1 ton Large Quarry or Mine Blast 2.5 4.6 tons 3.0 29 tons 3.5 73 tons
4.0 1,000 tons Small Nuclear Weapon 4.5 5,100 tons Average Tornado (total energy) 5.0 32,000 tons 5.5 80,000 tons Little Skull Mtn., NV Quake, 1992 6.0 1 million tons Double Spring Flat, NV Quake, 1994 6.5 5 million tons Northridge, CA Quake, 1994 7.0 32 million tons Hyogo-Ken Nanbu, Japan Quake, 1995; Largest Thermonuclear Weapon 7.5 160 million tons Landers, CA Quake, 1992 8.0 1 billion tons San Francisco, CA Quake, 1906 8.5 5 billion tons Chilean Quake, 1960
10.0 1 trillion tons (San-Andreas type fault circling Earth) 12.0 160 trillion tons (Fault Earth in half through center)
160 trillion tons of dynamite is a frightening yield of energy. Consider, however, that the Earthreceives that amount in sunlight every day.
Richter TNT for Seismic Example
New Madrid Earthquakes 1811-
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New Madrid Earthquakes, 18111812 (Isoseismals)
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Earthquake Effects
Transient loading or shakingChanges material propertiesSettlementLiquefactionPermanent ground displacementDynamic response Each thing has it own shaking response
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Buildings
Bridges
Problem: Earthquake Induced Liquefaction Causes Failures
Slide in Lower San Fernando Dam - 1971 Dams
Earthquake Effects
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Earthquake Effects
Liquefaction Sand boils Settlement Slope failures
Alluvial valleys often involve liquefiable material
Earthquake Effects
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Earthquake Effects
Liquefaction Sand boils Settlement Slope failures
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Seismic Failure Mechanism
Distance (ft) (x 1000)-1.0 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
E l e v a
t i o n
( f t ) ( x
1 0
0 0 )
0.900
0.925
0.950
0.975
1.000
1.025
1.050
1.075
1.100
1.125
1.150
Earthquake Effects
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Earthquake Effects
Permanent Ground
Displacement
>15 ft of thrust faulting created this waterfall and destroyed thebridge (Chi Chi Earthquake, Taiwan, 1999)
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Seismic Considerations in Dam Design
Freeboard design pools, analysis -> design geometryCrack stoppers filters, transition zones, drains, material propertiesSeepage & pore relief well, weep holes
pressure controlFoundation stability siting, in situ: replacement, improvementEmbankment stability deformation and dynamic material properties
bl h k d d d f
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Possible Earthquake Induced Modes ofFailure
Disruption of dam/levee by fault movement in foundationLoss of freeboard due to settlement or differential tectonicground movements
Slope failures induced by ground motionsSliding of dam/levee on weak foundation materialsPiping failure through cracks induced by groundmovements
Overtopping of dam/levee due to seiches in waterwayOvertopping of dam/levee due to slides or rockfalls intowaterway
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Taiwan earthquake
Dams Damaged by Earthquakes
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Dams Failed by Earthquakes
Sheffield Dam, CA Santa Barbara Eqk 1925, M=6.3 @ 7 mi
distance Slide failure induced by liquefaction
Izu Tailings Dams, Japan Earthquakes in 1978, M=7 and 5.7 Slide failures induced by liquefaction
World Total: 3 Dams
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Earthquake Performance of Dams
Well built dams usually survive strongearthquake loading
- Kirazdere Dam100 m height dam10 km from epicenter, M=7.4Izmut Turkey Eqk 1999
Vulnerability Assessment
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Vulnerability Assessment(Phased approach, to be detailed in upcoming new EM
1110-2-6001)
Seismic vulnerability of levees and damsare similar and are evaluated as such
Liquefaction triggering analysis
Seismic slope stability analysis
Post-earthquake stability analysis
Deformation analysis, if warranted
I i Af E h k
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Inspection After Earthquake
(paraphrased from USSD Guidelines for
Inspection of Dams After Earthquakes, 2003)
If an earthquake is felt at or near the dam (levee), or hasbeen reported to occur, with:
M 4.0 w/in 25 miles, M 5.0 w/in 50 miles, M 6.0 w/in 75 miles, M 7.0 w/in 125 miles, or
M 8.0 w/in 200 miles, immediate inspection isindicated.
Th k Y !
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Thank You !
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