geotechnical aspects of dam safety.pptx

8/14/2019 Geotechnical Aspects of Dam Safety.pptx

1/63

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 [email protected]

Dam Safety WorkshopBraslia, Brazil20-24 May 2013
mailto:[email protected]:[email protected]


2/63

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


3/63

Geotechnical Aspects of Concrete DamsFailure Modes

Foundation Leakage, Piping 11Overtopping 9

Deterioration 6Flow Erosion 3Gate Failure 3

Sliding 2Deformation 2Faulty Construction 2


4/63

Geotechnical Aspects of Concrete Dams-Foundation Piping


5/63

Geotechnical Aspects of Concrete Dams-Uplift Pressure


6/63

Geotechnical Aspects of Concrete Dams-Flow Erosion


7/63

Geotechnical Aspects of Concrete Dams-Sliding


8/63

Geotechnical Aspects of Concrete Dams-Foundation Improvements


9/63

Geotechnical Aspects of Concrete Dams- Arch Dam Abutments


10/63

Geotechnical Aspects of Dam SafetyTypes of Embankment Dams

Earth FillHydraulic FillHomogenous Rolled FillZoned Rolled Fill

Rock fillDiaphragm Rock FillCentral Core Rock Fill


11/63

Geotechnical Aspects of Dam SafetyTypes of Embankment Dams


12/63

Geotechnical Aspects of Earth Dams-Hydraulic Fill Dam


13/63

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


14/63

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


15/63


Slope Failure Design deficiencies Neglected remedial actions

Instability Excessive deformations Excessive stresses

Excessive loss of materials due to erosion


16/63


Earthquake conditions Excessive deformation

Excessive pore pressure buildup Sudden densification of loose, saturated, non-

cohesive soils that causes rapid build-up of pore fluidpressures


17/63

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


18/63

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


19/63

Geotechnical Aspects of Earth DamsThrough Seepage


20/63

Geotechnical Aspects of Earth Dams MilfordDam, KS


21/63

Geotechnical Aspects of Earth DamsFoundation Seepage


22/63

Geotechnical Aspects of Earth Dams-Hodges Village Dam - Seepage


23/63

Geotechnical Aspects of Earth DamsPiping Into Voids


24/63

Geotechnical Aspects of Earth DamsSink Hole, Clearwater Dam, MO


25/63


26/63


27/63

Geotechnical Aspects of Earth DamsInternal Drains


28/63

Geotechnical Aspects of Earth DamsBlanket Drain Exit

Embankment

Foundation

Blanket Drain

Gravel swale

Proper configuration facilitates free drainage


29/63

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


30/63

Geotechnical Aspects of Earth Dams-

Uplift in Rock and Seepage


31/63

Geotechnical Aspects of Earth DamsSeepage Reduction Measures


32/63

Geotechnical Aspects of Earth DamsToe Drains and Relief Wells


33/63

Geotechnical Aspects of Earth DamsEmergency Repairs


34/63

Geotechnical Aspects of Earth DamsEmergency Repair for Boils

i = h / l


35/63

Geotechnical Aspects of Earth DamsConduits

Seepage collars designers thought they would stop seepage


36/63

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


37/63

Geotechnical Aspects of Earth DamsSlope Stability

Type slopes Embankment slopes Cut slopes Reservoir rim slopes

Failure modes Shallow Slide Deep Slide Wedge (Block) Slide


38/63

Geotechnical Aspects of Earth DamsShallow Slide


39/63

Geotechnical Aspects of Earth DamsShallow Slide


40/63

Geotechnical Aspects of Earth DamsDeep Slide


41/63

Geotechnical Aspects of Earth DamsWaco Dam, TX


42/63

Geotechnical Aspects of Earth Dams Abutment Slide, Libby Dam, MT

Reservoir Rim Slides

G t h i l A t f E th D


43/63

Geotechnical Aspects of Earth DamSpillway Erosion

Painted Rock Dam, AZ


44/63


45/63

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


46/63

Earthquake Engineering

Near failure of Lower San Fernando DamSan Fernando Earthquake - 1971

Seismic dam safetybecomes a priority


47/63

Earthquake SizeIntensity Scale Damage based

Modified Mercalli I-XII

Magnitude Scales (Instrumental) Energy basedRichter M 1-9Local MLSurface Wave MsMoment Mw


48/63

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-


49/63

New Madrid Earthquakes, 18111812 (Isoseismals)


50/63

Earthquake Effects

Transient loading or shakingChanges material propertiesSettlementLiquefactionPermanent ground displacementDynamic response Each thing has it own shaking response


51/63

Buildings

Bridges

Problem: Earthquake Induced Liquefaction Causes Failures

Slide in Lower San Fernando Dam - 1971 Dams

Earthquake Effects


52/63

Earthquake Effects

Liquefaction Sand boils Settlement Slope failures

Alluvial valleys often involve liquefiable material

Earthquake Effects


53/63

Earthquake Effects

Liquefaction Sand boils Settlement Slope failures


54/63

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


55/63

Earthquake Effects

Permanent Ground

Displacement

>15 ft of thrust faulting created this waterfall and destroyed thebridge (Chi Chi Earthquake, Taiwan, 1999)


56/63

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


57/63

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


58/63

Taiwan earthquake

Dams Damaged by Earthquakes


59/63

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


60/63

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


61/63

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


62/63

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 !


63/63

Thank You !

geotechnical aspects of dam safety.pptx

Documents