Geotechnical Aspects of Dam Safety William Empson, PE,

Geotechnical Aspects of Dam Safety William Empson, PE,

Geotechnical Aspects of Dam Safety William Empson, PE, PMP Senior Levee Safety Program Risk Manager U.S. Army Corps of Engineers Risk Management Center [email protected] Dam Safety Workshop Braslia, Brazil 20-24 May 2013 Corps of Engineers

BUILDING STRONG Geotechnical Aspects of Dam Safety Topics Concrete Dams To be presented by Structural Instructor Earth and Rock Fill Dams Failure modes Seepage

Filters Stability Emergency Spillways Erosion Geotechnical Aspects of Concrete Dams Failure Modes

Foundation Leakage, Piping Overtopping 9 Deterioration

6 Flow Erosion 3 Gate Failure 3 Sliding 2 Deformation 2 Faulty Construction

2 11 Geotechnical Aspects of Concrete DamsFoundation Piping Geotechnical Aspects of Concrete DamsUplift Pressure Geotechnical Aspects of Concrete DamsFlow Erosion

Geotechnical Aspects of Concrete DamsSliding Geotechnical Aspects of Concrete DamsFoundation Improvements Geotechnical Aspects of Concrete DamsArch Dam Abutments Geotechnical Aspects of Dam Safety Types of Embankment Dams Earth Fill

Hydraulic Fill Homogenous Rolled Fill Zoned Rolled Fill Rock fill Diaphragm Rock Fill Central Core Rock Fill Geotechnical Aspects of Dam Safety Types of Embankment Dams

Geotechnical Aspects of Earth DamsHydraulic Fill Dam Geotechnical Aspects of Earth Dams Failure Modes Cause Failures Incidents Total

Embankment Piping 23 14 37 Foundation Piping 11 43 54 Overtopping 18 7

25 Flow Erosion 14 17 31 Sliding 5 28 33 Deformation

3 29 32 Slope Protection Damage 0 13 13 Deterioration 2 3 5

Gate Failure 1 3 4 Earthquake Instability 0 3 3 Faulty Construction 0 3 3

Geotechnical Aspects of Earth Dams Failure Modes (Cont.) Piping Along outlet conduits Through cracks across the impervious core Inadequately compacted core material at contact with uneven surfaces In zones susceptible to erosion within the foundation

Overtopping Inadequate spillway capacity Large, rapid landslides in the reservoir Too little freeboard Geotechnical Aspects of Earth Dams Failure Modes (Cont.) Slope Failure Design deficiencies Neglected remedial actions

Instability Excessive deformations Excessive stresses Excessive loss of materials due to erosion Geotechnical Aspects of Earth Dams Failure Modes (Cont.) Earthquake conditions Excessive deformation Excessive pore pressure buildup

Sudden densification of loose, saturated, noncohesive soils that causes rapid build-up of pore fluid pressures Geotechnical Aspects of Earth Dams Technical Requirements Dam and foundation must be sufficiently watertight and have adequate seepage control for safe operation Must have sufficient spillway and outlet capacity as well as adequate freeboard

to prevent over topping by the reservoir Must be stable under all loading conditions Geotechnical Aspects of Earth Dams Seepage Seepage through the foundation or abutments causing piping or solutioning of rock Seepage through embankments, along conduits, or along abutment

contacts causing piping or internal erosion Geotechnical Aspects of Earth Dams Through Seepage Geotechnical Aspects of Earth Dams Milford Dam, KS Geotechnical Aspects of Earth Dams

Foundation Seepage Geotechnical Aspects of Earth DamsHodges Village Dam - Seepage Geotechnical Aspects of Earth Dams Piping Into Voids Geotechnical Aspects of Earth Dams Sink Hole, Clearwater Dam, MO

Geotechnical Aspects of Earth Dams Internal Drains Geotechnical Aspects of Earth Dams Blanket Drain Exit Embankment Gravel swale Blanket Drain

Foundation Proper configuration facilitates free drainage Geotechnical Aspects of Earth Dams Blocked Drain Exit Embankment

Swale Blanket Drain Foundation Improper configuration blocks drainage Geotechnical Aspects of Earth DamsUplift in Rock and Seepage Geotechnical Aspects of Earth Dams

Seepage Reduction Measures Geotechnical Aspects of Earth Dams Toe Drains and Relief Wells Geotechnical Aspects of Earth Dams Emergency Repairs Geotechnical Aspects of Earth Dams Emergency Repair for Boils

i= h/l Geotechnical Aspects of Earth Dams Conduits Seepage collars designers thought they would stop seepage Geotechnical Aspects of Earth Dams Filter Design Facilitates the controlled flow of water and

prevents movement of soil particles Collection and control Adequate carrying capacity Prevents migration of fines Criteria Permeability Stability Geotechnical Aspects of Earth Dams Slope Stability

Type slopes Embankment slopes Cut slopes Reservoir rim slopes Failure modes Shallow Slide Deep Slide Wedge (Block) Slide Geotechnical Aspects of Earth Dams

Shallow Slide Geotechnical Aspects of Earth Dams Shallow Slide Geotechnical Aspects of Earth Dams Deep Slide Geotechnical Aspects of Earth Dams Waco Dam, TX

Geotechnical Aspects of Earth Dams Abutment Slide, Libby Dam, MT Reservoir Rim Slides Geotechnical Aspects of Earth Dam Spillway Erosion Painted Rock Dam, AZ Earthquake Aspects of Dam

Earthquakes & Dams 162 COE dams in high seismic areas (2 and above) subject to damage Most built in 1940s and 1950s with no seismic design

Seismic design for liquefaction came into practice in the late 1970s early 1980s Location of Embankment Dams Low hazard to life & property High hazard to life & property Seismic Zones

4 3 2 1 0 Earthquake Engineering Seismic dam safety becomes a priority

Near failure of Lower San Fernando Dam San Fernando Earthquake - 1971 Earthquake Size Intensity Scale Damage based Modified Mercalli

I-XII Magnitude Scales (Instrumental) Energy based Richter M 1-9 Local ML Surface Wave Ms

Moment Mw Comparison of earthquake energy release to the seismic energy yield of quantities of the explosive TNT Richter Magnitude TNT for Seismic Energy Yield

Example (approximate) -1.5 1.0 1.5 2.0 2.5 3.0

3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5

10.0 12.0 6 ounces 30 pounds 320 pounds 1 ton 4.6 tons 29 tons 73 tons

1,000 tons 5,100 tons 32,000 tons 80,000 tons 1 million tons 5 million tons 32 million tons 160 million tons 1 billion tons 5 billion tons

1 trillion tons 160 trillion tons Breaking a rock on a lab table Large Blast at a Construction Site Large Quarry or Mine Blast Small Nuclear Weapon Average Tornado (total energy) Little Skull Mtn., NV Quake, 1992

Double Spring Flat, NV Quake, 1994 Northridge, CA Quake, 1994 Hyogo-Ken Nanbu, Japan Quake, 1995; Largest Thermonuclear Weapon Landers, CA Quake, 1992 San Francisco, CA Quake, 1906 Chilean Quake, 1960 (San-Andreas type fault circling Earth) (Fault Earth in half through center) 160 trillion tons of dynamite is a frightening yield of energy. Consider, however, that the Earth

receives that amount in sunlight every day. New Madrid Earthquakes, 18111812 (Isoseismals) Earthquake Effects

Transient loading or shaking Changes material properties Settlement Liquefaction Permanent ground displacement Dynamic response Each thing has it own shaking response

Problem: Earthquake Induced Liquefaction Causes Failures Buildings Bridges Slide in Lower San Fernando Dam - 1971 Dams

Earthquake Effects Liquefaction Sand boils Settlement Slope failures Alluvial valleys often involve liquefiable materials Earthquake Effects Liquefaction

Sand boils Settlement Slope failures Seismic Failure Mechanism 1 .1 50 Elev ation (f t) (x 1000) 1 .1 25

1 .1 00 1 .0 75 1 .0 50 1 .0 25 1 .0 00

0 .9 75 0 .9 50 0 .9 25 0 .9 00 -1.0

-0.9 -0.8 -0.7 -0.6 -0.5 -0.4

-0.3 -0.2 -0.1 0.0 Distance (ft) (x 1000)

0.1 0.2 0.3 0.4 0.5

0.6 0.7 0.8 0.9 1.0

Earthquake Effects Permanent Ground Displacement >15 ft of thrust faulting created this waterfall and destroyed the bridge (Chi Chi Earthquake, Taiwan, 1999) Seismic Considerations in Dam Design

Freeboard design pools, analysis -> design geometry Crack stoppers filters, transition zones, drains, material properties

Seepage & pore relief well, weep holes pressure control Foundation stability siting, in situ: replacement, improvement Embankment stability deformation and dynamic material properties Possible Earthquake Induced Modes of Failure

Disruption of dam/levee by fault movement in foundation Loss of freeboard due to settlement or differential tectonic ground movements Slope failures induced by ground motions Sliding of dam/levee on weak foundation materials Piping failure through cracks induced by ground movements Overtopping of dam/levee due to seiches in waterway Overtopping of dam/levee due to slides or rockfalls into waterway

Dams Damaged by Earthquakes Taiwan earthquake 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 Earthquake Performance of Dams

Well built dams usually survive strong earthquake loading - Kirazdere Dam 100 m height dam 10 km from epicenter, M=7.4 Izmut Turkey Eqk 1999

Vulnerability Assessment (Phased approach, to be detailed in upcoming new EM 1110-2-6001) Seismic vulnerability of levees and dams are similar and are evaluated as such Liquefaction Seismic

triggering analysis slope stability analysis Post-earthquake Deformation stability analysis analysis, if warranted

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 has been 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 is indicated. Thank You !

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