Routine Instrumented and Visual Monitoring of Dams Based on - PowerPoint Presentation

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Routine Instrumented and Visual Monitoring of Dams Based on Potential Failure Modes Analysis

Authors:

Jay Statler (US Bureau of Reclamation) and Manoshree Sundaram (FERC-CRO)Presented By: Mike Carpenter, GEI Consultants, Inc.

USSD Committee on Monitoring of Dams and Their Foundations

White Paper (Draft)Slide2

U.S. Society on Dams

Vision

To be the nation's leading organization of professionals dedicated to advancing the role of dams for the benefit of society.Mission — USSD is dedicated to: Advancing the knowledge of dam engineering, construction, planning, operation, performance, rehabilitation, decommissioning, maintenance, security and safety;

Fostering dam technology for socially, environmentally and financially sustainable water resources systems;

Providing public awareness of the role of dams in the management of the nation's water resources;

Enhancing practices to meet current and future challenges on dams; and

Representing the United States as an active member of the International Commission on Large Dams (ICOLD).Slide3

White Papers by the USSD Monitoring of Dams and Their Foundations Committee:

“Why Include Instrumentation in Dam Monitoring Programs (Nov 2008, Barry Myers and Jay Stateler – published Nov 2008)

“Development of an Instrumentation Program” (Jim Hamby, Lead Author, with Pierre Choquet and Brad Long as Co-Authors, in progress)  “Operation and Maintenance of an Instrumentation System” (Amanda Sutter, Lead Author, with Pierre Choquet and Brad Long as Co-Authors, in progress)

“Instrumentation Data Management and Analysis” (Chris Hill, Lead Author, with Manoshree Sundaram as Co-Author, in progress)

“Routine Instrumented and Visual Monitoring of Dams Based on Potential Failure Modes Analysis” (Jay Stateler, Lead Author, with Manoshree Sundaram as Co-Author, in progress) Slide4

Why Provide Instrumentation?

The purpose of instrumentation and monitoring is to maintain and improve dam safety by providing information to:evaluate whether a dam is performing as expected and

warn of changes that could endanger the safety of a damSlide5

Principal Causes of Concrete

Dam Failures and Incidents (FERC Ch. 9, ICOLD 1992, ASCE 1988)

OvertoppingFoundation leakage and pipingFoundation slidingSlide6

Condition of lift chains for spillway gates – corrosion and pitting can lead to potential failure during operation leading to overtopping

Gate Hoist FailureSlide7

Piping in pervious foundation strataSlide8

Sliding Along FoundationSlide9

Principal Causes of Embankment

Dam Failures and Incidents(FERC Ch. 9, ICOLD 1992, ASCE 1988)

OvertoppingErosion of embankmentsEmbankment Leakage and pipingFoundation leakage and pipingSliding of embankment slopesSliding along clay seams in foundationsCracking due to differential settlementsLiquefactionSlide10

Spillway blockage; inadequate spillway capacity; erosion of aux. spillway Slide11

Flow through Conduits; aging conduitsSlide12

Piping in pervious foundation strataSlide13

Piping in EmbankmentSlide14

Slope Instability & LiquefactionSlide15

Purpose of Instrumentation

Provides data to:Characterize site conditionsVerify assumptions;

Evaluate initial constructionEvaluate performance design featuresObserve performance of known anomaliesEvaluate performance with respect to PFMs.Slide16

FERC Guidelines – Ch. 9 Instrumentation and Monitoring

“Every instrument in a dam should have a specific purpose.

If it does not have a specific purpose, it should not be installed or it should be abandoned.”Slide17

FERC Guidelines – Ch. 9 Instrumentation and Monitoring

“Installation of instruments or accumulation of instrument data by itself does not improve dam safety or protect the public. Instruments must be carefully selected, located, and installed. Data must be conscientiously collected, meticulously reduced, tabulated, and plotted, and must be judiciously evaluated with respect to the safety of the dam in a timely manner. A poorly planned program will produce unnecessary data that the dam owner will waste time and money collecting and interpreting, often resulting in disillusionment and abandonment of the program.”Slide18

PFMA Performance Parameter Process (BuRec)

Three basic steps:

Identify the most likely failure modes for the dam and associated structures. Identify the key instrument monitoring parameters. Define thresholds and actions.Slide19

Outcomes of the PMFA relative to surveillance and monitoring

Identification of enhancements to the surveillance and monitoring programs;Identification of gaps in data (Category III); Identification of risk reduction opportunities.Slide20

Assessment of Monitoring Needs Based on the PFMA

An instrument must answer a specific question or monitor an identified potential failure mode of the dam or foundation to:

Provide an early detection of unusual/ unexpected performanceProvide confirmation of satisfactory performance Slide21

Monitoring Consideration for Common PFMs

Seepage-related failure modes for embankment dams (example 1)Earthquake-related failure modes for embankment dams (example 2)

Failure modes for concrete dams under all loading conditions (example 3)Flood-related failure modes associated with spillway failure (example 4) Slide22

Illustrative Example – PFM No. 1

Seepage-Related failure due to breaching caused by flow through embankment dam that results in piping and transport of embankment material out of the dam or into the toe drain systemSlide23

Illustrative Example 1 – Monitoring Considerations

Perform regular visual inspections of: D/S slope and toe areaDam crest

U/S slopeReservoir water surfaceSlide24

Illustrative Example 1 – Monitoring Considerations

Toe drain and seepage flowsPiezometers and observation wellsIncrease monitoring frequency during a flood

Video inspect toe drain systemSlide25

Key monitoring concepts for seepage-related PFMs for embankment dams

Monitoring water pressuresData is obtained at discrete points

Regular visual monitoringSlide26

Illustrative Example – PFM No. 2

Seepage-related failure of embankment dam in the aftermath of an earthquake due to the formation of a transverse crack in the dam, where seepage flows through the crack and eventually erodes and breaches the damSlide27

Illustrative Example 2 – Monitoring Considerations

Compare baseline data to post-seismic event data

In the aftermath of a significant earthquake, perform an immediate visual inspection of: D/S slope, D/S toe, and areasDam crestU/S slope

Reservoir water surfaceSlide28

Illustrative Example 2 – Monitoring Considerations

In the aftermath of significant shaking, promptly obtain readingsSeismic monitoring equipment with telemetrySlide29

Key monitoring concepts for earthquake-related PFMs of embankment dams

PGA criteriaDetection of changed conditionsAutomated and/or remote detection capabilities

Baseline data is a must for post-earthquake comparisonSlide30

Key monitoring concepts for earthquake-related PFMs of embankment dams

Recognized and addressed earthquake issues prior to the eventInstallation seismic monitoring equipment

Strong motion data used to validate dynamic modelsSlide31

Illustrative Example – PFM No. 3

Sliding failure at the dam/foundation contact due to poor bonding of the dam’s concrete to the foundation rock and/or insufficient keying under normal, flood or earthquake conditionsSlide32

Illustrative Example 3 – Monitoring Considerations

Perform regular visual inspections of: D/S face of the dam and gallery walls, floors, and ceilingsPlace scribe marks

Structural monitoring survey pointsSlide33

Illustrative Example 3 – Monitoring Considerations

Significant seismic eventMajor flood eventSlide34

Key monitoring concepts for concrete dam failure modes

Failures of concrete dams caused by their foundationsOriginal construction photographsSliding along dis-bonded lift linesSlide35

Key monitoring concepts for concrete dam failure modes

Changes with respect to historical performanceVisual monitoring and instrumentation baseline dataDifficult gate operationsSlide36

Illustrative Example – PFM No. 4

Spillway flow surfaces have flaws such that when subjected to large flows, cavitation results leading to structural damage, headward erosion, and breaching of the reservoirSlide37

Illustrative Example 4 – Monitoring Considerations

Perform regular visual inspections of: Flow surfacesSpillway gallery

Spillway dischargesPost-flood conditionsSlide38

Key monitoring concepts for flood-related PFMs associated with spillway failure

Pre- and post-flood comparisonsSmaller flood events can identify issuesSlide39

Key monitoring concepts for flood-related PFMs associated with spillway failure

Issues need to have been recognizedRecognize when failure may be imminentSlide40

Closing Remarks

The PFM categories discussed are most commonThe PFMA team may find that the available instrumentation is:Sufficient to reach conclusions re. the PFM, (Category 1 or 2), or

Useful, but important issues remain unresolved and more instrumentation is needed (Category 3), orThat instrumentation can be eliminated or monitoring frequency reduced because the PFM was found to be non-plausible (Category 4)Slide41

Closing Remarks

The added value to integrating the PMFA with the dam safety surveillance and monitoring includes:

Uncovering data and informationIdentifying the most significant PFMsIdentifying risk reduction opportunities

Focusing surveillance, instrumentation, monitoring and inspection programsSlide42

Closing Remarks

Instrumentation monitoring program established at one dam may not be appropriate at another damEach project be independently evaluated Structured process that identifies plausible unique PFMs

Develop appropriate monitoring to plausible PFMsSlide43

Questions/Comments