Presentation on theme: "USSD Committee on Monitoring of Dams and Their Foundations"— Presentation transcript:
1Routine Instrumented and Visual Monitoring of Dams Based on Potential Failure Modes Analysis USSD Committee on Monitoring of Dams and Their FoundationsWhite Paper (Draft)RJA on technical committee for HUG and also sits on the USSD committee with Jay and Manoshree.Jay is the chairman.Rick or Manoshree could not make this conference, so I was railroaded, volunteered to give this presentation.Authors: Jay Statler (US Bureau of Reclamation) and Manoshree Sundaram (FERC-CRO)Presented By: Mike Carpenter, GEI Consultants, Inc.
2U.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; andRepresenting the United States as an active member of the International Commission on Large Dams (ICOLD).How many people are members of USSD?How many don’t know about USSD?I encourage you to become a member
3White 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)This paper is part of a series of White Papers by the USSD Monitoring of Dams and Their Foundations Committee to address important topics with respect to the development and successful implementation of dam safety monitoring programsPaper is a draft, so if there are suggestions I will pass them along
4Why 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 andwarn of changes that could endanger the safety of a damWhy do we need to have instrumentation? Two basic principals
5Principal Causes of Concrete Dam Failures and Incidents (FERC Ch Principal Causes of Concrete Dam Failures and Incidents (FERC Ch. 9, ICOLD 1992, ASCE 1988)OvertoppingFoundation leakage and pipingFoundation slidingOvertopping from inadequate spillway capacity or spillway blockage resulting in erosion of the foundation at the toe of the dam or washout of an abutment or adjacent embankment structureFoundation leakage and piping in pervious strata, soluble lenses, and rock discontinuitiesSliding along weak discontinuities in foundations
6Gate Hoist FailureCondition of lift chains for spillway gates – corrosion and pitting can lead to potential failure during operation leading to overtoppingHere’s some examples of concrete dam failures
7Piping in pervious foundation strata Hope Mills Dam – built in 2007 and failure in 2010 in NC
8Sliding Along Foundation St. Francis Dam – built in 1926, too slender of a dam lead to high uplift pressures & overturning – catastrophic failure lead to better oversight in CA by the DWR
9Principal Causes of Embankment Dam Failures and Incidents (FERC Ch 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 settlementsLiquefactionOvertopping from inadequate spillway capacity, spillway blockage, or excessive settlement resulting in erosion of the embankmentErosion of embankments from failure of spillways, failure or deformation of outlet conduits causing leakage and piping, and failure of riprapEmbankment leakage and piping along outlet conduits, abutment interfaces, contacts with concrete structures, or concentrated piping in the embankment itselfFoundation leakage and piping in pervious strata, soluble lenses, and rock discontinuitiesSliding of embankment slopes due to overly steep slopes, seepage forces, rapid drawdown, or rainfallSliding along clay seams in foundationsCracking due to differential settlementsSeismic liquefaction
10Spillway blockage; inadequate spillway capacity; erosion of aux Spillway blockage; inadequate spillway capacity; erosion of aux. spillwayDamaged emergency spillway after blockage of primary spillway inlet – note hay bailsTaum Sauk failure – instrumentation related failure mode
11Flow through Conduits; aging conduits Many of the dams that we’re dealing with in the mid-west are old. What might have been a Category IV failure mode 20 years ago, may now be a II or a I based on the aging infrastructureNote degradation of pipe in this photo – cause for potential concern.
12Piping in pervious foundation strata An example of inadequate foundation treatment during construction that did not start showing a problem until many years later when depressions and significant leakage was noted downstream of this abutment.Note the sand bags and topical concrete used to “seal” the fractures - yeah
13Piping in EmbankmentGround loss and sinkholes in an embankment dam – what kind of void is below these holes?The most recognizable piping failure – which dam is this?
14Slope Instability & Liquefaction Marchland Levee slope failure in Louisiana in 1983TVA Kingston ash pond static liquefaction failure in December 2008 – don’t have to deal with this on hydro dams but important to recognize the environmental consequences of failures as well as life and propertyHow many of you have seen signs of these failure modes?Does your PFMA address these PFMs?
15Purpose of Instrumentation Provides data to:Characterize site conditionsVerify assumptions;Evaluate initial constructionEvaluate performance design featuresObserve performance of known anomaliesEvaluate performance with respect to PFMs.Characterize site conditions before construction;Verify design and analysis assumptions;Evaluate behavior during construction, first filling, and operation of the structure;Evaluate performance of specific design features;Observe performance of known geological and structural anomalies; andEvaluate performance with respect to potential site-specific failure modes.
16FERC 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.”
17FERC 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.”What this say is Owners and regulators must be careful in identifying the instrumentation to be monitored and the frequency of monitoring.The staff obtaining the readings are the first line of defense against conditions indicating a potential unsafe condition.Staff must have an understanding what the instrumentation monitoring for – what failure modes is it monitoring.Give example of daily flume monitoring for a Category IV failure mode – something is out of wack
18PFMA 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.There are 3 basic steps to the PFMA processIdentify the most likely failure modes for the dam and associated structures – Category I or II PFMsIdentify the key monitoring parameters that will provide the best indication of the possible development of each of the identified failure modes, and define an instrumentation and visual monitoring program to gather the necessary information and data.3. Define the ranges of expected performance relative to the instrumentation and visual monitoring program, and define the action to be taken in the event of unexpected performance.
19Outcomes 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.Identification of enhancements to the surveillance and monitoring programs and tailoring of existing programs to focus monitoring efforts on early identification of the initiation/development of PFMs;Identification of gaps in data, information and analyses, that may prevent characterization of the significance of a PFM; andIdentification of risk reduction opportunities applicable to the surveillance and monitoring programs, operations, etc.
20Assessment 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 performanceAn 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
21Monitoring 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)
22Illustrative 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 system
23Illustrative Example 1 – Monitoring Considerations Perform regular visual inspections of:D/S slope and toe areaDam crestU/S slopeReservoir water surfaceD/S slope and toe area looking for sinkholes, depressions, unusual settlement, new or increase seeps or wet areas, boils, or evidence of material transportDam crest & U/S slope looking for sinkholes, depressions, and areas of unusual settlementReservoir water surface looking for whirlpools
24Illustrative Example 1 – Monitoring Considerations Toe drain and seepage flowsPiezometers and observation wellsIncrease monitoring frequency during a floodVideo inspect toe drain systemRegularly monitor toe drain flow and seepage flows, looking for flow increase or evidence of finesRegularly monitor water pressures from piezometers and observation wells in the embankment and foundation, looking for anomalous dataDuring major flood events when reservoir levels are high, increase monitoring frequencyOccasionally perform video inspections of the toe drain system
25Key monitoring concepts for seepage-related PFMs for embankment dams Monitoring water pressuresData is obtained at discrete pointsRegular visual monitoringMonitoring water pressures and subsurface water levels provides valuable info toward understanding seepage patterns within the dam and foundation, however…Data is obtained at discrete points and monitoring locations will probably NOT be located at or close to the flow path of a developing seepage problem, therefore…Regular visual monitoring, in conjunction with monitoring wells and piezometers, provides more valuable data for all areas at the site
26Illustrative 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 damIs anyone aware of any Category I or II PFMs in the upper mid-west related to seismic?
27Illustrative Example 2 – Monitoring Considerations Compare baseline data to post-seismic event dataIn the aftermath of a significant earthquake, perform an immediate visual inspection of:D/S slope, D/S toe, and areasDam crestU/S slopeReservoir water surfacePeriodically obtain all seepage and drain flow readings to maintain baseline information to use for comparison purposes in the aftermath of a significant seismic eventD/S slope, D/S toe, and areas D/S looking for new sinkholes, depressions, unusual settlement, new or increased seeps or wet areas, boils, or evidence of material transportDam crest looking for sinkholes, depressions, longitudinal cracks, horizontal or transverse cracksU/S slope looking for sinkholes, depressions, and areas of unusual settlement or deformationReservoir water surface looking for whirlpools
28Illustrative Example 2 – Monitoring Considerations In the aftermath of significant shaking, promptly obtain readingsSeismic monitoring equipment with telemetryIn the aftermath of significant shaking, promptly obtain readings at all seepage and drain flow monitoring locations and evaluate data for changed conditions from normal historical performanceConsider whether seismic monitoring equipment with telemetry would be appropriate at the site. If already present, compare dam performance (e.g. permanent deformation) with that predicted by analytical models
29Key monitoring concepts for earthquake-related PFMs of embankment dams PGA criteriaDetection of changed conditionsAutomated and/or remote detection capabilitiesBaseline data is a must for post-earthquake comparisonDetermination of “significant” shaking, PGA criteria, or fragility values developed for the dam based on seismic analysisPrompt post-earthquake response is a must to facilitate detection of changed conditionsWhere risk of eqk-related failure is possible and seismic hazard is high, automated and/or remote detection capabilities are importantDevelopment of good pre-earthquake baseline data is a must for post-earthquake comparison purposes
30Key monitoring concepts for earthquake-related PFMs of embankment dams Recognized and addressed earthquake issues prior to the eventInstallation seismic monitoring equipmentStrong motion data used to validate dynamic modelsNothing can be done during the earthquake to prevent failure. The issues need to have been recognized and addressed prior to the event via a PFMA processInstallation of seismic monitoring equipment is particularly important in highly seismic areas to determine whether a post-eqk inspection is warranted and can help prioritize post-eqk inspection response.Strong motion data also helpful in validating assumptions in dynamic analysis models.
31Illustrative 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 conditions
32Illustrative Example 3 – Monitoring Considerations Perform regular visual inspections of:D/S face of the dam and gallery walls, floors, and ceilingsPlace scribe marksStructural monitoring survey pointsD/S face of the dam and gallery walls, floors, and ceilings looking for new cracks or significant changes at the cracksPlace scribe marks in gallery wall and floor at each contraction joint to indicate relative offsetsPeriodically perform surveys of structural monitoring points on dam looking for evidence of unusual D/S movements. Maintain baseline survey information to use for comparison purposes in the aftermath of an eqk or flood event
33Illustrative Example 3 – Monitoring Considerations Significant seismic eventMajor flood eventIn the aftermath of a significant seismic event, perform an immediate visual inspection of the scribe marks, visual inspection of the galleries and D/S face (looking for changed cracked conditions), obtain readings of the foundation drain flows and foundation uplift pressures and perform a survey of the structural monitoring pointsDuring a major flood event, perform frequent visual monitoring for scribe mark offsets, D/S face and gallery, and perform a survey of structural monitoring points post-flood
34Key monitoring concepts for concrete dam failure modes Failures of concrete dams caused by their foundationsOriginal construction photographsSliding along dis-bonded lift linesMajority of failures of concrete dams caused by problems in their foundations (weak bedding planes, foliation, shears, weak contacts between rock units, etc.)Original construction photos very helpful in identifying weak areasPotential for sliding or separation along disbonded lift lines within concrete should also be considered, particularly during flood or eqk loading
35Key monitoring concepts for concrete dam failure modes Changes with respect to historical performanceVisual monitoring and instrumentation baseline dataDifficult gate operationsThe first signs of foundation or monolith movement indicating a threat to dam safety will typically manifest itself via changes with respect to historical performance – e.g. new cracks or displacement of existing cracks, observed movement between joints, changes in uplift readings, change drain flows, downstream trend in movement monitoring points with time, etc.Good visual monitoring and instrumentation baseline data is key to early detection of changing conditionsDifficulties in gate operations can also provide an early indication of dam movements
36Illustrative 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 reservoir
37Illustrative Example 4 – Monitoring Considerations Perform regular visual inspections of:Flow surfacesSpillway gallerySpillway dischargesPost-flood conditionsFlow surfaces looking for offsets at joints, areas of deteriorated concrete, and other flaws. Also observe for debris accumulationSpillway gallery looking for evidence of displacement, anomalies, and other evidence of irregular flow surfacesSpillway discharges looking for unusual flow patterns (e.g. Rooster tails) that could indicate obvious flow irregularitiesPost-flood conditions to assess damage to the spillway
38Key monitoring concepts for flood-related PFMs associated with spillway failure Pre- and post-flood comparisonsSmaller flood events can identify issuesObtaining and maintaining good baseline of pre-flood conditions is important for post-flood comparisonsCareful monitoring during smaller flood events can identify performance issues that may result in a threat to dam safety during large flood events
39Key monitoring concepts for flood-related PFMs associated with spillway failure Issues need to have been recognizedRecognize when failure may be imminentTypically, little can be done during the flood event to prevent failure. The issues need to have been recognized and addressed prior to the event via a PFMA processDuring the flood event, monitoring involves documenting performance and being in a position to recognize when failure may be imminent so that timely warnings can be issued and evacuation initiated
40Closing Remarks The PFM categories discussed are most common The PFMA team may find that the available instrumentation is:Sufficient to reach conclusions re. the PFM, (Category 1 or 2), orUseful, 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)The four PFM categories discussed are among some of the most common but there are othersThe PFMA core team may find that the available instrumentation is:Sufficient to reach conclusions re. the PFM, (Category 1 or 2), orUseful, 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)
41Closing RemarksThe added value to integrating the PMFA with the dam safety surveillance and monitoring includes:Uncovering data and informationIdentifying the most significant PFMsIdentifying risk reduction opportunitiesFocusing surveillance, instrumentation, monitoring and inspection programsThe added value to integrating the PMFA with the dam safety surveillance and monitoring includes:Uncovering data and information that corrects, clarifies, or supplements the understanding of potential failure modes and scenariosIdentifying the most significant potential failure modesIdentifying risk reduction opportunitiesFocusing surveillance, instrumentation, monitoring and inspection programs to provide information on the potential failure modes that present the greatest risk to the safety of the dam
42Closing RemarksInstrumentation monitoring program established at one dam may not be appropriate at another damEach project be independently evaluatedStructured process that identifies plausible unique PFMsDevelop appropriate monitoring to plausible PFMsDam owners with multiple dams should note that an instrumentation monitoring program established at one dam may not be appropriate at another dam regardless of the extent of similarities.Therefore, it is imperative that each project be evaluated independently to assess the objectives of the instrumentation program.The evaluation should be part of a structured process that identifies plausible failure modes unique to a dam and develops appropriate responses, including instrumentation requirements, data collection and evaluation procedures, budgetary resources, experience and qualification of monitoring personnel, and monitoring frequency requirements