(*)Classification des deteriorations des barrages et usines hydroélectriques: l'importance pour analyse de risque

CLASSIFICATION OF DETERIORATIONS OF DAMS AND HYDROELETRIC POWERPLANTS: THE IMPORTANCE FOR RISK ANALYSIS

(*)

Alexandre Duarte BARHOUCH AIRESDam Safety Engineer, CEMIG

BRAZIL

Paula LUCIANA DIVINOCivil Maintenance Engineer, CEMIG

BRAZIL

Amanda MOTTA DA COSTACivil Maintenance Engineer, CEMIG

BRAZIL

1. INTRODUTION

Deterioration of the structures is a natural phenomenon and many times inevitable. However, measures to identify deterioration cases and to proceed their classification, should be implemented in appropriate period of time to allow the evolution of knowledge and the improvement of the practices adopted in their correction and even prevention.

In this context, to classify deteriorations means to register all pertinent information and principally to associate them to previously defined categories so that it is possible to obtain statistic data on main occurrences as well as to subsidize risk analyses concerning the observed anomalies in the structures.

2. THE CLASSIFICATION PROVIDED FROM ICOLD

The art of engineering, mainly the engineering of dams, due to the empiric characteristics of the past practice and to the great heterogeneity of professional teams, possesses as an important tool: the use of acquired experiences. During the years, the world generated countless cases that, in order to be properly used as lessons learned, need an appropriate organization.

The International Commission on Large Dams produced a document that assisted this demand [1]. This technical report evaluated 1105 deterioration

cases, not only in dams, but as well in the other structures of hydroelectric plants, including problems occured in the reservoir. This considerable number of cases allowed the formulation of a consistent classification methodology that can be used in any hydroelectric installation or dam.

The methodology includes a set of tables for each structure listed below:

concrete dams earth and rockfill dams masonry dams appurtenant works (spillway, powerhouse, intake, penstocks, etc) reservoir downstream areas

Each table is divided in items (categories) and sub-items, generating a total of 216 classification topics.

The following categories are common to all the tables of dams. Other categories shown on the tables are specific of each dam type.

due to foundation due to unforeseen actions or to actions of exceptional magnitude due to structural behavior due to monitoring due to maintenance

For a better understanding, Table 1 can be consulted below, containing some items of one of the tables of ICOLD.

Table 1Classification of deterioration of earth and rockfill dams (partial)

2 EARTH AND ROCKFILL DAMS, INCLUDING FOUNDATIONS

2.1 Due to foundation

2.1.1 - Inadequacy of site investigations

2.1.2 - Deformation and land subsidence

2.1.3 - Shear strength

2.2 Due to embankment materials and method of construction, excluding filters and drains

2.2.1 - Fine clays

2.2.2 - Organic clays

2.2.3 - Dispersive clays

Concisely the methodology involves the classification of the deterioration in at least one item of the tables, its correlation being evaluated with external evidences. In relation to the deterioration causes, there is, as mentioned in the report, the difficulty of the correct and unquestionable identification. This

motivated the adoption of the same classification headings for the apparent problem, and for the cause, being optional the association of the causes to the headings.

An example of application of this methodology for earth dams with karst foundation, is the case of an inadequate treatment of consolidation of the foundation (2.1.12) that caused excessive percolation (2.1.4) and differential movement (2.4.10). In this deterioration case, the classification headings related to the external evidences are 2.1.4 and 2.4.10 and the heading associated to its cause is 2.1.12.

In the same way as the deterioration tables, the report also supplies tables of remedial measures for each one of the structures. Table 2 that depicts some examples of those headings. It can be pointed out that the table does not include only the items that specifically treat of repairs, but also the ones associated with an accompaniment of the evolution of the existing deterioration, besides additional studies, improvement of the diagnosis and other information.

Additionally , seeking a better analysis of the origin of the problem and a more effective repair, codes are proposed for the characterization of the moment at which the deterioration takes place. There are also codes for the identification of the detection method, with the intention to reveal the need of development of these methods and to supply information for the definition of observation programs. The related tables of these two measures, 3 and 4, are shown below.

Table 2 Table 3 Remedial measures (partial) Deterioration Time

Of a general nature

R101 Investigation

R102 Monitoring

R103 Lowering of reservoir level

R104 Raising of dam crest

In foundations

R201 Watertightening treatment

R202Drain and filter construction or repair

R203

Strengthening by grouting or other methods (excluding anchoring)

R204 Filling in of fractures and cavities

R205 Anchoring

In concrete and masonry dams

R301 Watertightening treatment

R302 Drain construction or repair

Table 4

T1 During construction

T2 During the first filling

T3 During the first five years

T4 After five years

T5 Not available

Detection Methods

D01 Direct observation

D02 Sampling and laboratory test

D03 Water flow measurements

D04 Phreatic level measurements

D05 Uplift measurements

D06 Pore pressure measurements

D07 Turbidity measurements

D08 Chemical analysis of water

D09 Seepage path investigation

D10 Joint and crack measurements

D11 Horizontal displacement measurements

D12 Vertical displacement measurements

D13 Angular displacement measurements

D14 Strain measurements

D15 Stress measurements

D16 Water level measurements

D17 Temperature measurements

D18 Hygrometric measurements

D19 Rainfall measurements

D20 Seismicity control

D21 Sounding investigation

D22 Water pressure measurements

D23 Silting measurements

D24 Design revision (new criteria)

D25 Not available

3. MODIFIED CLASSIFICATION FROM CEMIG

CEMIG, an electric power utility of the State of Minas Gerais, Brazil, owns 55 hydroelectric plants and dams and therefore needs a system of classification of the deteriorations cases for the control and prioritization of its interventions.

The database of deteriorations cases of the company plants is based in the classification of ICOLD, but in a modified way.

Following the recommendations of the report from ICOLD, that suggests periodic updating, every 10 years, of the methodology of classification of deteriorations, CEMIG judged appropriate to publish the modified ICOLD system and to submit it to discussions in the world technical community aiming at obtaining an unique and consolidated model that could assist the great majority of the cases and allow the production of a world register. This will contribute to the continuity of the ICOLD project, updating the database of deteriorations cases in dams and hydroelectric plants, guaranteeing conditions for the development of risks analyses.

The methodology of classification of deteriorations adopted by CEMIG differentiates the causes from the external evidences, according a demand of the original classification proposed by ICOLD. To do so the classification process begins with the use of an additional table for deterioration code, which should be used only for the description of the external evidences. This table is in Appendix I, with the listing of deterioration codes depicting the respective description in order to facilitate its use. It is of considerable importance to stress the advantages obtained with the differentiation of the causes from the external

evidences in the classification, which allow the execution of more appropriate and complete analyses.

The classification process continues with the use of the derived tables of ICOLD, presented in the Appendix II, where the codes are only related with the probable causes of the deterioration. The main modifications accomplished in those tables are listed below:

creation of tables of causes and repairs for Constructions, Industrial Area and Urbanization;

inclusion of items associated to wood dams in the table of masonry dams; adaptation of the table of concrete dam to include causes of deteriorations in

rolled compacted concrete (RCC) dams; adaptation of the table of earth and rockfill dam to include cofferdams; adaptation of the reservoir table.

It should be observed that the inclusion of typical structures of the constructive period and even the register of problems originating from construction of the other structures reinforces the need of prevention and diagnosis from the initial phases of the undertaking. Therefore, a very useful employment for this group of tables consists on the use as a check-list for designers, constructors and operation and maintenance professionals, with the intention of identification of potential problems and, consequently, to treat them previously, reducing the rework and the increase of cost and schedule of the project.

4. IMPROVEMENTS TO BE IMPLANTED IN THE CLASSIFICATION OF CEMIG

Considering the other recommendations of ICOLD and CBDB (Brazilian Committee of Large Dams) [2] and additional considerations obtained from CEMIG own experience; the inclusion of features of the structures and of the whole project can be analyzed, with the objective of allowing additional researches, such as:

moment of detection of the deterioration; moment of occurrence of the deterioration; detection method; specific type of dam(earth or rockfill); height of the dam; foundation type of the structure considered; year of completion of the structure; type of contract to realize the project.

At this point, a model can be proposed for the register form of deteriorations of dam and hydroelectric plants that includes all the mentioned considerations, aiming to assist the largest possible number of cases, including those occurring during the constructive period. In the Appendix III, it is shown register form of deterioration to illustrate the proposed methodology.

5. RISK ANALYSIS

A consistent and organized database allows the execution of the most types of analyses. Among them, one of the most important is the risk analysis, that allows acting previously in events that, if occurring, affect negatively the undertaking. Considering the uncertainty of the events, the risk management can only be implemented starting from a measure of these risk events.

Nowadays there is an extensive variety of procedures for implementation of risks analyses. The procedures commonly accepted in the area of project management for the execution of risks analyses, according to [3] and [4], involve basically the following stages:

1. Risk identification and categorization: it usually consists on brainstorming with the involved professionals and research of historical database for the determination of all the possible risks that can affect the project or specific project. The list of risks obtained will be subdivided in groups aiming at associating the identified risks (according to its causes, impact and other) with the intention of facilitating their treatment through the response actions, such as identifying areas most exposed to effects of uncertainty, as well as motivating the identification of new risks.

2. Risk analysis (qualitative and quantitative): it involves the prioritization of the identified risks allowing the concentration of efforts in the most important ones. Therefore, for each risk a probability of occurrence has to be defined, as well as the corresponding impact, if the risk does occur. The product of these two terms denominated Expected Monetary Value, Eq. [1], allows listing the risks according to its importance.

Expected Monetary Value = Probability x Impact …………………………[1]

The analysis is considered qualitative, when the prioritization is made with arbitrary values based on individual experiences. This is usually used when the historical database is insufficient to subsidize more complex analyses, as the quantitative one. This one allows determining the probabilities of each risk using statistical analyses of historical database, as well as the monetary value of the related impact.

3. Risk response planning: it consists on the definition of response actions to the identified and prioritized risks. The response to the risks, preventive or corrective, should consider the cost of the reaction face the original expected monetary value, as well as the resultant value monetary of the residual risk (in case the risk is not eliminated entirely due to response actions) for evaluation of the applicability of these reactions.

6. THE CLASSIFICATION OF DETERIORATIONS AS INPUT FOR RISKS ANALYSES

The risks analysis, as it was presented, permits the treatment of the most several types of risks. Applications of that methodology include evaluation of the degree of the risk (since the risks of rupture of structures to the ones of smaller magnitude), occurrence period, country, type and dimensions of the structure, as well as any considerations that be judged important. Consequently what defines the risk type to be analyzed will be the database used.

A database containing deteriorations regarding the design, construction and operation stages of an enterprise is the starting point for the estimate of occurrence of those problems, always considering similar enterprises. That estimate indeed allows the execution of risks analysis and can either determine modification on design, construction, and even operation procedures, considering those database is published for the technical community.

Fig. 1 [5] shows the evolution of risk in each stage of the enterprise dam. It is observed that the risks management in the design, project and operation stages, specially with the premature obtaining of the greatest amount of information possible still in the planning and design stages, generates significant reductions in the risks of the enterprise, mainly due to the low generated contingent and the facilities in impose modification of the enterprise in these stages. While a great ignorance in the initial stages can cause high financial alterations, culminating in inadequate performance of the structures and eventually accidents.

At the same time, this effort on risk management should not be interrupted, but being perpetuated in the operation through interventions and reevaluations.

Taking into account that the effort for the execution of a solid and reliable risk analysis is considerable, a reduced group can be analyzed in which are included only the deteriorations of higher significance, that really put in risk the safety of the structure.

Fig.1Risk evolution on different stages of dam

Évolution du risque dans les plusieurs phases de la vie d'un barrage

The stage of identification of risks, one of the most difficult, is activated due to the existence of a diversified, organized and classified database, considering that it consolidates the acquired experience in the technical community produced by several companies and countries and almost embracing the totality of risks, leaving out only a small portion of new risks.

The authors of this paper stress importance of an organized database for the identification of new risks, pointing out the easiness in this process due to the existence of the tables elaborated by the International Commission on Large Dams. With base in the report of ICOLD, it was possible to analyze the existent codes and, starting from the acquired experience in CEMIG, to do the necessary adaptations, specially including " new " risks in the existent categories.

Concerning the qualitative and quantitative analyses, the existence of an organized database, including data regarding on characteristics of the structures and of the enterprise, as suggested previously, allows to separate data and consequently obtain percentages of occurring of deteriorations for certain types of structures.

As example, considering the universe of CEMIG small hydroelectric, is presented in Fig. 2 [6] statistic data regarding deteriorations.

Risk /Risque

Acceptable Risk Risque acceptable

Fig. 2Main deteriorations in concrete dams

Détériorations principales dans les barrages en concret

As an additional comment, is mentioned the risks analysis in complex systems, where successions of initiators events should be considered, as well as associated consequences. It is the case of a dam failure, which can even demand complementary approaches.

The event tree is a graphic structure that shows the several alternatives included in a situation that is being considered and your respective implications as well as the generated sceneries. To each alternative, can be associated a cost and an occurrence probability, generating the Expected Monetary Value or even other measure of interest for the organization. Fig. 3 (modified of [7]) shows the probability for a succession of events associated to dam failure due to a seismic disturbance.

In [8] starting from a consistent and extensive database, a complex event tree was developed to evaluate the possibility of failure due to piping through the foundation, piping from the embankment and piping from the embankment into the foundation for UHE São Simão in Brazil. The probabilities are shown in the Table 5.

Fig. 3Example of event tree

Example de l’árbre d’évènements

Table 5Results from event tree

Failure Mode Probabilitypiping through embankment 5,30E-05piping through foundation 4,70E-05piping from the embankment into the foundation 1,30E-05

Sum 1,13E-04

Therefore, the probability is 1,13 x 10-4 a year, value compatible according [9], where a probability of the order of 10-4 reveals that the condition or event has not been observed, as well as it would not be identified plausible scenery.

7. CONCLUSIONS

The tables shown in this paper for the classification of deteriorations are important for the appropriate organization of a database and consequently for the execution of risks analyses. However, they need adaptations to facilitate the exchange of information among the involved professionals, making possible an appropriate knowledge management of the design, construction and operation activities of dam and civil structures of hydroelectric plants.

In this context, stands out the importance of creation workgroups in several countries for the accomplishment of necessary improvements in the tables and so that, in medium period, those information can be registered and published in world technical community.

Initial event / Évènement initial

Dam Liquefaction / Liquéfaction du barrage

Dam Failure / Rupture du barrage

Succesion of events / Succession d'éènements

No failureSans rupture Pr = 0,01 x 0,9 x 0,95 = 0,00855

Does not occur Liquefaction 0,95Ne ce déroule pas la

Liquéfaction

Pr = 0,9 failureSismic shake Rupture Pr = 0,01 x 0,9 x 0,05 = 0,00045

Secousse sismìque 0,005

Pr = 0,001No failure

Sans rupture Pr = 0,01 x 0,1 x 0,95 = 0,00067

soil liquefy 0,67Sol se liquéfie

Pr = 0,1 failureRupture Pr = 0,01 x 0,1 x 0,05 = 0,00033

0,33

To publish acquired experiences, especially face to the acquiring services in contracts type EPC means to make possible that, especially designers and constructors, have the knowledge about the current deficiencies of their own performance and therefore adopt new conceptions and methods to avoid the occurrence of the problems verified in the past.

It is pointed out that the continuous improvement intended with the accomplishment of the activities described will only become reality with the involvement of the largest number of professionals and companies.

ACKNOWLEDGEMENTS

The authors wish to acknowledge Cemig in providing information used in

this paper.

REFERENCES

[1] ICOLD – International Commission on Large Dams - Deterioration of dams and reservoirs - December 1983

[2] CBDB - Brazilian Committee on Large Dams - Cadastro Brasileiro de Deterioração de Barragens e Reservatórios - 2004

[3] PMI – A guide to the Project Management Body of Knowledge –PMBOK – 3rd edition - 2004

[4] JR. R., CORREA C. A. et all – Gerenciamento de Riscos em Projetos – Fundação Getúlio Vargas - 2007

[5] MENESCAL, R. A. – A Segurança de Barragens e a Gestão de recursos Hídricos no Brasil – Proágua - 2004

[6] MELO A. V. et all – Principais Deteriorações em Estruturas Civis de PCHS: a Experiência da Cemig – Simpósio Brasileiro sobre Pequenas e Médias Centrais Hidrelétricas - 2008-06-10

[7] HARTFORD D. N. D., BAECHER G.B.– Risk and Uncertainty in Dam Safety – CEA Technologies Dam Safety Interest Group– 2004

[8] LADEIRA J. E. R..– Avaliação de segurança em barragens de terra sob o cenário de erosão tubular regressiva por métodos probabilísticos – UFMG– 2007

[9] CUMMINS P – Guidelines on risk assessment – Australian National Committee on Large Dams – 2003

APPENDIX I

TABLE OF DETERIORATION CODES

LOCAL ICONS DESCRIPTION

Sedimentation Sediments deposition

Floating Materials Branches of trees, leaves,garbage or other floating material

Aquatic Plants Macrophytes, Typha

Invasion Ilegal occupation of areas belonging to the company

Erosion In soil or rock, Slopes, Reservoir banks, stilling basin. Not aplied to concrete

Burning Burned vegetation, Burned building

RE

SE

RV

OIR

AN

D IT

S B

AN

KS

Deforestation Vegetation removal

To form a puddle or pool Water Accumulation,Limited Area, Small Event

Flood Caused by pluvial discharge, Bigger Event

SurgencePercolation of Water Through Rock or Soil or under concrete structures or through or under earth structures

InfiltrationThrough Concrete, Construction Joints, Of Rock - Water percolates through a surface

Leakage In pipes, Expansion Joints, Gates

Moisture Infiltration without dripping, through concrete, masonry or earth

Turbidity Of water

WA

TE

R

Quality of Water Quality of water for human or industrial consumption

Landslide Sliding of Soil or Rock Slopes

Talus-Creep Of Talus

Toppling Of rock structures with columnar jointingSL

OP

ES

Erosion In soil or rock, Slopes, Reservoir banks, stilling basin. Not aplied to concrete.

Settlement Slumping

SubsidenceSettlement in a bounded and "closed" area due to transportation of the bottom material

Piping Desplacement of materials particles due to a forceFormation of Channels/Erosive Furrows Ravines

Insufficiency of Slope Protection Slope areas with vegetal or rockfill protection insufficient

Burrows/Animals Presence Ant Colonies, Termites, Armadillo, Owl

Growth of PlantsTrees and shrubs growing especially in slopes of earth dams and abutments, in the toe of the dam or in an important area that can influence the dam safety

EA

RT

H D

AM

S

High Uplift/Growing Pressurized water from foundation

Wrenching/Pluck out Grids, Metal Pieces, Rock bolts

Fixing Damaged Grids, Metal Pieces, Guard-Rails - Unfixed but not detached

Facing Damaged/ Unfixed Ceramics, Facings, Floor covering, Cement rendering

Drop plates Of concrete, Sprayed Concrete

Detachment Metal plates of suction, Between structures of different materials

OT

HE

R

DE

TE

RIO

RA

TIO

NS

Unatached and rolled rock blocks

SiltationPhysical, chemical and biological - foundation drains, joint drains, internal drainage, drainage holes

ObstructionClogging of Gutters, free jet chute, Water and Sewerage Pipes, Sinkers. Obstruction of drainage holes in case of material falling.

CL

OG

GIN

G

Dirty/Materials Deposition Deposition in the surface without clogging - Not applied to reservoir and waterInst - Omission/Mistake of Identification Including problems with register on database

Inst - Unreliable/Incorrect Reading Identified only through reading analysis data. Including problems with calibration

Inst- Insuficiency/InadequatedIncluding measurement inconsistent with magnitudes expected and the incorrect installation (field observation)

Inst - Damaged Instrument or readout instrument damaged

INS

TR

UM

EN

TA

TIO

N

Inst - Access/Cleaning Problems Including problems with access and instruments maintenance

Cavity/Hole Concreting Problems - Irregular Aggregates, Cavity eroded in concrete

Carbonation Efflorescence of calcium carbonate

Erosion by Cavitation Negative pressure due to water flow

Unlevelling Of Concrete or Rock, Reduction into minor pieces or particles

Deformation Deformation of structural elements, Deflection, Fluency, Structural problem

Bending Deformations of non-structural elements: Grids, Metal pieces, Shafts, Wood pieces

Wearing Process From abrasion. In Concrete, Floor coverings, Pavings

Horizontal Displacement Of concrete blocks

Unlevelling Level difference between concrete blocks or others surfaces

Concrete Expansion Due to alkali-aggregate-reaction (AAR) or sulphation

Gel Extrusion Gel from AAR

Reinforcing bars exposed Loss of reinforcing bars covering

CrackingMinor openings, Several, more Superficial, Generalised. Main Causes:Shrinkage, AAR, High Tensions

CrackCrossing, Bigger openings, In General only one cause: Shear, Differential Settlement

Failure Afeccts structural serviceability or stability

BreakBreak of Pieces, provided that doesn´t affect serviceability or stability of the structure. Main Cause: Mechanical Shock

Vibration Of concrete structure

Incorrect Shape Surfaces contacting flow

MA

INL

Y C

ON

CR

ET

E

Roughness Irregularity Or Projection in the surface that makes difficult the adherence of water

Deformation Metal parts

Organical Decomposition

Heating / High Temperature From environments, From equipment

Absence From Element Absence from element considering the whole

Inexistence When does not exist any part of the whole

Oxidation/Corrosion

Damaged Painting

Drying up Mastic

Noise Excessive or unexpected

Aging / Poor Conservation

Overtopping

Absense of alignment Curb, Axis (center lines)

Irregular road / Depression Irregular road, with wavy edge, holes, superficially wear, erosions

Inappropriate place Inappropriate Access, Inappropriate place For implementation of some activity (Environmental Inadequation use)

Environmental Inadequacy use Water and soil contamination, household and industrial waste, fish trapping

Unknown Of Stability conditions, the location of drainages, weight capacity, extravasation

Inadequacy to the design criteria

Absent Indication Absence from slabs of signalling, no Indication of level

Incorrect Indication

Inoperative Flood-gate

Lack Of space, ventilation, lighting, extravasation capacity

Others

Remove bases Remove base of blocks in support of the bridge pillars, pillars, walls

MIS

CE

LL

AN

EA

Health and Safety

APPENDIX II

Table of causes and remedial measures codes

Concrete dams (gravity, arch, buttress and Rolled Compacted Concrete) and their foundationsCODE CAUSE CODE REMEDIAL MEASURESC01 Concrete Dam 100 Of general natureC01.01 Due to foundation 101 InvestigationC01.01.01 Inadequacy of site investigation 102 MonitoringC01.01.02 Deformation and land subsidence 103 Lowering of reservoir levelC01.01.03 Shear strength 104 Raising of dam crestC01.01.04 Percolation 105 Overall reconstruction (same design)C01.01.05 Internal erosion 106 Reconstruction with new designC01.01.06 Degradation (including swelling) 107 NoneC01.01.07 Initial state of stress 108 Not availableC01.01.08 Tensile stresses at the upstream toe 109 Scheme abandonedC01.01.09 Preparation of foundation surface 200 In FoundationsC01.01.10 Strengthening treatment 201 Watertightening treatmentC01.01.11 Grout curtains and others watertight systems 202 Drain and filter construction or repairC01.01.12 Drainage system 203 Strengthening by grouting or other methods C01.01.13 Sealing of galleries, shafts and boreholes used for investigation 204 Filling in of fractures and cavitiesC01.02 Due to concrete 205 AnchoringC01.02.01 Reaction of concrete constituents (including alkali-aggregate reaction) 206 Instruments installation

C01.02.02Reactions between masonry constituents and the environment (including dissolution of calcium hydroxide)

300 Concrete Dam or Roller Compacted Concrete

C01.02.03 Resistance to freezing and thawing 301 Watertightening treatmentC01.02.04 Attack by bacteria 302 Drain construction or repairC01.02.05 Compressive strength 303 Thermal protectionC01.02.06 Shear strength 304 FacingC01.02.07 Tensile stresses 305 Reconstruction of deteriorated zonesC01.02.08 Permeability 306 Execution of jointsC01.02.09 Concreting (including order of casting of monoliths) 307 Strengthening by grouting C01.02.10 Cooling 308 Strengthening by anchoringC01.02.11 Structural joints (including watertight systems) 309 Strengthening by shape correctionC01.02.12 Arrangement of reinforcement and anchorages 310 Strengthening by structural element constructionC01.02.13 Compaction 311 Element substitutionC01.03 Due to unforeseen actions or to actions of exceptional magnitude 312 Anticorrosive treatmentC01.03.01 Hydrostatic pressure and pressure from accumulated silt 313 Contention, strengthening or protection of slopesC01.03.02 Uplift 314 Superficial drainage system constructionC01.03.03 Earthquakes (natural or man - made) 315 Vegetation suppressionC01.03.04 External temperature variation 316 Instruments installationC01.03.05 Temperature variations due to the heat of hydration 317 Installation/repairs of pumping systemC01.03.06 Moisture variation 318 Installation/repairs of lightening system

C01.04Due to structural behavior of the arch and multiple arch dams (including the construction period)

319 Health and safety adaptation

C01.04.01 Shape of the dam and its position in the valley 320 Environmental adaptationC01.04.02 Tensile stresses 321 Patrimonial conservationC01.04.03 Stress concentration due to shape discontinuities in the foundation surfaceC01.04.04 Stress concentration due at openings and shape discontinuities C01.04.05 Artificial abutmentsC01.04.06 Distribution and types of joints C01.04.07 FacingsC01.05 Due to structural behavior of gravity, buttress and RCC damsC01.05.01 Shape of the dam and its position in the valley C01.05.02 Tensile stressesC01.05.03 Stress concentration due to shape discontinuities in the foundation surface C01.05.04 Stress concentration at openings and shape discontinuitiesC01.05.05 Distribution and types of jointsC01.05.06 FacingsC01.05.07 Joints between placements liftC01.06 Due to monitoringC01.06.01 Inadequacy of instrumentationC01.06.02 Insufficient instrumentationC01.06.03 Periodic inspectionsC01.07 Due to maintenanceC01.07.01 Vegetation suppressionC01.07.02 Cleaning of drainsC01.07.03 Control of seepageC01.07.04 Maintenance of slope protectionsC01.07.05 Instrumentation deteriorationC01.07.06 Inadequate periodicity of maintenance C01.08 OthersC01.08.01 Incorrect designC01.08.02 Incorrect constructionC01.08.03 VandalismC01.08.04 Not identified

Earth and Rockfill Dams and Cofferdams and their foundations

CODE DESCRIPTION CODE REMEDIAL MEASURESC02 Earth and Rockfill Dams and Cofferdams 100 Of general natureC02.01 Due to foundations 101 InvestigationC02.01.01 Inadequacy of site investigations 102 MonitoringC02.01.02 Deformation and land subsidence 103 Lowering of reservoir levelC02.01.03 Shear strength 104 Raising of dam crestC02.01.04 Percolation 105 Overall reconstruction (same design)C02.01.05 Internal erosion 106 Reconstruction with new designC02.01.06 Degradation (including swelling) 107 NoneC02.01.07 Initial state of stress 108 Not availableC02.01.08 Liquefaction 109 Scheme abandonedC02.01.09 Permafrost 200 In foundationsC02.01.10 Preparation of foundation surface 201 Watertightening treatmentC02.01.11 Poding during construction 202 Drain and filter construction or repairC02.01.12 Strengthening treatment 203 Strengthening by grouting or other methods C02.01.13 Watertight systems (cutoff walls and trenches, grout curtains) 204 Filling in of fractures and cavitiesC02.01.14 Impervious blankets 205 AnchoringC02.01.15 Drainage systems and filters 206 Instruments installationC02.01.16 Sealing of galleries, shafts and boreholes used for investigation 400 Earth and Rockfill Dams and CofferdamsC02.02 Due to embankment materials and method of construction 401 Impervious core repairC02.02.01 Fine clays 402 Construction or repair of other watertight systemsC02.02.02 Organic clays 403 Drain and filter construction or repairC02.02.03 Dispersive clays 404 Slope protection construction or repairC02.02.04 Silts and fine uniform sands 405 Filling in of fractures and cavitiesC02.02.05 Soluble soils 406 Reconstruction of deteriored zonesC02.02.06 Expansive soils 407 Construction of upstream berm or other stabilization methods

C02.02.07 Residual soils with boulders 408Downstream slope flattening, construction of downstream berm or other stabilization methods

C02.02.08 Decomposed rocks 409 Stabilization of abutments slopesC02.02.09 Weatherable rocks 410 Superficial drainage system constructionC02.02.10 Grain-size distribution 411 Vegetation suppressionC02.02.11 Water content 412 Instruments installationC02.02.12 Placing 413 Health and safety adaptationC02.02.13 Compaction 414 Environmental adaptationC02.02.14 Drying 415 Patrimonial conservationC02.02.15 Temporary slopesC02.02.16 Frost effectsC02.03 Due to unforeseen actions or to actions of exceptional magnitudeC02.03.01 Hydrostatic pressure and pressure due to silt accumulation C02.03.02 UpliftC02.03.03 Pore pressureC02.03.04 PrecipitationC02.03.05 Waves in the reservoirC02.03.06 Freezing and thawingC02.03.07 Earthquakes (natural or man-made) C02.04 Due to structural behavior of the damC02.04.01 Shape of the dam its position in the valleyC02.04.02 Impervious coreC02.04.03 Other watertight systemsC02.04.04 Transition zonesC02.04.05 ShouldersC02.04.06 Filters (including materials and construction)C02.04.07 Drainage systems (including materials and construction)C02.04.08 Slope protection

C02.04.09Bonding between concrete (masonry, steel ...) structures and adjoining embankments

C02.04.10Differential movement (including load transfer, cracking, arching, hydraulic fracture)

C02.04.11 Percolation C02.04.12 Internal erosionC02.04.13 LiquefactionC02.04.14 Upstream slipsC02.04.15 Downstream slipsC02.04.16 Upstream blocks slidingC02.04.17 Downstream blocks slidingC02.05 Due to monitoringC02.05.01 Inadequacy of instrumentationC02.05.02 Insufficient instrumentationC02.05.03 Periodic inspectionsC02.06 Due to maintenanceC02.06.01 Vegetation suppressionC02.06.02 Cleaning of drainsC02.06.03 Control of seepageC02.06.04 Maintenance of slope protectionsC02.06.05 Burrows caused by animalsC02.07 OthersC02.07.01 Incorrect designC02.07.02 Incorrect constructionC02.07.03 VandalismC02.07.04 Not identified

Masonry and Wood Dams and their FoundationsCODE DESCRIPTION CODE REMEDIAL MEASURESC03 Masonry and Wood Dam 100 Of a general natureC03.01 Due to foundation 101 InvestigationC03.01.01 Inadequacy of site investigation 102 MonitoringC03.01.02 Deformation and land subsidence 103 Lowering of reservoir levelC03.01.03 Shear strength 104 Raising of dam crestC03.01.04 Percolation 105 Overall reconstruction (same design)C03.01.05 Internal Erosion 106 Reconstruction with new designC03.01.06 Degradation (including swelling) 107 NoneC03.01.07 Initial state of stress 108 Not availableC03.01.08 Tensile stresses at the upstream toe 109 Scheme abandonedC03.01.09 Preparation of foundation surface 200 In foundationsC03.01.10 Strengthening treatment 201 Watertightening treatmentC03.01.11 Grout curtains and other watertight systems 202 Drain and filter construction or repairC03.01.12 Drainage systems 203 Strengthening by grouting or other methods C03.01.13 Sealing of galleries, shafts and boreholes used for investigation 204 Preenchimento fratura/cavidadeC03.02 Due to mortar 205 AnchoringC03.02.01 Reaction of masonry constituents (including alkali-aggregate reaction) 206 Instruments installation

C03.02.02Reactions between masonry constituents and the environment (including dissolution of calcium hydroxide)

300 In masonry and wood dams

C03.02.03 Resistance to freezing and thawing 301 Watertightening treatmentC03.02.04 Attack by bacteria 302 Drain construction or repairC03.02.05 Compressive strength 303 Thermal protection (excluding facing)C03.02.06 Shear strength 304 FacingC03.02.07 Tensile stresses 305 Reconstruction of deteriorated zonesC03.02.08 Permeability 306 Execution of jointsC03.02.09 Masonry construction (including watertight systems) 307 Strengthening by groutingC03.02.10 Structural joints (including watertight systems) 308 Strengthening by anchoringC03.03 Due to stone 309 Strengthening by shape correctionC03.03.01 Weathering 310 Strengthening by structural element constructionC03.03.02 Joints between stones 311 Element substitutionC03.04 Due to unforeseen actions or to actions of exceptional magnitude 312 Anticorrosive treatmentC03.04.01 Hydrostatic pressure and pressure from accumulated silt 313 Contention, strengthening or protection of slopesC03.04.02 Uplift 314 Superficial drainage system constructionC03.04.03 Earthquakes (natural or man - made) 315 Vegetation suppressionC03.04.04 External temperature variation 316 Instruments installationC03.04.05 Variations due to changes of moisture content 317 Installation/repairs of lightening systemC03.04.06 Burning 318 Health and safety adaptationC03.04.07 Attack by animals 319 Environmental adaptationC03.05 Due to wood and other materials 320 Patrimonial conservationC03.05.01 Organical decompositionC03.05.02 Oxidation

C03.06Due to structural behavior of masonry and wood dams (including the construction period)

C03.06.01 Shape of the dam and its position in the valleyC03.06.02 Tensile stressesC03.06.03 Stress concentration due to shape discontinuities in the foundation surfaceC03.06.04 Distribution and types of jointsC03.06.05 FacingsC03.07 Due to monitoringC03.07.01 Inadequacy of instrumentationC03.07.02 Insufficient instrumentationC03.07.03 Periodic inspectionsC03.08 Due to maintenanceC03.08.01 Vegetation suppressionC03.08.02 Cleaning of drainsC03.08.03 Control of seepageC03.08.04 Pumping of percolated waterC03.08.05 Deterioration of instrumentationC03.08.06 Deterioration of materialsC03.08.07 Inadequate periodicity of maintenanceC03.09 OthersC03.09.01 Incorrect designC03.09.02 Incorrect constructionC03.09.03 VandalismC03.09.04 Not identified

Appurtenant works, their foundations and equipmentsCODE DESCRIPTION CODE REMEDIAL MEASURESC04 Appurtenant works 100 Of a general natureC04.01 Due to the foundations 101 InvestigationC04.01.01 Inadequacy of site investigations 102 MonitoringC04.01.02 Deformation and land subsidence 103 Lowering of reservoir levelC04.01.03 Shear strength 104 Raising of dam crestC04.01.04 Percolation 105 Overall reconstruction (same design)C04.01.05 Internal erosion 106 Reconstruction with new designC04.01.06 Degradation (including swelling) 107 NoneC04.01.07 Initial state of stress 108 Not availableC04.01.08 Preparation of foundation surface 109 Scheme abandonedC04.01.09 Strengthening treatment 200 In foundationsC04.01.10 Grout curtains and other watertight systems 201 Watertightening treatmentC04.01.11 Drainage systems 202 Drain and filter construction or repairC04.01.12 Sealing of galleries, shafts and boreholes used for investigation 203 Strengthening by grouting or other methods C04.02 Due to concrete 204 Filling in of fractures and cavitiesC04.02.01 Reactions of concrete constituents (including alkali-aggregate reaction) 205 Anchoring

C04.02.02Reactions between concrete constituents and the environment (including solution of calcium hydroxide) 500 In appurtenant works

C04.02.03 Resistance to freezing and thawing 501 Discharge increaseC04.02.04 Attack by bacteria 502 Construction of additional appurtenant worksC04.02.05 Mechanical strength (including tensile strength) 503 Overall reconstruction of appurtenant works

C04.02.06 Permeability504

Partial reconstruction with strengthening or structural changes

C04.02.07 Concreting (cooling included) 505 Shape correction of surfaces contacting flowC04.02.08 Cracking 506 Aeration devices: construction or increase of capacity

C04.02.09 Surface finishing (facing included)507

Repair of surfaces contacting flow (including facing and special treatments)

C04.02.10 Structural joints (watertight systems included) 508 Joint watertightening treatmentC04.02.11 Arrangement of reinforcements and anchorages 509 Construction and repair of drainsC04.02.12 Erosion by abrasion 510 Slope protection and stabilization

C04.02.13 Erosion by cavitation 511Sediment discharge removal from surfaces contacting flow

C04.03 Due to rip-rap 512Construction, modification and repair of valves and gates

C04.03.01 Disintegration of blocks513

Establishment and updating of rules for gate and valve operation

C04.03.02 Removal of blocks514

Reconstruction of deteriorated zones and other correcting measures

C04.04 Due to steel and other materials 515 Abandon of appurtenant worksC04.04.01 Chemical and biological agents 516 Health and safety adaptationC04.04.02 Erosion by abrasion 517 Environmental adaptationC04.04.03 Erosion by cavitation 518 Patrimonial conservationC04.04.04 Mechanical strengthC04.05 Due to unforeseen actions or to actions of exceptional magnitudeC04.05.01 Hydrostatic pressure and pressure due to silt accumulationC04.05.02 Pressure and impact of iceC04.05.03 UpliftC04.05.04 Earthquakes (natural or man-made)C04.05.05 Temperature and moisture variationsC04.06 Due to structural behavior

C04.07Due to water flow, water level and water-borne debris (including construction periods)

C04.07.01 Excessive rates of flowC04.07.02 TurbulenceC04.07.03 VorticesC04.07.04 WavesC04.07.05 Abnormal pressuresC04.07.06 Entrapped airC04.07.07 Inaccurate discharge curvesC04.07.08 Solid materials floating materialsC04.07.09 Discharge of floating materialsC04.08 Due to local scourC04.09 Due to operationC04.09.01 Sudden opening of the discharge equipmentC04.09.02 Inadequate instruction for operating the discharge equipmentC04.10 Due to monitoringC04.10.01 Inadequacy of instrumentationC04.11 Due to maintenanceC04.11.01 Periodic inspectionsC04.11.02 Cleaning of drainsC04.11.03 Control of seepageC04.11.04 Pumping of seepage waterC04.11.05 Deterioration of measurement instrumentationC04.11.06 Malfunction of discharge equipmentC04.11.07 Debris in stilling basins

Buildings, Industrial Area and UrbanizationCODE DESCRIPTION CODE REMEDIAL MEASUREC99 Buildings/Others 900 Of a general natureC99.01 Due to structural behavior 901 Investigation/researchC99.01.01 Stress concentration at openings and shape discontinuities 902 MonitoringC99.01.02 Distribution and types of joints 903 Drain and filter construction or repairC99.01.03 Incorrect design 904 Thermal protection (excluding facing)C99.01.04 Incorrect construction 905 FacingC99.02 Due to foundation 906 WaterproofingC99.02.01 Inadequacy of site investigations 907 Construction/repairs of jointsC99.02.02 Deformations and land subsidence 908 Strengthening of structureC99.02.03 Percolation 909 Strengthening of foundationC99.02.04 Diferential settlements 910 Reconstruction of deteriorated zonesC99.02.05 Drainage systems and filters 911 PaintingC99.03 Due to concrete 912 CleaningC99.03.01 Reactions of concrete constituents (including alkali-aggregate reaction) 913 Opening

C99.03.02Reaction between concrete constituents and the environment (including dissolution of calcium hydroxide) 914 Anchoring

C99.03.03 Compressive strength 915 Element substitutionC99.03.04 Shear strength 916 PavingC99.03.05 Tensile strength 917 ReforestationC99.03.06 Permeability 918 Torrent trainingC99.03.07 Concreting (including order of casting of monoliths) 919 Slope regularization, protection and strengtheningC99.03.08 Concrete curing 920 GroundingC99.03.09 Structural joints (including watertight systems) 921 StraighteningC99.03.10 Arrangement of reinforcements and anchorages 922 LevelingC99.04 Due to materials/facings 923 CalibrationC99.04.01 Inadequate materials 924 Overall reconstruction (same design)C99.04.02 Natural deterioration of materials 925 Reconstruction with new designC99.04.03 Abrasion resistance 926 Scheme abandonedC99.04.04 Mechanical resistance 927 NoneC99.04.05 Incorrect waterproofing 928 OthersC99.05 Due to unforeseen actions or to actions of exceptional magnitudeC99.05.01 Exceptional rain actionC99.05.02 Exceptional wind actionC99.05.03 Silt accumulationC99.05.04 Biological and chemical agentsC99.05.05 Exceptional shock or impactC99.05.06 BurningC99.05.07 WeatheringC99.05.08 Exceptional useC99.05.09 Forest fireC99.05.10 Exceptional upliftC99.05.11 External temperature variationC99.05.12 Moisture variationC99.05.13 Exceptional vibrationC99.06 Due to maintenanceC99.06.02 Cleaning Reservoirs and DownstreamC99.06.03 Slope protection maintenance CODE REMEDIAL MEASURESC99.06.04 Burrows caused by animals 100 Of a general natureC99.06.05 Seepage control 101 InvestigationC99.07 Due to monitoring 102 MonitoringC99.07.01 Periodic inspections 103 Lowering of reservoir levelC99.07.02 Inadequate instrumentation 104 Raising of dam crestC99.08 Others 105 Overall reconstruction (same design)C99.08.01 Incorrect design 106 Reconstruction with new designC99.08.02 Incorrect construction 107 NoneC99.08.03 Vandalism 108 Not availableC99.08.04 Not identified 109 Scheme abandoned

600 In reservoir601 Reforestation

Reservoirs and Downstream 602 Torrent trainingCODE DESCRIPTION 603 Sediment discharge diversionC05 Reservoirs 604 Slope regularization, protection and strengtheningC05.01 Slope sliding 605 DrainingC05.02 Overstuning of rock blocks 606 WatertighteningC05.03 Permeability 607 DredgingC05.04 Silting 700 DownstreamC05.05 Ecological balance 701 DrainingC05.06 Waves impact 702 Slope regularization, protection and strengtheningC06 Downstream 703 Reconstruction of deteriorated zonesC06.01 Equilibrium of river bed 704 Execution of joints C06.02 Slope instability 705 Strengthening by groutingC06.03 Ecological balance 706 Strengthening by anchoringC06.04 Waves impact 707 Strengthening by shape correction

APPENDIX III

DETERIORATION REGISTRATION FORM

SAMAMBAIA (low flow augmentation development)

DETERIORATION PLACE: Earth dam – downstream toe

DETERIORATION Surgence with material transportation beside the morning glory spillway concrete gallery

whose increase started a subsidence.

DETECTION TIME: 1991 - During the first filling

DETERIORATION TIME: T2 - During the first filling

DETECTION METHOD: D01 - Direct observation

CAUSE: C02.04.07 - Drainage systems incl mat and const; C02.07.02 - Others construction mistakeConstruction of the internal drainage system in disagreement with the design: the drain is constituted by a crushed stone layer involved with sand, connected to the vertical filter and located beside the gallery wall, with discharge and measurement point to be defined during construction. The drainage was built, but its discharge point was buried under downstream toe of the dam. Percolation water applied pressure over the embankment, resulting in piping of sand drain and furthermore subsidence.

CAUSE TIME: During construction

REMEDIAL MEASURES: R403 - Drain and filter const or repair, R405 - Filling in of cracks and cavitiesInitially, aiming to keep the dam stability, a sand layer was thrown inside the erosion and installed tubes for drainage of percolated water. At this point it was elaborated a design to recover the internal drainage system, that determined the construction of a multiple layers drain. Before the construction it was necessary a partial lowering of reservoir level and installation of a temporary pumping system to lower the phreatic surface level and avoid piping.

CURRENT BEHAVIOUR: No material deposition is observed, nor either indications of slumping or bad

operation of the dam internal drainage system.

FUTURE MEASURES: Installation of piezometers and water level indicators in the downstream toe and

additional monitoring with periodic inspections.

LESSONS LEARNED: During the construction of dams, the maximum attention should be given to

the drainage system, especially in the interfaces soil/concrete, because its obstruction can cause

serious risks to the structural safety. For interventions at dam toe it is advisable to lower the reservoir

level so much as possible to reduce uplift and risk of piping.

The following information are part of a specific database and they are presented for better understanding of the anomalous behavior.

SAMAMBAIA (low flow augmentation )

GENERAL DATA DAM

Owner: Companhia Energética de Minas Gerais - Brazil Type: homogeneous earth fill

End of construction: October1990 Foundation: alluvium

Type of contract: measure and value contract Maximum height: 26,5m

Crest length: 300m

KEY WORDS

Deterioration, dams, classification, risk analysis, São Simão.

ABSTRACT

Taking into account the great amount of used resources, the considerable number of people involved and affected in the construction of hydroelectric plants and mainly the risks imposed by the implantation of dams; studies that allow to diagnose and even to treat potential risks are extremely valuable.

In that context, it is pointed out that the collection and the cataloguing of deteriorations are fundamental for the construction of a solid, reliable and practice database, which subsidizes the risk analyses regarding dam safety.

This paper presents the method used by CEMIG for the cataloguing of deteriorations in dams and hydroelectric plants, including some applications on risk analysis. That method has as main bases the technical report of ICOLD 1983 that gathers information globally collected and the experience of the CEMIG’s dam safety team.

LE RÉSUMÉ

En considérant le grand montant de ressources utilisés, le nombre considérable de gens engagés dans la construction des usines hydroélectriques et principalement les risques produit par l’implantation de barrages, les études qui autorisent diagnostiquer et traiter des risques potentiels sont extrêmement précieux.

Dans ce contexte, il est signalé que la collecte et le catalogue de détériorations sont fondamentaux pour la construction d’une base de données solide, fiable et pratique qui subventionne les anlyses de risque quant à la securité de barrages.

Cet article présente la méthode utilisée par CEMIG pour les détériorations dans les barrages et les usines hydroélectriques. Cette méthode a comme bases principales le rapport technique d’ICOLD 1983 lequel rassemble, des informations collectées mondialement et l’expérience de la securité de barrages du CEMIG.