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INDIANA DAM SAFETY PART 4

INSPECTION MANUAL

DAM SAFETY FACT SHEETS 2003 EDITION

Department of Natural Resources

Division of Water

Indianapolis, Indiana
http://www.in.gov/dnr/waterhttp://www.in.gov/dnr/waterhttp://www.in.gov/dnr/waterhttp://www.in.gov/dnr/water


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INDIANA DAM SAFETY

INSPECTION MANUAL

PART 4 DAM SAFETY FACT SHEETS

2003 EDITIONPreface

The Indiana Dam Safety Inspection Manual is based on accepted practice and consists of informationdeveloped from existing documentation on dam safety inspections obtained from state and federalagencies. Dam safety is a complex and multi-disciplinary practice that continues to evolve asprofessionals gain a better understanding of how the various dam components behave under differentloading conditions and how societys level of risk tolerance changes with time. This manual is a livingdocument that will change to reflect evolving national practice. As this manual improves with time, it willprovide a stable reference for good dam safety inspection practice as administrators, program priorities,and statutes change. It consists of four separate parts:

Part 1 of the Manual describes ownership responsibilities and roles, risks and hazards of dam failure, andprovides a detailed overview of dams in Indiana.

Part 2 presents guidelines for operating and maintaining a dam, including specific instructions on how toprepare a management and maintenance plan and how to respond to emergencies.

Part 3 provides guidance on evaluating dam safety and performing dam inspections. It covers whoshould perform the inspections and how, and provides guidance on identifying and reporting damdeficiencies and problems.

Part 4, this part, is a compilation of Dam Safety Fact Sheets that present information on a variety of damoperational issues, such as seepage, slope protection, embankment stability, and spillway design, toname a few.

This manual should not be used in lieu of appropriate dam safety technical courses or training by a damsafety professional in the area of dam inspection. However, it should be used by experienced dam safetyprofessionals as a reference and reminder of the aspects required to make a thorough dam safetyinspection and evaluation. It should be stressed, however, that inspections alone do not make a damsafe; timely repairs and maintenance are essential to the safe management and operation of every dam.

The dam owner is responsible for maintaining the dam in a safe condition, and should do whatever isnecessary to avoid injuring persons or property. As once stated by a highly respected legal scholar, "It isclear that compliance with a generally accepted industry or professional standard of care, or withgovernment regulations, establishes only the minimal standard of care. Courts may assess a higherstandard of care, utilizing the "reasonable person" standard and foreseeability of risk as the criteria. It isfair to say that persons who rely blindly upon a governmental or professional standard of care, pose great

danger to others, and present a legal risk to themselves, when they know or reasonably should know thatreasonable prudence requires higher care."

This manual was prepared by:

Christopher B. Burke Engineering, Ltd.115 West Washington StreetIndianapolis, Indiana 46204

Department of Natural Resources

Division of Water

Indiana olis Indiana


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Indiana Dam Safety Inspection ManualComments Form

Although significant effort went into the completeness and accuracy of this manual, it is recognized thatsome information may not reflect all the various practices or viewpoints held by all dam safetyprofessionals. In a document of this size, it is further acknowledged that there may be errors, or worse

yet, a misleading phrase that would diminish the desired result of dam safety. The contributors of thismanual encourage dam safety professionals to provide comments to the Indiana Department of NaturalResources, Division of Water to help improve and keep this manual up-to-date.

Comments:

Comments provided by:

Name Date

Organization

Address

City State Zip Code

Please forward a copy of this form to:

Indiana Department of Natural ResourcesDivision of Water402 West Washington Street, Room W264Indianapolis, IN 46204-2748

Indiana Dam Safety Inspection Manual 8/28/03 iii


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Indiana Department of Natural Resources Dam Safety Inspection Manual

TABLE OF CONTENTS

PART 4 DAM SAFETY FACT SHEETS

PREFACE

ACKNOWLEDGEMENTS AND DISCLAIMER

INDIANA DAM SAFETY INSPECTION MANUAL COMMENTS FORM

Fact Sheet 03-01 Dam Hazard Classification

Fact Sheet 03-02 Geological Considerations

Fact Sheet 03-03 Earth Dam Failures

Fact Sheet 03-04 Embankment Instabilities

Fact Sheet 03-05 Inspection of Concrete Structures

Fact Sheet 03-06 Problems with Concrete Materials

Fact Sheet 03-07 Concrete Repair Methods

Fact Sheet 03-08 Seepage through Earthen Dams

Fact Sheet 03-09 Trees and Brush

Fact Sheet 03-10 Outlet Erosion Control Structures

Fact Sheet 03-11 Lake Drains

Fact Sheet 03-12 Ground Cover

Fact Sheet 03-13 Design and Maintenance of TrashRacks

Fact Sheet 03-14 Rodent Control

Fact Sheet 03-15 Upstream Slope Protection

Fact Sheet 03-16 Problems with Metal Materials

Fact Sheet 03-17 Problems with Plastic Materials

Fact Sheet 03-18 OpenChannel Spillways Chutes and Weirs

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Indiana Department of Natural Resources Dam Safety Inspection Manual

Table of Contents 8/28/03 v

Fact Sheet 03-19 Open Channel Spillways Earth and Rock

Fact Sheet 03-20 Spillway Conduit System Problems

APPENDICES

APPENDIX A References


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FACT SHEET 03-01 8-28-03

Dam Safety: Dam Hazard Classification

Classification of dams is defined in the IndianaCode (IC), Section 14-27-7.5. Dams which areexempt from the Indiana Department of NaturalResources (IDNR), Division of Water jurisdictionare defined in Indiana Revised Code, Section 14-27-7.5. The classification system divides damswhich are under the jurisdiction of the Division ofWater into three classes: high hazard, significanthazard, and low hazard. The dam owners

engineer must determine the hazard classificationof the dam during design. The dam owner hasthe option to have a detailed breach analyses(performed by the owners hydraulic engineer) tobetter determine the hazard classification.Classification of dams is necessary to provideproper design criteria and to ensure adequatesafety factors for dams according to the potentialfor downstream damage should the dam fail.

A dam is currently exempt from the statesauthority under IC Section 14-27-7.5 if it has adrainage area that is not more than one (1)square mile, if it does not exceed twenty (20) feetin height, and if its volume does not exceed morethan one hundred (100) acre-feet of water.However, a dam that does not fall under thestates authority is still categorized by the hazardclassification system, and will be required to

comply with the corresponding safetyrequirements.

Part 1 of the Indiana Dam Safety InspectionManual provides additional details on dam hazardclassification. Table 1 on page 2 of this FactSheet provides guidelines for determining thehazard classification of dams.

Any questions, comments, concerns, or fact sheetrequests should be directed to the Division ofWater at the following address:

The classification system for dams in Indiana wasmodeled after the Federal Guidelines for DamSafety established in 1979. The following

parameters are the governing criteria for theclassification: Indiana Department of Natural ResourcesDivision of Water402 West Washington Street

High Hazard - A structure the failure of which maycause the loss of life and serious damage tohomes, industrial and commercial buildings, publicutilities, major highways, or railroads.

Indianapolis, IN 46204(317) 232-4160 (Voice) (317) 233-4576 (Fax)http://www.in.gov/dnr/water

Additional ResourcesSignificant Hazard - A structure the failure ofwhich may damage isolate homes and highways,or cause the temporary interruption of public utilityservices.

State of Indiana, Department of NaturalResources, Division of Water,General GuidelinesFor New Dams & Improvements To ExistingDams In Indiana

Low Hazard - A structure the failure of which may

damage farm buildings, agricultural land, or localroads.

Indiana Code (IC) 14-27-7.5, Chapter 7.5,Regulation of Dams

Each dam would be evaluated on the precedingcriteria and placed in the highest class that anyone of these criteria might meet. The Division ofWater, in accordance with the IC Section 14-27-7.5, has the right to reclassify any dam as a resultof a change in circumstances not in existence atthe time of the initial classification.

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TABLE 1 - HAZARD CLASSIFICATION FOR DAMS

AREA AFFECTED BY DAM BREACHDAMAGE TO:

LOW SIGNIFICANT HIGH

LOCATION Rural or AgriculturalDamage would be minimal

and would mostly occur on

dam owners property. Nobuilding, road, railroad, utility,

or individual significantly

affected.

Predominantly Rural orAgriculturalbut roads, buildings,

utilities or railroads may be

damaged.

Developing or Urban

Where individuals could be seriously

injured or killed. Buildings, roads,

railroads or utilities seriouslydamaged.

POTENTIAL LOSS OF LIFE

Flood depths greater than 1

foot in occupied quarters.

Potential of loss of life in

recreational areas where adequatewarning systems are

not available.

No No Yes

ROADSCounty Roads/Single Lane State

Roads (serving as the only access to

a community), Dual lane State

Roads, U.S. and Interstate Roads.

No Damage May DamageDamage may occur when road

surface acts as weir and depth

of flow is greater than 2 feet

over road.

Serious DamageInterruption of service for more

than 1 day.

RAILROADS

Operating RailroadsNo Damage May Damage

Damage may occur when railroad

surface acts as weir and depth of flowis greater than 2 feet over railroad.

Serious Damage

Interruption of service for more

than I day.

BUILDINGS

Homes-Single family residences,

apartments, nursing homes, motelsand hospitals

No Damage May Damage

Any flooding against buildingSerious Damage

Damage will occur when the product

of velocity fps at the building, timesthe depth of flow

compromises the integrity of thestructure.

BUILDINGS (contd.)

Industrial/Commercial/Public

(schools, churches, libraries

Etc).

No Damage May DamageKind, construction and contents of

building must be evaluated.

General damage may occur at any

depth of flooding

Serious DamageKind, construction, and contents

of building must be evaluated.

General serious damage can occur at a

depth of 3 feet.

UTILITIES No Damage May Damage

Damage may occur to relativelyimportant utilities when buried lines

can be exposed by erosion and when

towers, poles and above groundlines can be damaged by

undermining or by debris produced

from flood plain.

Serious Damage

Interruption of service to interstate andintrastate power and communication

lines serving

towns, communities, and significantmilitary and commercial facilities in

which disruption of power and

communication would adversely affectthe economy, safety, and general well-

being of the area for more than 1 day.

Source: Indiana Department of Natural Resources, Division of Water,General Guidelines for New Dams and Improvements to Existing Dams in

Indiana, 2001 Edition.


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FACT SHEET 03-02 8-28-03

Dam Safety: Geological Considerations

Geological Setting

The geological setting is very important factorwhen designing or inspecting dams. It is crucialthat the inspector fully understand the geologicalfeatures and conditions of the site to better assessproblems and deficiencies. For example, a damlocated in a glacial outwash area is likely to besitting on permeable granular materials, whichwould tend to transmit water (seepage) in thefoundation and abutment areas.

Site-specific information obtained from ageotechnical exploration program will better defineand qualify the subsurface conditions in a givengeological setting. For example, a dam located ina karst geological setting will require subsurfaceexploration data to better define the physicalparameters and extent of the typical solutionfeatures (voids and joint openings) in thefoundation, abutment and spillway areas of the

structure.

All dams should be assessed in light of both thelocal site and regional geological conditions. Inaddition to knowing the construction history of thedam and appurtenant structures, the inspector orthe inspection team should have knowledge of thepotential geologic factors that may influence theperformance and safety of an existing dam.

Indiana dams typically consist of embankmentsmade of earth materials over soil or rockfoundations with auxiliary channel spillways

through natural ground. As such, dams in specificregions tend to have similar characteristic orpotential problems, some of which were notconsidered in the original design but lateremerged as geologic hazards.

Many existing dams were constructed withoutappropriate methods and/or components toadequately address the existing geologicmaterials or the geologic conditions. Some of thedam safety deficiencies, as listed below, are a

result of the dam builder not recognizing thephysical characteristics and technical problems ofcertain geologic materials/conditions andimplementing an appropriate design to mitigatethe problems.

Settlement, instability and/or cracking ofthe dam may reflect weak foundationconditions or unsuitable soil materials inthe embankment.

Seepage and/or leakage at thedownstream toe or abutment/groin areasare frequently associated with thepermeability characteristics of theunderlying bedrock or soil.

Natural hazards such as landslides,subsidence, and seismic events mayquickly cause a component of the dam tofail leading to an uncontrolled breach.

Physiographic Divisions

Indiana is located within the Central LowlandProvince, which consists of gently sloping andnearly flat-lying bedrock overlain with glacialmaterials in about two-thirds of the state. TheState lies over a broad crested structural area,known as an anticline, trending northwest tosoutheast, which separates the Michigan Basin onthe north from the Illinois Basin on the southwest.

The Indiana Geological Survey (IGS)has furtherdivided the state into physiographic regions anddivisions to better group landscapes of similar

features (see Figure 1, Physiographic Divisions ofIndiana). There are twenty three (23) distinctPhysiographic Divisions in Indiana.

Some of the geologic factors for eachPhysiographic Division that may influence theintegrity, safety, upgrade and operation of anexisting dam are shown in the attached table.

Although general, Physiographic Divisions doprovide the framework for a better understandingof the most common, known problematic aspects

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or geologic hazards associated with various areasin the State.

It is important to note that the division boundariesare not finite, and dam locations near boundariesmay have geologic factors associated with bothdivisions. Further, the geologic factors presentedfor a given division are indicators and will not bean issue at every existing dam site in a givenregion.

As more performance records and experience areobtained on dams in the Physiographic Divisions,the geologic factors will be updated. To that end,the dam inspector should have an understandingof geologic factors that may influence the safety ofan existing dam or consult with a licensedprofessional geologist for a report on the localcondition for a specific site.

Figure 1contains a physiographic map of Indianawhich shows regional geologic conditions. Table1 may help define potential conditions which maybe present based on the physiographic regionwhere the dam is located. This information can beuseful for evaluating dam seeps, foundation, orsettlement issues and should be checked beforethe field inspection is performed. If no other localor regional geological data is available, Figure 1and Table 1 can be used to help define potentialconditions at the dam site.

Glacial Control

The east and west flanks of the southern half ofthe state and the entire northern half of the stateare overlain by tens to hundreds of feet ofunconsolidated sediments. These accumulationsof till and outwash filled the bedrock valleys andcovered the bedrock hills to produce the flatterrain in the central and hilly landscapes in thenorthern parts of the state.

Till and stratified drift from continental glaciation isso extensive in Indiana that over half of theexisting dams in the state are made of soil and

located on materials deposited and/or altered byice advances and retreats. A basic understandingof glacial geology at a dam site will allow theinspector or inspection team to establish a morecomplete assessment of observed dam safetydeficiencies and develop recommendationsappropriate to improve the safety of the structure.

The large flat to gently rolling surface across thecentral portion of the state is referred to as theCentral Till Plain Region (see Figure 1).

Sediments laid down by the ice sheets weredeposited as till (an unsorted mixture of sand, silt,clay and boulders) when the glaciers advancedinto Indiana and stratified drift (i.e. outwash sandand gravel) when the ice mass retreated.

Glacial till typically provides suitable foundationsand embankments for dams when properlyexcavated, placed and compacted. Thepermeable outwash materials found in thenumerous glacial drainageways, however, presenta problem for seepage control in the foundationand abutment areas for dams.

The Northern Moraine and Lake Regionincludes tracts of lake plains, large outwashareas, and extensive topographic morainalfeatures (i.e. mounds, ridges or other distinctaccumulations of unsorted, unstratified drift orglacial till). This region also includes sand dunes,

alluvial fans, stratified drift, peat bogs and most ofIndianas natural lakes.

The Northern Moraine and Lake Region can be acomplex area to design and maintain a safe dam.The watersheds may include natural retentionbasins and the ground water regime maycontribute significantly to the inflow quantities.

With the extensive permeable soils in this region,some dams consist of sand and gravel. Further,the soft lacustrine and peat deposits presentsettlement and stability problems for embankment

and spillway foundations.

Glacial and Bedrock Control (Transition Area)

The Southern Hills and Lowland Region, in thelower portion of the state, has not been profoundlyaffected by the latest (Wisconsin) glaciation andthe bedrock is at or near the surface in much ofthe region. The topography and drainage patternof this region generally reflects the underlyingbedrock control. There are several hundredexisting dams in this region with a few structuresexceeding 100 feet in height.

Other glacial events, however, did alter landfeatures in a transition area between the southernlimit of Wisconsin glacial deposits to the southernlimit of older glacial deposits. This area typicallyhas the most complex site conditions for southernIndiana since the natural physical features thatinfluence the safety of the dam consists ofdeposits and alterations from glaciation incombination with the structural discontinuities andcharacteristics of the near surface bedrock.

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Buried glacial bedrock valleys, bedrock joints,rock type and other subsurface irregularities at thedam site present unique challenges for theinspector in evaluating seepage and stabilityissues.

Although present throughout the state, extensivesilt deposits known as loess exist in this inter-glacial transition area. Loess is a wind depositfrom large glacial outwash plains. Silt is a poormaterial for embankment dams and foundations.The inspector should be concerned about stabilityand erosion in dams and channel spillwaysconstructed with significant silt content.

Bedrock Controlled

Although bedrock may influence the performanceof a dam anywhere in the state, the predominatearea where bedrock is likely to present problemswith water impoundment structures is southernIndiana.

The distinctly bedrock-controlled area south of thesouthern limit of older glacial deposits consists ofsedimentary rock such as limestone, dolomite,shale, sandstone and siltstone. Shale tends toweather and erode to produce slopes where asthe more weather resistant rock such as siltstoneand sandstone will be found in ridges and hilltops.The weathering of limestone (also dolomite to alesser extent) by acid dissolution produces sinkholes, caves and other features known as karst.

The topography and steepness of slopes of thisarea vary dramatically as the bedrock type, ageand characteristic changes from east to west.The typical thin residual soil layer over thebedrock could indicate that adequatefoundation/abutment preparation may not havebeen accomplished in the construction of the damand seepage paths may have been developed ifthe soil was stripped off of the bedrock near thedam for borrow material.

The regional and local rock mass properties ofsedimentary rock have a significant influence onthe construction of the dam in addition to the longterm performance of the structure. The surfaceand subsurface movement of water is stronglycontrolled by orientation of the joints in thesedimentary rock.

Seismic

Considering the prehistoric evidence of strongearthquakes with epicenters within Indiana, the

history of earthquakes that have caused damagein Indiana since 1811, and the presence ofcompressional forces squeezing the rocks at greatdepths under the state, it is reasonable toconclude that Indiana may experience thepotentially devastating effects of a majorearthquake in the future.

Assessment of a dams risk from seismic loadingrequires a thorough understanding of the localgeology and the engineering properties of thefoundation and embankment soils. If there aresafety issues with the stability of the slopes,embankment, or spillway structure of an existingdam, seismic loading will only exacerbate theproblem.

Mining Issues

Mineral and fuel commodities mined in Indiana

include common clay and shale, limestone anddolomite, construction sand and gravel, industrialsand, sandstone, gypsum, peat, and coal. Thereare over 300 current mines in operation andhundreds of abandoned mines.

The main issues with mining that may impact thesafety of an existing dam are abandonedunderground unstable mines, dramatically alteredwatersheds from surface mining, and/oroperations such as blasting from nearby workingmines. The dam itself may have been a result ofa temporary mining operation with questionable

materials used to construct the embankment andundersized spillway to handle small runoff events.The inspector should thoroughly investigate allgeological sources to develop appropriate plansand recommendations, if the dam is near anabandoned or existing mining operation.


Indiana Department of Natural ResourcesDivision of Water

402 West Washington StreetIndianapolis, Indiana 46204(317) 232-4160 (Voice) (317) 233-4576 (Fax)http://www.in.gov/dnr/water

Additional Resources

Indiana Geological Survey, PhysiographicDivisions of Indiana, H.H. Gray, 2000, IndianaGeological Survey Special Reports, SR61, 611North Walnut Grove, Bloomington, IN 47405-2208

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Figure 1 - Physiographic Divisions of Indiana

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Table 1 - Typical geologic factors by Physiographic Divisions that may influence the integrity, safety, upgrade, and operation of anexisting dam

See notes on following page for clarification.

Northern Moraine & LakeRegion

1.a 1.b 1.c 1.d 1.e 1.f 1.g 1.h 1.i 1.j 1.k 1.l 1.m 1.n 2.a 2.b 2.c 2.d 2.e 2.f 2.g 2.h

Lake Michigan Border X X

Valparaiso MorainalComplex

X X X X

Kankakee Drainageways X X X X X X

St. Joseph Drainageways X X X X X

Plymouth MorainalComplex

X X X X X X X

Warsaw Moraines &Drainageways

X X X X X X X

Auburn Morainal Complex X X X X

Maumee Lake Plain Region

Central Till Plain Region

Bluffton Till Plain 3 X

Iroquois Till Plain 3 X

Tipton Till Plain 3 X

New Castle Till Plains &Drainageways

3 X X

Central Wabash Valley X X X X

Southern Hills & LowlandsRegion

Wabash Lowland X X X X X X

Boonville Hills X X X X X X X X

Martinsville Hills X X X

Crawford Upland X X X X X X X X

Mitchell Plateau X X X X X

Norman Upland X X X X X X X X X

Scottsburg Lowland(except Brownstown Hills)

X X

Charlestown Hills X X X

Muscatatuck Plateau X X X X X X X X X X

Dearborn Upland X X X X X X X X X

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Notes for Table 1:

1.Definitions for columns labeled 1.a through 1.n.a. Unconsolidated material over steep sloping,valley bedrock surface, instability potential atthe dam, spillway or around lake.

b.Steep valley walls, difficult to prepare site forconstruction or expansion of emergencyspillway. Seepage at abutment contact, erosionat groin area and/or long term settlement likely.

c. Near surface non-durable bedrock. Weakrock materials may have been used inembankments which disintegrate/collapse withtime causing settlement, sloughing andinstability of the dam.

d. Rugged watersheds & downstream areas.Quick peak flows into lake. Erosion potential.

Confined, fast flows during discharge or anuncontrolled breach.

e. Steep gradient tributaries require tallembankment dams for small lakes and ponds.High water pressures exist at base of dam;downstream embankment slopes extend aconsiderable distance.

f.Extensive karst development (sinkholes, largesubsurface voids and openings for uncontrolledwater movement, loss and gain of overlandflow) present significant dam safety issues.

g. Some karst development that leads touncontrolled leakage in foundation and/orabutment.

h. Jointed, fractured rock provides paths ofseepage after infilling material softens anderodes out with time.

i.Access for emergency response more difficultthan less rugged areas.

j. Near surface rock limits borrow material

quantities for upgrade on embankment andincreases cost for excavation.

k.Old mine works: Subsurface abandoned coalmines & long-term subsidence threaten integrityof dams & spillways. Acidic runoff detrimental tometal spillway pipes.

l. Current/future coal mining: consideration toblasting, undermining, major alterations towatershed and drainage ways. Acidic runoff

detrimental to metal spillway pipes.

m. Seismic, ground acceleration, loss of soilstrength due to liquefaction.

n. Foundation rock may consist of weatheredshale/claystone that, after a time of saturation,looses strength resulting in slippage planes andinstability of embankment.

2.Definitions for columns labeled 2.a through 2.h.a. May be associated with natural fresh waterlakes; draw down for repair and emergencypotentially hindered due to legal lake levels,wetlands, and sediment releases.

b.Large, broad areas where time of flood peakis attenuated, breach flood is wide, shallow &irregular due to low saddles between drainagedivide & wetlands.

c. Permeable unconsolidated materials infoundation and/or embankment, substantialseepage potential.

d. Soft, deep organic deposits in foundationresult in instability and settlement. Increasingheight is difficult due to unsuitable foundationsoils.

e. Significant interaction between subsurfaceground-water regime and surface watershedthat impacts spillway design and operation.

f. Non-plastic soils, erosion potential high onembankment, spillway and discharge areas.

g. Embankment, foundation and/or abutmentsmay contain significant amounts of loess (silt),which has poor engineering properties (lowstrength, liquefaction, erodes, etc.)

h.High variability of soil types and conditions atlocal sites. Complex.

3. Bedrock may be encountered in certain localareas in these districts. Geologic factors 1g, 1h, &1j may apply in those shallow bedrock areas.


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FACT SHEET 03-03 8-28-03

Dam Safety: Earth Dam Failures

Owners of dams and operating and maintenancepersonnel must be knowledgeable of the potentialproblems which can lead to failure of a dam.These people regularly view the structure and,therefore, need to be able to recognize potentialproblems so that failure can be avoided. If aproblem is noted early enough, an engineerexperienced in dam design, construction, andinspection can be contacted to recommend

corrective measures, and such measures can beimplemented.

Since only superficial inspections of a dam canusually be made, it is imperative that owners andmaintenance personnel be aware of the prominenttypes of failure and their telltale signs. Earth damfailures can be grouped into three generalcategories: overtopping failures, seepage failures,and structural failures. A brief discussion of eachtype follows.

Overtopping Failures

Overtopping failures result from the erosive actionof water on the embankment. Erosion is due touncontrolled flow of water over, around, andadjacent to the dam. Earth embankments are notdesigned to be overtopped and therefore areparticularly susceptible to erosion. Once erosionhas begun during overtopping, it is almostimpossible to stop. A well vegetated earthembankment may withstand limited overtopping ifits top is level and water flows over the top anddown the face as an evenly distributed sheet

without becoming concentrated. The ownershould closely monitor the reservoir pool levelduring severe storms.

If there is any question as to the seriousness ofan observation, a qualified dam safety

professional should be contacted.

Figure 1 Earth dam failure

Acting promptly may avoid possible dam failureand the resulting catastrophic effect ondownstream areas. Staff from the Division ofWater, Dams and Levees Section, are available atany time to inspect a dam if a serious problem is

detected or if failure may be imminent. Contactthe division at the following address andtelephone number:

Seepage Failures

Every embankment dam has water passingthrough or under the embankment because allearth materials are porous. The passage of waterthrough or under the embankment is known asseepage. Seepage quantities and rates increaseas the depth of the water in the reservoirincreases due to the greater pressure upstream ofthe embankment.

Seepage must be controlled in both velocity andquantity. If uncontrolled, it can progressively erodesoil from the embankment or its foundation,resulting in rapid failure of the dam. Erosion of thesoil begins at the downstream side of theembankment, either in the dam proper or thefoundation, progressively works toward thereservoir, and eventually develops a "pipe" ordirect conduit to the reservoir. This phenomenonis known as "piping." Piping action can be

Indiana Department of Natural ResourcesDivision of Water, Dams and Levees Section402 West Washington StreetIndianapolis, Indiana 46204(317) 232-4160.

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recognized by an increased seepage flow rate,the discharge of muddy or discolored water,sinkholes on or near the embankment, and awhirlpool in the reservoir. Once a whirlpool (eddy)is observed on the reservoir surface, completefailure of the dam will probably follow in a matterof minutes. As with overtopping, fully developedpiping is virtually impossible to control and willlikely cause failure. Seepage can cause slopefailure by creating high pressures in the soil poresor by saturating the slope. The pressure ofseepage within an embankment is difficult todetermine without proper instrumentation. Aslope which becomes saturated and developsslides may be showing signs of excessiveseepage pressure.

Structural Failures

Structural failures can occur in either theembankment or the appurtenances. Structuralfailure of a spillway, lake drain, or otherappurtenance may lead to failure of theembankment. Cracking, settlement, and slides arethe more common signs of structural failure ofembankments. Large cracks in an appurtenanceor the embankment, major settlement, and majorslides will require emergency measures to ensuresafety, especially if these problems occursuddenly. If this type of situation occurs, the lake

level should be lowered, the appropriate state andlocal authorities notified, and professional advicesought. If the observer is uncertain as to theseriousness of the problem, the Division of Watershould be contacted immediately.

Figure 3 Structural failure resulting in a slump condition

Figure 2 Seepage through tree roots

The three types of failure previously described areoften interrelated in a complex manner. Forexample, uncontrolled seepage may weaken thesoil and lead to a structural failure. A structuralfailure may shorten the seepage path and lead toa piping failure. Surface erosion may result instructural failure.

Minor defects such as cracks in the embankmentmay be the first visual sign of a major problemwhich could lead to failure of the structure. Theseriousness of all deficiencies should beevaluated by someone experienced in dam design

and construction. A qualified professionalengineer can recommend appropriate permanentremedial measures.


Indiana Department of Natural ResourcesDivision of Water402 West Washington StreetIndianapolis, Indiana 46204(317) 232-4160 (Voice) (317) 233-4576 (Fax)

http://www.in.gov/dnr/water

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FACT SHEET 03-04 8-28-03

Dam Safety: Embankment Instabilities

Figure 1 Beaching

The dam embankment and any appurtenant dikesmust safely contain the reservoir during normaland flood conditions. Cracks, slides, anddepressions are signs of embankment instabilityand should indicate to the owner thatmaintenance or repair work may be required.

When one of these conditions is detected, theowner must retain a qualified dam safetyprofessional to determine the cause of theinstability. A rapidly changing condition or thesudden development of a large crack, slide, ordepression indicates a very serious problem, andthe IDNR-Division of Water should be contactedimmediately. A qualified dam safety professionalmust investigate these types of embankmentstability problems because a so-called homeremedy may cause greater and more seriousdamage to the embankment and eventually resultin unneeded expenditures for unsuccessful

repairs.

Cracks

Short, isolated cracks are commonly due to dryingand shrinkage of the embankment surface andare not usually significant. They are usually lessthan 1 inch wide, propagate in various directions,and occur especially where the embankmentlacks a healthy grass cover. Larger (wider than 1inch), well-defined cracks may indicate a more

serious problem. There are generally two types ofthese cracks: longitudinal and transverse.Longitudinal cracks extend parallel to the crest ofthe embankment and may indicate the earlystages of a slide on either the upstream ordownstream slope of the embankment. They cancreate problems by allowing runoff to enter thecracks and saturate the embankment which inturn can cause instability of the embankment.

Transverse cracks extend perpendicular to thecrest and can indicate differential settlementwithin the embankment. Such cracks provideavenues for seepage through the dam and couldquickly lead to piping, a severe seepage problemthat will likely cause the dam to fail.

If the owner finds small cracks during inspectionof the dam, he/she should document theobservations, and seal the cracks to preventrunoff from saturating the embankment. Thedocumentation should consist of detailed notes(including the location, length, approximate

elevation, and crack width), photographs,sketches, and possibly monitoring stakes. Thecrack must then be monitored during futureinspections. If the crack becomes longer or wider,a more serious problem, such as a slide, may bedeveloping. Large cracks indicate serious stabilityproblems. If one is detected, the owner shouldcontact the Dam and Levees Section and/or retainan engineer to investigate the crack and prepareplans and specifications for repairs. When muddyflow discharges from a crack, the dam may beclose to failure. The emergency action plan shouldbe initiated immediately and theIDNR-Division ofWater contacted.

Slides

A slide in an embankment or in natural soil or rockis a mass movement of material. Some typicalcharacteristics of a slide are an arc-shaped crackor scarp along the top and a bulge along thebottom of the slide (see drawing). Slides maydevelop because of poor soil compaction, thegradient of the slope being too steep for theembankment material, seepage, sudden

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Depressions

Figure 2 Slide cross-sections

drawdown of the lake level, undercutting of theembankment toe, or saturation and weakening of

the embankment or foundation.

Depressions are sunken areas of the abutment,toe area, or embankment surface. They may becreated during construction, or may be caused bydecay of buried organic materials, thawing offrozen embankment material, internal erosion ofthe embankment, or settlement (consolidation) ofthe embankment or its foundation. To a certaindegree, minor depressions are common and donot necessarily indicate a serious problem. (Anembankment with several minor depressions maybe described as hummocky.) However, largerdepressions may indicate serious problems suchas weak foundation materials, poor compaction ofthe embankment during construction, or internalerosion of the embankment fill.

Depressions can create low areas along the crest,cracks through the embankment, structural

damage to spillways or other appurtenantstructures, damage to internal drainage systems,or general instability of the embankment. Theycan also inhibit maintenance of the dam and makedetection of stability or seepage problems difficult.

The owner should monitor depressions during theregular inspection of the dam. All observationsshould be documented with detailed notes,photographs, and sketches. Minor depressionscan be repaired by removing the vegetation andany unsuitable fill from the area, adding fill andthen topsoil to make the embankment uniform,

and finally establishing a healthy grass cover. Anengineer should be retained to investigate largedepressions or settlement areas. Plans andspecifications may need to be prepared for itsrepair depending on the findings of theinvestigation.

Slides can be divided into two main groups:shallow and deep-seated. Shallow slidesgenerally affect the top 2 to 3 feet of the

embankment surface. Shallow slides are generallynot threatening to the immediate safety of the damand often result from wave erosion, collapsedrodent burrows, or saturated top soil. Deep-seatedslides are serious, immediate threats to the safetyof a dam. They can extend several feet below thesurface of the embankment, even below thefoundation. A massive slide can initiate thecatastrophic failure of a dam. Deep-seated slidesare the result of serious problems within theembankment.

Importance of Inspection

Stability problems can threaten the safety of thedam and the safety of people and propertydownstream. Therefore, stability problems mustbe detected and repaired in a timely manner. The

entire embankment should be routinely andclosely inspected for cracks, slides, anddepressions. To do this thoroughly, propervegetation must be regularly maintained on theembankment. Improper or overgrown vegetationcan inhibit visual inspection and maintenance ofthe dam. Accurate inspection records are alsoneeded to detect stability problems. Theserecords can help determine if a condition is new,slowly changing, or rapidly changing. A rapidlychanging condition or the sudden development of

Small slides can be repaired by removing the

vegetation and any unsuitable fill from the area,compacting suitable fill and adding topsoil to makethe embankment uniform, and establishing ahealthy grass cover. If ashallow or deep-seatedslide is discovered, the IDNR-Division of Watershould be contacted and an engineer retained toinvestigate the slide. Plans and specifications mayneed to be prepared for its repair depending onthe findings of the investigation.

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a large crack, slide, or depression indicates a veryserious problem, and the IDNR-Division of Watermust be contacted immediately.


Indiana Department of Natural ResourcesDivision of Water402 West Washington StreetIndianapolis, Indiana 46204(317) 232-4160 (Voice) (317) 233-4576 (Fax)http://www.in.gov/dnr/water
http://www.in.gov/dnr/water/http://www.in.gov/dnr/waterhttp://www.in.gov/dnr/water/http://www.in.gov/dnr/water


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FACT SHEET 03-05 8-28-03

Dam Safety: Inspection of Concrete Structures

Dams, dikes, and levees must not be thought ofas part of the natural landscape, but as manmadestructures which must be designed, inspected,operated, and maintained accordingly. Routinemaintenance and inspection of dams andappurtenant facilities should be an ongoingprocess to ensure that structural failures do notoccur which can threaten the overall safety of thedam. The information provided in this fact sheet

pertains entirely to the inspection of concretestructures used at dams. The intention is to helpdam owners become more aware of commonproblems that are typically encountered withconcrete so that they can more readily addressthe seriousness of a particular condition wheneverit arises.

Structural Inspections

Concrete surfaces should be visually examinedfor spalling and deterioration due to weathering,unusual or extreme stresses, alkali or other

chemical attack, erosion, cavitation, vandalism,and other destructive forces. Structural problems

are indicated by cracking, exposure of reinforcingbars, large areas of broken-out concrete,misalignment at joints, undermining andsettlement in the structure. Rust stains that arenoted on the concrete may indicate that internalcorrosion and deterioration of reinforcement steel

is occurring. Spillway floor slabs and upstreamslope protection slabs should be checked forerosion of underlying base material otherwiseknown as undermining. Concrete walls and towerstructures should be examined to determine ifsettlement and misalignment of construction jointshas occurred.

What to Look For

Concrete structures can exhibit many differenttypes of cracking. Deep, wide cracking is due tostresses which are primarily caused by shrinkageand structural loads. Minor or hairline surfacecracking is caused by weathering and the qualityof the concrete that was applied. The results ofthis minor cracking can be the eventual loss ofconcrete, which exposes reinforcing steel andaccelerates deterioration. Generally, minorsurface cracking does not affect the structuralintegrity and performance of the concretestructure.

Cracks through concrete surfaces exposed toflowing water may lead to the erosion or piping ofembankment or foundation soils from aroundand/or under the concrete structure. In this case,the cracks are not the result of a problem but arethe detrimental condition which leads to pipingand erosion. Seepage at the discharge end of aspillway or outlet structure may indicate leakageof water through a crack. Proper underdrainagefor open channel spillways with structural concretefloors is necessary to control this leakage. Flowsfrom underdrain outlets and pressure relief holesshould also be observed and measured. Cloudy

flows may indicate that piping is occurringbeneath or adjacent to the concrete structure.This could be detrimental to the foundationsupport.Figure 1 Concrete spalling and cracking

Concrete surfaces adjacent to contraction jointsand subject to flowing water are of specialconcern especially in chute slabs. The adjacentslabs must be flush or the downstream oneslightly lower to prevent erosion of the concreteand to prevent water from being directed into the

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joint during high velocity flow. All weep holesshould be checked for the accumulation of silt andgranular deposits at their outlets. These depositsmay obstruct flow or indicate loss of supportmaterial behind the concrete surfaces. Tappingthe concrete surface with a hammer or someother device will help locate voids if they arepresent as well as give an indication of thecondition and soundness of the concrete. Weepholes in the concrete are used to allow freedrainage and relieve excessive hydrostaticpressures from building up underneath thestructure. Excessive hydrostatic pressuresunderneath the concrete could cause it to heaveor crack which increases the potential foraccelerated deterioration and undermining.Periodic monitoring of the weep hole drainsshould be performed and documented on aregular and routine basis to ensure that they arefunctioning as designed.

Structural cracking of concrete is usually identifiedby long, single or multiple diagonal cracks withaccompanying displacements and misalignment.Cracks extending across concrete slabs whichline open channel spillways or provide upstreamslope wave protection can indicate a loss offoundation support resulting from settlement,piping, undermining, or erosion of foundationsoils. Piping and erosion of foundation soils arethe result of inadequate underdrainage and/orcutoff walls. Items to consider when evaluating asuspected structural crack are the concrete

thickness, the size and location of the reinforcingsteel, the type of foundation, and the drainageprovision for the structure.

Inspection of intake structures, trashracks,upstream conduits, and stilling basin concretesurfaces that are below the water surface is notreadily feasible during a regularly scheduledinspection. Typically, stilling basins require themost regular monitoring and major maintenancebecause they are holding ponds for rock and

debris, which can cause extensive damage to theconcrete surfaces during the dissipation of flowingwater. Therefore, special inspections of thesefeatures should be performed at least once everyfive years by either dewatering the structure orwhen operating conditions permit. Investigation ofthese features using experienced divers is also analternative.

Figure 3 Stilling basin

Preparing for an Inspection

Before an inspection of the dam's concretefacilities is performed, it is recommended that achecklist be developed that includes all thedifferent components of the spillway and/or outletworks. The checklist should also include a space

for logging any specific observations about thestructure and the state of its condition.Photographs provide invaluable records ofchanging conditions. A rapidly changing conditionmay indicate a very serious problem. If there areany questions as to the seriousness of anobservation, the IDNR-Division of Water, or aqualified dam safety professional experiencedwith dams, should be contacted.

Figure 2 - Rupture of concrete spillway conduit



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FACT SHEET 03-06 8-28-03

Dam Safety: Problems with Concrete Materials

Visual inspection of concrete will allow for thedetection of distressed or deteriorated areas.Problems with concrete include constructionerrors, disintegration, scaling, cracking,efflorescence, erosion, spalling, and popouts.

Construction Errors

Errors made during construction such as adding

improper amounts of water to the concrete mix,inadequate consolidation, and improper curingcan cause distress and deterioration of theconcrete. Proper mix design, placement, andcuring of the concrete, as well as an experiencedcontractor are essential to prevent constructionerrors from occurring. Construction errors canlead to some of the problems discussed later inthis fact sheet such as scaling and cracking.

Figure 1 Scaling

Honeycombing and bugholes can be observedafter construction. Honeycombing can berecognized by exposed coarse aggregate on the

surface without any mortar covering orsurrounding the aggregate particles. Thehoneycombing may extend deep into theconcrete. Honeycombing can be caused by apoorly graded concrete mix, by too large of acoarse aggregate, or by insufficient vibration atthe time of placement. Honeycombing will result infurther deterioration of the concrete due to freeze-thaw because moisture can easily work its wayinto the honeycombed areas. Severehoneycombing should be repaired to preventfurther deterioration of the concrete surface.

Bugholes is a term used to describe small holes

(less than about 0.25 inch in diameter) that arenoticeable on the surface of the concrete.Bugholes are generally caused by too much sandin the mix, a mix that is too lean, or excessiveamplitude of vibration during placement. Bugholesmay cause durability problems with the concreteand should be monitored.

Disintegration and Scaling

Disintegration can be described as the

deterioration of the concrete into small fragmentsand individual aggregates. Scaling is a milderform of disintegration where the surface mortarflakes off. Large areas of crumbling (rotten)concrete, areas of deterioration which are morethan about 3 to 4 inches deep (depending on thewall/slab thickness), and exposed rebar indicateserious concrete deterioration. If not repaired, thistype of concrete deterioration may lead to

structural instability of the concrete structure. Aregistered professional engineer must prepareplans and specifications for repair of seriousconcrete deterioration. For additional information,

see the Concrete Repair Techniquesfact sheet.Disintegration can be a result of many causessuch as freezing and thawing, chemical attack,and poor construction practices. All exposedconcrete is subject to freeze-thaw, but theconcretes resistance to weathering is determinedby the concrete mix and the age of the concrete.

Concrete with the proper amounts of air, water,and cement, and a properly sized aggregate, willbe much more durable. In addition, properdrainage is essential in preventing freeze-thawdamage. When critically saturated concrete (when90% of the pore space in the concrete is filled withwater) is exposed to freezing temperatures, thewater in the pore spaces within the concretefreezes and expands, damaging the concrete.Repeated cycles of freezing and thawing willresult in surface scaling and can lead to

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disintegration of the concrete. Hydraulic structuresare especially susceptible to freeze-thaw damagesince they are more likely to be criticallysaturated. Older structures are also moresusceptible to freeze-thaw damage since theconcrete was not air entrained. In addition, acidicsubstances in the surrounding soil and water cancause disintegration of the concrete surface dueto a reaction between the acid and the hydratedcement.

Figure 3 Efflorescence

Cracks

Cracks in the concrete may be structural orsurface cracks. Surface cracks are generally lessthan a 0.2 inches wide and deep. These are oftencalled hairline cracks and may consist of single,thin cracks, or cracks in a craze/map-like pattern.

A small number of surface or shrinkage cracks iscommon and does not usually cause any

problems. Surface cracks can be caused byfreezing and thawing, poor construction practices,and alkali-aggregate reactivity. Alkali-aggregatereactivity occurs when the aggregate reacts withthe cement causing crazing or map cracks. Theplacement of new concrete over old may causesurface cracks to develop. This occurs becausethe new concrete will shrink as it cures. Surfacecracks in the spillway should be monitored andwill need to be repaired if they deteriorate further.

Structural cracks in the concrete are usually largerthan 0.25 inch in width. They extend deeper intothe concrete and may extend all the way througha wall, slab, or other structural member. Structuralcracks are often caused by settlement of the fillmaterial supporting the concrete structure, or byloss of the fill support due to erosion. Thestructural cracks may worsen in severity due tothe forces of weathering. A registered professionalengineer knowledgeable about dam safety must

investigate the cause of structural cracks andprepare plans and specifications for repair of anystructural cracks. For additional information, see

e Concrete Repair Techniquesfact sheet.

fflorescence

n due to freezing and thawing of theater.

rosion

ns for repair of thispe of erosion if it is severe.

thE

A white, crystallized substance, known asefflorescence, may sometimes be noted onconcrete surfaces, especially spillway sidewalls. Itis usually noted near hairline or thin cracks.Efflorescence is formed by water seeping throughthe pores or thin cracks in the concrete. When thewater evaporates, it leaves behind some mineralsthat have been leached from the soil, fill, or

concrete. Efflorescence is typically not a structural

problem. Efflorescence should be monitoredbecause it can indicate the amount of seepagefinding its way through thin cracks in the concreteand can signal areas where problems (i.e.inadequate drainage behind the wall ordeterioration of concrete) could develop. Also,water seeping through thin cracks in the wall willmake the concrete more susceptible todeterioratio

Figure 2 Cracking

wE

Erosion due to abrasion results in a worn concretesurface. It is caused by the rubbing and grindingof aggregate or other debris on the concretesurface of a spillway channel or stilling basin.Minor erosion is not a problem but severe erosioncan jeopardize the structural integrity of theconcrete. A registered professional engineer mustprepare plans and specificatiotyErosion due to cavitation results in a rough, pitted

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concrete surface. Cavitation is a process in whichsub atmospheric pressures, turbulent flow andimpact energy are created and will damage theconcrete. If the shape of the upper curve on theogee spillway is not designed close to its idealshape, cavitation may occur just below the uppercurve, causing erosion. A registered professionalengineer must prepare plans and specificationsfor repair of this type of erosion if the concretebecomes severely pitted which could lead totructural damage or failure of the structure.

palling and Popouts

re plans andpecifications to repair the spalling.

spection and Monitoring

aintenance, and inspection manual for the dam.

o the Division ofater at the following address:

t of Natural Resources

) 233-4576 (Fax)ttp://www.in.gov/dnr/water

Figure 4 Rupture of concrete spillway conduit

sSSpalling is the loss of larger pieces or flakes ofconcrete. It is typically caused by sudden impactof something dropped on the concrete or stress inthe concrete that exceeded the design. Spallingmay occur on a smaller scale, creating popouts.Popouts are formed as the water in saturated

coarse aggregate particles near the surfacefreezes, expands, and pushes off the top of theaggregate and surrounding mortar to create ashallow conical depression. Popouts are typicallynot a structural problem. However, if a spall islarge and causes structural damage, a registeredprofessional engineer must prepasInRegular inspection and monitoring is essential todetect problems with concrete materials. Concrete

structures should be inspected a minimum of onceper year. The inspector should also look at theinterior condition of concrete spillway conduit.Proper ventilation and confined space precautions

must be considered when entering a conduit. It isimportant to keep written records of thedimensions and extent of scaling, disintegration,efflorescence, honeycombing, erosion, spalling,popouts, and the length and width of cracks.Structural cracks should be monitored morefrequently and repaired if they are a threat to thestability of the structure or dam. Photographs

provide invaluable records of changing conditions.A rapidly changing condition may indicate a veryserious problem, and a qualified dam safetyprofessional should be contacted immediately. Allrecords should be kept in the operation,m

Any questions, comments, concerns, or fact sheetrequests should be directed tWIndiana DepartmenDivision of Water402 West Washington StreetIndianapolis, Indiana 46204(317) 232-4160 (Voice) (317h


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FACT SHEET 03-07 8-28-03

Dam Safety: Concrete Repair Techniques

Concrete is an inexpensive, durable, strong andbasic building material often used in dams for corewalls, spillways, stilling basins, control towers, andslope protection. However, poor workmanship,construction procedures, and constructionmaterials may cause imperfections that laterrequire repair. Any long-term deterioration ordamage to concrete structures caused by flowingwater, ice, or other natural forces must be

corrected. Neglecting to perform periodicmaintenance and repairs to concrete structures asthey occur could result in failure of the structurefrom either a structural or hydraulic standpoint.This in turn may threaten the continued safeoperation and use of the dam.

Considerations

Floor or wall movement, extensive cracking,improper alignments, settlement, jointdisplacement, and extensive undermining aresigns of major structural problems. In situations

where concrete replacement solutions arerequired to repair deteriorated concrete, it isrecommended that an experienced structuralengineer be retained to perform an inspection toassess the concrete's overall condition, anddetermine the extent of any structural damageand necessary remedial measures.

Typically, it is found that drainage systems areneeded to relieve excessive water pressuresunder floors and behind walls. In addition,reinforcing steel must also be properly designedto handle tension zones and shear and bendingforces in structural concrete produced by any

external loading (including the weight of thestructure). Therefore, the finished product in anyconcrete repair procedure should consist of astructure that is durable and able to withstand theeffects of service conditions such as weathering,chemical action, and wear. Because of theircomplex nature, major structural repairs thatrequire professional advice are not addressedhere.

Concrete damage less than 1 inches deep can

not be successfully repaired, unless the concreteis removed to a greater depth. Polymer concreterepair is sometimes used on shallow damagedareas, but will have a limited life.

The U.S. Bureau of Reclamation recommends aseven step repair procedure that has been provento be very effective:

(1) Determine cause of damage.(2) Determine extent of damage.(3) Determine need to repair.(4) Choose appropriate repair system.(5) Prepare damaged concrete area.(6) Apply the repair system.(7) Cure the repair properly.

For concrete damage that is 1 to 6 inches deep,epoxy bonded concrete repairs are best; theepoxy bonds the new concrete to the old concretefor longer life. Most concrete repairs are made byremoving all damaged concrete and replacing it

with new concrete. The new concrete should besimilar to the old concrete.

Silane sealer is often used on the surface ofconcrete to keep water out of the structure. Thesilane penetrates the outer surface of the concreteto make it water proof, to help prevent damagefrom freeze-thaw effects. Silane coatings have alife of 3 to 7 years.

Repair Methods

Before any type of concrete repair is attempted, itis essential that all factors governing the

deterioration or failure of the concrete structureare identified. This is required so that theappropriate remedial measures can beundertaken in the repair design to help correct theproblem and prevent it from occurring in thefuture. The following techniques require expertand experienced assistance for the best results.The particular method of repair will depend on thesize of the job and the type of repair required.

Most concrete repairs must follow a

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predetermined procedure. In all cases, loose anddamaged concrete must be removed before therepair is implemented. The following procedure iscommonly used:

(1) Saw cut perimeter of damage area.(2) Remove concrete to below the steel

rebar, using sand blasting, jack hammer,shot blasting, chipping hammer, or hydro-demolition methods.

(3) Use high pressure water to clean therepair area.

(4) Use epoxy bonding agents on the oldsurfaces.

1. The Dry-Pack Method: The dry-pack methodcan be used on small holes in new concretewhich have a depth equal to or greater thatthe surface diameter. Preparation of a dry-pack mix typically consists of about 1 part

portland cement and 2 parts sand to bemixed with water. You then add enough waterto produce a mortar that will stick together.Once the desired consistency is reached, themortar is ready to be packed into the hole

using thin layers.

2. Concrete Replacement: Concretereplacement is required when one-half to onesquare foot areas or larger extend entirely

through the concrete sections or where thedepth of damaged concrete exceeds 6 inches.When this occurs, normal concrete placementmethods should be used. Repair will be moreeffective if tied in with existing reinforcing steel(rebar). This type of repair will require theassistance of a professional engineerexperienced in concrete construction.

3. Replacement of Unformed Concrete: Thereplacement of damaged or deterioratedareas in horizontal slabs involves no special

procedures other than those used in goodconstruction practices for placement of newslabs. Repair work can be bonded to oldconcrete by use of a bond coat made of equalamounts of sand and cement. It should havethe consistency of whipped cream and shouldbe applied immediately ahead of concreteplacement so that it will not set or dry out.Latex emulsions with portland cement andepoxy resins are also used as bonding coats.

4. Preplaced Aggregate Concrete: This specialcommercial technique has been used formassive repairs, particularly for underwaterrepairs of piers and abutments. The processconsists of the following procedures: 1)Removing the deteriorated concrete, 2)forming the sections to be repaired, 3)prepacking the repair area with coarseaggregate, and 4) pressure grouting the voidsbetween the aggregate particles with a

cement or sand-cement mortar.5. Synthetic Patches: One of the most recent

developments in concrete repair has been theuse of synthetic materials for bonding andpatching. Epoxy-resin compounds are usedextensively because of their high bondingproperties and great strength. In applyingepoxy-resin patching mortars, a bonding coatof the epoxy resin is thoroughly brushed ontothe base of the old concrete. The mortar isthen immediately applied and troweled to theelevation of the surrounding material.

Figure 1 Concrete Wall Displacement

Before attempting to repair a deterioratedconcrete surface, all unsound concrete should beremoved by sawing or chipping and the patcharea thoroughly cleaned. A sawed edge issuperior to a chipped edge, and sawing isgenerally less costly than mechanical chipping.Before concrete is ordered for placing, adequateinspection should be performed to ensure that (1)foundations are properly prepared and ready toreceive the concrete, (2) construction joints areclean and free from defective concrete, (3) formsare grout-tight, amply strong, and set to their truealignment and grade, (4) all reinforcement steel

and embedded parts are clean, in their correctposition, and securely held in place, and (5)adequate concrete delivery equipment andfacilities are on the job, ready to go, and capableof completing the placement without additionunplanned construction.

Concrete Use Guidelines

In addition to its strength characteristics, concretemust also have the properties of workability and

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durability. Workability can be defined as the easewith which a given set of materials can be mixedinto concrete and subsequently handled,transported, and placed with a minimal loss ofhomogeneity. The degree of workability requiredfor proper placement and consolidation ofconcrete is governed by the dimensions andshape of the structure and by the spacing andsize of the reinforcement. The concrete, whenproperly placed, will be free of segregation, and itsmortar is intimately in contact with the coarseaggregate, the reinforcement, and/or any otherembedded parts or surfaces within the concrete.Separation of coarse aggregate from the mortarshould be minimized by avoiding or controlling thelateral movement of concrete during handling andplacing operations. The concrete should bedeposited as nearly as practicable in its finalposition. Placing methods that cause the concreteto flow in the forms should be avoided. The

concrete should be placed in horizontal layers,and each layer should be thoroughly vibrated toobtain proper compaction.

All concrete repairs must be adequately moist-cured to be effective. The bond strength of newconcrete to old concrete develops much moreslowly, and the tendency to shrink and loosen isreduced by a long moist-curing period. In general,the concrete repair procedures discussed aboveshould be considered on a relative basis and interms of the quality of concrete that one wishes toachieve for their particular construction purpose.

In addition to being adequately designed, astructure must also be properly constructed withconcrete that is strong enough to carry the designloads, durable enough to withstand the forcesassociated with weathering, and yet economical,not only in first cost, but in terms of its ultimateservice. It should be emphasized that majorstructural repairs to concrete should not beattempted by the owner or persons notexperienced in concrete repairs. A qualifiedprofessional engineer experienced in concreteconstruction should be obtained for the design oflarge scale repair projects.

Crack Repair

The two main objectives when repairing cracks inconcrete are structural bonding and stoppingwater flow. For a structural bond, epoxy injectioncan be used. This process can be very expensivesince a skilled contractor is needed for properinstallation. The epoxy is injected into the

Figure 3 Crack Repair

concrete under pressure, welding the cracks toform a monolithic structure. This method of repairshould not be considered if the crack is still active(moving). For a watertight seal, a urethane

sealant can be used. This repair technique doesnot form a structural bond; however, it can beused on cracks that are still active. Cracks shouldbe opened using a concrete saw or hand tool priorto placing the sealant. A minimum opening of 1/4inch is recommended since small openings arehard to fill. Urethane sealants can be reappliedsince they are flexible materials and will adhere toolder applications. As previously noted, all of thefactors causing cracking must be identified andaddressed before repairing the concrete toprevent the reoccurrence of cracks.

Part 2 of the Indiana Dam Safety InspectionManual provides additional details on concreterepair.




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FACT SHEET 03-08 8-28-03

Dam Safety: Seepage through Earthen Dams

Most dams have some seepage through or aroundthe embankment as a result of water movingthrough the soil structure. The rate at which watermoves through the embankment depends on thetype of soil in the embankment, how well it iscompacted, the foundation and abutmentpreparation, and the number and size of cracks andvoids within the embankment. Many seepageproblems and failures of earth dams have occurred

because of inadequate seepage control measuresor poor/incomplete cleanup and preparation of thefoundations and abutments. Seepage can lead tosoil piping and embankment sloughing or sliding,both of which can lead to dam failure. Therefore,seepage must be controlled to maintain damintegrity and safety.

Figure 2 - Boil near toe of embankment (12-inches diameter)

Detection

Seepage can emerge anywhere on thedownstream face, embankment toe, or abutmentsat or below the normal pool level. Seepage will

appear as soft wet areas, areas with flowing water,areas where the vegetation is noticeably lush andgreen, areas where the embankment is sloughingor bulging, or areas containing ponded water.Cattails, reeds, mosses, and other marshvegetation are often present in seep areas. Rust-colored iron bacteria are another indication of waterseeping from the ground. Figure 1 showsextensive seepage at the toe of an embankment.

In this case, the vegetation on the face of theembankment is dormant while that at the toe isgrowing vigorously. The seepage has causedminor sloughing with a resultant scarp formation (atthe arrow). If the seepage forces are large enough,soil can be eroded from the embankment orfoundation resulting in piping or boils. Figure 2shows a boil near the toe of an embankment. Inthis case, it appears seepage is flowing under the

embankment in the foundation soils. Piping is oftenassociated with muddy flows as sediment is

carried out of the embankment (or foundation) withthe water. Also, piping may occur along thedischarge conduit.

Figure 1 - Seepage at embankment toe caused sloughing

Sinkholes may develop on the surface as internalerosion removes soil from below ground. Seriousseepage may create whirlpools in the lakeupstream of the embankment. Whirlpools are

usually a precursor to dam failure.

Boils occur downstream of the embankment toeand are usually an indication of seepage under theembankment. Boils are formed when the seepagepressures are high enough to erode the surfacesoils. A conical mound of soil often forms aroundthe boil if the soils are granular.

Seepage can also develop behind or beneathconcrete spillways or headwalls. The signs of this

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Common Causes of Seepagetype of problem may be cracking, heaving, orrotating of the structure. Freezing and thawing willamplify the effects of seepage at concretestructures.

Seepage that results in piping, boils, or soil erosionis generally caused by the following conditions:

A continuous or sudden drop in the normal poollevel is another indication of seepage. In this case,the seepage is usually significant enough to resultin flowing water downstream of the dam. Thiscondition will require frequent and close monitoring.

poor compaction of embankment soils

unsuitable embankment soilspoor foundation and abutment preparation

rodent holes, rotted tree roots and wood

open seams, cracks, or joints in rocks in dam

foundations or abutmentsSaturation of embankment soils, abutments, andfoundations due to seepage generally result inreduced soil strengths leading to sloughing, sliding,and instability. In the worst case, seepage canresult in total embankment failure if left unchecked.

coarse gravel or sand in the foundation orabutment

cracks in rigid drains, reservoir linings, or damcores

cracks or breaks in conduits, or poor conduitjoints

Normal seepage through a relatively imperviousdam embankment may be un-noticeable. Theemerging seepage may evaporate or be taken up

by the vegetation as fast as it occurs. This type ofseepage generally poses no problems.

lack of filter protection on the downstream face

clogging of coarse drains

filters or drains with pores so large soil canwash through

frost action

shrinkage cracking in the embankment soil

Figure 3 Seepage flows on vegetated embankment

Thorough inspections are required to detectseepage. Seepage may be difficult to spot due tovegetation. Probing the soil in suspect areas canhelp to locate and identify whether seepage ispresent and the limits of the problem. Differencesin vegetation and flowing water on the downstreamside of embankments are the two most noticeablesigns of seepage. Soft soil areas and soilsloughing may also be signs of seepage from the

reservoir.

settlement of embankment soil

uprooted trees

earthquakes

Seepage that results in saturation and excessiveseepage forces is generally caused by the followingconditions:

insufficient structural drainage

unsuitable embankment soilspoor embankment compaction

poor foundation and abutment preparation

trapped groundwater on the abutment orfoundation

excessive uplift pressures

water collecting behind structures because ofinsufficient drainage

water flowing into cracks on the embankmentsurface

poor grading or improper drainage of crest

localized settlement on crest

Monitoring

Regularly scheduled monitoring and inspection isessential to detect seepage and prevent damfailure. The state of Indiana requires professionalinspections every two years for high hazard dams.However, more frequent inspections should beperformed by the owner or his representative. Theinspection frequency should be based on thehazard classification of the dam; high hazard damsrequire inspection more frequently than low or

Other factors may produce signs that appear to beseepage. Poor surface drainage may result in wetareas at the downstream toe or along theabutments of the embankment. Natural springs ator under the embankment, or in the groin of theabutments often have the same appearance asseeps. Monitoring of these conditions will still berequired to ensure that the dam is not degraded.

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significant hazard dams. At a minimum, all damsshould be visually inspected at least every sixmonths, before a predicted major storm event,during or after severe rainstorms or snowmelts, andafter an earthquake. All new dams should beinspected weekly after construction is complete andreservoir filling is ongoing, and for at least twomonths after the reservoir has been filled.

Dam inspections performed on a regular basis arethe most economical aid a dam owner can use toassure the safety and long life of the structure whilereducing liability risks.

If seepage is detected on a dam embankment orfoundation, it should be closely monitored on aregular basis until it is corrected. Seepage flowsshould be measured if possible and photographedto track its progression. If piping or boils arepresent, the size and the depth of the exit opening

should be measured and recorded at eachinspection, and the turbidity of the water should benoted. If the seepage is causing sloughing, sliding,or settlement, the affected area should bemeasured and recorded. The length, width, anddepth of these conditions should be measured andphotographed at each inspection. Sketches of thelocation of the seepage or instabilities should beprepared for the dam records.

Surveys of the seepage, sloughing, slides, or otherdeficiencies may be required on large dams.

Piezometers can be installed into the embankment

to monitor water levels in the soil fill. Typically,seepage will increase if the water level in theembankment rises. High water levels may also beused to predict seepage problems before theydevelop.

Control

If seepage flows increase or embankment soils areshowing signs of instability, corrective action shouldbe implemented quickly. Seepage problems at

high hazard dams need to be correctedimmediately; if allowed to progress, they may resultin loss of life and property downstream of the dam.

A qualified geotechnical engineer or dam safetyprofessional should be contacted for inspection andadvice for all high hazard dam seepage problems.

The type of controls deployed will depend on thesource, type, and extent of seepage. If excessivewater is flowing from soil piping or boils, or if thewater is carrying sediment, a qualified geotechnicalengineer or dam safety professional should becontacted to perform an inspection and to developrecommendations for further actions. The reservoirlevel should be lowered if serious piping orembankment sliding/sloughing is occurring, and thecause of the condition corrected. Reservoir drains,pumps, or siphons may be used to drawdown thewater level.

Figure 5 Progression of seepage through dam embankment

Figure 4 Staking wet area to record changes

Sloughing and sliding due to seepage at the toe ofthe embankment may be corrected by removing theunstable soil and constructing a toe drain with filter.This same remedy can be applied to areas wherewater is flowing but piping has not yet occurred.Unstable soils located at higher levels on theembankment should be removed and replaced withre-compacted, cohesive soil. The water level inthe reservoir should be lowered if significant repairsare required on the embankment.

Seepage, piping, and boils in existing dams may becorrected, or slowed, by intercepting the water

before it exits on the downstream side of the dam.

Typical methods include: impermeable upstreamblankets, cutoff trenches in the embankment, groutcurtains, sheet pile walls, relief wells, and toedrains. Impermeable upstream blankets, or liners,are the most effective method, but require completedrawdown of the reservoir. These blankets mayconsist of low-permeability soil or a synthetic geo-membrane. The blankets may also be deployed on

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Figure 6 - Apparent seepage along this concrete spillway

caused total erosion of the structure.

the floor of the reservoir to prevent foundationseepage.Temporary corrective actions for boils or seepsbelow the embankment toe include installing aweighted filter in and over the boil exit opening.Loose soil should first be removed from the hole. Alayer of filter sand should be installed in the bottomof the hole, covered by a medium-sized coarseaggregate. A larger aggregate should then beplaced at the top of the hole; the final layer must

consist of aggregate that is heavy enough to resistthe uplift force of the seeping water. A qualifiedngineer should be contacted for inspection and

d wide enough toeep the phreatic surface from exiting on the

nkment toe. All Disturbed and repaired areasust be regarded and planted with a suitable grass

ms, and anyamage they created should be repaired by

be ample warning ifutine inspections are performed. These two

tterns that lead toaturation, internal flooding, excessive uplift, or

crest can lowere height of the dam and create a potential for

vertopping during storm events.

eadvice for significant seepage problems.

New dams should be designed and constructed tocontrol seepage before problems develop. Thedam foundation should be carefully prepared byremoving all organic matter and unsuitable soils. Ifgravel or sand is present in the foundation, a cutofftrench should be constructed through the coarsestrata if possible. The embankment soils should bea cohesive soil placed in thin lifts (6 to 9 inchesthick after compaction) and compacted to 90%Modified Proctor density. Spillway conduits shouldbe properly installed and backfilled to preventseepage along the conduits. Internal or toe drainsshould be constructed if seepage is expected to

exit on the embankment downstream face. Filtersmust be used to prevent soils from blocking thedrains. Dams can be constructekembankment downstream slope.

Trees and brush should be removed fromembankments. Regular mowing of embankmentsshould be performed to prevent trees from growing.Trees that are less than 12 inches in diameter maybe cut flush with the ground and the roots left in

place. Trees greater than 12 inches in diametershould be removed completely. After the tree iscut down, the root ball and major roots should beextracted; the root ball cavity must then be cleanedand backfilled with compacted soil. If seepage ispresent in the cavity, a filtered drain should beinstalled to prevent soil piping. A complete toedrain may be required if a sufficient number of treesare removed. A filtered drainage system orweighted filter may be installed in the cavity fromtrees that are removed downstream of theembammix.

Cracks and erosion rills on the embankment shouldbe filled, re-graded, and re-seeded. Burrowingrodents should be eliminated from dadbackfilling with soil or a filtered drain.

Consequences of Uncontrolled Seepage

Excessive seepage can present a safety hazard tothe dam and the health and welfare of people andproperty downstream of the dam. Most failurescaused by groundwater and seepage can beclassified into one of two categories based on thetype of soil movement that is occurring. Thefailures will typically develop over a relatively longperiod of time so there willrocategories of failures include:

1) those that take place when soil particles migrateto an escape exit and cause piping or erosionfailures; and 2) those that are caused byuncontrolled seepage pasexcessive seepage forces.

High velocity flows through the dam embankmentcan cause progressive erosion and piping of theembankment or foundation soils. If this conditioncontinues unchecked, complete dam failure canresult. Saturated soil areas on the embankment

slopes, the abutment, or the area at the toe of thedam can slide or slough, resulting in embankmentfailure. Piping and badly saturated areas can resultin settlement of the soils in the embankment;excessive settlement of the damtho

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5

erns, or fact sheetrequests should be directed to the Division of

Resources

(317) 232-4160 (Voice) (317) 233-4576 (Fax)ater

Any questions, comments, conc

Water at the following address:

Indiana Department of NaturalDivision of Water402 West Washington StreetIndianapolis, Indiana 46204

http://www.in.gov/dnr/w

f Natural Resources,ivision of Water, Suggested Procedures for

s,

ivision of Water, Operation, Maintenance and

tate of Colorado, Office of the State Engineer,

edergren, Harry, 1989, Seepage, Drainage and

epage Analysis and Control forams, EM 1110-2-1901, 1993, Washington, D.C.

entation of Embankment Damsnd Levees, EM 1110-2-1908, 1995, Washington,.C. 20314-1000

Additional Resources

State of Ohio, Department oDSafety Inspections of Dams.

State of Ohio, Department of Natural Resource

DInspection Manual for Dams, Dikes and Levees.

SDivision of Water Resources, Dam Safety Manual.

CFlow Nets, John Wiley & Sons, New York, NY.Department of the Army, U.S. Army Corps ofEngineers,SeD20314-1000

Department of the Army, U.S. Army Corps ofEngineers, InstrumaD
http://www.in.gov/dnr/waterhttp://www.in.gov/dnr/waterhttp://www.in.gov/dnr/waterhttp://www.dnr.state.oh.us/water/http://www.dnr.state.oh.us/water/http://www.dnr.state.oh.us/water/http://www.dnr.state.oh.us/water/http://www.dnr.state.oh.us/water/http://www.dnr.state.oh.us/water/http://www.dnr.state.oh.us/water/http://www.dnr.state.oh.us/water/http://water.state.co.us/http://water.state.co.us/http://www.dnr.state.oh.us/water/http://www.dnr.state.oh.us/water/http://www.dnr.state.oh.us/water/http://www.dnr.state.oh

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