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URS Corporation

21st Century Dam Design

Advances and Adaptations

31st Annual USSD Conference

San Diego, California, April 11-15, 2011

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On the CoverArtist's rendition of San Vicente Dam after completion of the dam raise project to increase local storage and provide

a more flexible conveyance system for use during emergencies such as earthquakes that could curtail the regions

imported water supplies.The existing 220-foot-high dam, owned by the City of San Diego, will be raised by 117

feet to increase reservoir storage capacity by 152,000 acre-feet. The project will be the tallest dam raise in the

United States and tallest roller compacted concrete dam raise in the world.

The information contained in this publication regarding commercial projects or firms may not be used for

advertising or promotional purposes and may not be construed as an endorsement of any product or

from by the United States Society on Dams. USSD accepts no responsibility for the statements made

or the opinions expressed in this publication.

Copyright 2011 U.S. Society on Dams

Printed in the United States of America

Library of Congress Control Number: 2011924673ISBN 978-1-884575-52-5

U.S. Society on Dams

1616 Seventeenth Street, #483

Denver, CO 80202

Telephone: 303-628-5430

Fax: 303-628-5431

E-mail: stephens@ussdams.org

Internet: www.ussdams.org

U.S. Society on Dams

Vision

To be the nation's leading organization of professionals dedicated to advancing the role of dams

for the benefit of society.

MissionUSSD is dedicated to:

Advancing the knowledge of dam engineering, construction, planning, operation,

performance, rehabilitation, decommissioning, maintenance, security and safety;

Fostering dam technology for socially, environmentally and financially sustainable water

resources systems;

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

resources;

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

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

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Leakage Sealing 311

NEW MATERIALS AND TECHNOLOGIES FOR LEAKAGE SEALING

WITHOUT AFFECTING OPERATION HIGH PRESSURE RESIN

INJECTIONS

A. Gonzalo1J. Alonso2

F. Vazquez3

A. Vaquero4

ABSTRACT

Dam repair works often require the reservoir to be emptied, which can be a problem.New materials and technologies developed in Spain in the last decade avoid thisproblem, allowing large leaks to be sealed and structural monolithism to be recovered,even under high water pressure, without polluting the environment. The use of highviscosity, thixotropic polymers, almost visco-elastic solids, in addition to the designof new and powerful pumps able to inject these polymers up to 60 MPa, have enabledmore than 100 dams to be repaired without disturbing their operation.

INTRODUCTION

The resolution of certain problems in dams, such as fissure sealing, joint leak-tightness, upstream heel detachment in gravity dams, internal erosion of clay cores orlarge flows passing through deep lithoclases, often call for the reservoir to be emptied

before tackling the repair.

Figure 0. Leakage sealing works, with maximum water level.

1Dr, Civil Engineer. HCC General Manager . Madrid, Spain. alberto@hcc-es,com2Civil Engineer. ENDESA. Manager of Civil Works and Enviromment. Ponferrada. Spain.julianalberto.alonso@endesa.es3Civil Engineer. EMASESA. Operations Dams Manager.4Civil Engineer. HCC. Project Manager. Madrid. Spain. antoniov@hcc-es.com

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312 21st Century Dam Design Advances and Adaptations

Traditional repairs based on cement injection can not be carried out if there is waterflowing, otherwise the grout will be washed away. Reservoir emptying generallyinvolves high costs to which is added loss of profit, the environmental cost and, often,a political cost to the authorizing authority. In general, emptying involves a highfinancial loss to the owner or a decrease in the service guarantee, which is particularlyserious for water supply dams.

If the reservoir is emptied, the repair is carried out blind and the result thereof canonly be checked when the reservoir has been refilled. Often in work of this kind, oncethe operating level has been reached, the original problem has diminished but not

been completely solved.

Over the last few years, the formulation of polymers specially designed for carryingout such work has enabled this type of problem to be solved with a full reservoirwithout affecting its operation. Working with a maximum water level obviates all the

problems of traditional solutions. In fact, work is no longer carried out blind and,therefore, the efficacy of the repair is immediately apparent. (Figure 1).

From the economic point of view, although this type of material is notably moreexpensive, since no loss of profit occurs as the dam and its facilities are kept inservice, the end cost of the operation is usually completely favourable to this newtechnology without taking into account the greater efficiency of these products and,therefore, their lower consumption for achieving the same objectives.

MATERIALS

Epoxy resins

Epoxy resins are thermo-stable polymers which harden when mixed with their

pertinent hardener or catalyser. They were first marketed as adhesives in the first thirdof the 20th

century. Apart from their facet as a powerful adhesive, they commencedbeing used in surface applications as corrosion protection layers or primers to improveadherence between a substrate and the final paintwork. The treatment of the inside ofacid preserve cans or anticorrosion treatment of cars are usually epoxies too.

As early as in the fifties, they began to be used for making industrial pavements,electric material encapsulating, as printed circuits or for making laminates of whichthe maximum current exponent are the blades of wind turbines spread over ourlandscape. The epoxy resin industry annually moves more than $15,000 million theworld over, and it is practically all used in the aforementioned applications. It issignificant that amongst the applications of epoxy resins, their use in solving civil

engineering problems is not mentioned in encyclopaedias such as the widespreadWikipedia.

Epoxies earmarked for other purposes have been used for our applications. A largepart of commercial resins have a compressive strength close to 100 MPa and morethan 40 Mpa tensile strength. It is obvious that injecting concrete with a material withthese characteristics is a really senseless financial waste. The strength of the fullyhardened resins used is higher tan 55 MPa (compressive) and 15 MPa (tensile).

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The other disadvantage of commercial epoxy resins is their low viscosity, whichmakes them unsuited for injecting into fast flowing water as they are easily washedaway. Analysing the technical features as given by the main manufacturers of thesematerials, we can see viscosity figures generally between 400 cP and 10,000 cP(waters is 1cP). However, figures above 100,000 cP are required for sealing leakagesin a dam. (Figure 1)

Figure 1. High visco thixotropy putty flowing

In fact, leakage of several hundred liters per second require the material injected notto be miscible or allow water to wash it away and this is only achieved with very highviscosity putties and these polymers are not to be found in manufacturers catalogues.

Apart from high viscosity, we have seen that the polymer has to have high thixotropy.Thixotropy is a feature of non Newtonian fluids that lose viscosity when subjected toa shear stress, for example, when shaking them or when passing through a fissurehaving been injected into it. Due to thixotropy, the material advances through thefissures whilst being injected and behaves like a liquid but turns into highly viscous

putty as soon as the pump stops. This property is essential for controlling thematerials advance since it cannot be washed away by water and only spreads throughthe fissure when pushed by the pumps pressure.

To make the mastic flow, inside the fissures with thicknesses of 0.1 mm, needs a largeinput of energy or, in other words, the pump must be able to give high pressures. Themachines we use at this time are capable of reaching 60 MPa, at the pumps outlet.This type of injection can therefore be considered as active since the resin displacesthe water and its flow through the fissures is quite accurately controlled. Given thehigh pressures used, it is necessary to take a control of movements of the structurenear the injected zones. Dial indicators or precision topography, according to thecases, are used to make the control of these movements that usually remain under

tenth of millimetres.

Obviously, to the aforementioned properties is to be added the fact that the polymerhardens and adheres under water and does not pollute. Not only can large water leaksof up to hundreds of liters per second be sealed with these materials, but on adheringand having high mechanical characteristics, they return lost monolithism to thestructure being treated.

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Water reactive resins

These are polyurethane resins which foam in the presence of water, retaining the gasthat forms inside the polymer itself which hardens with time. A closed pore structureis achieved that reaches volumes of up to twenty times the initial resin volume (Figure2).

Figure 2. Expansion of a water reactive resin

The degree of foaming and, therefore, the final characteristics of the material, dependon the degree of mixing with water. As this mixture occurs naturally on injecting theresin into a wet area or a flow of water, the applier cannot control either whereswelling is to occur or how much the material is going to foam. It is therefore a

passive technique since we are injecting a resin into a flow of water which, onwashing it along, makes it mix without our knowing a priorithe effect it is going tohave. Being highly fluid, generally below 1,000 cP, it is washed along by the flow and

we have no control at all over the foaming area.

Obviously, this material does not return monolithism to the structure and can only beapplied to remove small filtrations or wet patches, always with precaution. In the caseof joint treatment, it is not highly recommendable either. In fact, once polymerised,foam is an apparently elastic material. Its elasticity is due to the inclusion of gas

bubbles in the hardened resin and we have seen that when subjected to heavycompression, like that which would occur when a joint closes, these occlusionsimplode and do not recover their initial volume when the structure contracts again andtherefore leave routes for water to leak through.

This material is placed with conventional equipment, i.e., with commercial pumps

suitable for liquids that work at pressures generally below 6 MPa. This type ofmaterial is very popular. Due to its easy application, it may be suitable to remove wet

patches in basements but not for sealing filtrations in dams.

Visco expansive resins

Over the last two years, we have tried to develop a new material with the advantagesof epoxies like visco thixotropy, which cannot be washed away by water, are non

polluting, adhere to concrete and rock, have high mechanical characteristics and, that

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which most interested us out of the water reactive resins, their capability to expand. Inthis case, we wanted the expansion occur independently of the presence of water.(Figure 3).

Figure 3. Expansion of a visco expansive resin.

This swelling property is very important when filling not regular fissures but porousconcrete, foundation contact or rock lithoclases, in short, wherever large voids or

cavities existed. In fact, injecting voids with epoxy resins may not be economicallyviable, however, doing so with a material that, regardless of the presence of water, canswell to thirty times its initial volume reduces working costs by no less than thirty.

Figure 4. Specimens taken from a dams badly vibrated concrete with generalisedhoneycombing. The top specimen was injected with a resin filling the hollows.

The first test injection was made with this material at the end of 2009 in La MinillaDam (Seville, Spain, Emasesa) and it commenced large scale use in January 2010 inLa Ribeira Dam (Galicia, Spain, Endesa). In both cases, results far outpacedexpectations, as will be discussed later.

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INJECTION PUMP

We designed our own pumps to inject this new material, able to pump high viscosityputties of more than 150,000 cP over long distances and able to pressurise resins up to60 MPa. But we still had an unsolved problem: resin mixing. In fact, all these

polymers come in two components which require them to be mixed before injecting.

This is an operation that had always been carried out by hand.

Hand mixing has numerous problems:

The amount mixed has to be quickly injected since the reaction begins quickly. If theinjection process does not advance at the rate planned, the mixed material has to bewasted.

Incomplete mixing leads to an irregular degree of polymerisation and it must be bornein mind that the work site is sometimes a narrow gallery where a large water leak hasto be tackled urgently and workers are therefore under conditions of stress. This maylead to the injected material never becoming polymerised or its final characteristics

being unsuitable.

On the other hand, an excessive mixing may be even more harmful. In fact, it hasbeen seen that too long a time mixing ends towards air bubbles forming in the massbut, above all, causes unwanted heating up of the resin. On the one hand, all thesepolymers have a heavily exothermal polymerisation reaction which, in a fissure, is notimportant since the area of injected material, in contact with concrete or rock, is verylarge and, therefore, the surroundings absorb the increase in heat. However, there isno possibility of heat being absorbed in a container whilst mixing or in a hoppersupplying the material to the pump.

The problem lies in the fact that these materials obey the Arrhenius equation,according to which on a chemical reactions temperature increasing 10 C, its ratedoubles. This means that if the worker is careless and shakes/stirs the mixture a fewminutes too long, the resin may suffer spontaneous combustion in the container orharden too soon during injection, causing serious problems in both cases.

In order to avoid the foregoing, we have designed a new type of pump which makesthe mixture automatically in just a few seconds (Fig,5). The mixer has been designedand is periodically calibrated to obtain the optimum quality of the grout. In addition astrict quality program based on the ISO standards is carried out.

With this new machine, each component of the resin is poured separately into a

hopper where they are pressurised to 60 MPa. From there, they go on to the mixerwhich achieves a perfect, homogeneous mixture. This mixer can also make thematerial thermally suitable before injecting.

This pump can handle both traditional epoxies and the new visco expansive materials.

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Figure 5. Pump diagram

APPLICATIONS

The main application for this technology, which enables extraordinarily viscothixotropic polymers to be injected, lies in dam repairing, in leakage sealing withoutdisturbing operations, i.e., with no need to empty the reservoir. Using this technology,leakage of 200 l/sg has been sealed under more than 100 meters of water column.

Vertical joints have been injected using this technique both in arch and gravity dams

always without having to empty the reservoir (Figure 6).

Figure 6. Sealing of vertical joints of a gravity dam, without emptying the reservoir

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The introduction of the new visco expansive resins has enabled previouslyunapproachable problems to be solved with acceptable costs. In fact, we submit thatthe problem of sealing a gravity dams upstream heel when, with a full reservoir, it

becomes detached with the consequent, dangerous increase in uplift, can only besolved with these materials and technology.

Likewise, up to now, sealing lithoclases in the foundation rock or contactconsolidating when heavily deteriorated, were unapproachable problems with a fullreservoir.

The great advantage of working with a maximum water level is that operation is notinterrupted and the loss of profit a hypothetical emptying of the reservoir would

produce is avoided. Also, sealing or repairing under the worst possible conditions is aguarantee that the repair will be long lasting.

Two examples of repair work carried out with these visco expansive polymers aregiven below.

LA MINILLA DAM

La Minilla dam, located in Seville, Spain, and owned by EMASESA is a gravity damwith foundations on pyrites. The same pyrites were used as aggregate in making theconcrete. Irrespective of fissuring and filtration problems in the galleries, the concretein contact with the foundations was particularly decomposed. When an attempt wasmade to take samples from the contact for risk analysis, it was impossible to takespecimens since they crumbled and did not provide any useful data at all (Figure 7).

Figure 7. Specimen drilled with a theoretical length of five metres from which only ascarce metre was recovered.

A video camera inspection through the boreholes drilled showed, (Figure 8), thathollows were produced as a consequence of the drilling itself which proved, as wassuspected, that the concrete and rock itself were so deteriorated in this area that they

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were behaving like granular material. Obviously, it was our own action when trying totake specimens that caused a substantial alteration to the whole unit.

Figure 8. Frame from the TV camera inspection of a drill hole where numerousfractures and hollows can be seen.

In the light of this fact, it was decided to make a consolidation injection. Theoperating level of dam, which supplies water to Seville, fluctuates very little andemptying the reservoir was out of the question. The injection material therefore had tohave the following properties:

Not miscible and not swept away by water.

Not produce any pollution at all.

Fill existing fissures.

Encapsulate still active pyrites.

Consolidate granular areas.

Increase in volume without the need for water.

Achieving a material complying with all these requirements took two years ofresearch and tests. Finally, at the end of December 2009, a position was reachedwhere work could commence.

The process started by rotation drilling 46 mm diameter holes spaced atapproximately 1.5 meters. The visco expansive resin was then injected into the firstdrill hole, sequentially changing to the next one as the injection advanced in the areato be treated.

After a few days, 100 mm diameter specimens were taken from the area injected. Thefirst conclusion was obvious: more than one meter long, unbroken specimens wereobtained (Figure 9).

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Figure 9. Photo of a specimen taken from the contact rock-concrete

It was also seen that not only had the resin monolithised more or less large fragmentsof the contact concrete or rock, but it had also penetrated into the more sandy areas,forming authentic mortar.

LA RIBEIRA DAM

Located on the river Eume in Galicia, Spain, La Ribeira dam was suffering fromheavy uplift, particularly at the abutments. Cleaning drains with high pressure waterrelieved the uplift but the drain system was found to be insufficient and new drainswere then drilled. In order to locate the inflow areas and, therefore, optimise the depthto which the drains had to be drilled, geophysics equipment was used (Figure 10),consisting in a computer, a motor driven winch controlled by the computer and probesemitting electric signals picked up by a data logger which converts and sends them tothe computer.

Figure 10. Diagram of the geophysics equipment.

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Temperature and conductivity probes were used to accurately ascertain the depth atwhich water flowed into the drain and the amount of flow to evaluate its importance.Two main flow areas, at 10 and 25 meter deep were found. The new drains weredrilled using this data whilst monitoring the result in real time with a previouslyinstalled, dense system of piezometers.

As expected, uplift pressures reduced, as the new drains were drilled. However, whendrain flows reached more than 60 l/mn, drilling had to be stopped (Figure 11).

Figure 11. Initial and remaining uplifts at the time the drain work was stopped.

In order to reduce the large drain inflows, it was obvious that localised imperviouscurtains needed to be made upstream of the dam to seal the lithoclases through whichinflows were occurring (Figure 12).

Figure 12. Localized injection of visco expansive resins.

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As stated previously, the main limiting factor was the impossibility of emptying thereservoir. The work had to be carried out at a maximum storage level. This naturallydid away with the idea of cement injecting and so an attempt was made with epoxy

putty. Encouraging results were obtained but the heavy consumptions made thesolution economically unviable. Neither was the use of water reactive resins theanswer since they would have been washed away by the heavy groundwater currents.

Work was held up for a year until the visco expansive resins with which injectingcommenced were refined. Large reductions in flow measures were achieved from thevery beginning and, as a consequence, with the treated lithoclases flows noticeablydropping, the drains were able to work adequately and the final objective, to reducethe uplift to admissible values, was achieved.

The great thickness of the lithoclases, perfectly sealed with the resin which expandedinside, can be seen in the specimens taken from the treated areas (Figures13 & 14).

Figure 13. Specimen with injected lithoclases of several mm thickness.

Figure 14. Specimen of injected rock with visco expansive resin, which not only sealsbut adheres so returning monolithism to the fractured rock.

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CONCLUSIONS

This new technology of injecting thixotropic resins, at very high pressures, allows thesealing and repairing of dams, without affecting operation and therefore, withoutemptying the reservoir.

Injecting visco expansive polymers at a very high pressure enables previouslyunapproachable problems to be solved. Although this material does not require the

presence of water to swell, it has been seen that in a humid or submergedenvironment, expansion continues for days, though in a more moderate fashion.

More than one hundred dams in Europe, and now in America have been successfullyrepaired with these technology and new materials. Thousand of tons of these

polymers have been injected in the last 15 years.

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