6TH INTERNATIONAL CONFERENCE ON DAM ENGINEERING C.Pina, E.Portela, J.Gomes (ed.)

Lisbon, Portugal, February 15-17, 2011

1

TRIDIMENSIONAL GPR MAPPING IN THE UPSTREAM FACE OF AN RCC DAM

Isabella F. R. Figueira*, Luiz Alkimin de Lacerda*, Ernesto Goldfarb Figueira†, Emerson Luiz Alberti‡

* Instituto de Tecnologia para o Desenvolvimento (LACTEC) Br-116, Km 98 – s/n° Centro Politécnico da UFPR, 81531-980 Curitiba, Brasil e-mail: isabella.figueira@lactec.org.br, webpage: http://www.lactec.org.br/pt/

Keywords: Dams, Concrete, Ground Penetrating Radar, Non Destructive Tests.

Abstract. Mapping with geophysical techniques such as the Ground Penetrating Radar (GPR) is based on the propagation of electromagnetic waves and has a wide range of applications in civil engineering. This work presents a non-destructive investigation with GPR in the conventional concrete face of a roller compacted concrete (RCC) dam. The objective is the identification of subsurface anomalies, such as niches of higher porosity in the conventional concrete, whose thickness is not greater than 50 cm. The acquisition of radargrams was carried out with a 2 GHz antenna with dual polarization, which allowed assembling a three-dimensional subsurface image from a single direction reading path. The images were treated with a specific package of filters for concrete surveys. After this post-processing, the group of images was integrated to form a block diagram. The interpretation of the whole block was performed with a controlled thickness slicing procedure for identification of anomalies within sound concrete. A general view of the investigated area is presented with the indication of anomalous regions which may require a localized repair.

1 INTRODUCTION

The integrity, load capacity and service life of concrete dams is directly correlated to the quality of constituent materials and construction methods. The common practice of investigation of concrete in civil structures uses invasive methods to extract samples for laboratory tests. Besides being destructive, these methods cannot consistently reveal abnormalities within the analyzed structure.

Civil engineering has recently started using non destructive geophysical techniques for the inspection of hydraulic structures. However, investigation of anomalies such as niches of higher porosity, cracks and damaged areas within concrete is not trivial. With geophysical surveys one can determine concrete conditions, detecting anomalous areas and mitigate the damage.

The Ground Penetrating Radar (GPR) is a geophysical tool whose principle is based on the propagation of electromagnetic (EM) waves. It is a non destructive method of investigation used for different purposes, such as to detect the thickness of slabs1, the integrity of masonry structures2, the integrity of reinforcement in bridge decks3, buried

† Esteio Engenharia e Aerolevantamentos S.A. ‡ Elejor – Centrais Elétricas do Rio Jordão S.A.

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gical surve and voids

use of GPR practice inis also an ir a better a

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6

h 10 cm thick

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acerda, Ernest

7

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enna.

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gure 10: Rada

es it was noated with thn in Figure

Figure 11: P

dargrams thh are relaturing the cocorrespondi

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oticed the phe occurren11.

Presence of m

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acerda, Ernest

8

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presence of nce of met

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the occurrepresence

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to Goldfarb a

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f isolated hytallic fragm

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ence of strof metal ems are show

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depth of 0,50

yperboles oments inside

e of the dam.

riking hypeelements uwn in Figur

Luiz Alberti.

0 m.

of small ame the conv

erboles of used to fasre 12 along

mplitude, entional

greater sten the gside the

Figure 1

The increassurfacelevel flindicati

For specificinterpogenerat

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2: Example o

GPR profed presenc

e with showuctuations ion of inter

a better vic processinlation baseted by the G

ueira, Luiz A

of striking hy

files alongce of irreguwing aggreg

(Figure 13rnal flaws.

Figure 13

isualizationng procedued on posiGPR.

Alkimin de La

yperboles (rigwhich were l

g the linesular and trgates. Wear). None of

: Normal wat

n of the proure called itive and n

acerda, Ernest

9

ht) resulting left embedded

just beloruncated rer in this arthese hiper

ter level zone

ofiles at diC-Scan w

negative p

to Goldfarb a

from metal ed in concrete

w the noreflectors, drea is particrboles dete

e showing gre

ifferent depwas perforeaks of th

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lements used.

rmal reservdue to the cularly highcted in the

eater wear.

pths from tmed8, con

he electrom

Luiz Alberti.

d to fix the for

voir level irregular c

h due to thradargram

the mappednsisting of magnetic re

rms (left)

showed concrete he water

ms are an

d area a a data

eflectors

The identifiareas in

The defined

Figu

Voidwith reto 35 cm

Lookpresencthe damFigure

A clranges

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product ofication of hn blue (Figumetal elem

d and equid

ure 14: 5 cm C

ds or niched colors. Inm, slightly king at thece of a contm can be ob16 detail).

Figure 15: R

oser look afrom depth

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f this interhighly condure 14). ments used istant spots

C-Scan of the

es of highern the surveabove the 5

e radargramtinuous plabserved. Th

Radargrams a

at the C-scah 15 cm to 3

Alkimin de La

rpolation isductive are

for fastenis of high co

e mapped area

r porosity eyed volum5,00 m levems betweenane anomalyhe anomaly

at levels 4,60

an shows th35 cm.

acerda, Ernest

10

s a block, eas, depicte

ing the climonductivity

a. The circled

with high me the circle

el, is an evin levels 4y in a diagy goes from

m, 4,70 m an

he anomaly

to Goldfarb a

which afteed in warm

mbing formbetween 4

d areas indica

water quaned red spotidence of o,60 m andonal positio

m 15 cm to

nd 4,80 m wit

y in detail, w

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r a 5 cm sm colors, an

ms are clea0 cm and 4

ate anomalies

ntity wouldts detected ne or more

d 4,80 m, on with res35 cm dep

th the anomal

which is ov

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slicing, allond highly r

arly shown 45 cm depth

at various de

d also be infrom depth

e anomaliesin Figure

spect to thepth (Figure

ly indicated.

ver 80 cm l

ows the resistive

at well h.

epths.

ndicated h 20 cm . 15, the

e face of e 14 and

ong and

5 CO

The investiganomal

It is or for in

In threvealeabove correcti

The convenwere us

6 AC

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ONCLUSIO

GPR has gation of thlies with higa relatively

nvestigatiohe examineed the presethe normaive interven

GPR radntional concsed for fast

KNOWLE

authors wofinancial su1233240-8)

FERENCE

REZ-GRACsolution in amples. ND09.

AMROUCH ARLIGUI

vestigation structive Te

ASER K. Ridge Deck gineering N

RSANI J.Lofísica Rasaofísica 24(1

OLLA C.. Dlutazione e struttive Mo

ueira, Luiz A

Figure 1

ONS

proved tohe upstreamgh precisioy quick men of specifi

ed area of thence of a plal reservoirntion was n

dargrams acrete zone, ening the c

EDGEMEN

ould like toupport for ) through la

ES

CIA V., DI NDT Stud

DTCE’09 N

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esting in Civ

R.. IntegratioCondition

Nantes, Fran

L.; BORGESa do IAG/U1): 49-61 20

Diagnosi dConservazi

onitoraggio

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CAPUA Ddies of Str

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di Muraturaione di CosDiagnostica

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11

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EJOR – Ceut this resea0.

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ALAYSSACdeling of Gin Brick

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ODRIGUES ação e Resu

a, Calcestrustruzioni e Ia, Itália 200

to Goldfarb a

ith identified

ementary nms, allowing

ion, whichr periodic aSanta Clarahe conventementation

esence of vertical and the dam co

entrais Hidrarch, and C

ALEZ-DRIGements: Exng in Civel

C J.; AUREGround-penMasonry Ss, France 20

ing Radar aE’09 Non-D

S.I.; HIODultados GPR

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and Emerson L

anomaly.

non destrucg the identif

can be appassessmentsa RCC damional concr

n of a refi

metal eled horizontalonstruction

relétricas dCNPq for th

GO R., PUJxperimental l Engineerin

ENS S.; RHnetrating RaStructures. 009.

nd InfraredDestructive

DO F.Y.. O SR 2D-3D. R

gno Tramitere. II Giorna

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uctive tool fication of

plied to largs.

m, the GPR rete. Its locined inspec

ements insl directions

n.

do Rio Jordhe research

JADES L. GMethodolo

ng Nantes,

HAZI J.; BAadar (GPR)

NDTCE’0

d ThermograTesting i

Sítio ControRevista Bras

te Georadarale delle Pr

for the internal

ge areas

profiles cation is ction or

side the s, which

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ALLIVY for the

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Isabella Figueira, Luiz Alkimin de Lacerda, Ernesto Goldfarb and Emerson Luiz Alberti.

12

[6] SPORER A.. Inspeção não Destrutiva de Estruturas de Concreto por Georadar (GPR).

Revista Abendi nº 32. Artigo Técnico, Brasil 2009.

[7] PADARATZ, I.J.; FORDE, M.C.. Influence of antenna frequency on impulse radar surveys of concrete structures. 6th Int. Conf. on Structural Faults and Repair, London, 2, 331-336. 1995.

[8] GRED 3D Copyright© 2008