tridimensional gpr mapping in the upstream face of … · tridimensional gpr mapping in the...
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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: [email protected], 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.
pipes4, embedd
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gical surve and voids
use of GPR practice inis also an ir a better a
sents a tridie of the RCy the possicrete, whosal polarizatie direction rhe read sectof the image
slicing, se
UND PENE
enetrating romagneticcture. t used in thdual polarizy one direcwith limitedistance mtrigger for uisition.
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eys5 and oin concreteis widespr
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ETRATING
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igure 1: GPR
acerda, Ernest
2
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particular, h resolutionlogical andher hydrauwill form tudies. ution GPR ara in Para
omalies in han 50cm. T
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it has been. d geotechnilic concretethe basis fo
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The mappinformation ol images wefilters for coysis of each ace anomal
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igure 1. It ch allows penna allowse. antenna, whctromagneti
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en used to
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or the defin
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ONTROLLE
ore applyinuate its capconstructior the GPR
m. Eighteen3. The anfilled withits higher pmolds, as
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for h = 1,2d not be over survey thehe transmit
cy (fr) signa
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ng the GPR pacity for deon plan conreadings. T
n anomaliesnomalies hah aggregateporosity. Tshown in F
ure 3: Schema
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f < 0,
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D TEST
system in etecting anonsisted of aThe block ws were insead differenes size 1 a
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sted to estim
test was perdded in concps with a md had thickation, as shonsisted ofh a plastic the concretconcrete bl
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w of the and are
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4 APPDAM
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Figure 6: Rad
PLICATIO
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7: Location in
selected arg. Once theach line, alwfirst GPR pof the conreservoir w
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dargram of se
ON OF GP
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n the upstream
rea was dise lines wereways in the profile (0,0crete pavem
water level.
Alkimin de La
ection B with
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Clara was pto evaluate
m face where
scretized we marked, tsame direc0 m) was rment. The .
acerda, Ernest
6
h 10 cm thick
E UPSTRE
performed the conditi
the GPR surside.
with 75 linethe GPR rection (Figurread at the l
last profile
to Goldfarb a
anomalies pl
EAM FACE
in a limitedion of the c
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and Emerson L
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pth near to 10
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ure 8: GPR su
files showedciated with
profiles at thed hyperbolel (Figure 9)
Figure 9: Rada
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ectors, makhis depth CC.
acerda, Ernest
7
upstream face
nce of faintregularities
0.0 and 0.10s a clear ev
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th of 0,50 waves in
king data is also ass
to Goldfarb a
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t irregular ain the conc
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and truncatecrete surfac
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nal quality ete. Beyondion even mo the trans
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enna.
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flectors in tte reinforce
m.
is poor dud this deptmore difficsition betw
s, which medium
he form ement at
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In sowhich aconcret
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ome profileare associate as shown
pecific radude, whichng forms duram of the c
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gure 10: Rada
es it was noated with thn in Figure
Figure 11: P
dargrams thh are relaturing the cocorrespondi
Alkimin de La
argram showi
oticed the phe occurren11.
Presence of m
here was tted to the oncrete woring level.
acerda, Ernest
8
ing noisy data
presence of nce of met
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the occurrepresence
rk. The form
to Goldfarb a
a beyond the
f isolated hytallic fragm
nts in the face
ence of strof metal ems are show
and Emerson L
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
and Emerson L
lements used.
rmal reservdue to the cularly highcted in the
eater wear.
pths from tmed8, con
he electrom
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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
ueira, Luiz A
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
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ONCLUSIO
GPR has gation of thlies with higa relatively
nvestigatiohe examineed the presethe normaive interven
GPR radntional concsed for fast
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proved tohe upstreamgh precisioy quick men of specifi
ed area of thence of a plal reservoirntion was n
dargrams acrete zone, ening the c
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to Goldfarb a
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anomaly.
non destrucg the identif
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uctive tool fication of
plied to largs.
m, the GPR rete. Its locined inspec
ements insl directions
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do Rio Jordhe research
JADES L. GMethodolo
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HAZI J.; BAadar (GPR)
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Sítio ControRevista Bras
te Georadarale delle Pr
for the internal
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profiles cation is ction or
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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.
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[8] GRED 3D Copyright© 2008