Dams condition can be monitored using geophysical tools.

1. Assessment of Dam Infrastructure &
Condition Monitoring Using
Geophysical Tools
SHUBHAM SHUKLA
Roll no.16419GEP026
M.Sc. (Tech.)-VI Semester
Department of Geophysics
Banaras Hindu University
sshuklabhu@gmail.com
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2. Outline..
 Introduction
 Problems With Dam Health
 Methodology and Instruments
 Electrical Resistivity Tomography
 Spontaneous Potential SP
 GPR
 Case Studies
 Result and Conclusion
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3. What is a Dam?
Dams are massive barrier built across rivers and streams to
confine and utilize flow of water for human purpose.
 Reasons to build a Dam
To generate electricity (Nearly 20% of world’s electricity by
hydropower)
To supply water for agriculture, industries and household.
To control flooding and assist river navigation.
Reservoir fisheries and leisure activities such as boating.
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4. Types of Dams
Arch dam
Gravity dam
Buttress dam
Barrages
Embankment dam
Rock-fill dam
Earth-fill dam
Check dam
Fig1: Types of dam ( source ppt on dam by johnplayer.)
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5. Structure of Dam..
Fig2: Dam and its parts (source Johnplayer et al) 5

6.  Problems in Dams
 Cracking
 Concrete failure
 Internal erosion
 Seepage
 Causes of Seepage
 Joints in rocks, cracks, frost action
 Unconsolidated rocks in foundation
 Poorly compacted soils, rat holes
 Uprooted trees, earthquakes.
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Fig3:Problems in Dam (source Kayode et al 2018)

7. Effects of seepages on earth dams..
• Piping, excessive internal pressure or saturation
• Solutioning of soluble rocks such as gypsum, limestone
and rock-salt.
• Internal erosion.
• Excessive uplift and heave or blowout.
• Potential seepage can lead to dam failure.
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9. Methodology and instrumentation
1. Electrical resistivity Imaging
•It’s a multielectrode system with multicore cable.
•Provide a linear pseudo depth section, of 2-D variation in
resistivity.
•Provides picture of internal resistivity distribution of the dam
structure, identifying the zones of water accumulation and wetting.
•Generally Gradient array is used.
•Res2DInv Software for processing and interpretation.
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10.  3D resistivity imaging is analogues to 3D seismic which can
easily be correlated with dam structure.
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Fig4: (a) Four-electrode Wenner array (b) Data collection and construction of a psuedosection for 2D ERT (Source Chih-Ping Lin et al 2013)

11. 2. Streaming Potential(SP Method)
Fig5: A typical
example of SP data
(source Burke J
Minsly etal)
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12. 3. GPR(Ground Penetrating Radar(GPR)..
 GPR is high frequency(10-1000 MHz) EM technique of
imaging subsurface at higher resolution.
 Velocity controlled by the dielectric constant (relative
permittivity) and conductivity of the subsurface.
 Reflection depend on soil sediment mineralogy, clay
content and moist .
 Identify shallow cracks, cavities and voids in dam body.
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13.  The depth of investigation depends on frequency and
geology (i.e. water content and porosity) of area
surveyed. Raphaël Antoine et al 2018
•The data is processed using the ReflexW software
Fig6. a GPR in use at embankment (source Raphaël Antoine etal)
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14. Case studies..
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Fig7:Satellite view of dam(source P. Michalis et al)

15.  ERT was applied to investigate seepage conditions and other
potential mechanisms inside the body of the dam.
 3 Different ERT arrays (M1, M2 and M3) were installed on the
crest of the dam an between shoulder of dam.
 Arrays length of 96 m with 2 m interval spacing between
electrodes for greater penetration depth.
Fig8: view of dam and
ERT lines (P. Michalis et
al)
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16.  Low resistivity zones (< 24 ohm.m
at depth between 5–11 m.
 Associated with saturation zones
in clay sediment influenced by
seepage.
 Present in whole body of dam.
dam.
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Fig9:Inverted resistivity sections M1, M2 and M3 (clockwise
from top)(P. Michalis et al)

17.  The Czech reservoir Vitineves using SP:
17Fig10: Different geophysical lines on embankment (source Sentac et al)

18.  The most significant +ve anomaly between 165-170 m.
 Positive anomaly due to seepage in reservoir due to loss of
dissolved anions and being captured on walls of soil pores.
 seepage has also been confirmed by visual observations.
Fig11: Sp data with ERT for verification of full reservoir as well as empty reservoir( source Philippe Sentenac et al 2018)

19. 3. Orleans Embankment using GPR..
 The embankment is alongside of Loire river, Saint Firmin,
France.
 Built on Turonian limestone and chalks and made of modern and
ancient alluvial soils.
 GPR frequency 200MHz with depth of penetration 2m.
 Several leakage appeared
in last 5 years and found near
profile p2 and p3.
P5 is near spillway.
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Fig12:Transverse cross section of the embankment and location of the
GPR profiles On the sloped pave(p1 to p5) of the canal and on its
crest(P6) (source Raphaël Antoine et al 2015)

20.  Spillway verification:
Two distinct diffraction hyperbolas are visible (dotted lines) at
404 m at a depth of about 35 cm followed by large amplitude
reflections tell the presence of a pipe inside the embankment.
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Fig13: profile P5 on the pave showing the hyperbolae directly above a spillway( source
Raphael antonie er al 2015 )

21.  Leakage Detection:
 Profiles P2 and P3 made under the paved revetment at 0.75 and
1.25 m in height show an anomaly characterized by strong
reflections at 70 m .
 The 5 -10 m wide
anomaly may
correspond to water
infiltration as the fines
have been washed out
by the leaking water.
21Fig14: the profile P3 and P2 showing the leakage zone near 70 m( source Raphael
antonie et al 2015)

22. Conclusion..
 Geophysics is an important tool to assess the on-going
performance of dams and define their safety levels in non-
destructive manner.
 SP and ERT provided the best interpretation of seepages with
higher resolution. Repeated geoelectrical measurement
revealed the relative changes of water saturation in the
selected reservoir embankment.
 GPR is the best tool for diagnosis as it is easy to implement,
provides real time and detailed information concerning
potential structural voids and Seepage.
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23. Thanks for your
attention…
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