Comprehensive Assessment of Dam Concrete Structures using Geophysics

This report provides a detailed overview of the application of geophysical techniques for assessing the integrity and safety of concrete dam structures. It explores various non-destructive methods, including Electrical Resistivity Tomography (ERT), the Direct Current Resistivity Method, Seismic Refra...Read More

Table of Contents
Bibliography 3
Electrical Resistivity Tomography- 3
Direct Current Resistivity Method 5
Seismic Refraction Method 7
Temperature Measurements Method 9
Case study 12
Conclusion 12
Reference 15
2

Bibliography
The preventive execution and efficient maintenance of the dam infrastructure is essential
taking into consideration certain financial, social and economic influences in incidents of
destruction or failure. Although, the investigation of the dam structures specifically relies on the
geodetic and certain geotechnical assessment and specific instrumentation. Generally, a large
portion of these instruments does not give consecutive and credible details about the general
mechanisms taking place inside the structure of the dams that could deal with the composition of
the basic structure of the dam (Posudin, 2016). Geophysical techniques can give crucial details to
state the security parameters of dam construction and concrete. Rapid dam monitoring would
also let early remedial execution and maintenance steps to be proceeded out enhancing public
safety and eliminating reasonability for dam constructors, insurers and those who maintain it
after the construction. The study therefore shows initially, the state of Murdock reservoir dam
implemented two varieties of the non-destructive geophysical procedures.
Electrical Resistivity Tomography-
Electrical Resistivity Tomography or ERT specifications were equipped on the crest
region of the dam to state the structural assessment of the dam reliable on the resistivity steps
3

(Electrical resistivity tomography for identification of frozen and cooled saline ground. 2019).
Electromagnetic sensing technique was then implemented as a statutory process to confirm the
values obtained with the ERT generally for the upper region of the soil layers of the particular
dam crest. The hypothesis of the outcomes procured from the electromagnetic study revealed
high resistivity for the supreme soil layers under the crest portion of the dam. The electrical
resistivity surveys showcased that low resistivity area that could be impacted by the seepage
states in the body of the dam (Eliot, 2019). And, geophysical outcomes stated in this study gives
vital basics of measurements which with the association of coming geophysical and geotechnical
statistics will present elementary details about the continuous performance of the dam
infrastructure(Li, 2013).
Dam plays a pivotal role in all the countries, they implement financial and investment
and caters great advantages to the population by supporting irrigation, electricity and also plays a
big role in flood control. Most of the major dams are traditional and also efficient in maintenance
and regulation of these dams is of major essentiality for certain advantages. This is not basically
like soil investigations de Rijke, K. (2017), complicated state of dams, does not allow obsolete
invasive inspections by methods of drilling, and these inspections are best and preventive and are
taken in consideration when problem digs up.
Geophysical techniques are most prominently non-invasive and are in favour of the
surroundings and nature, presents an efficient solution for investigation or regular maintenance
of the dams, and investigation of deformities states which may convert into big issues if they are
not properly assessed and maintained Clement, R. and Moreau, S. (2016).
Certain geophysical procedures are present to detect the issues of certain earthen,
masonry, concrete, traditional or composite dams include Leak path detection, internal soil
erosion, and detection of the zone of water collection, Cavity, leakage or sinkhole and concrete
quality degradation (Yang and Wu, 2017).
4

Direct Current Resistivity Method
Generally, in the Direct Current (DC) resistivity procedure, electrical currents specifically
originated are taken into consideration into the soil by a pair of electrodes Case, J. (2012). And
calibre taking variations are basically calculated on the above region of the surface by certain
another set of electrodes, in the region of the impact of the electric field. The current
heterogeneities in the soil and rocks like bedding Ren, Z. and Tang, J. (2010), soil foliation, and
certain fractures along with elements like mineralogy, moisture percentage, porosity and soil
permeability can bring outcomes in significant alterations in the system of an electric field and
reliable statements of the variants of the structures to the local pattern . By the significant
intensity of the current that flows specifically through the region of the basement, the structure or
5

the geometry of the systematics of the electrodes (K) and the general potential difference
calculated most often by the electrodes receivers (ΔV), it is certain to calculate the present
resistivity value certainly due to heterogeneity. The following equation represents the whole
procedure
ρa=K.ΔV/IΩ.m.
Specifications say that the unity of the apparent resistivity is calculated in terms of
Ohm.m, the potential difference is calculated in the millivolt (mV), and the current intensity is
taken in miliampère (mA) and the basic geometric coefficient K is measured in meters . In terms
of construction of the earth dams, the variety of external properties of properties like water and
soil will state the basic deformities in the structure.
At the location of general study Yang, D. and Wu, S. (2017) , three basic electrical
resistivity tomography or ERT were proceeded out from the southwest towards the northeast
direction. The array was specifically implemented was Wenner with particular 53 electrodes
spaced within the duration of every 2m. Every Electrical Resistivity Tomography was 104m
long, which permitted to base the complete length of the dam and given a resolution of about
17m of depth. The ETR-1 was released closest in downstream location (Fratta, Puppala and
Muhunthan, 2010); ETR-3, closest to the upstream location. The system or appliance used for
this analysis was an ABEM Terrameter LS comprising 84 channels and electricity power of
about 250 Watts.
In a specific day, 312m of the geophysical data were collected and ranged in three
Electrical Resistivity Tomography maintained in the parallel direction to the specific ridge and in
the direction of the varied elongation of the body of the constructed dam. Each line was carried
about a distance of 104 meters long, with some 53 electrodes spaced every 2m, with the vacuum
between Electrical Resistivity Tomography was of 3 meters in length.
Geophysical Techniques also involve the gradual escape of a liquid or certain gas by a
porous material or through the small openings is known as seepage. It is a method of seeping in
soil engineering as the water in the soil is located. Seepage generally creates a specific issue
often in the building construction and foundations and also a regular issue in the earth dams.
6

Dams are the specific structures constructed to retain the water or preventing the leakage.
Seepage by the region or surrounding the dams has been the serious cause for most of the
occurring dam destruction or the failures Han, J. and Alzamora, D. (2011). Dam failures are
certainly occurring with major anomalies and leading to the devastation of the concrete or the
infrastructure and elements. Although, maintaining the seepage through and surrounding regions
of the dams become essentiality in other areas to guide the dam's stability. The prominent field of
working of this consideration is noted to the location of specific elements and the base quality
guarantee.
The great diversity of existing geological environments at hypothesised and present dam
sites signifies the unique complications in association to the diverse and varied geologically
elements, mapping, conditions, seepage analysis and maintenance Heagy, L. and Oldenburg, D.
(2019), integrity estimation, slope accountability, foundation states, circumstances and certain
seismic hazard evaluation. Geophysical methods give direct answers and enriched deep analysis,
report and data to nullify other studies and more enlarged and significant methods of estimation
like drilling.
Seismic Refraction Method
The seismic refraction method is the most generally implemented geophysical methods of
detecting the geological conditions at the dam sites Johnsen, L., Bruce, D. and Byle, M. (2016).
Multichannel reports on the land surface or the overwater region generate the intense and
detailed picture and report of depths to the bedrock , overlaid by specific layering and authentic
competency or the rip ability of the bedrock. Shear or the fault zones in the specific bedrock are
general and recognized in the seismic refraction detections.
Other Geophysical parameters include the Seismic refraction analysing may be
processed in some of the major courses by certain seismic reflection Reichling, K., Raupach, M.
and Klitzsch, N. (2014),or the overwater region and acoustic maintenance and profiling, ground
seeping radar or the resistivity imaging techniques and procedures. These surveys may be taken
into consideration in order to give more intense and detailed geological layering knowledge,
geological details in areas of intense or quick flowing water and the availability and analysis of
7

harsh conditions or spaces and the voids in the lower region of the soil or in the base and
foundation of the to be constructed structure.
A great variety of geophysical procedures are implemented to estimate the conditions at
present locations of the dam sites. Most of these processes discover utilisation on earth or basic
rockfill systems with some ways which are also effective on the concrete dams. The most
important applications or utilizations of the geophysical processes at the existing dams are
associated with the seepage assessment, certain integrity estimations, foundation conditions and
the seismic critical estimation. Deformed seepage is generally recognized with the self or the
streaming-potential procedure. This technique implements two potential electrodes to detect the
small voltage deformities generated by the fluid flow and the method of electrokinetic coupling.
Potential differences can be also estimated in the above region or the normal flow path either
from the area of the dam surface or from the specific or some boreholes. Along with the primary
seepage hypothesis and modern technologies are electrical resistivity imaging, more prominently
Electromagnetic (EM) profiling and Ground Penetrating Radar Eliot, G. (2019). Certain
Resistivity and Electromagnetic profiling studies recognize low resistivity deformities regulated
with the active seepage locations. Ground Penetrating radar records can showcase that the zones
of increased water content and outcome cavities or specific fault zones in the rock. Generally,
streaming potential studies are utilized for monitoring methods after conduction of remedial
steps has been processed out to minimize the seepage Eliot, G. (2013). Some amount of internal
region erosion to cause the structural association of the dam. Critical soil erosion has the
sinkholes in the dam and required on the specific reservoir floor. Preventive techniques for
specifying the sinkhole elements within an earthen dam involve resistivity imaging and
streaming potential. Things like streaming potential surveys that are augmented by high-
resolution sonar can be effectively used in the reservoir area to find the sinkholes.
Outlining of sinkholes within the dam is significantly proceeded out by implementing
specific down hole and cross-hole seismic shear wave and the specific shear wave tomography
studies Herman, S. (2012). Downhole and cross-hole shear wave hypothesis are quite
complicated to space ratio because of a certain loss of the soil or fines which leads to a
minimization in relieving stress Michal ski, L. (2012). Structured shear wave tomography studies
8

from the boreholes can properly outline the shape of the sinkhole features that are general and
bigger than coming results majorly because of the stress relief in the adjoining soils.
In key parameters of Geophysical procedures include the estimation of the seismic hazard
soil factors and basic conditions are usually processed out implementing the downhole and cross-
hole, compressional and shear waves methods. Basically, material factor procured from in situ or
on location estimations is implemented to analyze ground accelerations because of the
earthquake loading. Lines of the seismic velocities are the crucial factors in denoting the
spontaneous answer and credibility of a structure, as well as site liquefaction calibre.
Temperature Measurements Method
9

Temperature measurements are an accomplished procedure of monitoring that makes the
implementation of the seasonal differences that act on a particular waterbody or the dam. The
two basic techniques of data collecting for water impounding sources include either joining
discrete thermistors to the major portion of the dam or applying the rows of certain temperature
sensors into the body of the dam through small boreholes (Shuang Chen et al. , 2013). The other
method called as temperature sounding is majorly useful as it can credibly suspect the seepage
implementing water temperature as a tracer.
The boreholes required are very tiny in size that they can be generated implementing
certain hand-tools, and the specific sensors can be expelled in for the long duration of guiding
Eliot, G. (2018). Actually, continued estimations can permit for statement and the keen analysis
of the seepage velocities other than only seepage recognition Eliot, G. (2010), quite resembling
but not as efficient and precise as self calibre. No other procedure can be started out on a dry
source. Although, there is one major benefit of temperature sounding is that water temperature
deformities are still detectable enough for a long duration of time after a brief consequence of the
flood Eliot, G. (2012). This generally makes the procedure more commendable and appreciative.
Temperature measurements are considered as the most reasonable and authentic when the only
layer of surface area present. Deformities that are keen to the surface are generally complicated
to detect and know. This method is generally applied by professional engineers or keen
surveyors for reaching an efficient decision and lead to the most genuine study, most generally
because to its probability in the application and the implementation to a more obsolete
geotechnical hypothesis.
Generally, the basic and discrete data can be interpolated to generate a tomography of the
location with the proper measurement intensity reaching to about 35-40 below the surface of the
location or water asset Eliot, G. (2015). Temperature sounding is unbothered by the availability
of metal or considering and integrating with the potential sources that can generally be disrupted
by the geo-electric procedure. It can be assessed in almost all the materials in a situation if there
is a temperature contrast between it and the water present on the location. And, it is undisturbed
by the certain vibrations that could be there, particularly in urban environments.
Temperature sounding is time taking and as compared to the cost reasonability for the
level of certain studies and informative details it can assess from a particular site Eliot, G.
10

(2013), but its credibility and utilization to an outer external disturbance cause itself as a
processed technique for specific occasional uses. Progression and development in this area have
led to greater sensitivities in knowing and using basic fibre optic temperature estimation
equipment.
Micro-gravimetry implements sensitive equipment to take calculations of differences in
the gravitational acceleration due to the availability of high or low-density material Eliot, G.
(2017). This has specific usage for detecting voids, vacuums and cavities in water bodies, which
are called as the negative gravity deformities . It can also be implemented more usually for basic
material zoning by alterations in soil density. Data collection for this technique is quite a time-
taking and smooth as the material implemented is quite sensitive needing certain methodology
Eliot, G. (2014). Data cannot be collected progressively so there is a complication of absent
deformities, and is critically prone to limiting factors in the surroundings. These parameters
result in the micro-gravimetry leading as one of the most Costly geophysical techniques.
Magnetic Profiling is basically and more prominently a quick and reasonable, cost-effective and
cheap procedure of investigation, generally with a very precise range of detection qualities. It is a
passive procedure, detecting the small occurrences in the earth’s magnetic field in a particular
fashion to microgravimetry studies and hypothesis of gravitational occurrences. It can be
implemented quickly and easily in the area using only specific person equipment Button, V.
(2017)leading it as useful as an overall informative and result in yielding technique. Magnetic
profiling has not been basically involved in the comparison to the summary due to its very fewer
outputs as it is only an assessed and implemented for knowing or identifying the presence of
some buried or metallic objects and for example material like the outlet pipes. This is still a
required factor for the specified mapping locations of unpopular formations like making
magnetic profiling a successful and complementary procedure.
Some other procedures of assessment of dams concrete structure using Geophysical
techniques have specifically been considered and studied for implementing in the dam or
reservoir/dyke assessment and management, like radio-magnetotellurics, the very low range of
frequency procedure and certain seismic reflection. They have massively been discarded by
some geophysicists for this kind of investigation procedure due to their several limitations and
traditional technology.
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Case study
An intense Geophysical assessment proceeded at the famous Marathon Dam location
surrounding the region of Athens Eliot, G. (2011), Greece in order to calculate certain destructed
regions which acquire massive capabilities related to liable to water purification and infiltration
or some leakages, this was also conducted to estimate the spontaneous elements of the materials
discovered on the upper surface of the water Shebang Chen, S., et al Y. (2013). The
investigations were also taken into consideration of the dam in the inner region to estimate the
quality state of the concrete used. These kinds of surveys are essential because the dam faced a
devastating, strong and massive earthquake in the year 1999. The procedures used involve
certain geoelectrical Hirleman, E., Bachalo, W. and Felton, P. (2015), specific seismic and
efficient Ground Penetrating Radar techniques. The caliber of the seismic methods to analyze the
concrete properties of the material used in the construction of dams evident the durable reliability
of some electrical procedures of the particular moisture content and the great resolving power of
Ground Penetrating Radar in identifying and assessing the local structure deformities noted to be
the prominent factors to the appropriate estimation of the dam. Specifically, geophysical
techniques also signify a few susceptible elements in the dam that need to be closely assessed by
professional engineers.
Conclusion
Dams are a very important part of any country. Dams are known to be an essential source
of water supply and high vitality for several other reasons. They process the water for many
purposes involving domestic use, irrigation methods and also for the industrial applications.
Dams are also included in the hydroelectric power generation and in the major river flowing and
navigation. Geophysical techniques for assessment if dam’s concrete involve Electrical
Resistivity Tomography or ERT specifications were equipped on the crest region of the dam to
state the structural assessment of the dam reliable on the resistivity steps. Electromagnetic
sensing technique was then implemented as a statutory process to confirm the values obtained
with the ERT generally for the upper region of the soil layers of the particular dam crest. Seismic
refraction method is the most generally implemented geophysical methods of detecting the
12

geological conditions at the dam sites. Multichannel reports on the land surface or the overwater
region generate the intense and detailed picture and report of depths to the bedrock, overlaid by
specific layering and authentic competency or the rip ability of the bedrock. Shear or the fault
zones in the specific bedrock are general and recognized in the seismic refraction detections. A
great variety of geophysical procedures are implemented to estimate the conditions at present
locations of the dam sites. Most of these processes discover utilization on earth or basic rock fill
systems with some ways which are also effective on the concrete dams. The most important
applications or utilizations of the geophysical processes at the existing dams are associated with
the seepage assessment, certain integrity estimations, foundation conditions and the seismic
critical estimation. Deformed seepage is generally recognized with the self or the streaming-
potential procedure. Temperature measurements are an accomplished procedure of monitoring
that makes the implementation of the seasonal differences that act on a particular water body or
the dam. The two basic techniques of data collecting for water impounding sources include either
joining discrete thermistors to the major portion of the dam or applying the rows of certain
temperature sensors into the body of the dam through small boreholes. The other method called
as temperature sounding is majorly useful as it can credibly suspect the seepage implementing
water temperature as a tracer. The boreholes required are very tiny in size that they can be
generated implementing certain hand-tools, and the specific sensors can be expelled in for the
long duration of guiding. The great diversity of existing geological environments at hypothesized
and present dam sites signifies the unique complications in association to the diverse and varied
geologically elements, mapping, conditions, seepage analysis and maintenance, integrity
estimation, slope accountability, foundation states, circumstances and certain seismic hazard
evaluation. Geophysical methods give direct answers and enriched deep analysis, report and data
to nullify other studies and more enlarged and significant methods of estimation like drilling.
Geophysical Techniques also involve the gradual escape of a liquid or certain gas by a
porous material or through the small openings is known as seepage. It is a method of seeping in
soil engineering as the water in the soil is located. Seepage generally creates a specific issue
often in the building construction and foundations and also a regular issue in the earth dams.
Dams are the specific structures constructed to retain the water or preventing the leakage.
Seepage by the region or surrounding the dams has been the serious cause for most of the
occurring dam destruction or the failures. Direct Current (DC) resistivity procedure, electrical
13

currents specifically originated are taken into consideration into the soil by a pair of electrodes,
and calibre taking variations are basically calculated on the above region of the surface by
certain another set of electrodes, in the region of the impact of the electric field. The current
heterogeneities in soil and rocks like bedding, soil foliation, and certain fractures along with
elements like mineralogy, moisture percentage, porosity and soil permeability can bring
outcomes in significant alterations in the system of an electric field and reliable statements of the
variants of the structures to the local pattern. By the significant intensity of the current that flows
specifically through the region of the basement, the structure or the geometry of the systematics
of the electrodes (K) and the general potential the difference calculated most often by the
electrodes receivers (ΔV), it is certain to calculate the present resistivity value certainly due to
heterogeneity. By implementation of these techniques or procedures, there can be a successful
assessment of dams concrete structure using Geophysical techniques.
14

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Electrical resistivity tomography for identification of frozen and cooled saline ground.
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Heagy, L. and Oldenburg, D. (2019). Direct current resistivity with steel-cased
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Johnsen, L., Bruce, D. and Byle, M. (2016). Grouting and ground treatment. [Reston, VA]:
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Ren, Z. and Tang, J. (2010). 3D direct current resistivity modeling with unstructured mesh
by adaptive finite-element method. GEOPHYSICS, 75(1), pp.H7-H17.
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Eliot, G. (2011). The Mill on the Floss. London: Alma Books.
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(2013). Calibration method for 2D instantaneous OH-PLIF temperature measurements in
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