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17th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 22 Feb 2004 - 26 Feb 2004
- Location: Colorado Springs, Colorado, USA
- Published: 22 February 2004
61 - 80 of 165 results
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Electromagnetic Smoke Rings Diffusion In A Horizontally Anisotropic Conducting Half-Space
More LessThe electromagnetic smoke ring provides an intuitive basis for qualitative interpretation of electromagnetic data.
Anisotropy in Earth materials often leads to unexpected geophysical responses that cannot be
anticipated from simple isotropic models. In this paper, I investigate the effect of lateral anisotropy on
the smoke ring diffusion in a conducting half-space excited by a horizontal loop.
Forward modeling computer program has been developed to investigate the effect of fractures on
the elliptic-like smoke ring diffusion in a horizontally anisotropic half-space to a sudden step-on of
electric current excited by the horizontal loop. Modeling of elliptic-like smoke ring diffusion is done for
two cases, namely σ (fractures are more conductive than the matrix) and σ (fractures are more
resistive than the matrix). It is observed that for a horizontal loop source in a horizontally anisotropic
medium the smoke ring becomes elliptic-like, with the long axis parallel to the direction of more
conductivity and short axis parallel to the direction of less conductivity and this shows the paradox of
anisotropy. Smoke rings in a horizontally anisotropic medium diffuse downward and outward as the
time elapses. The short axis and the long axis and the depth of smoke ring change their behavior
depending on their evaluating time. When σ , the short axis depends on parallel conductivity at
early time and perpendicular conductivity at later time and the long axis depends on perpendicular
conductivity at earlier time and combination of both conductivities at later time. When σ , the
short axis depends on perpendicular conductivity at earlier time and on parallel conductivity at later
time; the long axis depends on the parallel conductivity at earlier time and combination of both
conductivitities at later time. Accurate interpretation of electromagnetic data over a fractured medium
depends on the ability of the geophysicists to recognize the effect of anisotropy.
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Skytem – New High Resolution Helicopter Tem System
Authors Kurt I. Sørensen, Max Halkjær and Esben AukenDuring the last decade, approximately 60,000 ground-based, single-site TEM soundings have
been carried out for detailed groundwater investigations in Denmark -an areas of 42,000 km2-. In future
the investigations will be even more intensified.
Detailed groundwater investigation in Denmark calls for high-resolution, continuous off-time
TEM measurements in the decay time interval from approximately 10 microseconds. to 10 milliseconds,
providing resolution of the protective clay caps and the aquifer layers down to 200 – 250 meters.
To meet these requirements, a new airborne TEM system, SkyTEM, has been developed. The
transmitter coil, together with the Rx coil, is mounted on a 12.5 x 12.5 m frame carried by a helicopter at
an altitude of 15 to 25 meters above ground and with a speed of 20 to 30 km/hr.
The transmitter current has a square waveform with a 50% duty cycle with a fast turnoff and the
transmitted moment pattern is segmented with the highest moment reaching 45,000 Am2. The
transmitter waveform, together with other controlling parameters, is measured “on the fly” to ensure
high data quality. Off-time decay signals are measured in the time interval of 15 microseconds to 10
milliseconds in digital controlled analog gates to ensure maximum noise rejection. The data quality of
the SkyTEM system is equal to – and in many cases higher than - the data quality obtained by
conventional ground-based systems.
The total weight including power supply of the SkyTEM system is approx. 300 kg. SkyTEM
operates automatically without operator in the helicopter and transmits measured data to a ground base
for further “on the fly” processing and interpretation allowing ground personal to maximize the positions
of the profiles.
Interpretation programs optimized for the SkyTEM data sets are developed in order to get a fast
and efficient operating system.
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Synthetic Studies To Determine The Effects Of Anomalous Magnetic Permeability On A New Electrical Resistivity Tomography/Magnetometric Resistivity Survey System
Authors Matthew A. Ludwig, David Alumbaugh, Douglas LaBrecque, Roger Sharpe and Gail HeathThree-dimensional model studies are presented to determine the effects of electromagnetic
induction and magnetic permeability on magnetometric resistivity measurements, as well as on images
resulting from inversion of the data. This involves the use of two different forward modeling algorithms;
a full electromagnetic code that includes anomalous magnetic permeability, and a steady-state algorithm
that assumes free-space magnetic permeability. To determine the nature of problems caused by
electromagnetic induction in the presence of permeable materials, the two synthetic data sets are
compared directly, as well as inverted with a steady-state inversion algorithm. Including a magnetically
permeable target causes significant changes in the synthetic data and produces noticeable artifacts in the
inverted sections, especially at depth. However, despite the presence of artifacts, the images are still
dominated by the conductivity, and thus the extent of both conductive and resistive targets are well
defined.
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Use Of Geophysical Surveys For Fill Characterization And Quantity Estimation At Brownfield Sites – A Case History
Authors John A. Mundell and Gregory B. ByerNew building construction planning typically includes site characterization with standard
geotechnical drilling and sampling methods under the direction of a professional engineer. For project
sites with the potential for variable types and thicknesses of fill materials, including contaminated
wastes that pose a possible environmental hazard, this traditional site characterization approach can
result in under sampling and lead to an unrepresentative site characterization. This can also result in
significant cost overruns and other surprises. In recent years, as reuse of ‘brownfield’ properties has
increased, the need for better, more reliable site characterization methodologies has grown. The
combined use of geophysical surveys and standard drilling and sampling methods during the project
planning phase has been shown to be a valuable approach to meet these needs.
This paper presents a case history of an actual construction project in which geophysics was
combined with traditional drilling and sampling at a brownfield location where a 70,000 cubic yard
excavation for two commercial building basements was planned. Historical information combined with
the initial drilling results and geophysical testing revealed a potential two-dimensional bias to the fill
distribution. Closely-spaced, 2-dimensional resistivity profiles were independently acquired and
inverted, and then jointly interpolated in 3-dimensions to render a 3-dimensional image of the fill
materials. The 3-dimensional imaging allowed for the quantification of fill types and quantities for
proper management during excavation, and the development of estimates for transportation and disposal
of the materials. In addition, it also allowed the construction management team to plan for proper
segregation and handling of these materials to minimize total construction costs and schedule delays
while maintaining safe working conditions.
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Mapping An Industrial Landfill Area From Penetration Of Gpr Data
Authors Marica Calabrese, Luigi Zanzi and Maurizio LualdiThe investigation target is a landfill situated in Italy. The area covers a surface of about 7.000
m2. At the beginning the area was used for production of inert material. Later the area was used to
dispose the industrial waste of a company operating in the iron and steel field. In the eighties, the landfill
became exhausted and the activity for the rehabilitation of the site started. Within these activities an
electrical survey was performed. In this work, the GPR survey carried out in July 2003 is described. 250
MHz and 50 MHz antennas were used: the analysis of the profiles shows a strong difference in the
penetration between the landfill and the surrounding fields. Due to the high conductivity of the industrial
waste, the penetration in the landfill is very low while the penetration outside the landfill can reach a
depth of several meters. As a result, GPR is a successful method and was extensively applied for
accurate mapping the lateral extension of the landfill and for estimating possible variations of the
contamination level. Instead, the DC method is the most appropriate technique for an approximate
estimate of the landfill depth.
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Student Research Involving Shallow Geophysics In And Around Colorado Springs
More LessFour students taking an introductory geophysics course at Colorado College in October 2003
were responsible for running small research projects. Using the college’s geophysical equipment we (1)
investigated the stability of a dam at the Catamount Institute using resistivity and found low apparent
resistivities near the pond and a low-resistivity lens on the Eastern side of the dam; (2) surveyed a
magnetic profile across the college’s soccer field and modeled two anomalies, at 5 and 2 m depth,
respectively; (3) ran a gravity survey across a postulated fault on the West side of the Upper Arkansas
graben and obtained a gravity signature consistent with an East-dipping normal fault having ~180 m
vertical offset; (4) attempted to obtain seismic velocities across a known fault juxtaposing sediments
against crystalline rock on the East side of the Upper Arkansas graben but found only a shallow,
low–velocity overburden and no high velocities typical of crystalline rock; and (5) tested the feasibility
of using a resistivity survey to monitor septic systems and imaged a plume with low apparent resistivity
extending downhill from a septic leach field. Although the short amount of time allowed only for basic
data processing, centering the course on real problems was a rewarding experience for all involved.
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Delineation Of Subsurface Geometry By 2D And Joint Inversion Of Resistivity And Em Sounding Data From A Dam Site At Owena River Area South Western, Nigeria
More LessA total of twenty nine DC resistivity and several EM soundings were carried out along four
soundings profiles around river Owena, the area falls within the Basement Complex region predominant
in South Western Nigeria and is marked out for the construction of a multipurpose dam. The 1D
inversion of the sounding data, although satisfactory, revealed some complex, unresolved
geological/geometrical structures at some sounding stations. In light of this, the same data set was
reinterpreted using a 2D Inversion Scheme based on a modified form of the finite element method was
used to obtain a clearer image of the resistivity structure and geometry of the Owena river area, the
results obtained reveled sudden departures in the subsurface geometry between some sounding stations
and also between the profiles. The results presents a more clearer picture of the structure of the location
and compared with the inferred interpretation from 1D inversion reiterates the importance of carrying
out 2D inversion rather than the more common 1D inversion, the 2D inversion scheme used also makes
the inversion process less computationally expensive.
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Geophysics Applied To A Bioreactor During Leachate Recirculation And To Leachate Samples
Authors Solenne Grellier, Roger Guérin, Christophe Aran, Henri Robain and Gérard BellierThe bioreactor is a new concept of landfill where parameters of biodegradation can be controlled
in order to stabilize the waste mass. A high waste moisture, generally brought by leachate recirculation,
favours biodegradation and methanogenesis reactions.
This study conducted by CreeD, Paris 6 University and IRD aims to establish the validity of
geophysical measurement methods and the link between the geophysical measurements and the water
content variations in the waste mass. Electrical resistivity is mainly linked to water and ionic content.
This is the reason why geophysics methods measuring electrical resistivity are used in this study.
The originality of this study will consist in in situ and laboratory measurements:
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Waste Volume Estimation Using Geophysical Methods In A Complex Geologic Setting
Authors Mike Thompson, Drew Clemens, Steve Miller, John Tesner, Wayne Mandell, Phil Durgin, Bill Davies and Jim McKennaGeophysical surveys using electrical resistivity and seismic refraction profiling were used to
estimate the waste volume at Radford Army Ammunition Plant (RFAAP), Virginia. The Radford
area is underlain by a complex sequence of folded and faulted carbonate and clastic units, where
solution-enhanced fractures and sinkhole development is highly variable, depending on the
formation and degree of fracturing. This extremely heterogeneous and anisotropic environment
greatly complicates environmental characterization and evaluation of remedial action alternatives.
Complementary methods used in this effort increased the level of confidence in the resulting
models. 2D electrical resistivity imaging tended to overestimate the base of the waste area, but the
final interpretation was constrained using results from seismic refraction profiling and borehole
geophysical surveying.
The combined borehole and surface geophysical methods established a defensible, more
accurate estimate of waste boundaries and volumes. Because the waste base was much shallower
than originally thought, subsurface characterization was completed more quickly using less
expensive methods. The resulting conceptual site model provided a vastly improved assessment of
heterogeneities within the underlying hydrogeologic system. Borehole geophysics proved an
invaluable Quality Assurance tool for highlighting inconsistent interpretations and verifying
conceptual site models.
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Comparisons Of Ip And Resistivity Data At Several Old, Buried Landfills
Authors Norman R. Carlson and Scott A. UrquhartWhile resistivity and conductivity continue to be two of the most common methods used for
mapping old, buried landfills, we continue to encounter sites where the resistivity contrast between the
landfill and the background material is either non-existent or inconsistent. Several recent examples are
presented, including two landfill pits located just 2500 feet apart. Based on boring results, at one of the
landfills both resistivity and induced polarization (IP) data clearly delineated the waste boundaries, but
at the other landfill, in the same geological background material, resistivity (and conductivity) failed to
delineate the waste while there was a clear, well-defined correlation between IP effects and waste. The
location and volume of waste would have been severely misjudged had we relied on resistivity or
conductivity in advising the environmental firm tasked with evaluating the property.
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Design And Installation Of A Remotely Controllable Autonomous Resistivity Monitoring System At The Gilt Edge Mine Superfund Site, South Dakota
Authors Roelof Versteeg, Gail Heath, Clark Scott, Ken Wangerud and Dave PaulAcid mine site remediation is a significant problem in the U.S and globally. Due to the volume
of acid producing rock involved, the only practical solution is minimizing acid production by reducing
or eliminating water flow through the rock materials. One method to achieve this is utilizing a capping
system. Detailed monitoring information on cap and rock behavior allows for rapid and cost-effective
intervention in case of cap failure. A remotely controllable autonomous resistivity monitoring system
was integrated in the repository below the geo-membrane cap at the Gilt Edge Mine Superfund site. The
structure of this system allows users to have access to raw and processed data in real time.
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Integration Of Geophysics, Geologic Mapping And Water-Level Monitoring To Characterize The Hydrogeology Of A Fractured Bedrock Site In Berlin, New Hampshire
Authors James R. Degnan, Stewart F. Clark Jr. and Philip T. HarteElemental mercury is found in fractured depressions and potholes on the bedrock surface, in the
overburden, and is dissolved in ground water at the site of a former chlor-alkali plant (cell house) along
the bank of the Androscoggin River, in Berlin, N.H. The cell house has been demolished, ground-water
flow impeded by installation of an up-gradient-slurry wall, and capped with an impermeable geomembrane.
Mercury has been removed from fractures at the surface on the riverbank five times; however,
more continues to be found. Potential pathways for movement of mercury and ground water were indicated
with the results of a geohydrologic study. The study demonstrates the integration of geophysical
surveys, geologic mapping, and water-level monitoring in three areas: (1) the riverbank, (2) the site
perimeter, and (3) the capped area.
Results from ground-penetrating radar and two-dimensional-resistivity surveys along the riverbank
indicate electrically conductive zones that are interpreted as bedrock fractures, which are potential
ground-water-flow paths. Geologic mapping along the riverbank shows that bedrock fracturing is more
prevalent in gneiss than pegmatite and is associated with schist in shear zones that correspond to geophysical
anomalies. Nearly horizontal anomalies in ground-penetrating-radar survey results beneath
areas mapped as pegmatite may represent locations where vertical fractures in gneiss terminate on a horizontal
fractured contact between gneiss and pegmatite. Significant hydraulic connections were identified
by analysis of stage changes in the Androscoggin River and bedrock water levels. Assessment of hydraulic
heads in bedrock and overburden show vertical ground-water gradients in both directions. Resistivitysurvey
results along the site perimeter indicate fractures and overburden-filled bedrock troughs where
ground water may bypass a slurry wall. Overburden water levels and discharge from a drainage pipe suggest
that ground water is passing through or beneath the slurry wall. Response of overburden water levels
do not show connections with the river.
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Laboratory Determination Of Electric Properties Of Ornamental Stones In Georadar High Frequency Band
Authors Luigi Sambuelli, Paola Marini, Riccardo Tascone, Davide Vaccaneo and Francesca BrattaA new measurement system of dielectric permittivity and loss tangent of ornamental stones used
for example on historical buildings has been developed. Complex permittivity has been measured in the
frequency range 1.1 – 1.7 GHz on samples chosen between marbles, sandstones and limestones. The
values of dielectric parameters were measured experimentally by placing the sample in a resonant cavity
obtained from a waveguide. The research has been developed to define a laboratory testing method in
order to improve GPR interpretation by creating a data base of electromagnetic properties of the
analysed materials.
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Modeling Heterogeneity In Gpr Data
Authors Jennifer J. Holt and Jeffrey J. DanielsThe subsurface is rarely perfectly homogeneous due to different soil moisture levels, grain
packing, and soil types that all influence the ground properties. Ground Penetrating Radar (GPR)
is a common technique for investigating objects in the near surface. Physical properties play an
important role in GPR. Traditional geophysical models of GPR have not accounted for this
heterogeneity or its effect on spacial dispersion. This forward model incorporates heterogeneity
by replacing the traditional homogenous spatial regions with a distribution of physical properties.
The physical model values within each boundary were determined by a statistical distribution that
will more truly represent the physical properties of the earth than the traditional single value
approach. These statistical approximations to the physical properties are a better approximation
to the actual physical properties present that are beyond the resolution capabilities of the
instrumentation or the sampling procedures. This paper looks at heterogeneity, its influence on
spacial dispersion, and defining the response from a range of standard deviations.
Variations in soil properties should be taken into account when analyzing ground
properties while using GPR. This paper presented a theoretical analysis of random property
variations concentrating on a half space and a two layer earth model with a Ricker wavelet input.
At 9 ns and 12 ns, most of the visible dispersion in the electric field occurred in the near field.
However, the largest average difference occurred at 1.0 m distance from the dipole. Spacial
dispersion occurs when there is a standard deviation of 2.5% and a standard deviation of 25%
does not mask the response from a layer. The larger the area of the heterogeneity the more the
wave will reflect off that area.
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Application Of Ground Penetrating Radar To Assess Ground Control Problems In Two Underground Limestone Mines
Authors Michael A. Trevits, William D. Monaghan and Thomas P. MuchoIn this study we tested the ability of ground penetrating radar (GPR) to resolve ground conditions
in two underground limestone mines. The objective of our work was to determine if GPR signals could
be received from distant fractures in the limestone unit. At site A, located in western Pennsylvania, a
large fracture penetrated and crossed the mine workings and created mine roof problems. GPR was used
to evaluate the mine roof areas along the projection of the fracture. At site B, located in central
Pennsylvania, fracturing of the host limestone provided difficult water problems at the mine face. GPR
was used at this site to evaluate the conditions ahead of the mine face to determine if a significant jointbased
solution channel system existed that would signal a continuation of the water problems. We
conclude that at both sites, it was possible to utilize GPR to delineate potentially dangerous and
threatening ground conditions.
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Implementation Of Gps Navigation And 3D Volume Imaging Of Ground Penetrating Radar For Identification Of Subsurface Archaeology
The navigation of GPR equipment during surveys at archaeological sites has largely relied on the
time-consuming process of manually locating grid lines. When GPS has been available, positions are
generally only recorded at the ends of a GPR profile or at the corners of the survey grid. If the GPR
antenna deviates from individual grid lines during the field survey, or if the survey grid is inaccurately
established because of uneven terrain, targets of interest may be improperly located. In the summer and
fall of 2003, GPR data sets were recorded simultaneously with 1-second, real-time DGPS navigation at
several archaeological sites. The purpose of the GPR and DGPS integration is to automate the
collection of GPR data sets, particularly at sites where establishing grids would be problematic. In
addition, this integration allows for generation of accurate, geo-referenced time slice maps for
presentation or GIS purposes. Using the DGPS navigation at the archaeological sites, 3D volumes of
recorded energies were used to map subsurface archaeological structures. DGPS-navigated time slices
were compared with traditionally navigated time slices collected during an investigation at the Jena
Choctaw Tribal Cemetery in Louisiana. Results of this investigation indicate that DGPS navigation is
sufficient to map unmarked burials without sacrificing accuracy.
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Uncovering The Mysteries Of Gore Place: A Gpr Case History
Authors Ariane Heinz, Doria L. Kutrubes, Susanne M. Olson, Lana Lewis, Jeffrey Baker and John F. KickTheGore Place Estate, a historical landmark, was investigated using ground penetrating radar (GPR)
and total field magnetometry to identify any features of interest related to former ventilation, heating or
septic systems associated with the Revolutionary War era mansion.
GPR results from the north side of the building confirmed that a large buried structure is present
below the brick archways on the building north facade. Large reflectors indicating a collapse are also
observed in that area, and may correlate to the former building which burned in the 1790s.
On the south side of the building, time-depth slices reveal a linear feature, presumably a shallow air
duct, trending from the center of the building towards the southwest. A brick-lined air duct was discovered
at ground surface, approximately 300 feet southwest of the building, following the same trend as the linear
feature detected with GPR. The purpose of the air duct was presumably to create a powerful draw for the
heating and ventilation system.
Amagnetic anomaly in excess of 2,000 gammaswasobserved coincident with thepresumed location
of a Revolutionary War era cistern. However, since the magnitude of the anomaly suggests the presence of
steel, not just brick, this structure, first believed to be the original cistern, must represent a more modern
structure.
Two ducts were detected using time-depth slice imaging within the Great Hall floor. The more
contemporary metal duct shows up clearly on the time-depth images, and connects two air vents located
south of the east and west chimneys. The older air duct, located just south of the chimneys centerline,
appears partially collapsed on the GPR records.
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Computer Assisted Radar Tomography – True Value Or Just Pretty Pictures
Authors Jorgen Bergstrom, Scott Smith and Kathleen McKinleyComputer Assisted Radar Tomography (CART) is a new technology that can deliver images of
the subsurface with an unparalleled level of accuracy and detail. Based on the physics of Ground
Penetrating Radar (GPR), CART can image objects of any material including metallic and non-metallic
utilities, valves, drums, trenches, underground storage tanks, paved over manholes and railroad tracks.
The CART system is tied to a total station with auto tracking capabilities for precise positioning. The
benefit of CART is that high density, accurately positioned data can be collected in a fairly short amount
of time. State-of-the art processing software is then used to create time slices and 3-D images of the
subsurface. Customers that are used to looking at wiggly GPR lines are often awed by the clarity and
the life likeness of CART images. But where is the true value for the customer? What problems can we
solve with CART that we cannot with GPR or can we do the same job quicker and cheaper with CART?
This paper will highlight our company’s experience with GPR and CART on a variety of projects and
discuss the strengths and limitations of both methods.
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The Capillary Rising Of Ground Water Monitored By Soil Dielectric Coefficient
The automatic monitoring station was established to the forested catchment in Eastern Finland. The
ground water level was situated approximately 0.5 m below the lowest one of the three dielectric
coefficient probe. There were three dielectric coefficient probes (CS615; Campbell Sci, UK) at three
different depths (0.25 m, 0.6 m, 0.8 m). Data collecting was happened with CR10X datalogger
(Campbell Sci, UK). The ground water level was measured by PDCR1830 (Druck, UK) from the nearest
ground water pipe.
The main aim of this study was to investigate how the rising ground water table effects to the measured
soil dielectric coefficients and how transpiration and evapotranspiration are seen in measured dielectric
coefficient and ground water level.
The main result was that how well dielectric coefficient follows changes of ground water level. The
transpiration of trees had an effect both dielectric coefficient (i.e. soil moisture) and ground water level.
It looked like that transpiration ends at the beginning of September; because of the pumping effect of
capillary increase disappear. And the ground water level is stable after the beginning of October, which
means that evapotranspiration have been ended in that time.
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Fracture Characterization Using Borehole Radar: The Link Of Geophysical And Hydrogeological Model
By Lanbo LiuPrecise characterization of subsurface fractures (their orientation, aperture, distribution,
hydraulic conductivity, etc.) is critical to many geoscience sub-disciplines such as water resources
exploration and management, contamination remediation, underground construction, as well as
subsurface energy resource (hydrocarbon, geothermal, etc.) exploration and management. This paper
presents the forward modeling results of borehole radar signature of fractures generated by the
hydrogeological model of a fractured rock aquifer environment. A fracture system consists of interconnected,
permeable fractures filled with either freshwater, air, or brine and the isolated, nonpermeable
ones filled with only freshwater forms hydrogeological test model. The fracture groups were
statistically generated with different and desired features in space density, length, orientation and
aperture. Electromagnetic (EM) wave was generated with the finite-difference time-domain (FDTD)
forward modeling technique and propagated through the fractured rock aquifer models to form the
synthetic radar data sets. The features in radar syntheses were then examined and corresponded to
predefined fracture models. Based on the comparison, it shows that (1) the amplitude of radar waves
was generally diminished when brine replacing freshwater in the permeable fractures; (2) replacing
freshwater with air significantly increases the fracture fluid property contrast and results in significant
changes in some time records at certain transmitter-receiver configurations, depending on their relative
position to the permeable fractures; (3) in general, radar syntheses in reflection mode contains more
information on fracture properties than its transmission counterpart; (4) it is easier to identify more
fractures when air replacing water than brine replacing water. Combination of computer forward
simulation and field data reduction bears the hope to successfully characterize fractures for various
scientific and engineering purposes.
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