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18th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 03 Apr 2005 - 07 Apr 2005
- Location: Atlanta, Georgia, USA
- Published: 03 April 2005
81 - 100 of 146 results
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Towed Geo-Electrode Arrays for Analysis of Surface Water Groundwater Interaction
Authors David A. Allen and Noel P. MerrickHigh productivity analysis of surface water groundwater interaction is possible using GPS
positioned vertical electrical conductivity imaging along with depth recording. Short submerged geoelectric
arrays provide a great deal of detail right at the base of surface water bodies; however they
cannot be used in treacherous waterways with debris scattered through them. Long floating arrays can
be towed through such waterways and have the additional benefit of greater depth of exploration.
Floating arrays also can have reasonable resolution at the base of surface water bodies provided that they
are designed optimally and that data from them is inverted effectively. Array design must optimize a
balance of signal strength maximization, exploration depth resolution, weight and drag minimization,
crosstalk and current leakage minimization and simple, minimal response to three dimensional
heterogeneity. Pragmatic interpretation of the huge volumes of data that are typically acquired is best
achieved using three dimensional ‘ribbon’ images. Prominent features of interest are, in most cases
related to groundwater salinity. Low conductivity anomalies often indicate fresh surface water seepage
into more saline groundwater. High conductivity anomalies that intersect the bases of surface water
bodies usually indicate saline inflow to the surface water bodies.
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Application of Non-Desructive Geophysical Techniques for Risk Evaluation (Sannour Protected Area, Beni Suef, Egypt)
Authors Sherif M. Hanafy and Essam A. MorsA large cavity was recently discovered in the Wadi Sannour area, near Beni Suef City, Upper
Egypt, in the same general area in which alabaster is known to have been quarried since approximately
200 years ago. This cave has a span of up to 300m, is 10-30m in width, reaches a height of 15m, and
generally forms a crescent cross section. The opening is situated on a raised outcrop approximately
39.5m below the original ground surface. In order to evaluate the site for potential risks, to protect the
cave features from irreversible damage, and to make the site more secure for visitors, a Ground
Penetrating Radar (GPR) study was conducted inside, over, and in areas adjacent to the cavity. Here,
twenty GPR reflection lines were acquired uniformly over a 35 x 11m area in front of the cave’s
entrance, and during the course of this survey a new subsurface cavity was discovered. The depth and
dimensions of this new cavity were determined from the acquired radar data.
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Estimating Source Depth Extent From Inversion of Magnetic Field Data – A Synthetic Modelling Study of The Cretaceous Volcanic Intrusions Into The Edwards Aquifer, Texas
More LessDepth to the top or base of a small magnetic source body cannot be reliably determined from
single profile measurements of any one magnetic field parameter. However simultaneous measurement
of transverse horizontal gradients or the magnetic gradient tensor allows estimation of any offset of the
source from the profile and this substantially improves the ability to interpret sparsely sampled
anomalies. Surveys at low elevations improve resolution of detail and detection of weak magnetizations
but the measured anomalies are dominated by the topmost section of the source bodies thereby reducing
sensitivity to their base depths. Aeromagnetic surveys flown to help resolve structure of the Edwards
Aquifer have discovered many Cretaceous intrusions but many of these anomalies are detected only on
single profiles and depths to their top and base are poorly constrained. Models derived from inversion of
the anomalies can however be used in the design of any follow-up survey and to investigate the possible
benefits of transverse gradient or gradient tensor measurements. Inversion of a multi-line anomaly has
resolved the source to be a steeply-dipping sheet illustrating implications of the magnetic modeling to
local groundwater flow models.
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On Time-Domain Transient Electromagnetic Soundings
Authors Jia Ruizhong and R.W. GroomWe have developed two techniques for simulating EM responses of a layered earth model; a
general and an approximate method. The general method allows the computation of the magnetic field
produced by systems with various current waveforms and survey configurations, including in-loop and
out-of-loop for both moving and fixed transmitter with arbitrary location and orientation of receivers.
The approximate method only allows the calculation of the vertical transient responses of the secondary
currents during the off-time with receiver inside of the transmitter loop. I ncorporating these two forward
modelling techniques and both Marquardt and an Occam s inversion algorithm approaches, we have
developed four methods to perform inverse modeling of transient electromagnetic soundings. A time
domain conductivity-depth image (CDI) technique is also implemented. To prepare the data for this
technique, an algorithm converting impulse response into step response has been developed. Armed with
these inversion techniques, we can process ground and airborne data collected with systems using
various current waveforms and survey configurations. The applications of these inversion techniques to
synthetic layered-earth models demonstrate the effectiveness of these techniques. Interesting field data
uses are also shown.
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Laterally Constrained 1D-Inversion of 3D TEM Data
Authors E. Auken, A.V. Christiansen, L. Jacobsen and K.I. SørensenIn this presentation we show that the interpretation of spatial densely sampled TEM data over 2D
earth structures is greatly enhanced by inverting the data using the 1D-LCI algorithm (Laterally
Constrained Inversion). In the 1D-LCI algorithm neighboring models are constrained laterally on layer
resistivities and interfaces.
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Incorporation of Variable Background Velocity In Subsurface Imaging With GPR
Authors Beiyuan Liang and Lanbo LiuFor fast imaging subsurface targets with ground penetrating radar (GPR) it is common to assume
a homogeneous background of electromagnetic (EM) wave velocity. Nevertheless, if some information
about EM velocity is available, it is desirable to use more realistic velocity distribution in subsurface
target imaging. This paper introduces a ray tracing function into GPR imaging process with using
reflection energy stacking. We demonstrate the effectiveness of this approach by comparing the imaging
results with different velocity layers for a typical subsurface imaging example. Use of the ray tracing
technique in the imaging process built in GPR software, GIT-Radar, is better to image and determine the
depths and shapes of the targets. Also, the application of the ray tracing in a 3D imaging process does
not substantially retard the speed of calculation if a layered velocity model is used.
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Comparison of Discrete and Voxel 3-D Gravity Inversions Over Karst-Related Gravity Anomalies On The Coastal Plain of North-West Malaysia
More LessA negative gravity anomaly of amplitude 12 μm/sec2 and diameter 400 metres on the coastal
plain of north-west Peninsula Malaysia has been modelled as due to cavities in buried limestone
bedrock. A model of equi-dimensional cavities using spheres does not reproduce the sharpness of the
measured anomaly but a model using ellipsoids is successful. The value of the expected density contrast
is the only constraint required to develop these parametric models. Maximum-smoothness voxel
inversions are poorly suited to the binary density distribution of cavity models, but when guided by
earlier parametric inversion results the voxel inversions enable the testing and development of more
complex source shapes. For the deeper equi-dimensional cavity model the computed field is only weakly
sensitive to source shape but for the shallower ellipsoid model the voxel inversion may provide a valid
improvement in representing the shape of the source body.
The anomalies can also be modelled as due to changes in overburden thickness. Parametric and
voxel models of basement topography are similar to each other and differ significantly from simple
Bouguer slab predictions establishing the importance of 3-D modelling even for such a simple
geological model. There appears to be no inherent superiority of either parametric or voxel inversions
provided each has the versatility to select models according to guiding geological concepts.
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Simultaneous Geophysical Surveys Using A Towed Multisensor Platform and Its Application To Characterisation of Brownfield Sites
Authors Chris Leech, Ian A. Hill and Tim M. GrosseyA rapid measurement technique for assessment of landfill areas and other environmentally sensitive areas. A multi sensor platform with real time data logging and navigation has been built to
allow rapid reconnaissance surveys over large areas thereby reducing survey time and costs dramatically. Sensors from many different disciplines can be mounted on the platform and data acquired simultaneously. Case histories from geological, environmental and archaeological sites are presented showing the attributes of the technique in all three applications.
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Time-Lapse Azimuthal Resistivity Survey In A Highly Industrialized Area: Problems, Diagnosis, and Solutions
Authors Les P. Beard, Jacob R. Sheehan and Scott C. BrooksA time-lapse azimuthal resistivity survey was proposed to support a fluid flow test pertinent to
an upcoming bio-remediation experiment. The site is in a highly industrialized area, and preliminary
resistivity measurements showed steady, but substantial, drift in apparent resistivities measured over
tens of minutes. The drift was of such magnitude that collection of time-lapse data would be precluded
unless a solution could be found. We hypothesized that the problem was either instrumental, was
induced by the electrodes, or was site specific. Internal checks of the Sting R1 indicated a properly
functioning instrument. We tested three different electrode types and found no particular differences in
the rate of drift with any of the three types chosen. A test of the resistivity system in a plastic tub filled
with a sodium chloride solution produced steady measurements over a span of about an hour. We
concluded that stray currents at the site itself must be producing the drift. We found that by averaging
two measurements at a given azimuth, one with electrodes positioned AMNB, the other BNMA, we
could obtain steady resistivity results over acceptably long durations, and so we were able to acquire
useable data during the flow test.
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A Wide-Band Electromagnetic Impedance Profiling System for Non-Invasive Subsurface Characterization
Authors Hung-Wen Tseng, Ki Ha Lee and Alex BeckerA non-invasive, wide-band electromagnetic (EM) impedance difference system for shallow subsurface electrical structure characterization in environmental and engineering problems has been
developed at the Lawrence Berkeley National Laboratory (LBNL). Electrical parameters of interest are electrical conductivity and dielectric permittivity that are deduced from the impedance difference data. The prototype system includes a magnetic loop transmitter, which operates between 0.1 MHz and 100 MHz, an electrical dipole antenna for observing the electric field, and a loop antenna for measuring the magnetic field. All antennas are mounted on a cart made of non-metallic material for easy movement of the whole array for profiling. Surface EM impedance difference is obtained by taking the difference of the ratios of the electric fields to the magnetic fields at selected frequencies at two different levels. Numerical simulations verify this approach. A set of the impedance difference data acquired at the University of California’s Richmond Field Station compares reasonably well with simulation results based on a model obtained with the resistivity method and in situ TDR (time domain reflectometry) measurements.
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Application of Multi-Channel Electrical Method In Investigation of Hydraulic Channels In Qiu Jia Wan Main Dike of The Yangtze River, China
Authors Yixian Xu and Jianghai XiaQiu Jia Wan, the main dike of the Yangtze River in Jia Yu County, Hubei Province,
China, is a section scheduled for reconstruction due to underground water leakage. Prior to the
reconstruction, the paths of water movement (sand layers or local bodies) and their covering
material must clearly be investigated. The traditional methods, e.g. borehole drilling, are
expensive and may re-damage the dike, so the noninvasive multi-channel electrical method was
chosen to perform the investigation. One surveying profile parallel to and other three profiles
perpendicular to the main dike were carried out in the Qiu Jia Wan section. Acquired data were
inverted by a two-dimensional inversion method. Our interpretation was able to relate anomalies
in resistivity cross sections to water leakage through a sand and gravel layer from the Yangtze
River to the back of the dike. The results were consistent with hydro-geological analysis and
therefore supplied basic data for the reconstruction task.
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A High Resolution 3-D Imaging Radar Survey of A Concrete Ring-Wall Collar for Mapping The Extent of Concrete Deterioration and Delamination
Authors Brian Jones, Mario Carnevale, Daniel J. Delea and Jutta HagerA high-resolution 3-D GPR survey was conducted on a large concrete structure in the central
coastal area of California. The survey imaged the top 6-meter-high collar of a 19.81-meter-diameter
ring-wall. The purpose was to determine the presence and extent of concrete deterioration in the form of
air or water-filled cavities, as well as identify areas of concrete delamination or advanced stages of
concrete deterioration. The imaged section of the ring-wall was 0.91 meters thick. A 900-MHz GPR
system was used to image the full circumference of the ring-wall from the outside. A 1.5-GHz GPR
system was used concurrently to image the full circumference of the top of the ring-wall. This survey
plan was developed to provide a suitable combination of resolution and GPR signal penetration to image
the upper ring-wall structure.
The high-resolution top-of-wall and outer-wall surveys were conducted to identify delamination
zones and discontinuities within the concrete. A total of 6,047 data files were collected. This equates to
a data set size of 1.725 GB. The total linear distance surveyed was 3,907 meters. 3-D analysis of the
GPR data was used to create a continuous 3-D composite model for both the 900-MHz and 1500-MHz
data sets. “Wrap-around” time-slice views were provided to the client in video format to illustrate the
ring wall in quarters and octants. The investigation indicated that approximately 25% of the surveyed
wall contained some degree of rebar rust jacking and concrete defects in the form of voids and/or
delamination. This study demonstrates that a comparison of the 3-D results of two concurrent surveys at
different frequencies can provide comprehensive, high-resolution images of defect distributions in large
concrete structures.
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Use of Ground–Penetrating Radar (GPR) As An Evaluation Tool In Nineteenth-Century Building Restoration
Authors James S. Mellett and Shelley SmithA GPR survey using a 1.5 GHz transducer was carried out on the inside walls of a nineteenth
century church tower in Westchester County, NY to gather information on moisture infiltration and to
guide remediation. The tower walls have a thickness of 40 cm (16 in) and are faced with granite ashlar
blocks about 15 cm (6 in) thick. The inner face is a rubble wall, with stones having diameters from 7 to
20 cm (3 to 8 in). In between is a mortar mix that filled in the spaces between the rubble stones. Over
the past decade, the inner walls in the church have been showing evidence of leaks and water damage.
Recent remediation included masonry repointing and injection grouting of the parapet walls. The leaks
subsided significantly, but evidence of moisture infiltration continued. GPR scans detected apparent
voids in walls below the parapet, with large void spaces around the central windows. In the area below
the windows, just above the church crossing, the voids appeared to increase in frequency and size. We
believe that voids were initiated around the windows and the entrained water developed a hydraulic head
that pushed it into lower levels of the church. Additional injection grouting will be performed in all wall
areas showing voids.
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Time Domain Reflectometry Uses In Geotechnical Engineering
More LessTime Domain Reflectometry (TDR) makes use of a device that propagates transverse
electromagnetic waves through soils by means of special soil probes as shown in Figure 1 for field
testing and in Figure 2 for testing a specimen. For field testing four spikes are driven into the soil while
for testing a specimen in a mold, only a center rod is driven into a metal mold on a non-conducting base.
The same probe head is used in both situations.
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Pavement Evaluation and Design With Seismic Methods
More LessThe primary parameters that affect the performance of a road or an airfield pavement are the
thickness, the Poisson's ratio, and more importantly, the modulus of each layer in the pavement
structure. Stress wave propagation or seismic techniques have been used to measure these parameters
through nondestructive testing (NDT). Other factors affecting the performance of a pavement are the
interfacial bond quality of asphalt concrete (AC) or Portland cement concrete (PCC) overlays and the
existence of flaw or delamination in a PCC slab. They can also be detected with seismic methods. To
make field tests and data analyses with seismic methods faster, more practical and cost-effective,
automated testing devices have been developed. The principles of seismic methods as applied to
pavement analysis, design and diagnosis are discussed through several case studies.
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Reflection Seismology: Application To Identifying Fault Structure
Authors Richard T. Williams, Vladimir A Babeshko and Ernest KutsenkoReflection seismology has been developed to an advanced state by the petroleum industry,
capable of determining not only the geometric shapes of subsurface layers and faults, but also yielding
substantial information about the elastic properties of the rocks and the nature of any fluids present. The
technology is expensive, but highly successful and justified in comparison to the cost of drilling wells
several thousand feet deep to discover and produce petroleum. Geologists drill few oil wells and no
deep ones without the support of seismic reflection data. Geotechnical investigations share some of the
same goals, to image subsurface layers and faults, and to determine the elastic properties of the strata
without the expense of excavation or drilling, but the economics are quite different. This paper reviews
the state-of-the-art as it is practiced in the petroleum industry, and examines which elements of the
technology can be adapted in a cost-effective way to geotechnical site investigations. Not all of the
petroleum industry technology is appropriate for engineering applications, but the basic field equipment
and software can be easily adapted. Recommendations are presented as to the kinds of problems where
reflection seismology may be the more effective than other geophysical methods including refraction
seismology and ground penetrating radar.
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Shear-Wave Velocity and Liquefaction Potential for Soils Under Dynamic Loading
More LessThis paper presents an overview of the procedure for evaluating liquefaction potential of soils
using shear-wave velocity measurements described in recent journal papers by the author and others.
The procedure follows the general format of the Seed-Idriss simplified procedure, and was developed
using suggestions from participants of two workshops and several independent reviewers. Comparative
studies show good agreement between predictions by the shear-wave-based procedure and the
penetration-based procedures.
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Shear-Wave Velocity (VS) Profiling By Surface Wave (MASW) Method
More LessThe multichannel analysis of surface waves (MASW) method (Park et al., 1999) is a non-destructive
(NDT) seismic method to evaluate shear-wave velocity (Vs) (or stiffness) of the ground. It analyzes
dispersion properties of seismic surface waves propagating horizontally along the surface of
measurement. It gives the Vs information in either 1-D (depth) or 2-D (depth and surface location)
format in a cost-effective and time-efficient manner. The main advantage of the MASW method is its
ability to take a full account of the complicated nature of seismic waves that always contain harmful
noise waves such as higher modes of surface waves, body waves, scattered waves, traffic waves, etc
(Figure 1). Since its first introduction to the related communities in mid 90s, there have been various
types of applications with the MASW method at different parts in the world. Nowadays, the keyword
MASW can be effectively used to search for related information on the Internet. Complete list of the
MASW publications made at the Kansas Geological Survey (KGS) during the last one decade can be
found at www.kgs.ku.edu and includes various types of case studies as well as theoretical ones.
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Surface Wave Analysis Using Wavelet Transforms
Authors Nenad Gucunski and Parisa ShokouhiComprehensive and efficient shallow evaluation of layered systems, like soils and pavements,
can be done using surface waves. The most commonly used surface wave techniques include the
Spectral Analysis of Surface Waves (SASW), Multichannel Analysis of Surface Waves (MASW), and
its high frequency counter part for paving layer evaluation, the Ultrasonic Surface Wave (USW). The
techniques have been primarily used in evaluation of elastic moduli and layer thickness of layered
systems, and to a certain extent in evaluation of profile variations and detection of anomalies, such as
cavities, soil lenses and buried objects. Since the SASW is using only a pair of receivers and data
evaluation is based on a standard spectral analysis, it has limitations in the accuracy and completeness of
the obtained information. The MASW, with its multi-channel data collection and analysis based on
double transformation of the signal from the spatial-time domain into the frequency-wave number or
frequency -phase velocity domain, can provide a more comprehensive description of the subsurface
conditions. Further enhancements can be achieved through surface wave analysis using wavelet
transforms. Application of three types of wavelet transforms of surface waves is presented.
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Applications of Controlled Source and Natural Source Audio-Frequency Magnetotellurics To Groundwater Exploration
Authors Norman R. Carlson, Phillip M. Paski and Scott A. UrquhartAudio-frequency magnetotellurics (AMT), using either a controlled source (CSAMT) or natural
source (NSAMT), has become an efficient, cost-effective tool for groundwater exploration.
Advancements in field equipment have improved data quality and increased data acquisition speed, and
the availability of 2D inversion modeling has significantly improved data interpretation. Since depth of
investigation is not related to the receiver electric field dipole size, AMT can be used as either a highresolution
tool (using short dipoles) or as a reconnaissance tool (using large dipoles).
Several recent field examples are presented, including fractured bedrock targets, in which lateral
resolution is important, as well as reconnaissance-style basin mapping, in which speed and economic
efficiency is critical. In one project, located in Tule Desert, Nevada, CSAMT was used successfully to
map an undeveloped basin, and was instrumental in subsequent court hearings to support water right
applications to develop groundwater resources from this basin.
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