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14th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 04 Mar 2001 - 07 Mar 2001
- Location: Denver, Colorado, USA
- Published: 04 March 2001
81 - 100 of 129 results
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An Investigation Of Alluvial Sediments Using S-Wave Refraction: A Case Study
Authors Karl J. Ellefsen and Adrienne BarnettIn the Big Thompson River valley of north-central Colorado, an S-wave refraction survey was
conducted to determine the thickness and the gross stratigraphy of the alluvial sediments, because this
information is needed to evaluate resources like ground water and aggregate. The refraction data were
collected along three roads that cross the valley; the data were processed to estimate velocities and
thicknesses for a layered-earth model; and from these models, three cross sections of the river valley
were constructed. The river valley is covered by a layer of soil, which is 0.2 to 1.5 m thick. Beneath the
soil, there is one layer of alluvium at some locations and two layers at other locations. For the two
westernmost cross sections, the total thickness of the alluvium ranges from about 6 to 10 m near the
center of the valley and from about 2 to 6 m near the sides of the valley. The easternmost cross section is
somewhat more complex than the other two, because it is near a large tributary. In this cross section, the
thickness of the alluvium ranges from about 8 to 10 m in the southern half of the valley and from about
3 to 13 m in the northern half. In all three cross sections, the alluvium overlies bedrock, which is the
upper transition member of the Pierre Shale.
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Detection Of The Oil, Natural Gas, And Coal Production Infrastructure By Magnetic Surveys, Front Range Of Colorado
Aeromagnetic surveys flown over areas of past and current production of oil, natural gas, and
coal in the northern Front Range of Colorado have proven useful in identifying natural gas wells and
magnetic clinker associated with abandoned coal mines. Magnetic anomalies spatially associated with
wells that produce natural gas in the greater Wattenberg area, north of Denver, are commonly of short
wavelength (<150 m) and variable amplitude (15-90 nT), depending on the location of the well with
respect to the flight line of the aircraft performing the survey. Steel pipe, which serves as casing in the
wells, is the likely source of the magnetization detected by the airborne magnetometer. Magnetic clinker
is associated with “baked” rock overlying the coal that has burned since mine abandonment. Anomalies
associated with clinker are commonly of longer wavelength (>250 m) than those associated with gas
wells and are variable in amplitude (17-40 nT). Because producing or abandoned gas wells and
abandoned coal mines can present challenges to future land development, geophysical surveys that help
locate such features can greatly benefit land use planners in making informed decisions.
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Seismic Refraction And Dozer Trenching To Estimate Borrow Quantities At Casitas Dam Borrow Site, Ventura California
Authors Richard A. Hopkins, Richard D. Markiewicz, Jeanne L. Major and Curtis P. CainFrom May 5 to May 12, 1998, personnel from Reclamation’s Technical Service Center
(TSC), Denver Federal Center completed approximately 5,280 line feet of seismic refraction
surveys at the Casitas Dam Borrow Area, near Ventura, California (Figure 1). The seismic
refraction surveys were concentrated in an area identified as potentially having 3.3 million cubic
yards (CY) of borrow material required for the proposed remediation. The seismic refraction
surveys were conducted to provide information about the configuration of the top of bedrock for
both the Tertiary age Sespe and Vaqueros Formations (limestone, siltstone and sandstone),
bedrock velocities, and possible weathered zones above the bedrock interface. These parameters
affect borrow material volume calculations. Initial exploration drilling provided inconsistent or
irregular refusal depths.
Rippability test sites were selected to evaluate conditions for both the Sespe and
Vaqueros Formations. A single site was selected within the Sespe Formation. Vaqueros site
locations were selected to determine the quality of the rock exposed at the surface and to
evaluate the lower and higher bedrock velocities interpreted from the seismic refraction data.
Subsurface condition information gained from the rippability testing would then be extrapolated
to quantify the exploration drilling and seismic refraction interpretations in areas not groundtruthed.
Seismic refraction surveys conducted at Casitas Dam Borrow Area are interpreted to
have three subsurface seismic velocity layers. There was general agreement between the "bucket
auger” refusal depths and calculated depth to the surface of seismic layer 3. Rippability results
indicate the Sespe Formation is relatively uniform laterally and vertically to the depth associated
with the top of seismic layer 3 and thus support the geophysical interpretation. Seismic layer 3
within the Sespe Formation appears to be a high velocity mudstone/claystone material that is
both tight and moist rather than an unweathered sandstone or conglomerate unit. The results of
the rippability testing support lateral variability within the Vaqueros Formation as interpreted
from the seismic refraction data. The results also infer that the seismic velocity is more
responsive to clay/moisture content.
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Buried Landfill Delineation With Induced Polarization: Progress And Problems
Authors Norman R. Carlson, Jennifer L. Hare and Kenneth L. ZongeIn recent years, the use of induced polarization (IP) data for delineating buried landfills has
increased significantly, due to technological advances that have made this method faster and less
expensive, and therefore more applicable to the environmental industry. As the database of IP
information grows to include information over waste of differing composition and in differing
environments, interpretation has improved significantly. Problems and limitations still exist, of course,
but the IP method has become an efficient and economic tool in evaluating waste sites. We discuss here
progress in interpretation, including methods to process large amounts of data rapidly in order to
decrease costs, and we discuss problems that still exist, such as electrode stability, which still limit the
field survey speed.
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Joint Application Of Radiomagnetotellurics (Rmt) And Induced Polarization (Ip) To I Waste Site Exploration
Authors Biilent Tezkan, Stephan Recher, Mark Hsnig and Fritz M. NeubauerOn a waste site near Cologne/Germany RMT and time domain IP measurements were
carried out on the same profiles. At 320 stations RMT apparent resistivity and phase data were
measured for eight frequencies between 16 and 240 kHz. Civilian and military radio stations were
used as transmitters broadcasting in the RMT frequency range. The lateral borders of the waste
site are characterized by strongly decreasing apparent resistivities compared to the surrounding
host. A clear phase difference outside and inside the waste site is also observed.
The RMT data were interpreted by a 2D inversion algorithm quantitatively. The derived
2D conductivity models indicate the waste site as good conductive anomaly and show lateral and
vertical extension of it. A transient electromagnetic system was used for the IP measurements at
the RMT profiles where the complete transient curve was recorded (anolog to seismic roll along
procedure). For the interpretation of the observed data, a modified electromagnetic algorithm is
used to calculate the response of layered polarizable ground. The transient signals are then inverted
using the Marquardt method to derive the Cole-Cole parameters of each layer. Sensitivity
studies with synthetic data sets for 1D polarizable media show a significant dependence of the
parameter resolution on the magnitude of the IP-effect. Application of the algorithm to the field
data is used to derive pseudosections of the Cole-Cole parameters for near surface structures.
At several locations at the waste site, where the models of RMT and IP data show
anomalous features in conductivity and Cole-Cole parameters, drillings were caried out yielding
soil examples which will be examined in the laboratory.
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A Survey Of Waste Pits At The Idaho National Engineering And Environmental Laboratory Using The New Usgs Prototype Atv Towed Vetem Platform
Authors Jared D. Abraham, David VonG. Smith and David L. WrightThe Very Early Time Electromagnetic (VETEM) system is a prototype EM system that can be
configured in a number of ways for different applications. The main aim for VETEM is to improve
state-of-the-art shallow subsurface electromagnetic imaging in environments where the electrical
conductivity is too high for ground-penetrating radar (GPR) to be effective. The VETEM system also is
unusual in that it records both the transmitted as well as the transient decay part of the signal, and
operates within a much higher frequency spectrum than traditional Time-domain Electromagnetic
(TDEM) systems. The VETEM system, as a research prototype, is constantly being improved to make it
more effective for a wider range of shallow earth imaging problems of interest to the Department of
Energy and to other agencies with similar needs.
The USGS prototype VETEM system was successfully deployed over Pit 4 and Pit 10 in the
Subsurface Disposal Area (SDA) of the Radioactive Waste Management Complex (RWMC) at the
Idaho National Engineering and Environmental Laboratory (INEEL). This field deployment was the
first use of the new VETEM all-terrain-vehicle (ATV)-towed platform, which has an integrated realtime-
kinematic global positioning system (RTK-GPS) system that can provide positioning at a decimeter
level of accuracy. Coverage of these large areas would have been impractical without our very recent
development of the ATV-towed version of VETEM.
The uniformly high quality data obtained over Pit 4 and Pit 10 have yielded high-resolution timeslice
images of subsurface conductivity variations. These time-slice images illustrate the high-resolution
time-dependent response of the VETEM system to the buried waste. These data can be directly
inspected for the lateral position of objects and relative conductivity variations within the subsurface.
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Evaluation Of New Geophysical Tools For Investigation Of A Landfill, Camp Roberts, California
Authors W.E. Doll, T.J. Gamey, J.E. Nyquist, W. Mandell, D. Groom and S. RohdewaldCharacterization of material changes with depth (profiles) in many landfill sites can be
problematic for some conventional geophysical methods. Localized anomalies within the
landfill can complicate mapping of underlying layers, and layered-model techniques are
inappropriate for imaging laterally discontinuous landfills.
Recently-developed geophysical hardware and software tools provide the opportunity to
image the vertical structure of a landfill and its geologic setting. In May, 2000 a sequence of
geophysical data sets were acquired at a landfill site at Camp Roberts, CA to test the benefits of
new hardware and software for characterizing the three-dimensional boundaries of the landfill
and the geologic setting. Conventional magnetic and electromagnetic measurements provided a
backdrop for these new methods. A Geometrics G-858 magnetic gradiometer equipped with a
real-time GPS positioning system was used to map the areal extent of the landfill.
Resistivity, seismic refraction, and electromagnetic data were acquired along profile lines
to characterize the vertical extent of the landfill and geology. Seismic refraction data were
processed with conventional time-delay methods, and with newer tomographic methods. The
multielectrode resistivity data were compared with data acquired with the capacitively-coupled
OhmMapper system
The landfill boundaries that are defined in map view by the magnetic data are supported
in profile by the seismic refraction data and multielectrode resistivity data. The seismic data are
most effective in identifying trench locations when a tomographic inversion is used, instead of a
conventional delay-time approach to interpretation. This shows a localized high-velocity zone
that coincides with the trench boundaries that are defined by the magnetic data. The
multielectrode resistivity data show a disruption of layering where trenching has occurred.
Both the seismic data and the multielectrode resistivity data provide evidence that the
shallow geology is laterally discontinuous and heterogeneous. The high electrical conductivity
of the near surface imposed limitations on the penetration depth of both the OhmMapper and
multielectrode resistivity systems. The multielectrode system was better suited for penetrating
this zone than was the OhmMapper.
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Characterisation Of Hazardous Waste Sites Using The Bgr Helicopter Geophysical System
The Federal Institute for Geosciences and Natural Resources of Germany (BGR) completed a
research and development project aiming at optimising its helicopter-borne geophysical system for
circumstances relevant for high resolution site characterisation. The overall objective was to adapt the
existing helicopter-borne geophysical system previously used for groundwater and mineral exploration
to survey conditions where the anomalies to be recorded are much smaller in shape and size.
The BGR helicopter-borne system permits simultaneous electromagnetic (AEM), magnetic, and
natural gamma-ray surveying. At the suggestion of the BGR, the AEM system manufactured by
Geoterrex-Dighem, Toronto, includes several improvements
increased dipole moment
only horizontal coplanar coils
minimum interference by overlapping coils
operation at five frequencies
new calibration concept: amplitude and phase calibration during flight.
These instrumental modifications were tested running various surveys over two former military
training areas south of Berlin, Germany. Special detection surveys to locate typical waste, such as
individual steel drums, scrap metal, steel pipes, petrol tanks, ordnance, buried at depths varying from
0.3 – 1.5 m were carried out with a nominal flight line spacing of 50 m. AEM and magnetic anomalies
produced by these materials are extremely weak and in the order of only 1 ppm or 0.1 nT at a height of
app. 25 m a.g.l. Therefore, suitable detection algorithms were developed and tested using an airborne
data set collected over an area where thousands of individual anomalies were identified. Lots of them
were subsequently verified on the ground. More than 95% of the anomalies selected for verification
could be confirmed either by visual inspection of the ground surface or ground geophysical surveying or
excavation. The GPS/GLONASS positioning error was less than 10 m in most cases.
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Changes In Geoelectrical Properties Accompanying Microbial Degradation Of Lnapl
Field geophysical studies have identified anomalously high conductivities within and
below the free product zone in soils at sites with "aged" contamination by light, nonaqueous
phase liquids (LNAPL). Laboratory experiments and simple numerical modeling
studies were conducted to test the hypothesis that these anomalously high conductivities
result from products of LNAPL biodegradation. These experiments consisted of 20-L
glass vessel reactors with 18 L of inoculated sand and 6 L of pore water. Diesel fuel was
added to the top of the sand. These experiments simulated a smear zone with a top layer
of LNAPL. Duplicate reactors of the following types were maintained for 120 days;
nutrients added (at levels observed in the field), no nutrients added, killed (autoclaved)
control with nutrients. The killed control showed no signs of diesel fuel biodegradation.
The biologically active reactors showed evidence of diesel fuel biodegradation (e.g.,
reduced dissolved oxygen, increasing numbers of oil-degrading microbes). Diesel fuel
biodegradation was accompanied by increases in the concentrations of volatile organic
acids, calcium ion, pore water conductivity, total dissolved solids, surfactant production,
and diesel fuel emulsification. These results are complemented by the numerical
modeling results, which also showed potential enhancements in aqueous phase
conductivity of 3700 mS/cm when complete mineralization is assumed. However, the
more realistic equilibrium models predict enhancements in the 500-1500 mS/cm range.
From this study, two important observations are made that have significant ramifications
on the measured geoelectrical properties at aged LNAPL sites. First, microbial
degradation of LNAPLs produces a variety of acids that enhance chemical weathering of
the aquifer materials, resulting in high TDS content and thereby increasing the
conductivities of the pore waters. Second, emulsification of the LNAPL by surfactant
production has the potential to change the wetting phase from LNAPL wetted to water
wetted, providing electrically conductive paths within LNAPL saturated zones. Both of
these observations are consistent with our field investigations where we have reported
conductivity values 2-5 times background values from contaminated zones. Finally, our
field studies have also shown that the LNAPL saturated zone is conductive and not
resistive. Thus, the above laboratory experiment and numerical modeling results
demonstrate that LNAPL biodegradation readily explains the temporal changes in
conductivity observed in geophysical investigations of impacted aquifers.
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Dielectric Permittivity Of Clay-Water-Organic Compound: Frequency Dependence
By Birsen CananThrough non-invasive or other geophysical techniques, the ultimate goal of a geophysical survey
is the identification of subsurface materials and their spatial distributions. Reaching this goal will only
be possible through a complete understanding of the physical properties of different materials. A
detailed petrophysical work is essential to gain insight of what kind of changes can be observed through
geophysical techniques.
In this research, the effects of organic contaminants in a clay-water mixture were investigated via
dielectric permittivity under controlled laboratory conditions. For this investigation four organic
contaminants, trichloroethylene (TCE), tetrachloroethylene (PCE), ethylene glycol, and phenol, were
added to previously prepared samples of clay-water mixtures, and their dielectric permittivities were
measured. The dielectric permittivities of contaminated versus uncontaminated samples were compared
to determine if there was any pattern to help to identify a particular organic contaminant via dielectric
permittivity values of the mixtures.
Depending on the nature of the organic material, the changes observed are: 1) A decrease of the
magnitude of dielectric permittivity and shift of the relaxation frequency to lower frequencies for
ethylene glycol and phenol and, 2) An increase in the magnitude of dielectric permittivity and shift of
the relaxation toward higher frequencies for TCE and PCE contaminated samples between 100 KHz and
350 MHz frequencies.
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Laboratory Complex Resistivity Investigation Of Organic Contaminants: Denver Federal Center Soils
More LessThe Denver Federal Center is a DNAPL contamination site that lends itself to the use of complex
resistivity in monitoring the migration and concentrations of contamination. The physical properties of
DNAPLs often render monitoring-well data misleading by underestimating actual concentrations present
in the liquid and vapor phases. Smectite-rich soil at the site and chemical degradation of volatiles
through dechlorination, however, suggests the use of complex resistivity as a monitoring tool sensitive to
clay-organic reactions. To aid the interpretation of complex resistivity field data, this study involves
controlled contamination of site soils in the laboratory for comparison.
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The Role Of Advanced Monitoring In Steam Stripping For Insitu Remediation Of Dnapl
More LessThe use of advanced subsurface monitoring was an integral part of a 1999 pilot study of Steam
Stripping/Hydrous Pyrolysis Oxidation at a Trichloroethene (TCE) contaminated site at the Portsmouth
Gaseous Diffusion Plant in Ohio. The Pilot Study was conducted to determine costs, strategies, and
design parameters for the use of Steam Stripping to remove TCE from a moderately permeable sand/silt
aquifer (Gallia Member) and the upper two feet of the underlying, organic-rich Sunbury Shale.
Two complimentary systems were used to monitor temperature and steam movement. Point
measurements of temperature were made using an array of 314 thermocouples. Measurements between
boreholes were made using electrical resistivity tomography (ERT). Without ERT, even the relatively
large number of in-situ thermocouples gave a sparse and often misleading view of the temperature
distribution and steam front location within the aquifer.
Preferential flow paths exist within the aquifer. Previous studies on the same site had concluded
that “channels” existed within the aquifer and these preferential flow paths had adversely impacted the
remediation of the area. Although extensive characterization had been conducted on the site during this
study and previous studies the locations and extent of these areas were not well defined.
The use of ERT/thermocouples to provide high resolution, near-real-time monitoring of the
temperature increases due to steam injection, showed that portions of the aquifer were not being heated.
The areas not being heated appeared to correlate with depressions in bedrock elevation but the bedrock
topography is complex the correlation was not always obvious. Using monitoring results, areas not
heated during the few weeks were targeted for new injectors. Using this adaptive approach, the aquifer
was adequately heated and the bulk of the TCE removed from the study area.
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Nondestructive Monitoring Of Sub-Asphalt Water Content Using Surface Ground Penetrating Radar Techniques
Authors Katherine R. Grote, Susan S. Hubbard, John Harvey and Yoram RubinThe strength of sub-asphalt aggregate layers is crucial to understanding the relationship between
traffic loading and pavement damage. Because these strengths are greatly influenced by water content,
and because there are currently no techniques available for obtaining reliable, non-destructive subasphalt
water content estimates, pavement damage assessment is often inaccurate. Although Ground
Penetrating Radar (GPR) methods have the potential to provide high-resolution, non-destructive water
content estimates, the accuracy of this technique is largely unknown. Based on the successful results of
a pilot study conducted under ideal conditions to estimate water content using GPR techniques, we
applied this concept to estimate the sub-asphalt water content in two differently layered pavement
sections. Both pavement sections were subjected to infiltration over several weeks, and GPR data were
collected periodically throughout the infiltration period. By relating the changes in GPR response during
infiltration to the water content of the aggregate layers, we can observe the movement of water in the
sub-asphalt layers. Analysis of the GPR data indicates that the water content of the aggregate layers
varies with depth, lateral location, and time. These results suggest that GPR techniques may provide an
efficient and high-resolution method for obtaining non-invasive water content estimates.
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Ground Penetrating Radar Survey To Evaluate Roadway Collapse In Northern Ohio
Authors Ernest C. Hauser and Mark J. HowellA Ground Penetrating Radar survey was conducted to evaluate roadway collapse in a residential
neighborhood in northern Ohio. The primary targets of the survey were voids or void-forming
conditions in the underlying fine-grained soils. Boring logs indicated that the subsurface materials
consist of sandy and silty fill overlying natural soils. The thickness of the fill varied from 2 to 13.5 feet
(0.5-4 m) below the pavement surface. Natural soils included silty sand, sandy silt, sand and silty clay
containing variable amounts of rock fragments.
Three roads near the Lake Erie shoreline were selected for the investigation due to a history of
pavement and structural subsidence. Large concrete repairs to the roadway were observed in several
locations, one of which exhibited a large void as seen through a borehole that had lost part of its
patching material. This observed void measured 7 feet (2 m) deep and 3 to 4 feet (1 m) in minimum
extent.
GPR data were collected with a GSSI SIR-2® system. The 300 MHz antenna used gave less
resolution than an 800 MHz antenna also tested, but the 300 MHz penetrated to at least 15 feet (~4 m)
below the surface and was selected for the survey.
GPR data were collected along parallel profiles on each of the three roadways. The profiles were
located near the centerline (crown) of the road, and approximately 4 feet off of the unoccupied curb. The
known 7-foot deep void gave an anomalous, high-amplitude response in the GPR profiles; moreover,
other locations showed similar high-amplitude anomalies. Following the review of the main GPR
profiles, suspect areas were surveyed to determine the lateral extent of the radar anomalies. A good
spatial correlation of the mapped GPR anomalies and subsidence related features observed on the
surface suggest that significant voids likely exist and could pose a potential for roadway subsidence and
collapse. Subsequent borings are reported to have confirmed the presence of voids or loosely compacted
substrate at the anomalous areas mapped by GPR.
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Void Detection Underneath Rigid Pavements: Numerical Simulation Of The Impulse Response Method
Authors Nenad Gucunski and Hudson JacksonThe Impulse response (IR) technique is a seismic method used in evaluation and
condition monitoring of rigid pavements. It enables nondestructive evaluation of in situ
pavement material properties and detection of several defects within the pavement
structure. Voids or loss of support underneath rigid pavements can be detected due to
changes in the flexibility spectrum and damping characteristics of the pavement system.
Numerical simulation of the IR technique for void detection underneath concrete slabs in
rigid pavements is presented. The simulations were conducted using the finite element
method. Effects of several pavement parameters on the pavement response and the ability
to detect voids are presented and discussed.
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Development Of Ground Penetrating Radar For Railway Infrastructure Condition Detection
More LessRailway track engineers are focused on cost-effective track maintenance to support revenue train
traffic. Therefore, effective detection of railway track maintenance needs and planning of maintenance
activities are required to improve efficiency. One area requiring improvement to ensure safe train
operations and efficient maintenance is identification and diagnosis of track support problems. This
paper presents some of the research that was conducted to investigate the ability of ground penetrating
radar (GPR) data to accurately measure railway track condition in an effort to help guide railway
engineering and maintenance activities. The research effort included evaluation of data collection
techniques, data interpretation methods, and comparison of GPR data to available track condition
information.
The main indicators of poor track condition detectable using GPR are increased moisture or
changes in the ballast layer below the tie, both resulting in dielectric permittivity changes. Poor roadbed
ballast condition generally is due to fouling, which indicates ballast contamination, typically due to
particle abrasion, but potentially from other sources. Increased moisture is a strong indicator or poor
track condition since trapped water can dramatically accelerate the ballast fouling process and fouled
ballast tends to hold water in the track structure. The initial research indicated that GPR could be used
to identify poor track conditions such as water trapped in the track structure and fouled ballast due to
strong dielectric contrast between the tie and the supporting layers depending on ballast moisture and
degree of fouling. Additional testing demonstrated the ability to identify obstacles to mechanized
maintenance using GPR, although improvements are required to improve accuracy.
Further research on the application of GPR to railway track engineering is required to further
define the expected dielectric permittivity of common track materials and better target the transmitted
energy from the GPR antenna to ensure the strongest signal from the track substructure layers is
available for analysis.
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High Frequency Masw For Non-Destructive Testing Of Pavements—Accelerometer Approach
Authors Nils Rydén, Peter Ulriksen, Choon B. Park, Richard D. Miller, Jianhai Xia and Julian IvanovThe dispersive nature of surface waves in pavement systems is imaged through a multichannel approach using one accelerometer as receiver and multiple shot points. The image obtained from a wavefield transformation method shows multimodal dispersion curves up to 10 kHz.
We present results from a simplified MASW data acquisition method applied to a pavement
surface. The method can simulate an arbitrary number of channels. The sensor separation can be
chosen arbitrarily small. In these experiments, the upper frequency limit is 10 kHz, which can be
increased by the exchange of one sensor. The method is tested by one manual and one automated
procedure. Both rely on source-receiver reciprocity. The automated procedure is regarded as
necessary when a large number of channels is combined with a small sensor separation. The
manual method will not provide the necessary accuracy and endurance for that kind of
measurement, but is promising for less complicated setups. We present recommendations for
high frequency measurements on pavements.
In the subsequent data processing, we follow the procedure of multichannel analysis of
surface waves - MASW. It has recently been developed as a geophysical method for near-surface
investigation. We demonstrate that the MASW technique can identify detailed aspects of the
high frequency total wave-field of both surface and body-wave events.
Results of dispersion curve extraction indicate that higher modes of surface waves are
dominating at depths associated with the transition between the asphalt and the base layer.
However, the deviation from the fundamental mode is not large because all modes are
converging in an asymptotic manner with increasing frequency. The study indicates that the MASW method is a fast and cost efficient method for measuring pavement stiffness parameters.
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Seismic Investigation Of Pavements By Masw Method — Geophone Approach
Authors Choon B. Park, Julian Ivanov, Richard D. Miller, Jianghai Xia and Nils RydenA feasibility test of the multichannel approach to seismic investigation of a pavement system is
described. This test followed the procedure normally taken in the multichannel analysis of surface waves
(MASW) method by using geophones and a light (8-oz) hammer source. A wavefield transformation of
recorded multichannel data shows a strong fundamental-mode dispersion curve image in the frequency
range of 30-600 Hz with normal (30-50 Hz) and reverse (50-600 Hz) trends. However, the transformation
shows that this fundamental mode disappears quite abruptly and higher modes start to dominate in
the higher frequencies up to 2000 Hz. Simultaneous recording of both vertical and horizontal components
of seismic wavefields facilitates identification of seismic events. In order to record the horizontally
travelling direct (or possibly guided) P-wave event in the uppermost layer, it seems critical to use horizontal
phones with longitudinal orientation. Results of test indicate that for an investigation focused into
the uppermost layers of a pavement system it is essential to use a different acquisition system that can
deal with much higher (> 2000 Hz) frequencies. In addition, complicated and unique elastic properties
of pavement systems call for an inter-disciplinary study to develop an effective multichannel seismic
method for this area of application.
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Electrical Density Gauge Replacement For Nuclear Density Gauge
Authors Dennis M. Anderson, William J. Ehni and John LundstromThe paper will present the mathematics as well as the form and function of applying new
geophysical engineering equipment, the Electrical Density Gauge (EDG), for geotechnical
engineering application, such as building and highway foundation analysis.
In 1992 the Dennis M. Anderson and William J. Ehni, theorized that the relationship
between soil electrical resistivity and geotechnical engineering could be developed for applications
in soil engineering. The paper provides a systematic approach to investigating soil electrical
properties, setting geo-electric constants for a test specimen, and then using the observed
electrical properties of an undisturbed, in-situ soil specimen to calculate the in-situ density of the
soil that is under test.
The EDG's primary advantage over existing geophysical technology is that the equipment
does not use a nuclear source, but still offers a high level of efficiency for quality control/quality
assurance (QC/QA) work and testing related to soil in-situ density. EDG technology will eclipse
nuclear density gauge technology within three to eight years. The electrical density technology
represents the next generation in foundation analysis for civil construction.
The EDG equipment and electronics have been designed and built to meet the
geotechnical industry needs. Mr. John Lundstrom, Electrical Engineer is the primary electronic
designer and manufacturer of the EDG. The EDG uses solid state electronics on a printed circuit
board so that the instrument will be field durable for the construction industry. The electronics of
the first generation EDG is contained a durable high-density plastic case that is 14 inches by 10
inches by 7 inches. The EDG is powered by rechargeable batteries. It has a 386 micro-chipprocessor,
an alphanumeric keypad, and a liquid crystal display (LCD) read out. The EDG comes
equipped with a set of standard tools for setting the soil material electrical constant and a standard
probe for field investigations. The first generation commercial instrument will be capable of
measuring in-situ density and moisture. The EDG operator makes the field measurements. Then
internal math processors will perform the analytical analysis, and present the operator with the insitu
density data for the test site. The lightweight, compact size, durability, and non-nuclear
character of the EDG will allow the user to easily transport and use the instrument on
construction sites domestically and worldwide.
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Seismoelectric Investigations At Clean And Contaminated Sites
Authors Elizabeth Strachan and Paul J. WolfeWe have conducted studies of the seismoelectric effect at a site with a clean aquifer and a site
with fuel leaking from a storage tank farm. The main problem with applying the seismoelectric effect is
background electrical noise from power lines. At the clean site there was a shallow water table, about
2 m deep, and no man-made obstacles. We conducted detailed studies to determine the physical
characteristics of the site. We used this site to develop appropriate data acquisition techniques and the
resulting data to test data processing techniques. From the arrival time of the seismoelectric signal we
were able to determine the depth of the water table which was verified by drilling.
On the basis of these results we designed a survey to attempt to determine the extent of the fuel
layer on the water table at an inactive military fuel site along the Ohio River. Monitoring wells had
previously recorded a fuel layer up to 50cm thick. The water table in the contaminated zone is about
15m below the ground surface. We made seismoelectric measurements at 8 stations expected to cross
the fuel plume. We had a control site closer to the river where no contamination had been observed and
the water table was 9m deep.
The control site showed a clear seismoelectric response at a time corresponding to the water
table. The records from the contaminated zone did not show a clear response. We expected the stations
at the ends of the profile to be out of the fuel zone but there were no monitoring wells near our end
stations. Our conclusion is that fuel suppressed the seismoelectric response and that the extent of the fuel
plume was larger than expected. This conclusion is tentative but the results suggest the need for further study.
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