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8th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 23 Apr 1995 - 26 Apr 1995
- Location: Orlando, Florida, Canada
- Published: 23 April 1995
1 - 20 of 104 results
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Properties Of Light Non-Aqueous Phase Liquids And Detection Using Commonly Applied Shallow Sensing Geophysical Techniques
More LessProperties of light non-aqueous phase liquids (LNAPLs) and their interaction with the unsaturated, shallow
subsurface provide a variety of detection criteria for commonly applied geophysical mapping techniques including
electromagnetic induction (terrain apparent conductivity) and galvanic resistivity (terrain apparent resistivity) and
ground penetrating radar for profiling discrete horizons in the sub-surface. These physio-chemical phenomena in
the unsaturated zone may include: aqueous phase dynamic displacement due to downward migration of the
immiscible phase, alteration of interfacial tension effects if the immiscible phase replaces air as the wetting fluid
to the aqueous phase or if the immiscible phase is partially soluble or is volatile, capillary fringe collapse and
restructuring of the effective geophysical water table due to free product buoyancy, and additives to the non-aqueous
phase which may promote the formation of emulsions and provide surface conductance effects. Early literature on
direct geophysical detection of shallow organic contaminants has provided a simplistic approach. Simply stated,
the presence of LNAPLs in the subsurface with apparent conductivities orders of magnitude less than natural
groundwater, should produce measurable anomalies by acting as an insulating layer. It has become apparent that
the “insulating layer” concept is inadequate to explain mapped geophysical anomalies over and about LNAPL spills.
Considerable effort has been devoted to studying geophysical detection of pooled hydrocarbons but this has generally
been restricted to immiscible/miscible organic contaminant interactions with groundwater in controlled field or
column experiments. It is common to apply geophysical techniques at sites where multiple immiscible contaminants,
exhibiting a variety of properties, may exist in a complex subsurface. This paper provides insight into some of the
resultant geophysical detection criteria for these immiscible contaminants.
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Detection And Mapping Of An Lnapl Plume Using Gpr: A Case Study
Authors Michael Maxwell and Jeffrey SchmokGround penetrating radar was used to delineate a gasoline (LNAPL) plume at the site of a
former gasoline station. Monitoring wells indicated the approximate location of the plume
and a free product thickness of up to 1.7 m above a water table typically 3-4 m below ground
surface. Anomalous GPR responses were detected well above the expected depth of mobile
LNAPL. The shallow depths of anomalous responses indicates that a residual or possibly
vapour contaminant found in the non-saturated zone produces the characteristic GPR
anomaly detected during this survey.
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Can Accurate Estimates Of Permeability Be Obtained From Measurements Of Dielectric Properties?
Authors Michael D. Knoll, Rosemary Knight and Elizabeth BrownA laboratory study was conducted to investigate relationships between dielectric properties and hydraulic
permeability of sand-clay mixtures. The mixtures were generated in such a way as to vary systematically parameters
such as porosity, clay volume fraction and specific surface. Each of these parameters affects both dielectric properties
and permeability. For each mixture, measurements were made of porosity, clay content, permeability and dielectric
constant at two levels of water saturation (room dry and fully saturated). For the suite of mixtures generated,
porosity ranges from 0.240 to 0.605, clay content ranges from 0.000 to 1.000, and permeability ranges from
5.3~10~‘~ to 2.7~10~~ cm2. At a frequency of 1 MHz, the dielectric constant ranges from 3.54 (dry quartz sand) to
49.4 (saturated kaolinite clay). Crossplots are used to investigate relationships between various parameters. Results
show that many relationships such as porosity-permeability and dielectric constant-permeability are multivalued and
involve critical points or minima in some parameter. In addition, the experimental data are compared to predictions
from three interrelated petrophysical models: (1) a microgeometrical model which describes the relationship between
porosity and clay content in sand-clay mixtures, (2) a permeability model based on the Kozeny-Carmen equation, and
(3) a dielectric model which incorporates geometric information through the use of wetted matrix parameters.
Results show excellent agreement between predicted and observed data. At least for these mixtures, permeability
estimates accurate to within an order of magnitude may indeed be derived from dielectric measurements. Such
petrophysical relationships can be used in ground penetrating radar and very early time electromagnetic surveys to
estimate permeability values and connectivity functions in the field.
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Dual Geophysical Data Set Interpretation For Landfill Plume Delineation
Authors T.H. Rowley, Paul R. Donaldson, James L. Osiensky and J. Carlton ParkerA contaminant plume containing high concentrations of Dense Non-Aqueous Phase Liquids (DNAPLs) and
inorganic contaminants emanates from the Bannock County Landfill, in Fort Hall Canyon, Idaho. These DNAPLs
and inorganics have been detected in nearby domestic and municipal water supply wells in an alluvial fan aquifer.
The alluvial fan aquifer is underlain by cemented, fluvial gravels. A surface electrical field survey was conducted
down gradient from the Bannock County Landfill to help delineate the extent of the plume. The field site is
relatively free of cultural interference that would adversely affect electrical-potential fields. Data collected during
the survey were correlated with seismic refraction data.
The mise-a-la-masse method for plume delineation was utilized for this investigation. The method is much easier to
use and data interpretation is less subjective than other electrical methods; however, it does not yield depth
information. The mise-a-la-masse method was used successfully to identify electrical-field anomalies near the
Bannock County Landfill. The seismic refraction method was used to determine depth to the subsurface structure.
The seismic refraction survey suggested that three buried channels exist beneath the site.
The electrical-field map correlates very well with the seismic data in those areas where the data sets coincide. Most
electrical-field highs are located above areas interpreted seismically as buried channels or basins. These features
may provide preferential flow paths for the contaminated groundwater and DNAPLs.
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Ultrasonic Crosshole And Crossmedium Tomography For The Detection Of Defects In Structural Concrete
Authors Farrokh Jalinoos, Larry D. Olson and Marwan F. AouadThe use of ultrasonic crossmedium and crosshole tomography is described as a means for nondestructive
evaluation (NDE) of flaws or imperfections in structural concrete. Tomography is an inversion procedure that can
provide for ultrasonic images of a concrete specimen from the observation of transmitted compressional or shear first
arrival energy. Two applications for ultrasonic tomographic imaging are presented here. Crossmedium tomographic
images are obtained from concrete walls or columns with two-sided access. Crosshole tomographic images are acquired
from drilled shafts or slurry walls containing steel or PVC access tubes set in place during the concrete placement.
In order to study the application of crossmedium tomography for imaging flaws in concrete, four concrete
walls containing simulated flaws or defects were cast-in-place in the laboratory as part of a 1993 National Science
Foundation (NSF) SBIR study. A new specialized rolling ultrasonic scanner source was developed for this testing and
was used for rapid scanning of structural concrete with two-sided access. Using the new scanner, a typical 116 cm (45.5
in) survey line for 1764 different source-receiver combinations was acquired in 1% hours. A comparable tomographic
test line, performed on a single source-receiver measurement basis, takes approximately 40-60 hours. Therefore, the
scanner source now makes locating and imaging flaws in critical concrete structures practical. Tomographic analysis
was performed using two series expansion algorithms from geotomography: Simultaneous Iterative Reconstruction
Technique (SIRT) and a least square matrix inversion approach using an optimized Conjugate Gradient (CG) approach.
The results of this study indicated that travel time tomography was most successful in locating simulated voids in
concrete. The crossmedium tomography was also used to locate and image simulated honeycombs, simulated open
cracks, microcracks, and weak concrete.
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Three Dimensional Visualization Of Concrete Structures
Authors D. Wiese, M. Thomas and H. CaratinThis paper describes the application of geophysical tomography and scientific visualization techniques for
evaluating the internal condition of massive concrete structure. The resulting output is a three dimensional
representation of the structure showing the spatiai distribution of ultrasound data. As various aspects of ultrasound
data (e.g. velocity and attenuation) are related to concrete quality, the location and orientation of areas of inferior
material or discontinuities can be identified. In addition, specific features within the image can be highlighted and
quantified.
There are several nondestructive, noninvasive techniques for determining various in-situ properties of concrete.
Most of these techniques only measure properties of the concrete at, or close to, the concrete surface. However,
geophysical techniques such as ultrasound or seismic velocity measurements taken across a section give an
indication of the quality of concrete between the points of transmission and reception at the concrete surface.
Generally, higher velocities are indicative of good quality concrete.
In the current study, a large number of measurements (ultrasonic pulse velocity) are taken to provide a network of
velocities across a section, algebraic tomographic techniques are then applied to reconstruct a two dimensional
image. By taking a series of contiguous sections and stacking them together, a three dimensional model of the
sample or structure is created. FinaIly the three dimensional data set is visualized using advanced graphics
techniques such as volume rendering. Scientific visualization gives form and shape to numerical data that may be
abstract and difficult to interpret. Direct volume rendering in particular is appropriate for tomographic images
because it enhances the detailed spatial distribution of heterogeneous information without distortion or smoothing.
Results will be presented from a preliminary study carried out to assess the potential application of this technique
for evaluating the internal condition of large concrete elements. Measurements were made on a large concrete
block constructed with a number of internal defects such as cracks, areas of poorly compacted concrete and
uncemented aggregate, and large voids (polystyrene blocks). Overall, the initial results were promising, indicated
that the presence and location of internal defects can be determined and visualized using this technique. The
successful development of a technique for determining and visualizing the internal condition of large concrete
structures would be a significant advance in the area of concrete inspection and maintenance.
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Ground Penetrating Radar Technique In Monitoring Defects In Roads And Highways
Authors Tom Scullion and Timo SaarenketoIn recent years the trend in the highway industry has been on maintaining and rehabilitating existing
structures rather than building new ones. In this area the use of nondestructive testing techniques
particularly Ground Penetrating Radar has been growing in importance. Before planning major
improvements to any highway it is essential to detect any major defects in the structure. Traditional
methods include expensive coring and boring which have limited success at detecting random subsurface
defects. GPR offers much potential in providing a cost effective and relatively rapid procedure for
nondestructive testing of pavements.
The main focus of the paper will be to present a series of case studies in which GPR techniques have
been used to tackle a variety of highway related problems. These case studies involve studies undertaken
in both Finland and Texas, two completely different environments.
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The Use Of Dielectric And Electrical Conductivity Measurements And Ground Penetrating Radar For Frost Susceptibility Evaluations Of Subgrade Soils
More LessIn this study several tests have been made to evaluate, if in situ dielectric value and electrical conductivity
measurements together with ground penetrating radar survey (GPR) results could be used to estimate frost
susceptibility of subgrade soils in Finnish Lapland. Dielectric value and electrical conductivity were measured in
situ from the soil beside the road with a Dielectric Constant & Conductivity Meter made by Adek Ltd, Estonia
and GPR surveys were performed with 500 MHz ground coupled antenna. GPR measurements were performed
both in winter when the ground was frozen and in summer when it was totally thawed. The test site on highway
21 at Pello was selected as it exhibited variations of frost heave damages and a section with no frost heave was
also surveyed. The measurement results were compared with the frost heave measurements and the visual frost
damage mapping on the road surface.
The study results showed good correlation between frost heave and dielectric constant. If the dielectric value was
less than 8, no frost heave could been found. The highest frost heave values were achieved with the dielectric
constant between 15 and 22 in the case of glacial till and 20 and 30 in the case of silt. With higher dielectric
values frost heave started to decrease. Electric conductivity measurements gave information about the soil type
and compressibility.
With Ground Penetrating Radar it is possible to measure the frost depth and estimate the presence of unfrozen
water in road structures and subgrade soils. This is based on the fact that the dielectric value of ice is 3.6-4.0
and the presence of unfrozen water can be seen as major reflectors in GPR data. GPR results gave also the total
thickness of road structures, which is needed for dimensioning road structures against frost heave. Other
valuable information gained from the radar results were the presence of bedrock, presence of boulders and
information about the quality of the existing road structure.
As a result of this study a method of classifying the frost susceptibility of subgrade soils was proposed. This
classification is based upon the in situ measurements of dielectric value and electrical conductivity.
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Correlating Gpr And Resistivity Surveys With Cone Penetrometer And Shallow Coring Studies Along The Aberjona River.
Authors David B. Cistt, Randall L. Mackie, Peter J. Zeeb and M. Nafi TöksozA multi-modality survey using 3-D GPR and Resistivity techniques was performed to
assist hydrologists in characterizing groundwater flow near the Well-H region of the
Aberjona river in Woburn, Massachusetts. Concurrent cone penetrometer and coring
studies provided “ground truth” data about the stratigraphy, soil chemistry and
composition of the first ten meters of peat and sand. What remained for GPR and
resistivity was to extend such point-source ground truth information into a 3-D map of
the stratigraphy of the entire region by inferring soil properties from the electrical
measurements.
Electrical conductivity values were measured at some of the same points where coring
and cone penetrometer measurements had been made, to physically correlate electrical
properties with structural data collected at the same location. Conductivities at these
locations were also estimated independently using GPR and resistivity and then compared
to probe measurements.
EM wave velocity estimates were determined by CMP gathers which were used to infer
the depth to the reflective layers. A synthesis of the conductivity changes was then
compared to the stratigraphic surfaces detected by the resistivity and GPR surveys as well
as the penetrometer data. Finally, an empirical relationship between soil stratigraphy and
attenuation of the radar signal at these isolated locations was assembled.
Cone penetrometer measurements were made along two orthogonal lines against which
GPR surveys along the same profiles could be compared. The results show a strong
correlation between the probe data and the electrical measurements. By combining the
probe data that had been collected along these profiles with the GPR and resistivity data
of the area, we were then able to create a 3-D map of the subsurface properties and to
generate a structural interpretation of the entire region.
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Geophysical Investigations Of A Waste Deposit In Southern Sweden
Authors Torleif Dahlin and Hans JeppssonGeophysical surveying was performed in order to investigate the existence and location of
buried metal waste, which might be drums containing hazardous waste. Three methods were
used: magnetometry, slingram (dual loop EM) and electrical resistivity. The magnetic and
slingram surveys were carried out manually, whereas a computer controlled data acquisition
system was used for the resistivity surveying.
The magnetic profiles show the presence of object with high magnetic susceptibility. The
anomalies can be joined together and lie parallel to extension of the valley. Magnetic
modelling shows that the anomalies fit well with metallic objects in the bottom of the original
valley.
The slingram results indicate objects with high electrical conductivity. The anomalies are
more point shaped than the magnetic ones, but correspond well in location.
The resistivity data were measured and interpreted as two-dimensional sections, using the
Wenner array, which were merged to form a three-dimensional model. A number of low
resistive objects can be identified in the images, which agree with the magnetic as well as the
slingram results.
Excavation revealed many metal objects, including a large number flattened metal drums,
corresponding to the geophysical anomalies. However, no hazardous waste was found.
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High Resolution Magnetic Characterization In Complex Settings: Two Case Studies
More LessThis paper describes the results of two separate deployments of the GPS navigated, high density magnetic
characterization system, STOLS. In both cases, complex cultural signatures from nearby structures contaminated
the magnetic field data and obscured the magnetic signatures of the buried targets. Specialized processing
techniques were required to determine the location and size of each target. The high density of the survey data (-25
samples I m* ) and the high quality of the sensor positioning via GPS allowed for the application of image and data
processing techniques. The first case comes from the Department of Energy Project Office in Grand Junction,
Colorado, where the location of buried 55 gallon drums was in question. The site was a small sensor test facility
adjacent to several buildings, powerlines and fences. Data was collected and filtered to produce a high spatial
frequency map of the facility. A 2D spatial correlation filter was applied to statistically rank all likely targets. The
second case comes from the Chocolate Mountain Aerial Gunnery Range, in southeastern California, where STOLS
was deployed to quickly and accurately detect and characterize, in terms of position, depth and size, all buried
unexploded ordnance. At Chocolate Mountain an 18 mile gas pipeline easement within the Aerial Gunnery Range
was successfully surveyed. The magnetic anomaly data collected along the easement were severely contaminated
by two existing pipelines, A new processing technique which isolates the signatures of ordnance items was
developed and applied to the data to remove the pipeline effect and reveal anomalies adjacent to the pipeline. This
technique enabled STOLS to detect and locate all UXO in the easement.
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Using High-Density Magnetic And Electromagnetic Data For Waste Site Characterization A Case Study
Authors John R. Cochran and Kim E. DaltonMagnetometers are frequently used to characterize hazardous waste sites. Due to cost and time
considerations, data are typically collected on a coarse grid with nodes on 3 to 6 meter (ml
centers. Hardware and software are now available which allow the rapid and cost effective
collection of information on a much finer sampling grid. In this paper we present and compare total
field magnetometery data collected on 3 m centers to total field magnetometery data collected on a
grid with centers of 0.5 m or less. We also compare the magnetometery data to time-domain
electromagnetic (EM) data collected on a 1 m by 0.2 m grid using the recently introduced Geonics
Ltd. EM61 metal detector. All three data sets were collected at an abandoned landfill.
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Interpretation Of Hybrid Data For Characterization Of Shallow Landfills
Authors Edward Hensel and Kim E. DaltonNew Mexico State University has been actively developing a pre-commercial public domain software
package for analyzing and interpreting the data which arises from site surveys that can be performed with
field survey systems. The Multi-sensor Analysis Program for Environmental Restoration, MAPER, allows
analysis of multiple data types, and yields an optimal estimate of the distribution of subsurface materials
at a site. Researchers at New Mexico State University analyze data acquired by public and private sector
collaborators to determine the subsurface distribution of buried waste in landfills. A central aspect of the
effort is to achieve sensor data fusion, by taking data available from multiple sensing technologies and using
it to provide a comprehensive characterization of a buried waste site. The MAPER software modules have
recently been used in the analysis of geomagnetic anomaly detection (GAD) and ground penetrating radar
(GPR) data obtained at several DOE waste sites.
In this article, we review the mathematical approach that is being used in the current development of
the MAPER software, present some preliminary results that have been obtained with a research version of
the software, and discuss our plans for converting MAPER from an academic research tool into a suite of
analysis programs and modules available for public and private sector use. The development of the MAPER
concept has proceeded from the very beginning with the understanding that the ultimate goal of the research
program was to eventually arrive at a set of routines appropriate for field application.
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3D Diagnosis Of A Tunnel Through Infrared Thermography Combined With Ground Penetrating Radar
Authors Jean Christophe Gourry, Colette Sirieix, Lucien Bertrand and Francis MathieuIn 1994, BRGM began a research project based on the combined use of infrared thermography and ground
penetrating radar (GPR) for the non-destructive testing of civil engineering works. This project aims to
combine these two techniques to enable: a). a more-precise knowledge of the nature and three-dimensional
extension of each anomaly, and b). a reduction in time spent on the measurement stage, and c). a better
interpretation.
The first measurements were taken during the survey of a railway tunnel, 1601 m long, in the east of France in
August 1994. The two entrances to the tunnel were tested over a distance of a few hundred metres.
A thermal imaging radiometer was used to take infrared scenes, 4 m wide and positioned by thermal markers,
whilst six parallel radar profiles (or radargrams) were recorded at three different frequencies.
A large amount of anomalies are detected when both techniques are combined, with correlation between the
total anomalies located during the present survey being 55%. In addition, this high level of correlation between
anomalies confirms both their existence and dimension. GPR systematically detects voids in masonry and
country rock whereas the depth penetration of infrared thermography is 1 m. On the other hand, the latter
technique is far more sensitive to problems of spoiled subsurface areas and humidity.
Finally, combined use of the two techniques provides a much clearer picture of the extension of each anomaly
in three-dimensions. Much work remains to be done however, specifically the calibration of radar profiles by
systematic velocity analysis. In addition, a better understanding of the ditTusion effect of each thermal anomaly
is required for a more precise estimation of the true extension.
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An Investigation Of Cracks In Rock Slope Using Ground Penetrating Radar
Authors Katsuo Sasahara, I. Asahi, Tsuneo Tsuchida, Tsuyoshi Kobayashi and Thomas J. FennerRock slope collapse is an important problem in road maintenance works. Earlier investigations in collapsed
rock slope suggest that the internal structures of the cracks are important in forecasting rock collapses. Various
geophysical exploration methods may be applied in cases when visual inspection alone dose not provide sufficient
information. Recognizing the high resolution capability of ground penetrating radar (GPR), a site experiment was
conducted on a vertical wall of welded tuff in order to determine the applicability of GP to substance crack investigations.
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Multiple Geophysical Studies At The Urban Central Environment Of Athens In Connection With The Construction Of The Metro’S Main Station
Authors St.P. Papamarinopoulos, M.G. Papaioannou, X. Kappopoulos and Y. BalatsasTwo main objectives were set to the personnel of the Laboratory of Geophysics of Patras University
and of the company Geome Ltd. by the scientists of the consortium of companies who were interested
in exploring a ten hectare area in the most central part of Athens. The objectives were, the location
of public utility networks unknown to the archives of the city and possible geological unconformities.
The case of the public networks was twofold. Firstly, it was important to know in advance of any
engineering and /or excavation procedure, the location of any network of pipes in order to avoid
damages which could raise the cost of the venture but they would not have consequences on the
public. Secondly, and more important, it was absolutely necessary to locate forgotten fragments of
gas pipes which have been installed in the past and which probably had trapped gas for ages. It is
understood that this case could be extremely dangerous for anybody who would operate for whatever
reason in close distance in connection with these buried pipes. In order to answer these questions a
magnetic gradiometer, a conductivity meter and a ground penetrating radar were utilized. The study
of the site for locating possible geological unconformities, involved resistivity measurements with
Schlumberger soundings, from which vertical parallel geoelectric sections could be produced, along
the main axis of the main avenue. On the same transects the antenna of the 80 MHz of the ground
penetrating radar was utilized.. The geophysical approach was fruitful by pin pointing a variety of
ferro-mettalic objects, geological contacts and a sub-terranean river.
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Piezocone Technology: Downhole Geophysics For The Geoenvironmental Characterization Of Soil
Authors Michael P. Davies and Richard G. CampanellaThe electronic cone penetration test with pore pressure measurement, commonly referred to as the piezocone test or
CPTU, has been established by the worldwide geotechnical community as the premier stratigraphic logging tool for
most soil conditions. Besides stratigraphic information, the piezocone also provides accurate estimates of key
geotechnical parameters and yields extensive information on the physical groundwater regime. Groundwater
parameters assessed include accurate location of the phreatic surface, determination of in-situ gradients, and estimates
of hydraulic conductivities.
In recent years, additional geophysical measurement capabilities have been added to the standard piezocone. These
additions have included seismic pick-ups (geophone or accelerometer) for downhole and/or cross-hole seismic wave
measurements and resistivity modules which can be modified to include induced-polarization measurements. With
these additions, current piezocone technology represents an unparalleled means of accurately, rapidly ti
economically geoenvironmentally characterizing most natural and man-made soil deposits.
This paper introduces traditional piezocone technology and summarizes recent key advances with this geophysical
logging tool. A brief case study is presented to demonstrate the technological and economical advantages of the
piezocone over more traditional site characterization methods.
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Application Of Geophysical Methods To The Detection And Monitoring Of Acid Mine Drainage
More LessThe application of geophysical methods to the detection and monitoring of acid mine drainage is beyond
the experimental stage and is being applied in the management of waste from a number of producing and
abandoned mines. Experimental studies, mainly in North America and Australia, have shown that non-invasive
measurements by airborne, ground and waterborne platforms can be used effectively in recognising and mapping
the movement of acid effluents in and around mine workings. Some methods can only recognise changes in the
first metre or so of the ground surface; others are limited to depths of one to five meters; others are capable
of detecting plumes at depths of several tens or even hundreds of metres. Some methods are qualitative in
nature while others can provide quantitative answers within various degrees of accuracy and reliability. Studies,
mainly sponsored by government agencies, but supported in many cases by industry, are attempting to establish
the effectiveness of a wide variety of methods and techniques, mainly by conducting test surveys and examining
available data in the vicinity of abandoned mines. One of the more ambitious of these studies was carried out
recently in the Sudbury area, Ontario, under the MEND2 program by INCO Exploration and Technical Services
Limited, (Ring, 1994). This study establishes useful parameters for applications of specific techniques in a
specific geological environment. A more comprehensive study (Paterson et al, 1994), was commissioned by
MEND in 1993, and is the basis for following paper. The project involved a review of available literature, an
information survey of users and suppliers, and discussions with experts in a variety of disciplines.
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Seismic Field Investigation At A Subsidence Site In The Anthracite Fields Of Eastern Pennsylvania: Tools To Aid Multiple Phases Of Characterization And Remediation
Authors K. Kluger Cohen, M.A. Trevits and J. PweedleThis study used several seismic techniques to aid different phases of a subsidence investigation at an
abandoned coal mine subsidence site in a community located in the anthracite fields of eastern
Pennsylvania. Two surface collapse features, each about 3-5 m (lo-l.5 ft) in diameter, developed on
an athletic field underlain by an abandoned room-and-pillar mine 20 m (60 ft) deep. In a multiphase
investigation, surface seismic techniques were utilized to characterize mine level and overburden
conditions, and to design an effective drilling pattern for the remediation phase. Subsequently,
borehole pressure grouting techniques were used as an abatement procedure to stabilize the ground.
During this phase, borehole seismic techniques were used to further characterize subsurface
conditions as more than 680 stere (890 cubic yards) of grout was injected. The surface seismic study
included walkaway tests followed by a series of common offset lines that traversed the athletic field.
A signal enhancement seismograph, lOO-Hz geophones, and a sledge hammer were used for data
acquisition. The seismic data combined with information from a mine map and several borehole logs
suggested that the athletic field was divided into two zones: the western portion of the field
characterized by open mine voids, and the eastern portion of the field characterized by mine voids
more likely to be ftied with collapsed rubble. Using these results, a drilling pattern was
recommended and more than 20 boreholes were drilled in preparation for the remediation phase.
Borehole logs corroborated the predicted trends. All boreholes that would allow placement of grout
were selected for the grouting operations and the borehole seismic study was conducted concurrently
with grouting. One shot hole and three receiver holes were selected. An air gun served as an energy
source and downhole receivers consisted of 4O-Hz geophones arranged in a triaxial configuration.
Shot-receiver crosshole traveltimes were acquired for selected depths and these were used to
determine crosshole velocity distributions prior to and during injection. Preliminary analyses of the
crosshole data indicated a correlation between high velocities and competent mine overburden. In
contrast, velocities tended to decrease as the mine level was reached. Both the surface seismic and
the crosshole seismic studies provided valuable data and additional subsurface constraints for the
characterization and remediation of this abandoned coal mine site.
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Detection Of Abandoned Mine Hazards On Government Lands Using Geophysical Methods
Authors Ken Hauser and James A. JessopSubsurface hazards are numerous in the United States, and are cause for increasing concern. The number of
hazardous sites related to previous mining activity on public lands is particularly alarming, and Congress has
stated that the problem must be addressed. Specifically, the proclivity of abandoned mine sites on government
lands has created dangerous situations in many of our nation’s National Forests, National Park Lands, and on a
variety of lands overseen by the Department of the Interior. The affects of subsidence due to historical mining
activity can be a long-term economic drain on the limited resources available to maintain roads and trails
through these areas. Catastrophic failure and collapse of the ground above old mine workings carries the
implication of severe health and safety hazards for hikers, bicyclists, horseback riders and recreational vehicle
users. In response to these issues, the U. S. Bureau of Mines has been successful in addressing the problem of
subsurface hazard detection and characterization on public lands using geophysical technologies in several recent
projects. At the Shawnee National Forest in southern Illinois, in addition to creating dangerous conditions for
recreational land users, poorly mapped abandoned tripoli mines pose a potential problem for future logging
operations. Old mine workings have been collapsing in certain areas on the property and introduction of the
heavy equipment associated with logging may be dangerous. An integrated geophysical investigation, including
ground penetrating radar, common offset seismic reflection profiling and magnetic gradient surveying was
implemented in attempts to remotely identify the subsurface workings. At the Prince William Forest Park in
Virginia, speculation regarding both the location and structural integrity of the main shaft of an abandoned
pyrite mine required that some investigation be made. Electrical and magnetic geophysical methods were used
to locate the shaft and to assess shaft conditions.
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