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12th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 14 Mar 1999 - 18 Mar 1999
- Location: Oakland, California, USA
- Published: 14 March 1999
21 - 40 of 108 results
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Integrated Geophysical Investigation Helps Improve A Landfill Closure Design
More LessThis paper describes the geophysical investigation conducted at the Fort Hunter Liggett
(FIX) Landfill in Monterey County, California. The geophysical data were obtained using
a custom survey system that facilitated the simultaneous acquisition of ground penetrating
radar (GPR), electromagnetic (EM), and magnetic (MAG) data. This paper also describes
how the investigation results helped to improve a landfill closure design.
The preliminary closure design concept for the landfill incorporated a standard regulatory
cover constructed over 54 acres - the estimated landfill extent as determined from aerial
photographs. The preliminary design was problematic for a number of reasons, including
its high cost and its impact on plant species protected by county ordinance.
To mitigate these drawbacks, an alternative design concept was developed. Included in
the design work was a geophysical investigation to verify the overall extent of the landfill
and accurately delineate individual refuse trenches within the landfill. GPR EM and MAG
data were obtained simultaneously by towing geophysical sensors from a custom-built
non-metallic trailer.
The investigation determined that the landfill encompassed approximately 36 acres, as
opposed to the 54 acres estimated from the aerial photographs. Eleven large refuse
trenches were delineated, as were several small outlying pockets of debris, including a
cache of buried 55-gallon drums. As a result of the geophysical investigation, the area to
receive cover was significantly decreased, thereby reducing the amount of cover material
required (hence the overall cost), and sparing many of the protected native trees. Potential
on-site borrow sources were also identified.
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Routine Application Of Radar In Underground Mining Applications
Authors Hylton White, Alten du Plessis, Keith Noble and Mike TreloaR & D into in-mine geophysics was initiated by the South African mining industry in the 1980’s when
a need was identified for techniques to routinely delineate geological structures from underground
excavations. Since then ground penetrating radar (GPR) has been established as a routine tool in
underground mining in South Africa for geological structure delineation and roof integrity studies.
Routine underground application of GPR requires reliable ruggedized instrumentation and innovative
survey methodologies. To this end the RockRadar system was developed, which provides excellent
data quality in the harsh confined conditions encountered underground. The system allows for rapid
data acquisition and in-mine data processing and interpretation. GPR is best used as a complementary
tool to in-mine exploration drilling, enabling more complete characterization of sites. GPR is seldom
used as a “blind’ technique where little information is available about the geology ahead of mining.
This strategy has enabled the successful routine underground use of radar while other in-mine
techniques such as radio tomography and in-mine seismics have as yet developed limited routine
implementation. Applications in metamorphic, igneous and sedimentary environments have been
developed. These include ore-body delineation, mapping of faults and intrusives, and delineation of
roof discontinuities. Data will be presented from the gold mines (delineation of ore-body and
faulting), platinum mines (delineation of roof discontinuities and ore-body disruptions), and basemetal
mines (delineation of roof discontinuities).
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Land Streamer: A New System For Highresolution S-Wave Shallow Reflection Surveys
More LessA new field system named “Land Streamer” has been developed and successfully
applied for high-resolution S-wave shallow reflection surveys at the paved areas. The land
streamer is a multi-channel receiver system with a CDP cable and a pair of non-stretchable
textile belts. A total of 48 geophone units are clamped on each belt with 50 cm spacing.
The streamer is 30 m in total length with 23.5 m long active section. It is easily towed by a
vehicle that carries the seismograph or by a few crew members. The system provides us
considerably clean records although each geophone unit of the streamer is indirectly
coupled with paved ground surface through a small baseplate of aluminum 8 cm wide and
11 cm long. Because of its easiness to move the spread, we can accomplish a high
performance of the field work.
A field survey carried out on the sidewalk along a heavy traffic roadway reveals the tool
is quite hardy to the traffic noise. We successfully obtained high-resolution profiles for the
near surface to about 60 m in depth using the land streamer.
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Physical Ultrasonic Modeling Of Rayleigh Wave Field In The Near Vicinity Of An Anisotropic Wave Barrier.
Authors Elizabeth Its, Alexei Anisimov and Vitalii KashkevichSince composite wave barriers were suggested by Biagi et al. (1990), Leung et al. (199(l), Its
and Lee (1993a) to increase the screening efficiency for protection of buildings from groundtransmitted
vibration, several theoretical and experimental studies were conducted to analyze
scattering of surface waves at various models of the barriers. In particular, 3D physical ultrasonic
experiments were carried out (Its, Anisimov, and Lee; 1998) to study Rayleigh wave
scattering at a narrow vertical anisotropic slab embedded between two isotropic blocks. These
experiments were designed to analyze the surface wave in the far-field zone. The experimental
scattering coefficients were compared with the theoretical results obtained by the Green’s
function method (Its and Lee; 1993b, 1994). In this paper we report the results of ultrasonic
experiments which were designed for the near-field zone. The same model of the anisotropic
barrier as in (Its, Anisimov, and Lee; 1998) was used, but the profiles were shot in a wavelength
vicinity as well as inside the slab.
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A Shallow Marine Seismic Reflection Survey In Suisun Bay
Authors Zhuping Liu, James W. Rector and Patrick Williams23 shallow marine seismic reflection profiles were collected in Suisun Bay, CA, to help
characterize the shallow faults associated with the earthquakes occurred in California during the
past 40 years. We analyzed the noises in these shallow marine seismic reflection data, and applied a
series of traditional seismic data processing techniques to improve the S/N ratio. Due to the low
fold of the reflection data, we constructed analogue single-channel marine reflection profiles,
sorted them to CMP domain and stacked the data, which proves to be an effective way in showing
shallow structures.
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Seismic Refraction Case Studies At Environmental Sites
Authors Craig Murray, Dean Keiswetter and Edward RostoskySeismic refraction was used to investigate two sites with groundwater contamination.
Although seismic refraction is not a viable technique for directly locating the
contaminants, it can provide very useful geologic information. The ground water at both
of these sites is contaminated with dense, non-aqueous phase liquids (DNAPL) that sink
through the groundwater until reaching an aquitard, a geologic layer that is relatively
impermeable. Seismic refraction was used on both of these sites to map the surface of
the aquitard and locate low areas in which DNAPLs might accumulate. Tricloroethene
contamination is present in the groundwater of a military installation located in a karst,
limestone setting. Fractures and solution cavities in the limestone dominate the
hydrogeology. The surface of the limestone is quite uneven as a result of dissolution and
glacial action. We collected detailed seismic refraction data in the region surrounding the
source to map the elevation of the limestone and locate low areas where the DNAPLs
might collect. The velocities of the limestone were also useful for indicating where the
most intense dissolution had created fractures and cavities. A mixture of several
DNAPLs contaminated the groundwater at the second site. There are no consolidated
sediments within 100 feet of the surface, but a very dense unconsolidated aquitard
separates the contaminated sand and gravel aquifer and the lower, clean aquifer used for
groundwater supply. Several techniques, ground probing radar, resistivity and seismic
refraction were used on this site, but seismic refraction was the most effective at locating
low spots in the clay layer. The seismic refraction data also revealed several areas with
very coarse-grained gravel that could serve as pathways for contamination to leave the
site.
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Recovering Of Scattering Objects By Means Of Focusing Transformation Of Seismic Multioffset Data
More LessFocusing transformations of multi-offset data is a powerful tool to study complex
media (trapp intrusion, complicated upper part of a cross-section, thin interior layers
and so on). Its main advantage is a possibility to perform focusing simultaneously
with respect to sources and geophones and on this base to strength spatial structures
with specific disposition. But the choice of their optimal parameters (number of
sources and geophones, distance between centers of their bases, a degree of nonsymmetry
and so on) for a specific geological situation is rather bulky procedure.
The method to perform this choice by means of synthetic data gained with the
help of finite difference simulation of wave propagation for realistic models is proposed
and tested. The necessary condition to provide efficiency of the method is to
take into account all specific features of the specific process of wave propagation.
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High-Resolution, Multichannel, Marine Seismic Surveying Using A Small Airgun Source
Authors A. Pugin, S.E. Pullan, R.A. Burns, M. Douma and R.L. GoodA high-resolution, multichannel, CMP, marine seismic reflection survey was carried out in Lake
Simcoe, southern Ontario, Canada, in June 1998, to examine large channel features within the glacial
sediments beneath the lake bottom. Over 300 line-kilometers were obtained at close line spacings
with an oil-filled hydrophone receiver array and a 1 cu. in. airgun fired accurately at 5 meter
horizontal intervals. Firing on distance was accomplished by integrating a real-time DGPS
(Differential Global Positioning System) and a computer-driven triggering system which adjusts the
firing rate depending on the ship’s velocity. The survey was conducted with an average boat speed
of approximately 4 knots (7 km/hour), and multichannel records were recorded on a Geometrics R-
24 seismograph at 2.2-3 second intervals.
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Tests Of Shallow-Penetrating Em Systems Over An Underground Bunker
Authors David L. Campbell and J. Christopher EckhartWe compared three shallow-penetrating EM systems by making surveys along identical
grids over a 1940s-era, abandoned, buried bunker (?) at the Denver Federal Center. These
systems were the Geophex GEM-2, GSSI GEM-300, and Geonics EM3 1. All three systems
detected certain objects, including likely foundations for large tanks, possible underground
openings, and present-day electric light poles. A feature of particular interest was a long, narrow
anomaly that we think may reflect a buried cement wall. This wall shows up on the quadrature
(or quadrature-phase, q-p) component as a relative high at low frequencies and as a relative low
at high frequencies. At intermediate frequencies it was invisible on the q-p component. In
particular, this includes 9.8 kHz, the operating frequency of the EM3 1. Although the EM3 1 did
pick up indications of the wall on its in-phase (i-p) component, the strong signatures of the many
bunker features drove its i-p values off scale over much of the survey area, so that they were
relatively less useful than the i-p maps from the other two systems. An advantage of the GEM-2
and GEM-300 instruments, therefore, is that they can be used to sweep a range of frequencies
and more clearly detect features such as the (cement block without rebar?) bunker wall. A
disadvantage, however, is that neither GEM-2 nor GEM-300 appear to be well calibrated.
Conductivity values from interpretations of their multifrequency data sets, made using a standard
EM modeling program, seemed unreasonable. We conclude that the programmable
multifrequency systems, such as GEM-2 and GEM-300, have an advantage for reconnaissance of
certain archaeological sites, but that better-calibrated systems like the EM3 1 should be used
where it is important to know true conductivity values, as in studies of geology, water resources,
or ore deposits.
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Gravity In Cave Exploration
Authors Mary Krasovec and Frank Dale MorganA new method for the inversion of gravity data is introduced which is applicable to
regions with a limited number of allowable density values, such as uniform density bodies
set in a contrasting background. The method relies on geometrical constraints, such as
compactness, size, or shape of the anomalous body or bodies. A gridded forward model
is used to separate the geometry of the model from the density by dividing the earth into
regular prisms. Each prism is allowed only a limited number of density values: in this
case the density can be the background rock density or the cave density of 0. The prisms
are chosen to increase in size with depth in order to realistically model structures which
can be resolved with gravity data.
In this application, a genetic algorithm is used to find the best configuration of zero
density prisms to fit the data and is subject to geometrical constraints as mentioned
above. The method is described and tested on 2D synthetic models, then applied to
gravity data collected at the Indian Echo Caverns in Hershey, Pennsylvania.
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Detection Of Near-Surface Voids Using Surface Wave
Authors Choon Byong Park, Richard D. Miller and Jianghai XiaGround roll is displayed, on an uncorrelated field record obtained using a monotonic
sweep, in increasing or decreasing order of frequency with each frequency well separated from
all others. Phase velocity and attenuation characteristics of each frequency contain the average
elastic property of near-surface materials down to approximately half the wavelength.
Uncorrelated field record, therefore, by itself can be associated with a two-dimensional display
of the change in near-surface elastic property. Through the redundancy in data acquisition and
a simple data processing step, the uncorrelated field records can be transformed into a stacked
section that can be correlated directly to image of the change in elastic property of near-surface
materials with respect to a certain reference location. This method can be effectively used to
detect near-surface anomalies of various kinds.
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Cave Detection Using Gpr
Authors Philip M. Reppert, Yervant Vichabian, John Sogade and Frank Dale MorganThis presentation demonstrates a new method for the detection of caves. The method is
based on using instantaneous frequency and instantaneous amplitude. The results
indicate that the new methodology can accurately detect caves at great depth and with
varying geometry.
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A Case Study Of The Use Of Multi-Electrode Earth Resistivity In Thinly Mantled Karst
Authors M.J.S. Roth, J.R. Mackey and J.E. NyquistSinkhole formation in many areas of the northeast United States occurs in clay soils over
relatively shallow (methods of site investigation have a low probability of encountering subsurface karst features
that are associated with future sinkhole formation. Non-intrusive methods such as ground
penetrating radar and electromagnetic methods have only limited applicability, and there are
difficulties associated with their interpretation. This paper details a case study of the use of earth
resistivity equipment with multiple electrodes to investigate a site in eastern Pennsylvania. Site
geology, selection of resistivity line orientation, data interpretation, and comparison of results
with intrusive borings are discussed. Recommendations for site investigations in thinly mantled
karst are given.
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Resistivity In Cave Exploration
Authors Frank Dale Morgan, Weiqun Shi, Yervant Vichabian, John Sogade and William RodiSimple d.c. resistivity and profiling have been used in the past for cave mapping. One can
also attempt to obtain an inversion tomogram using a pseudo-section type gatherer. In
this presentation we will demonstrate that the pseudo-section method can be inadequate
and leads to very poor imaging accuracy, unless the desired target is in the center region
of the survey.
A new, more comprehensive method of obtaining the data will be presented. The method
is tested using examples from Harrison’s Caves, Barbados, West Indies and Indian Echo
Caverns, Pennsylvania. The technique can also be applied to accurate imaging of tunnels
and underground structures.
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Electromagnetic Cave-To-Surface Mapping System
Authors John Sogade, Yervant Vichabian, Amy Vandiver, Philip Reppert and Frank Dale MorganThe principle, design, and construction of an instrument for remote location of position
and depth of a transmitter in a cave will be presented. Two people can use the system to
map a cave location on the ground surface. The instrument consists of an EM dipole
transmitter/receiver configuration. The vertical component of the transmitted field reaches
a maximum at the point where the transmitter and receiver are vertically collinear. At this
position the horizontal component of the field reaches a minimum. A survey procedure is
developed and tested to efficiently locate this position.
Results of calibration work done at MIT and a field test of the system at Indian Echo
Caverns, in Hershey, Pennsylvania are presented. We were able to verify theoretical
results with the calibrations. The system was subsequently able to successfully map the
cave system at Indian Echo Caverns.
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Induced Polarization In The Detection Of Cave Systems
Authors John Sogade, Yervant Vichabian and Frank Dale Morgan2D Induced Polarization (IP) surveys were carried out across a protile extending over the
North Canyon of the Indian Echo Caverns in Hershey, Pennsylvania . In this
presentation, we show the resulting images from inverted IP data. We expect zero
chargeabilities in the areas which correspond to the cavity/void (air) and relatively higher
chargeabilities in the areas which correspond to the surrounding water saturated rocks.
The resulting contrast provides the mechanism for detection of cave systems. The data
was inverted using a robust 2D IP modeling/inversion code.
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Self Potentials In Cave Detection
Authors Yervant Vichabian and Frank Dale MorganIn this presentation, we show an example of the use of self potential geophysics to locate
caves or voids. We develop a simple model of water flow where a cavity is a preferential
drainage path generating streaming potentials above the local groundwater flow. Two
temporal data sets with the same positions were collected at the Indian Echo Caverns
located in Hershey, Pennsylvania. One was in dry conditions and the second, one year
later, with the ground saturated with rainfall. The data was gathered using the gradient
method and later processed by integration. The data set in the dry conditions shows a
single anomaly located over a known cave location and the data set in the wet conditions
has several anomalies. Both sets show groundwater flow feeding into a nearby river.
The differences of the two data sets are due to the change in resistivity of the soil caused
by rainwater and the enhancement of very near surface infiltration paths of rainwater.
We show that SP can be used for cave detection under the proper conditions.
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Defining The Bedrock/Overburden Boundary In Covered Karst Terranes Using Dipole-Dipole Electrical Resistivity Tomography
Authors Wanfang Zhou, Barry F. Beck and J. Brad StephensonSinkhole collapse is one of the main limitations on the development of karst areas, especially
where bedrock is covered by unconsolidated material. Studies of sinkhole formation have shown
thatsinkholes are likely to develop in cutter zones as a result of subterranean erosion by flowing
groundwater. Because of the irregular distribution of pinnacles and cutters on the bedrock
surface, uncertainties arise when “hit-or-miss” borehole drilling is used to locate potential
collapse sites. A high-resolution geophysical technique capable of depicting the details of the
bedrock surface is essential for guiding the drilling program.
Dipole-dipole electrical resistivity tomography (ERT) was used to map the bedrock surface at a
site in southern Indiana where limestone is covered by about 9 m (meters) of clayey soils.
Forty-nine transects were conducted over an area of approximately 42,037 m2. The electrode
spacing was 3 m. The length of the transects varied from 81 to 249 m. The tomographs were
interpreted with the aid of soil borings. The repeatability of ERT was evaluated by comparing the
rock surface elevations interpreted from pairs of transects where they crossed each other. The
average difference was 2.4 m, with a maximum of 10 m.
The discrepancy between interpreted bedrock-surface elevations for a transect intersection may
be caused by variations in the subsurface geology normal to the transect. Averaging the elevation
data interpreted from different transects improved the ERT results. A bedrock surface map was
generated using only the averaged elevation data at the transect junctions. The accuracy of the
map was further evaluated using data from four exploratory boreholes. The average difference
between interpreted and actual bedrock surface elevations was less than 0.4 m. The map shows
two large troughs in the limestone surface: one coinciding with an existing sinkhole basin, while
the other is in alignment with a small topographic valley. Because sinkholes were observed at
the same elevation interval in similar valleys in the vicinity, the delineated trough may have
implications for future land use at the site.
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Electrical Resistance Tomography Of Unsaturated Flow And Transport In Yucca Mountain
Authors Michael Buettner, William Daily, Abe Ramirez and Gilles BussodElectrical Resistance Tomography (ERT), a new geophysical imaging technique, was used to study
the movement of a tracer through the test block at the Unsaturated Zone Transport Test (UZTT) at
Busted Butte, Nevada. Data were collected four times starting in July and ending in early
September, 1998. ERT baseline images show a resistivity structure which is consistent with the
known lithology in the rear part of the test block. There appears to be a low resistivity region in
the front half of the block, particularly near the bottom. Difference images from August 19 and
September 9 show clear and consistent resistivity decreases in the region near injection holes 18,
20, and 21 which can be associated with the injection of conductive water. The images show very
little effect in the region around the other injection holes, 23, and 24 through 27 where far less
water was injected. Difference images from August 19 and September 9 show resistivity decreases
which could be interpreted as water moving down into the block. This is the same region which
has an anomalously low resistivity in the baseline image. These results should be considered
preliminary, and are subject to further interpretation.
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Variability Of Electrical Resistivity At The Rice Creek Field Station, Oswego, New York: Implications For The Distribution Of Groundwater
Authors Samuel T. Peavy and David W. ValentinoElectrical resistivity measurements were made to determine the variability of surficial
deposits, the depth to bedrock and to characterize the distribution of groundwater at the Rice
Creek Field Station near Oswego, New York. The field station is underlain by drumlin deposits
and ablation till associated with Pleistocene glaciation. These deposits reside on Ordovician
quartz sandstone of the Oswego Formation that outcrops within 1500 m of the study site.
Locally the Oswego Formation contains subvertical fractures with an average spacing of less than
0.5 m. Twenty offset Wenner electrical resistivity surveys were conducted in June and August of
1998 along trails and across an open field within the field station grounds. Analysis of
pseudosections and simple 1-D modeling and 2-D least squares inversion indicate the following:
1) low resistivity zones associated with perched water tables within the chaotic drumlin deposits;
2) highly variable and resistive near-surface measurements along Rice Creek indicative of large
(>l m diameter) glacial erratics as observed in the creek bed; 3) a transitional zone below -250 ft
elevation of subcircular highs separated by relatively low resistivities that continue into the
deepest portions of the data, which is coincident with the projected depth to bedrock beneath the
field station and is interpreted to be an undersaturated zone within the fractured Oswego
Sandstone; and 4) low resistivities below an elevation of - 190 ft are interpreted to be the top of
the saturated domain within the fractured bedrock.
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