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18th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 03 Apr 2005 - 07 Apr 2005
- Location: Atlanta, Georgia, USA
- Published: 03 April 2005
51 - 100 of 146 results
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Soil Composition Determination Based on Soil Optical Properties In The Thermal Infrared
Authors J. Michael Cathcart and Robert D. BockCurrent research into the use of electro-optical sensing modalities for the detection of landmines and other objects in complex backgrounds has led to the need to understand the optical properties of background materials (e.g., soils) in more detail. In particular, the use of spectral and polarimetric signatures in the optical and infrared domains has been the subject of much study; an understanding of soil, foliage, and other background optical properties and their variations is critical to evaluating the utility of these signatures. Our research examined both soil polarimetric signatures and emissive characteristics in the context of a real world environment; specifically, we examined the infrared spectral and polarimetric properties of soil components within the complex natural radiative environment. A modified Hapke radiative transfer model was employed to compute these properties. This paper will present a brief overview of this computational model and results from the optical property calculations for several mineral types and soil compositions. In a parallel study, hyperspectral data of soils were analyzed and compared to evaluate the influence of local environmental conditions on soil spectral features. The results of this study will also be presented and compared to the modeling computations.
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Frequency Domain Analyses of TDR Waveforms for Soil Moisture Measurements
Authors Chih-Ping Lin, Chung-Chih Chung and Shih-Hung TangWhen time domain reflectometry (TDR) is applied to the field characterization of soil moisture, the waveforms have typically been analyzed using traveltime along the waveguide. The apparent dielectric constant traditionally determined by the traveltime analysis using a tangent-line method does not have a clear physical meaning and is influenced by several system and material parameters. The frequency domain analysis, however, can determine the actual frequency-dependent dielectric permittivity and can be performed using a very short probe. This study presents a numerical modeling approach for common unmatched TDR probes to analyze the TDR signals in the frequency domain. This approach is also adopted to examine how dielectric relaxation, and electrical conductivity affect traveltime analysis. Simulation results indicated that, although the effects of TDR bandwidth and probe length could be quantified and calibrated, the calibration equation for soil moisture measurements was still affected by dielectric relaxation and electrical conductivity, due to differences in soil texture and density. The effects of density can be removed by adding a density term to the calibration equation. Correlating with water content the dielectric permittivity at frequencies between 500 MHz and 1 GHz, rather than the apparent dielectric constant, can minimize the influence of soil texture.
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A New Approach for Real Time Pipe Locating
More LessA new method of detecting and following pipes has been developed that should facilitate efforts to track and locate natural gas leaks. This ground penetrating radar (GPR) tool is deployed like a metal detector; the user swings a 400 MHz antenna back and forth over the ground. The data are then reduced and processed in real-time to automatically display the location and depth of targets found along the arc. Swinging the device around the body guarantees that any pipe crossing the arc will produce a “hyperbolic” shape in the data. This shape is then recognized and displayed in real time according to recognition confidence, depth and X,Y GPS position. The advantages of mapping pipe (metal, PVC, clay) are clear. But perhaps the more intriguing application has to do with locating gas leaks. As one follows a gas pipe along its course, GPR has demonstrated the ability to detect gas leaks by sensing changes in the surrounding soils. This means GPR can detect the leak site rather than the surface exit point of the gas. Our goal is to map these subtle changes in soil properties in real-time, offering a new method for constraining, and hopefully pinpointing, natural gas leaks.
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Statistical Comparison of Models for Soil Dielectric Spectrum
Authors X. Yu, V.P. Drnevich and R.L. NowackDielectric spectra have been widely explored to obtain information about material structural characteristics and physical constituents. As a mixture of three phases (cohesionless soil) or four phases (cohesive soil with significant amount of bound water), soil dielectric behavior is complicated by the phase interactions. Understanding the soil dielectric behavior is the prerequisite for application of technologies such as active remote sensing, ground penetration radar, Time Domain Spectroscopy, and other electromagnetic wave technologies for soils. The soil dielectric spectrum can be measured in the frequency domain, using a Network Analyzer or in the time domain by model-based inversion of recorded electromagnetic time signal. The model-based inversion is advantageous in that it is fast and the spectrum is less influenced by the presence of signal noise at individual frequencies. This paper evaluates the performance of several commonly used models for soil dielectric spectrum, including Debye’s model, Cole-Cole’s model, a power-law type volumetric mixing model, and a simplified model based on the concept of apparent dielectric constant. The model parameters were obtained from inversion analysis of TDR (Time Domain Reflectometry) measurements on soils. The performances of individual models are compared using statistical analysis of residuals. The analyses indicate that there is no significant difference between the capability of Debye’s model and Cole-Cole’s model for describing soil dielectric behavior, which possibly indicates that there are no pronounced distributive relaxation mechanisms inside the measured soil mixtures. While the volumetric mixing model better describes the trend of actual soil dielectric spectrum, it also causes increased non-uniqueness in the inversion process. The simplified model, although it could not fully characterize the soil dielectric spectrum, provides robust indication of soil dielectric behaviors within the TDR measurement range. The relative merits and shortcomings of each individual model are discussed in this paper.
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Hydraulic Conductivity Estimation From Spectral Induced Polarisation Data – A Case History
Authors Andreas Hördt, Roland Blaschek, Andreas Kemna, Julia Suckut and Norbert ZisserWe carried out a spectral induced polarisation (SIP) survey at the Krauthausen hydrogeological test site in Germany. Multifrequency data were recorded along two profiles, and single frequency data along ten densely-spaced profiles with a dipole-dipole configuration and 2 m electrode spacing. The data were inverted with a 2-D inversion code to obtain images of resistivity and phase distribution for each frequency. We used a focusing regularisation scheme that does not suppress sharp boundaries and yields realistic images of the subsurface. From the complex conductivity distribution we calculated the hydraulic conductivity using different empirical equations. The results obtained with the constant phase angle model are encouraging in the sense that the hydraulic conductivities have the same order of magnitude as those determined from grain size analyses. The gross structural features compare well with the known lithology,
which consists of an aquifer over an impermeable clay layer at approx. 10 m depth.
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An Interpretation of Various Well Logs Acquired In Unconsolidated Soil for Hydraulic Property Estimation
Authors Chisato Konishi and Genyuu KobayashiIn order to obtain some parameters for hydraulic property estimation, we carried out various well loggings, including velocity (Vp, Vs), electric, induction, IP, density, natural gamma, water conductivity, and temperature. This time, we considered a simple sand-clay model and tried to estimate its hydraulic conductivity from well logs. In this process, we recognized that the grain size or pore size crucially affects hydraulic conductivity if we calculate it from porosity by such kind of Kozeny-Carman equation. Although the natural gamma log is commonly used for discriminating sand and silt formations, we could not use it, because not all part of high gamma zone of the well corresponded to clay rich zone. Therefore, we examined a possibility of discriminating sand and clay by fuzzy clustering techniques (Imamura and Nakayama, 1997). The computed soil classification by fuzzy clustering using following three logs: conductivity, P-velocity, and density, showed good agreement with the soils determined by core observation. Among these three logs, we tried to apply conductivity log as an indicator of content of small particles. Using the conductivity log, we calculated pseudo clay content log and average grain size of sand-clay mixture. The calculated average grain size and porosity were substituted to Kozeny-Carman equation, and then hydraulic conductivity could be estimated. The estimated hydraulic conductivity was consistent with that measured by slug test and EKL deeper than 50m depth.
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2-D Resistivity Imaging and Determination of Hydraulic Parameters of The Vadose Zone In A Cultivated Land In Southwestern Nigeria
Authors Abel I. Olayinka and Michael A. OladunjoyeA combined 2-D resistivity imaging survey and determination of hydraulic parameters of the vadose zone in a seasonally-flooded part of southwestern Nigeria that has been cultivated for the past 18 years is presented. The survey area is about 22 000m2 (2.2 ha) with the bedrock geology comprising Pre-Cambrian granite gneiss. Imaging data were measured along 11 lines, with a minimum inter-electrode spacing of 1 m; control data were obtained along two lines nearby. Soil samples were collected from 30 shallow pits at depths of 0.5, 1.0 and 1.5 m, respectively. The resistivity of the near-surface sandy-clay lithology is low at less than 50 Ωm while that at the control site is much higher. The natural moisture content ranges between 3.3 and 27.4% with a mean of 12.2%; porosity ranges between 9.9 and 36.8%, with a mean of 14.4%. The coefficient of permeability ranges between 9.61x10-7 and 1.01x10-5 cm sec-1. The study has shown that
changes in electrical properties of the soil could be due to variations in moisture content and that there is a close relationship between the sandy clay lithology and the recharge. Moreover, the soil could constitute an environmental problem at the peak of the rainy season.
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Evaluation of Mine Seals Using Ground Penetrating Radar
Authors William D. Monaghan, Michael A. Trevits and Michael J. SapkoMine seals are used extensively in underground coal mines to segregate mined-out areas and to isolate fire zones or underground areas that are susceptible to spontaneous combustion. Over the years, 30,000 mine seals have been erected in underground coal mines in the United States. Mine seals, along with rock dusting and ventilation, represent the fundamental means of preventing underground coal mine explosions. In this study the National Institute for Occupational Safety and Health (NIOSH) used ground penetrating radar (GPR) technology to determine if each of three test mine seals were uniformly constructed. Three mine seals representing different construction methods and materials (cast-in-place foamed cement; solid block, polyurethane foam and gravel; and wire mesh, rebar and gunite) were erected at the NIOSH Lake Lynn Laboratory’s underground mine as part of an on-going research program. The seals were imaged using GPR with 400-, 500-, 900-, and 1,000-MHz antennas. We found that variations in uniformity existed in the material for the cast-in-place foamed cement seal. Variations in uniformity also existed in the seal made from solid block, polyurethane foam and gravel. The postprocessed radar records correlated closely with recovered core samples (areas of gravel and polyurethane foam, and areas containing only polyurethane foam). Finally, the radar records of the seal made of wire mesh, rebar and gunite showed the various components. The results of this work suggest that GPR could be used as a tool to evaluate mine seal characteristics and construction uniformity.
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Electrical Imaging of Deep Clay-Mine Voids
More LessIn the late 1890s through the 1920s, deep mining of a local clay bed beneath 35 to 50 feet of Pennsylvanian-aged rock resulted in mine voids in the St. Marys, Pennsylvania area. Recently, long subsidence troughs have been noted locally in this area. The history of the deep mining has been all but lost to the local residents; however, recent mine maps show that deep mining has occurred near these residents. Shallow-focused continuous vertical electric sounding profiles imaged subsurface haulways and rooms. Inverted measured apparent resistivity values indicate areas of subsurface voids presumable saturated. The deep mine map prepared in the 1920s shows an excellent correlation between the electrical imaging prediction of voids and the mapped voids.
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Electrical Properties of Leach Ore, Cripple Creek Mining District, Colorado
Authors Gary W. Horton and Will FrangosThe Cripple Creek and Victor Gold Mining Company in Victor, Colorado is a leading gold producer in North America. The mine is an open pit/heap leach recovery facility where the ore is placed in an unconsolidated pile and treated with a dilute cyanide solution. The pregnant solution is then pumped to an adsorption facility for gold extraction. Annual recoveries of gold reach 365,000 oz/yr at a mine cutoff of 0.018 opt. The project investigated 1) saturation characteristics within the heap itself through the use of a series of Schlumberger soundings at locations with different solution saturation (e.g., fresh ore with no solution as opposed to fully leached rock), and 2) laboratory induced polarization spectra of ore samples to determine electrical properties that may characterize saturation conditions. Spectral induced polarization electrical frequencies used were from 0.01 to 500 Hz. If there were a characteristic difference in the electrical properties of saturated vs. unsaturated ores then these differences could be detected by surface measurements, revealing subsurface regions of under-saturation and insufficient leaching. Findings indicate the competent, low-sulfide rock is highly resistive and has very low IP response. Conclusions that could be drawn from the Schlumberger arrays on the heap showed that subtle variations in bulk resistivity could be differentiated using a vertical electrical sounding (VES) program in addition to conventional log/log plots. Results of resistivity and induced polarization measurements on individual samples exhibit wide variation in resistivity, but when normalized to 1Hz all samples regardless of mineralogical composition showed little variation. With respect to IP effect little variation existed but more study needs to be performed to determine the dominant mechanism (ionic or electrode polarization). Column tests showed distinct differences in resistivities based on whether the ore was non-leached (fresh) or leached which is consistent with heap characteristics described by the Schlumberger soundings. IP effect was consistent with field result also. An important conclusion that can be drawn from the column tests is that it is possible to replicate field conditions in the laboratory.
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Internal Structure and Preferential Flow of A Waste Rock Pile From Geophysical Surveys
Authors Michel Chouteau, Jérôme Poisson, Michel Aubertin and Daniel CamposThe authors have carried out a geophysical investigation on a waste rock pile at the Laronde gold mine (Agnico-Eagle Ltd, Quebec). GPR, low-induction number EM and 2D resistivity tomography measurements have been conducted during consecutive field surveys in 2002 and 2003 on top of the pile to map its internal structure. Repeated infiltration tests and geophysical monitoring from ground surface have also been performed to map preferential flow paths. Using the field data, the authors propose here a three-layer model for the first 5-6 m of the pile, mainly based on electrical conductivities. Electrical conductivity increases with the degree of oxidation of the sulphidic minerals contained in the waste rock. The contact between unoxidized-oxidized waste rocks is typically marked by a well-defined resistive-conductive boundary, as shown by digging a 2.5 m-deep trench. Integration of geophysical and hydrogeological information indicates that there is a lateral conductivity variation, which may be due to the deposition method, mechanical alteration caused by machinery, and by increased oxidation of sulphides near the external boundary of the pile. GPR monitoring during infiltration tests seems to indicate preferential flow paths towards a zone of low sulphide content materials and low oxidation by products. The resistivity and GPR methods appear to be efficient geophysical methods to characterize the internal structure of the Laronde waste rock pile.
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Spectral Induced Polarization (SIP) Measurements for Stability Assessment of Tailings Dams
Authors Ernst Niederleithinger, Sabine Kruschwitz and Matthias BehrensTailings dams pose major risks to human life and the environment. The often poor construction and low maintenance level has caused serious accidents in both developed and developing countries. The EC funded project TAILSAFE is aimed to find ways for better investigation, stabilization and management of these facilities. Geophysical methods play an increasing role in the investigation of tailing dams. But the interpretation of the results and the translation into something useful for the engineers is often difficult. Thus several geophysical techniques have been tested at tailing dams in Germany, Hungary and Romania. The focus was on detecting structures in the dams and determining the water level. The measurements are accompanied by sampling and lab investigations. The focus of the paper is on the use of the SIP technique.
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Using Helicopter Electromagnetic Surveys To Identify Potential Hazards at Coal Waste Impoundments
More LessIn July 2003, the National Technology Transfer Center contracted with Fugro Airborne Surveys
to perform helicopter electromagnetic surveys of 14 coal waste impoundments in southern West
Virginia. The purpose of these surveys was to detect conditions that may lead to impoundment failure
either by structural failure of the embankment or by the flooding of adjacent or underlying mine works.
Specifically, the surveys attempted to: 1) identify saturated zones within the coal waste, 2) delineate the
paths of filtrate flow through the embankment and into adjacent strata or receiving streams, and 3)
identify flooded mine workings underlying or adjacent to the waste impoundment. In-phase and
quadrature data from the helicopter surveys were inverted using EM1DFM software to generate
conductivity/depth images. Conductivity/depth images were then spatially linked to georeferenced air
photos or topographic maps for interpretation. Preliminary analysis of the data indicates that helicopter
electromagnetic surveys can provide a picture of the hydrologic conditions that exist within the
impoundment. However, results from the helicopter electromagnetic surveys must be corroborated with
data from other sources to accurately assess the potential for impoundment failure or the potential for
filtrate from the impoundment to contaminate local streams and aquifers.
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Efficient Large-Scale Utility Mapping With Radar and Induction Arrays
Authors Michael Oristaglio, Ralf Birken, Thorkild Hansen, Ross Deming, Scott MacIntosh and Qifu ZhuA project sponsored by the United States Department of Transportation (U.S. DOT) has developed a new mobile geophysical system combining an array of broadband electromagnetic
induction (EMI) sensors with an array of ultra-wideband ground-penetrating radar (GPR) antennas. This “dual-array system” was designed for mapping underground utility networks efficiently over large areas, but can also be useful in environmental surveying for applications such as leak detection and hazardous waste monitoring. The project was part of the Pipeline Safety Research and Development Program1 of the U.S. DOT Research and Special Programs Administration. Several utility companies, including Consolidated Edison Company of New York and Regional Water Authority of South Central Connecticut, participated in the project. The EMI array consists of 16 vector magnetometers (induction coils) with a flat frequency response from about 1 to 100 kHz. Signals from each sensor are recorded and digitized as time series, with a sampling rate of 1 MHz. The EMI sensors are arranged in two linear arrays, each consisting of 8 sensors with a spacing of 30 cm; the arrays are offset vertically by about 50 cm. The system works with two types of transmitters: “clamp-on” transmitters which can inject current at discrete frequencies onto individual pipes (by galvanic or toroidal clamps) and a 3-axis induction coil which rides “on-board” with the transmitters and operates over the same frequency range as the sensors. The GPR array, which is based on the commercial CART Imaging System (Birken et al., 2002), consists of 17 antenna elements in an arrangement that creates 16 independent radar channels (transmitter-receiver pairs). The GPR array system has two antenna sets: one set has a central frequency of about 200 MHz and a channel spacing of about 14 cm; the other, a central frequency of 400 MHz and a spacing of 8 cm. The positioning system is designed to allow surveying in arbitrary patterns. Each array is mounted on a trailer whose position is monitored by a laser surveying instrument as the array moves over the survey area. Special algorithms merge data from different passes of each array to create a regular data grid. The radar data are imaged into a 3D volume using standard synthetic-aperture seismic imaging techniques adapted for GPR. The EMI data are inverted using a parametric model that assumes currents in the subsurface flow mainly along a network of (possibly interconnected) pipes. Two large surveys have been conducted with the dual-array system. One survey in the spring of 2004 successfully mapped a complex network of subsurface water, electrical, gas and telecommunication lines in Connecticut for a local water utility company. This survey covered over 2000 sq m with radar traces on a 10 cm grid and EMI data on a 30 cm grid. A second survey done in the summer of 2004 mapped electrical lines emerging from an electrical substation in New York. 1The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the RSPA or the U.S. Government.
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Voodoo Methods: Dealing With The Dark Side of Geophysics
By Greg HodgesThe exploration industry has been plagued since the dawn of technology with near-magical oil,
gold and waterfinders. They do untold damage to the reputation and business of honest geophysical
applications and research. A geophysicist with sound scientific knowledge can usually recognize when
geophysics is "from the dark side", but it can be difficult to convince non-scientists. Exposing the
voodoo methods can be a complex and expensive nightmare of politics, marketing, and litigation.
Some common characteristics of voodoo geophysical methods are: dubious theoretical bases,
fantastic levels of instrument sensitivity, phenomenally accurate interpretations, extraordinary levels of
secrecy, and combative or evasive response to challenges. The evaluator should also determine whether
the questionable method is the product of over-zealous marketing, misguided science, or fraud.
Funding agencies and corporations must insist on assessment and approval by technical experts
before investing in a new system. The technical investigators must be open-minded, but rigorous. The
tests must be definitive, and the testers must have the right to publish results. Fraudulent methods shy
away from technical testing and publication, and refusal of the purveyor of a new system to comply with
evaluation and publication of results must be viewed with the greatest suspicion.
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Human-Sensed Fields: Does Dowsing Response Correlate With-Self Potential Or Conductivity Anomalies?
Authors Charles T. Young and James TrowDowsing is the use of metal rods, forked sticks, pendulums, etc to locate minerals, water, pipes
etc. Dowsing has been practiced for centuries and in various world cultures, and there are abundant
reports of dowsing success in the non-scientific, popular literature. The natural question arises whether
the dowsing response correlates with any geophysical measurement such as self potential or
electromagnetic response. The dowsing reported here uses U-shaped bent metal rods carried along a
survey line. Both authors have found that the rods move in their hands. We report dowsing responses for
the two authors and compare these responses with self-potential and electromagnetic response across a
folded graphitic slate body and across metallic copper deposits, both in Michigan’s Upper Peninsula.
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Smoke Without Mirrors: A New Tool for The Geophysical Characterization of Shallow Karst Cavities
Authors Jonathan E. Nyquist, Mary J.S. Roth, Sandra Henning, Ron Manney and John PeakeWe are involved in a multi-year study to evaluate electrical resistivity as a tool to characterize
thinly-mantled karst. Guided by the results of a multielectrode resistivity survey, we drilled into a cave
7m below the surface. While mapping the cave's dimensions, triangulating using laser pointers and a
downhole camera, we observed a snake crossing the floor of the cave. Hypothesizing that one or more
animal burrows must intersect the karst network, we purchased a Hurco Technologies, Inc., Power
Smoker II, designed for smoke testing plumbing systems for leak detection. It is a 2.5 hp Honda Motor
modified to heat and blow Hurco's LiquiSmoke into plumbing systems. We injected non-toxic smoke at
a rate of approximately 700 cfs, but did not discover an animal burrow. After about half an hour,
however, we noticed puffs of smoke coming up through the grass about 30 ft from the borehole along a
straight line about 10 ft long. Comparison with the resistivity data shows that the smoke emerged downstrike
from the borehole along the same limestone ridge as the cave. We conclude that "leak-testing"
with non-toxic smoke may prove to be an effective complement to geophysical investigations of karst.
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Application of 2D-Ert In Feasibility Study of Hydropower Projects In Nepal
More LessIn Nepal seismic refraction is the traditional method of subsurface exploration for geotechnical
applications. Until the mid-90s seismic refraction was routinely used to investigate proposed sites for
hydropower projects of Nepal. These areas lie in the mountain and are inaccessible for vehicular
transportation. Very high heterogeneity of surface material creates poor energy coupling for both source
and receiver. Because of the high-energy content and easy transportability, explosives were the preferred
source for the generation of seismic waves.
Due to the rebel activities in the recent years, however, the government has tightened regulations
on transporting and using explosives. This situation has forced the hydropower projects to search for
alternative geophysical methods in place of seismic refraction. Electrical resistivity tomography (ERT)
was selected as a possible replacement method. In the initial stage of the application of ERT, various
electrode arrays and data acquisition approaches were evaluated for data quality and subsurface
resolution. Experience in different projects reveals that the pole-dipole electrode arrangement with data
levels at different electrode spacing is suitable for better resolution of the subsurface material.
Furthermore, manual acquisition, although less productive than automatic acquisition, seems to secure
higher quality data. With these systems of data acquisition ERT was able to fulfill most of the objectives
of the subsurface investigation at hydropower projects.
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Geophysical Exploration at The Giza Plateau, Egypt A Ten-Year Odyssey
More LessThe Giza Plateau of Egypt has many above-ground marvels (Pyramids and the Great Sphinx) and
many hidden or suspected tunnels/rooms that may lurk in the limestone beneath the sands. Since 1991,
we have been granted several opportunities to look for buried structures on the Plateau as well as on, in,
and under some of the Plateau’s more famous structures. Five separate campaigns have included
geophysical surveying utilizing ground penetrating radar (2D and 3D), electromagnetic conductivity,
magnetic field, and seismic reflection, refraction, and refraction tomography techniques. The results of
these surveys can be qualified as ranging from glowing successes, to tantalizing opportunities, to
fascinating failures. 2D and 3D GPR surveys within the Sphinx Enclosure and in the sands west of the
Sphinx have detailed anomalous structures within the shallow limestone that defy geologic interpretation
(man-made?) and are waiting to be excavated. Whether or not they will ever see exposure may be the
source of the Sphinx’s inscrutable smile.
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Measuring Sub-Seabottom Seismic Velocities - Some Unusual Experiments
During the last 30 years, we have performed a number of unusual experiments to measure P- and Swave
velocity structure of unconsolidated sediments below the seafloor at sites to water depths of 700
m. These experiments were designed to aid in specific geotechnical problems related to soil stability
along pipeline routes or beneath bottom-founded structures as well as to provide regional information
for military purposes. Some of these experiments were done in open-water conditions, but many were
performed beneath ice-cover.
Early testing was directed towards mapping sub-seafloor ice-bonded permafrost in the Beaufort Sea
and elsewhere in the Arctic Archipelago, mainly using dynamite sources. Continuous ice-cover at high
latitudes presented specific challenges for refraction methods and various devices and hydrophone
arrays were designed for deployment beneath the sea-ice through open leads or drilled holes. Later
testing evolved from seabottom-laid hydrophones to towed, near-bottom arrays and non-dynamite
sources. As well, mapping of shear wave velocity structure was tested using seabottom coupled
interface waves.
All of these experiments (successful or otherwise) were learning experiences in one form or other,
and it is hoped that documentation of these experiments herein will be of some future research value.
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How Far Will You Go To Collect The Data?
Authors K. Michael Garman and Scott F. PurcellSubsurface Evaluations, Inc. has been using three-dimensional multi-electrode resistivity (3DMER)
surveys in the Tampa, Florida, area to image karst features beneath undeveloped sites; around and
beneath buildings; beneath bridges, canals, and tertiary treatment ponds; and around bridge and highway
support structures. The surveys have been very successful for identifying karst features such as buried
depressions, breached confining layers, cavities and caves. Although the survey data have been very
useful for site evaluation and positioning test borings, many interesting and unpredicted problems
develop during the long days it takes to setup and collect the surveys when over a mile of cable has been
deployed in urban areas and the unpredictable Florida weather turns bad. Alligators, Soccer Moms in
minivans, lightning, flash floods, traffic, and small boats create unusual situations that often require
novel solutions. Somehow, the data usually gets collected even though the field crew often believes
management has acted irresponsibly. We provide some interesting examples of 3D-MER surveys with
the stories of how the data were collected.
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Integrated Geophysical Methods for Lng Site Characterization In A Jungle Environment
Authors Finn B. Michelsen and Martin MieleThe contribution of integrated geophysical survey methods to site characterization in difficult
and challenging environments is extremely valuable to design engineers and planners of new Liquid
Natural Gas (LNG) facilities, especially if the site is located in a remote and geologically complex area.
In particular, subtropical jungle environments present unique equipment and instrument preparation
requirements, field operation problems, and have certain human risk factors that must be taken into
account. Qualifying and characterizing jungle sites for installation of an LNG facility is costly, time
consuming, and requires the application of a variety of geoscientific investigation methods, including
geophysics. In conjunction with geotechnical and other site investigation methods, data from
continuous resistivity profiling, seismic refraction tomography, P-S wave downhole seismic, and
Wenner sounding surveys are used as an aid the design and planning of an LNG expansion facility
located on Bioko Island, Equatorial Guinea.
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The Pentagon Building Performance In The 911 Crash
Following the 911 crash of an airliner at the Pentagon, the American Society of Civil Engineers
established a team to study the damaged structure and make recommendations for the future. The team
reviewed available information on the structure, the crash loading, and focused assessments by others.
The team then analyzed the essential features of column response to impact, the residual frame capacity,
and the structural response to the fire. Plausible mechanisms for the response of the structure to the crash
were determined and recommendations were offered for design and construction. This paper
summarizes the study and discusses the role of geophysics in such forensic inquiries.
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Testing A Safe Acquisition Procedure for An Effective Application of GPR To Security Operations
Authors Maurizio Lualdi and Luigi ZanziTerrorism is posing new technological problems to security forces. The need of checking for
hazardous targets such as explosives, bombs, weapons, etc., hidden inside unexpected packages or
embedded within blocks of other materials is increasing. GPR has been already explored for Anti-
Personnel Mines (APM) detection and most prototypes are based on single or arrays of antennas
surveying the suspected area from a distance of a few centimeters. We are exploring a flexible solution
that is expected to be: a) applicable to different scenarios such as soil inspections (as for landmines) but
also investigations on packages, blocks of materials, walls, etc., b) adaptable to a set of antennas to
ensure proper penetration and resolution, c) safe for operator and equipment, d) accurate in antenna
positioning to produce 3D reconstructions, e) based on a survey procedure that allows the contact with
the medium to eliminate the energy loss produced by the non-contact approach. A single antenna plus an
armored PSG (Pad System for Georadar) seem to fulfill the requirements. Radar performances were
tested to explore the effects of the armor material. Tests were executed on the landmine field managed
by the Joint Research Center (JRC) in Ispra (Italy). The results demonstrate the feasibility and the
advantages of this solution.
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Tunnel Detection Along The Southwest U.S. Border
The U.S. Army Engineer Research and Development Center (ERDC) has worked with U.S. Law
Enforcement Agencies (LEAs) since 1995 to address the problem of clandestine tunnels beneath the
U.S./Mexico border. ERDC has performed tunnel-related research, equipment development, or tunneldetection
missions at the request of the LEAs, coordinated by Joint Task Force 6 (JTF-6, Fort Bliss, TX,
now known as JTF-N for Northern Command, US Army). This support to LEAs has revealed the
importance of understanding the geologic context of a suspected tunnel site as a basis for selecting the
appropriate geophysical tools and interpreting anomalies indicated by geophysical data. Tunnel detection
missions always involve multiple tools and techniques. A combination of geophysical instruments is used to
record data based on different physical principals. When interpreted in a regional geologic context, the
combined geophysical methods improve the likelihood of success for tunnel detection.
A variable-frequency electromagnetic survey tool was developed in the 1990s as part of tunneldetection
research, and proven at a tunnel test bed near Otay Mesa, CA. Also at the Otay Mesa site, an
ERDC-led team installed and tested a prototype passive-seismic fence, a system that can detect machine and
impact noise during the tunnel excavation process. This seismic fence concept has strong potential for
deterring tunneling in geographic areas where tunnels have been found most frequently and where cultural
clutter limits the usefulness of surface geophysical techniques and tunnel detection.
Current ERDC tunnel detection efforts (March 2005) are coordinated with the National Geo-
Intelligence Agency (NGA, formerly NIMA) to combine electromagnetic and radar methods with emerging
technology in microgravimetry.
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Simultaneous Geophysical Surveys Using a Towed Multi-Sensor Platform and Its Application to Characterisation of Brownfield Sites
Authors Chris Leech, Ian Hill and Tim GrosseyThe multi-sensor platform allows dense data sampling with an array of geophysical sensors, chosen for the particular purpose e.g. magnetic, EM, Radiometric, VLF or metal detection. Geophysical data and navigation parameters are telemetered in real-time to a base station where they are viewed and logged on a laptop PC. Data can be collected from up to 6 geophysical sensors plus navigation at data rates in excess of 10 Hz. The system can be pulled at up to 7-8 km per hour in normal terrain, using a lawn tractor, or ATV. The combination of multi-parameter measurements at each point of the survey maximises the ability to characterise the material underlying the site. The real-time transmission of the data allows real-time data QA, survey design modification, and facilitates rapid in-field processing of the data. The method is applied to the geological, and archaeological sites in addition to part of a large integrated site investigation over a land fill site.
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Final Disposal of Spent Nuclear Fuel Triggers Security-Related Geophysics
By Olli T. OkkoA geological site investigation including a comprehensive geophysical program confirmed the suitability
of the studied crystalline bedrock sites for the safe disposal of highly radioactive spent nuclear fuel.
According to a legal decision endorsed by the Parliament in 2001, the final repository of Finnish spent
nuclear fuel shall be located at the Olkiluoto site in Eurajoki, western Finland. The next phase of the site
investigations includes the construction of underground premises for rock characterization purposes. The
excavation of these galleries began in 2004. Since these premises are scheduled to form a part of the
final repository, these investigations are subject to regulatory control with safety, security, safeguards
and societal aspects. The national geophysical site characterization and monitoring program planned for
the long-term safety assessment shall also be applied to other repository performance related matters.
The construction documentation and the adjoining geophysical monitoring program are applied to
safeguard the repository for homeland security purposes. The regulatory use of geophysical methods
creates new challenges to the geophysical community.
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Detection of Subsurface Utilities Using GPR Techniques
Authors Sherif M. Hanafy and Mohamed A GamalThe nondestructive evaluation of buried utilities is of interest for engineering and environmental
applications. The use of Ground Penetrating Radar (GPR) for buried utility detections is one of the most
common geophysical techniques due to its capacity for accurate results in either horizontal or vertical
directions. Electric cables and metallic pipes are easily recognized on GPR profiles due to their high
dielectric values relative to surrounding soils. In this study, 12 different sites are investigated using GPR
techniques to detect buried utilities, such as electrical cables, water, and derange pipes located within the
first 3 meters of the ground’s surface. At each investigation site, two perpendicular GPR profiles, using
a 200 MHz antenna, are collected in order to detect any buried utilities. The area under study is
excavated after GPR data acquisition for manual verification. It is found that electric cables are easy to
recognize on radar profiles by their sharp hyperbola edges and multiples extending to the bottom of the
data set. Water pipes have especial characteristics on GPR lines, indicated by a thick, small hyperbola
without any multiples. The presence of cement blocks masks any object beneath them, but they are
prominent on radar lines as high amplitude reflections.
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Underground Utility Location Challenges Using GPR: Life On The Streets
Authors Randy Sorenson and David TillsonThis paper presents a historical account of our evolutionary experiences over the last 8 years
using conventional GPR to locate underground utilities, typically prior to the installation of new water
lines, sewer lines, gas lines, telecommunication cables, etc. Brief summaries of several case histories
are presented to illustrate how GPR can be utilized, with and without, other geophysical techniques.
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Location of Mammoth Remains In Perma-Frost of Northern Siberia Using GPR and Multifrequency Em
Authors Ken-Ichiro Makino and Hidetoshi MiuraIt is generally considered that that Wooly Mammoths have been extinct for around 10,000
years BP, however it is unknown whether the reasons for their extinction were due to an abrupt
change in the Earth’s climate, disease, or to indiscriminate hunting. This paper describes a
geophysical investigation conducted in 2004 to hunt for remains of Mammoths to assist in
studying the causes of their extinction. Ground Penetrating Radar (GPR) and
Multifrequency Electromagnetics (MF-EM) were used to map the subsurface of the
permafrost at sites along the Artic coastline of Northern Siberia. The sites were preselected by
helicopter reconnaissance, followed by ground geophysical surveys. The results obtained from
one control site plus two field sites are presented here. It is concluded that GPR is a valid method for mapping skeletal remains from Mammoths,
however there is little signature obtained with MF-EM due to the poor contrast between the
remains and the properties of the surrounding permafrost.
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Towed Geo-Electrode Arrays for Analysis of Surface Water Groundwater Interaction
Authors David A. Allen and Noel P. MerrickHigh productivity analysis of surface water groundwater interaction is possible using GPS
positioned vertical electrical conductivity imaging along with depth recording. Short submerged geoelectric
arrays provide a great deal of detail right at the base of surface water bodies; however they
cannot be used in treacherous waterways with debris scattered through them. Long floating arrays can
be towed through such waterways and have the additional benefit of greater depth of exploration.
Floating arrays also can have reasonable resolution at the base of surface water bodies provided that they
are designed optimally and that data from them is inverted effectively. Array design must optimize a
balance of signal strength maximization, exploration depth resolution, weight and drag minimization,
crosstalk and current leakage minimization and simple, minimal response to three dimensional
heterogeneity. Pragmatic interpretation of the huge volumes of data that are typically acquired is best
achieved using three dimensional ‘ribbon’ images. Prominent features of interest are, in most cases
related to groundwater salinity. Low conductivity anomalies often indicate fresh surface water seepage
into more saline groundwater. High conductivity anomalies that intersect the bases of surface water
bodies usually indicate saline inflow to the surface water bodies.
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Application of Non-Desructive Geophysical Techniques for Risk Evaluation (Sannour Protected Area, Beni Suef, Egypt)
Authors Sherif M. Hanafy and Essam A. MorsA large cavity was recently discovered in the Wadi Sannour area, near Beni Suef City, Upper
Egypt, in the same general area in which alabaster is known to have been quarried since approximately
200 years ago. This cave has a span of up to 300m, is 10-30m in width, reaches a height of 15m, and
generally forms a crescent cross section. The opening is situated on a raised outcrop approximately
39.5m below the original ground surface. In order to evaluate the site for potential risks, to protect the
cave features from irreversible damage, and to make the site more secure for visitors, a Ground
Penetrating Radar (GPR) study was conducted inside, over, and in areas adjacent to the cavity. Here,
twenty GPR reflection lines were acquired uniformly over a 35 x 11m area in front of the cave’s
entrance, and during the course of this survey a new subsurface cavity was discovered. The depth and
dimensions of this new cavity were determined from the acquired radar data.
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Estimating Source Depth Extent From Inversion of Magnetic Field Data – A Synthetic Modelling Study of The Cretaceous Volcanic Intrusions Into The Edwards Aquifer, Texas
More LessDepth to the top or base of a small magnetic source body cannot be reliably determined from
single profile measurements of any one magnetic field parameter. However simultaneous measurement
of transverse horizontal gradients or the magnetic gradient tensor allows estimation of any offset of the
source from the profile and this substantially improves the ability to interpret sparsely sampled
anomalies. Surveys at low elevations improve resolution of detail and detection of weak magnetizations
but the measured anomalies are dominated by the topmost section of the source bodies thereby reducing
sensitivity to their base depths. Aeromagnetic surveys flown to help resolve structure of the Edwards
Aquifer have discovered many Cretaceous intrusions but many of these anomalies are detected only on
single profiles and depths to their top and base are poorly constrained. Models derived from inversion of
the anomalies can however be used in the design of any follow-up survey and to investigate the possible
benefits of transverse gradient or gradient tensor measurements. Inversion of a multi-line anomaly has
resolved the source to be a steeply-dipping sheet illustrating implications of the magnetic modeling to
local groundwater flow models.
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On Time-Domain Transient Electromagnetic Soundings
Authors Jia Ruizhong and R.W. GroomWe have developed two techniques for simulating EM responses of a layered earth model; a
general and an approximate method. The general method allows the computation of the magnetic field
produced by systems with various current waveforms and survey configurations, including in-loop and
out-of-loop for both moving and fixed transmitter with arbitrary location and orientation of receivers.
The approximate method only allows the calculation of the vertical transient responses of the secondary
currents during the off-time with receiver inside of the transmitter loop. I ncorporating these two forward
modelling techniques and both Marquardt and an Occam s inversion algorithm approaches, we have
developed four methods to perform inverse modeling of transient electromagnetic soundings. A time
domain conductivity-depth image (CDI) technique is also implemented. To prepare the data for this
technique, an algorithm converting impulse response into step response has been developed. Armed with
these inversion techniques, we can process ground and airborne data collected with systems using
various current waveforms and survey configurations. The applications of these inversion techniques to
synthetic layered-earth models demonstrate the effectiveness of these techniques. Interesting field data
uses are also shown.
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Laterally Constrained 1D-Inversion of 3D TEM Data
Authors E. Auken, A.V. Christiansen, L. Jacobsen and K.I. SørensenIn this presentation we show that the interpretation of spatial densely sampled TEM data over 2D
earth structures is greatly enhanced by inverting the data using the 1D-LCI algorithm (Laterally
Constrained Inversion). In the 1D-LCI algorithm neighboring models are constrained laterally on layer
resistivities and interfaces.
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Incorporation of Variable Background Velocity In Subsurface Imaging With GPR
Authors Beiyuan Liang and Lanbo LiuFor fast imaging subsurface targets with ground penetrating radar (GPR) it is common to assume
a homogeneous background of electromagnetic (EM) wave velocity. Nevertheless, if some information
about EM velocity is available, it is desirable to use more realistic velocity distribution in subsurface
target imaging. This paper introduces a ray tracing function into GPR imaging process with using
reflection energy stacking. We demonstrate the effectiveness of this approach by comparing the imaging
results with different velocity layers for a typical subsurface imaging example. Use of the ray tracing
technique in the imaging process built in GPR software, GIT-Radar, is better to image and determine the
depths and shapes of the targets. Also, the application of the ray tracing in a 3D imaging process does
not substantially retard the speed of calculation if a layered velocity model is used.
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Comparison of Discrete and Voxel 3-D Gravity Inversions Over Karst-Related Gravity Anomalies On The Coastal Plain of North-West Malaysia
More LessA negative gravity anomaly of amplitude 12 μm/sec2 and diameter 400 metres on the coastal
plain of north-west Peninsula Malaysia has been modelled as due to cavities in buried limestone
bedrock. A model of equi-dimensional cavities using spheres does not reproduce the sharpness of the
measured anomaly but a model using ellipsoids is successful. The value of the expected density contrast
is the only constraint required to develop these parametric models. Maximum-smoothness voxel
inversions are poorly suited to the binary density distribution of cavity models, but when guided by
earlier parametric inversion results the voxel inversions enable the testing and development of more
complex source shapes. For the deeper equi-dimensional cavity model the computed field is only weakly
sensitive to source shape but for the shallower ellipsoid model the voxel inversion may provide a valid
improvement in representing the shape of the source body.
The anomalies can also be modelled as due to changes in overburden thickness. Parametric and
voxel models of basement topography are similar to each other and differ significantly from simple
Bouguer slab predictions establishing the importance of 3-D modelling even for such a simple
geological model. There appears to be no inherent superiority of either parametric or voxel inversions
provided each has the versatility to select models according to guiding geological concepts.
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Simultaneous Geophysical Surveys Using A Towed Multisensor Platform and Its Application To Characterisation of Brownfield Sites
Authors Chris Leech, Ian A. Hill and Tim M. GrosseyA rapid measurement technique for assessment of landfill areas and other environmentally sensitive areas. A multi sensor platform with real time data logging and navigation has been built to
allow rapid reconnaissance surveys over large areas thereby reducing survey time and costs dramatically. Sensors from many different disciplines can be mounted on the platform and data acquired simultaneously. Case histories from geological, environmental and archaeological sites are presented showing the attributes of the technique in all three applications.
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Time-Lapse Azimuthal Resistivity Survey In A Highly Industrialized Area: Problems, Diagnosis, and Solutions
Authors Les P. Beard, Jacob R. Sheehan and Scott C. BrooksA time-lapse azimuthal resistivity survey was proposed to support a fluid flow test pertinent to
an upcoming bio-remediation experiment. The site is in a highly industrialized area, and preliminary
resistivity measurements showed steady, but substantial, drift in apparent resistivities measured over
tens of minutes. The drift was of such magnitude that collection of time-lapse data would be precluded
unless a solution could be found. We hypothesized that the problem was either instrumental, was
induced by the electrodes, or was site specific. Internal checks of the Sting R1 indicated a properly
functioning instrument. We tested three different electrode types and found no particular differences in
the rate of drift with any of the three types chosen. A test of the resistivity system in a plastic tub filled
with a sodium chloride solution produced steady measurements over a span of about an hour. We
concluded that stray currents at the site itself must be producing the drift. We found that by averaging
two measurements at a given azimuth, one with electrodes positioned AMNB, the other BNMA, we
could obtain steady resistivity results over acceptably long durations, and so we were able to acquire
useable data during the flow test.
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A Wide-Band Electromagnetic Impedance Profiling System for Non-Invasive Subsurface Characterization
Authors Hung-Wen Tseng, Ki Ha Lee and Alex BeckerA non-invasive, wide-band electromagnetic (EM) impedance difference system for shallow subsurface electrical structure characterization in environmental and engineering problems has been
developed at the Lawrence Berkeley National Laboratory (LBNL). Electrical parameters of interest are electrical conductivity and dielectric permittivity that are deduced from the impedance difference data. The prototype system includes a magnetic loop transmitter, which operates between 0.1 MHz and 100 MHz, an electrical dipole antenna for observing the electric field, and a loop antenna for measuring the magnetic field. All antennas are mounted on a cart made of non-metallic material for easy movement of the whole array for profiling. Surface EM impedance difference is obtained by taking the difference of the ratios of the electric fields to the magnetic fields at selected frequencies at two different levels. Numerical simulations verify this approach. A set of the impedance difference data acquired at the University of California’s Richmond Field Station compares reasonably well with simulation results based on a model obtained with the resistivity method and in situ TDR (time domain reflectometry) measurements.
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Application of Multi-Channel Electrical Method In Investigation of Hydraulic Channels In Qiu Jia Wan Main Dike of The Yangtze River, China
Authors Yixian Xu and Jianghai XiaQiu Jia Wan, the main dike of the Yangtze River in Jia Yu County, Hubei Province,
China, is a section scheduled for reconstruction due to underground water leakage. Prior to the
reconstruction, the paths of water movement (sand layers or local bodies) and their covering
material must clearly be investigated. The traditional methods, e.g. borehole drilling, are
expensive and may re-damage the dike, so the noninvasive multi-channel electrical method was
chosen to perform the investigation. One surveying profile parallel to and other three profiles
perpendicular to the main dike were carried out in the Qiu Jia Wan section. Acquired data were
inverted by a two-dimensional inversion method. Our interpretation was able to relate anomalies
in resistivity cross sections to water leakage through a sand and gravel layer from the Yangtze
River to the back of the dike. The results were consistent with hydro-geological analysis and
therefore supplied basic data for the reconstruction task.
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A High Resolution 3-D Imaging Radar Survey of A Concrete Ring-Wall Collar for Mapping The Extent of Concrete Deterioration and Delamination
Authors Brian Jones, Mario Carnevale, Daniel J. Delea and Jutta HagerA high-resolution 3-D GPR survey was conducted on a large concrete structure in the central
coastal area of California. The survey imaged the top 6-meter-high collar of a 19.81-meter-diameter
ring-wall. The purpose was to determine the presence and extent of concrete deterioration in the form of
air or water-filled cavities, as well as identify areas of concrete delamination or advanced stages of
concrete deterioration. The imaged section of the ring-wall was 0.91 meters thick. A 900-MHz GPR
system was used to image the full circumference of the ring-wall from the outside. A 1.5-GHz GPR
system was used concurrently to image the full circumference of the top of the ring-wall. This survey
plan was developed to provide a suitable combination of resolution and GPR signal penetration to image
the upper ring-wall structure.
The high-resolution top-of-wall and outer-wall surveys were conducted to identify delamination
zones and discontinuities within the concrete. A total of 6,047 data files were collected. This equates to
a data set size of 1.725 GB. The total linear distance surveyed was 3,907 meters. 3-D analysis of the
GPR data was used to create a continuous 3-D composite model for both the 900-MHz and 1500-MHz
data sets. “Wrap-around” time-slice views were provided to the client in video format to illustrate the
ring wall in quarters and octants. The investigation indicated that approximately 25% of the surveyed
wall contained some degree of rebar rust jacking and concrete defects in the form of voids and/or
delamination. This study demonstrates that a comparison of the 3-D results of two concurrent surveys at
different frequencies can provide comprehensive, high-resolution images of defect distributions in large
concrete structures.
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Use of Ground–Penetrating Radar (GPR) As An Evaluation Tool In Nineteenth-Century Building Restoration
Authors James S. Mellett and Shelley SmithA GPR survey using a 1.5 GHz transducer was carried out on the inside walls of a nineteenth
century church tower in Westchester County, NY to gather information on moisture infiltration and to
guide remediation. The tower walls have a thickness of 40 cm (16 in) and are faced with granite ashlar
blocks about 15 cm (6 in) thick. The inner face is a rubble wall, with stones having diameters from 7 to
20 cm (3 to 8 in). In between is a mortar mix that filled in the spaces between the rubble stones. Over
the past decade, the inner walls in the church have been showing evidence of leaks and water damage.
Recent remediation included masonry repointing and injection grouting of the parapet walls. The leaks
subsided significantly, but evidence of moisture infiltration continued. GPR scans detected apparent
voids in walls below the parapet, with large void spaces around the central windows. In the area below
the windows, just above the church crossing, the voids appeared to increase in frequency and size. We
believe that voids were initiated around the windows and the entrained water developed a hydraulic head
that pushed it into lower levels of the church. Additional injection grouting will be performed in all wall
areas showing voids.
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Time Domain Reflectometry Uses In Geotechnical Engineering
More LessTime Domain Reflectometry (TDR) makes use of a device that propagates transverse
electromagnetic waves through soils by means of special soil probes as shown in Figure 1 for field
testing and in Figure 2 for testing a specimen. For field testing four spikes are driven into the soil while
for testing a specimen in a mold, only a center rod is driven into a metal mold on a non-conducting base.
The same probe head is used in both situations.
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Pavement Evaluation and Design With Seismic Methods
More LessThe primary parameters that affect the performance of a road or an airfield pavement are the
thickness, the Poisson's ratio, and more importantly, the modulus of each layer in the pavement
structure. Stress wave propagation or seismic techniques have been used to measure these parameters
through nondestructive testing (NDT). Other factors affecting the performance of a pavement are the
interfacial bond quality of asphalt concrete (AC) or Portland cement concrete (PCC) overlays and the
existence of flaw or delamination in a PCC slab. They can also be detected with seismic methods. To
make field tests and data analyses with seismic methods faster, more practical and cost-effective,
automated testing devices have been developed. The principles of seismic methods as applied to
pavement analysis, design and diagnosis are discussed through several case studies.
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Reflection Seismology: Application To Identifying Fault Structure
Authors Richard T. Williams, Vladimir A Babeshko and Ernest KutsenkoReflection seismology has been developed to an advanced state by the petroleum industry,
capable of determining not only the geometric shapes of subsurface layers and faults, but also yielding
substantial information about the elastic properties of the rocks and the nature of any fluids present. The
technology is expensive, but highly successful and justified in comparison to the cost of drilling wells
several thousand feet deep to discover and produce petroleum. Geologists drill few oil wells and no
deep ones without the support of seismic reflection data. Geotechnical investigations share some of the
same goals, to image subsurface layers and faults, and to determine the elastic properties of the strata
without the expense of excavation or drilling, but the economics are quite different. This paper reviews
the state-of-the-art as it is practiced in the petroleum industry, and examines which elements of the
technology can be adapted in a cost-effective way to geotechnical site investigations. Not all of the
petroleum industry technology is appropriate for engineering applications, but the basic field equipment
and software can be easily adapted. Recommendations are presented as to the kinds of problems where
reflection seismology may be the more effective than other geophysical methods including refraction
seismology and ground penetrating radar.
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Shear-Wave Velocity and Liquefaction Potential for Soils Under Dynamic Loading
More LessThis paper presents an overview of the procedure for evaluating liquefaction potential of soils
using shear-wave velocity measurements described in recent journal papers by the author and others.
The procedure follows the general format of the Seed-Idriss simplified procedure, and was developed
using suggestions from participants of two workshops and several independent reviewers. Comparative
studies show good agreement between predictions by the shear-wave-based procedure and the
penetration-based procedures.
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Shear-Wave Velocity (VS) Profiling By Surface Wave (MASW) Method
More LessThe multichannel analysis of surface waves (MASW) method (Park et al., 1999) is a non-destructive
(NDT) seismic method to evaluate shear-wave velocity (Vs) (or stiffness) of the ground. It analyzes
dispersion properties of seismic surface waves propagating horizontally along the surface of
measurement. It gives the Vs information in either 1-D (depth) or 2-D (depth and surface location)
format in a cost-effective and time-efficient manner. The main advantage of the MASW method is its
ability to take a full account of the complicated nature of seismic waves that always contain harmful
noise waves such as higher modes of surface waves, body waves, scattered waves, traffic waves, etc
(Figure 1). Since its first introduction to the related communities in mid 90s, there have been various
types of applications with the MASW method at different parts in the world. Nowadays, the keyword
MASW can be effectively used to search for related information on the Internet. Complete list of the
MASW publications made at the Kansas Geological Survey (KGS) during the last one decade can be
found at www.kgs.ku.edu and includes various types of case studies as well as theoretical ones.
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Surface Wave Analysis Using Wavelet Transforms
Authors Nenad Gucunski and Parisa ShokouhiComprehensive and efficient shallow evaluation of layered systems, like soils and pavements,
can be done using surface waves. The most commonly used surface wave techniques include the
Spectral Analysis of Surface Waves (SASW), Multichannel Analysis of Surface Waves (MASW), and
its high frequency counter part for paving layer evaluation, the Ultrasonic Surface Wave (USW). The
techniques have been primarily used in evaluation of elastic moduli and layer thickness of layered
systems, and to a certain extent in evaluation of profile variations and detection of anomalies, such as
cavities, soil lenses and buried objects. Since the SASW is using only a pair of receivers and data
evaluation is based on a standard spectral analysis, it has limitations in the accuracy and completeness of
the obtained information. The MASW, with its multi-channel data collection and analysis based on
double transformation of the signal from the spatial-time domain into the frequency-wave number or
frequency -phase velocity domain, can provide a more comprehensive description of the subsurface
conditions. Further enhancements can be achieved through surface wave analysis using wavelet
transforms. Application of three types of wavelet transforms of surface waves is presented.
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Applications of Controlled Source and Natural Source Audio-Frequency Magnetotellurics To Groundwater Exploration
Authors Norman R. Carlson, Phillip M. Paski and Scott A. UrquhartAudio-frequency magnetotellurics (AMT), using either a controlled source (CSAMT) or natural
source (NSAMT), has become an efficient, cost-effective tool for groundwater exploration.
Advancements in field equipment have improved data quality and increased data acquisition speed, and
the availability of 2D inversion modeling has significantly improved data interpretation. Since depth of
investigation is not related to the receiver electric field dipole size, AMT can be used as either a highresolution
tool (using short dipoles) or as a reconnaissance tool (using large dipoles).
Several recent field examples are presented, including fractured bedrock targets, in which lateral
resolution is important, as well as reconnaissance-style basin mapping, in which speed and economic
efficiency is critical. In one project, located in Tule Desert, Nevada, CSAMT was used successfully to
map an undeveloped basin, and was instrumental in subsequent court hearings to support water right
applications to develop groundwater resources from this basin.
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