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21st EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 06 Apr 2008 - 10 Apr 2008
- Location: Philadelphia, USA
- Published: 06 April 2008
1 - 50 of 136 results
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Geophysical Surveys To Characterize The Hydrogeology Of The Arbuckle Uplift, South-Central Oklahoma
Airborne and ground electrical resistivity and magnetic surveys as well as ground gravity measurements have been conducted to map the subsurface geologic and hydrologic features of the
Arbuckle Uplift. The main target of these investigations is the Paleozoic Arbuckle-Simpson aquifer and the surrounding stratigraphic units of the Arbuckle Uplift in south-central Oklahoma. In March, 2007, helicopter-borne electromagnetic (resistivity) and magnetic survey was flown of four areas with distinctly different geology were flown using measurement systems. The airborne resistivity measurements were made at six different frequencies ranging from 400 Hz to 115,000 Hz which provided a depth of penetration from a few meters to about 80 m. Ground resistivity profiling has been conducted in several areas of the uplift for subsurface resistivity imaging. Two of the resistivity profiles are in the area encompassed by the airborne survey. Total field magnetic and high precision location (GPS and laser altimeter) measurements were also made as part of the airborne survey. Ground gravity and magnetic profiling was also conducted to refine location of structures in specific areas. The geology of the study area consists of dolomitic limestone (Arbuckle and Simpson Groups) that generally lies in fault contact with younger Paleozoic clastic and carbonate rocks. The formational units are gently dipping except on the flanks of the uplift. The geophysical maps, resistivity depth sections, and interpreted cross sections from the magnetic and gravity data are being used to improve the geologic mapping and better define hydrologic features of the area.
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Geophysical Investigation Of The Fresh-Saline Water Interface In The Coastal Area Of Abergwyngregyn
Authors Ismaila B. Obikoya and James D. BennellThe importance of the study of saline/fresh water incursion cannot be over-emphasized. Borehole sampling has been extensively used, but it is intrusive, quite expensive and time consuming.
Electrical resistivity and electromagnetic techniques have proved successful in groundwater studies since geologic formation properties like porosity and permeability can be correlated with electrical conductivity signatures. Non-intrusive surface geophysical mapping comprising electrical resistivity and electromagnetic methods has been employed to investigate freshwater intrusion and delineate the fresh-saline water interface at the inter-tidal area of Abergwygregyn, North Wales, United Kingdom. Frequency Domain Electromagnetic Profiling and Constant Separation Traversing were used to produce 2-D images and contour plots enabling the identification of freshwater plumes onshore and in the central parts of the study area. Ground truth methods comprised chemical analyses and detailed, point specific information on the stratigraphy. The freshwater intruding from the coastal area appears to be pushing
the saline-water further offshore due to the high piezometric head caused by the mountains and hills of Snowdonia adjacent to the study area. The fresh/saline water interface correlates quite well with previous studies carried out in the area. On the basis of the results of the resistivity and conductivity geophysical investigations the freshwater plumes and fresh/saline water interface in the study area were effectively identified and delineated..
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New Discovery Of Important Archaeological Artifacts From Shallow Seismic Observations At The Ancient Hierakonpolis Temple-Town Site In Upper Egypt
Authors Shelton S. Alexander, Elizabeth Walters and Recep CakirProminent high-velocity, high-frequency signals from very shallow depths were observed along some of the numerous seismic refraction profiles run within the perimeter wall of the ancient Hierakonpolis Temple-Town in Upper Egypt. These anomalies are characterized by laterally continuous high-frequency (200-300 Hz) arrivals with velocities comparable to or exceeding the deeper water table refraction velocities. These anomalous zones are imbedded in the 1 to1.5 m-thick upper layer of unconsolidated, air-filled sediments that have extremely low velocities and very low Q. The considerable spatial extent of these shallow anomalous zones was determined from sets of crossing refraction profiles.
Subsequent excavations (2001, 2005-6) at two locations in the western portion of the site revealed the presence of a zone of closely spaced artifacts (dense in potsherds and stone fragments) that revealed new evidence of occupation in the ancient town as early as Dynasty I, c. 3200 BCE. In the northwest excavation an ‘in situ’ deposit of special pottery lay next to a bench, a large block of dressed limestone. Further to the north, layered occupation suggests a secular context with pottery of Dynasty II, 2900 BCE and a new early date, terminus ante quem, for the accompanying figurines, thus far exclusive to two temple sites in southern Egypt. Further excavations of the mapped anomalous zones are expected to provide many additional artifacts not previously found at the site.
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Use Of Masw For Geotechnical Site Characterization Using Corrected Triaxial Geophones
Authors D. Lane, W. Ragland, R. Williams and D. PenumaduA comparison of 3-component surface wave data to uncorrected vertical geophone records at a soft soil site on the flood plain of the Tennessee River is presented. The data is collected using 10 Hz vertical and 4.5 Hz horizontal geophones, which are calibrated against a reference piezoelectric accelerometer and servo-hydraulic testing system. The records from the field associated with MASW survey are corrected for the mechanical response of the geophones using experimentally-determined transfer functions. MASW data are obtained using 1 m geophone spacing with a 22 kg weight dropped from a height of 1.5 m. It is expected that the vertical and radial (horizontal toward the source) geophones will record Rayleigh waves, but the horizontal transverse geophones should not record a Love wave, because it is not generated efficiently by a vertical impact on laterally homogeneous strata. Contrary to expectations, both Rayleigh and Love wave dispersion curves are observed. Rayleigh waves appeared on the vertical and radial geophones, but their dispersion curve cutoff at frequencies lower than approximately 27 Hz. Love wave dispersion was observed on the transverse horizontal geophones at frequencies below 27 Hz. Hypothetically, the Love waves could have been caused by scattering related to small scale in heterogeneities in the soil.
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Preliminary Analysis Using Surface Wave Methods To Detect Shallow Manmade Tunnels
Authors Niklas H. Putnam, Ali Nasseri-Moghaddam, Oleg Kovin and Neil L. AndersonMulti-channel Rayleigh wave data were acquired across a 1m diameter spillway tunnel along three parallel traverses with surface to tunnel separations of 0.90 m, 2.15 m, and 3.13 m, respectively. The data were acquired by placing a 24-channel array across the tunnel (perpendicular to the center-line of the spillway tunnel) and walking the sledge hammer source through the array starting with a far-offset of 10 m. The 4.5 Hz geophone array spacing was at 0.5 m intervals. Single shot data were analyzed to visually locate and to highlight attenuation effects associated with the tunnel. The field records were then velocity filtered in order to enhance back-scattered Rayleigh wave energy thereby allowing for visual identification of the tunnel location. The same single shot data were analyzed using the Attenuation Analysis of Rayleigh Waves (AARW) method. The intent was to demonstrate the utility of these approaches to tunnel delineation at a site where the geometry of the target and the nature of the encompassing soil was known. Electrical resistivity data was also acquired along the traverses for comparison purposes.
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Reduction Of Topography Effect In Apparent Conductivity Profiles (Em38): Application On Sambaqui Site (Shell Mound) In Santa Catarina State, Brazil
More LessModern land developments have motivated the application of geophysical methods in archaeological investigation in order to recognize hidden patterns in poorly known areas and select suitable places for excavation. Due to quick data acquisition and interpretation, low-induction EM38 measurements (conductivity and magnetic susceptibility) have been successfully applied to map fire places, burials, and concentration of ceramic materials in many Brazilian prehistoric sites. Conductivity anomalies, however, are much affected by the soil water content, which in sites with rugged topography creates a site-scale effect that masks the expression of subtle archaeological features. Here, we apply a procedure to remove the dependence of the soil conductivity with respect to the site topography by using a linear relationship determined by cross-plotting conductivity and elevation values measured in a given site. Corrected conductivity values helped us to identify regions of archaeological interest (further confirmed by excavation), which formerly were not easily recognized from crude data. This procedure has shown proved utility as an exploration tool to study sambaqui (shell mounds) archaeological sites, at the sandy coastal plain of the Santa Catarina State, in southern Brazil.
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Application Of Borehole Geophysics To Delineate Preferential Contaminant Migration Pathways In A Complex Fractured Clay/Shale Aquifer
Authors Robert J. Onderko, George Sauer and J. PetersonDuring development of a Hydrogeologic Conceptual Site Model (HCSM) for a large chlorinated solvent plume, Earth Tech determined that significant groundwater movement was occurring below auger refusal depths within a shallow fractured rock aquifer. Data was available for deeper zones, but not for the zone of interest. Earth Tech developed an approach that utilized various borehole geophysical tools to investigate this possible preferential migration pathway. A multi-phased investigation program was developed in which multiple borehole logging tools were tested to determine the suitability and the applicability of the geophysical methods to investigate the zone of interest. Once the geophysical method suite was optimized, the investigation program was streamlined. Although this investigation program developed over time, the multiple objectives of investigation remained focused on:
1. Determining the presence or absence of a significant groundwater flow horizon just below
auger refusal depths;
2. Determining the hydraulic characteristics of the system;
3. Refining the HCSM for the shallow aquifer system; and
4. Determining the extent of contamination and the effectiveness of the remedial measures that
were applied at or above the auger refusal depths at the site.
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Seismic Inversion For Geotechnical Properties Relevant To Coal Mining
Authors P.J. Hatherly, M. Urosevic and B. ZhouThe 3D seismic reflection method has an established role in Australia in mapping geological structures, faults and discontinuities that might affect the operation of an underground coal mine.
However, successful longwall mining also requires knowledge of geotechnical properties of the roof and floor strata. Most geotechnical information is obtained from core drilling, geophysical logging and underground mapping. In particular, log analysis can now be used to determine geotechnical properties of the strata through the Geophysical Strata Rating (GSR). However such “point” measurements need to be extrapolated into a full three dimensional geotechnical model for longwall mining operations. Geotechnical variability is related to lithological variations that can be inferred from high resolution seismic reflection data. Hence geotechnical variability could be studied directly from seismic data or a particular seismic attribute. Here we investigate a relationship between acoustic impedance derived from seismic data and log-derived GSR values to produce a 3D geotechnical model.
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Using Electrical Resistivity To Model Channel Seepage From Irrigation Canals
Authors Jacqui Watt, Shahbaz Khan and Akhtar AbbasThere is increased pressure on water managers, as a whole, to improve their water use efficiency. In irrigation areas, a major aspect of water usage is the seepage of water from irrigation
canals. In Australia significant amounts of water may be lost from irrigation canals through seepage and evaporation. The methodology applied for this paper uses the measurement of the soil resistivity to aid water managers in the determining the quantity of seepage from irrigation canals. Initially, the resistivity of the irrigation canal bed was measured, followed by soil sampling
and analysis. The spatial and resistive variability was established from the resistivity measurements and was inputted into the HYDRUS 2D/3D model according to resistive groupings. The soil
analysis resulted in the particle size, bulk density and hydraulic conductivity and these were inputted for the respective soil group into the model. The modelling was conducted over 30 years and the results determined the soil type plays an initial role in the seepage from irrigation canals. However, once the profile becomes saturated it does not matter which soil types are present. The method outlined employs the rapid assessment technique of resistivity to improve the understanding of seepage of irrigation canals.
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The Multi-Channel Analysis Of Surface Waves (Masw) Method As A Tool For Ground Improvement Certification
Authors Robert W. Burke and Nick B. SchofieldGround improvement techniques such as High Energy Impact Compaction (HEIC) of fill requires testing to allow certification of the compaction process. HEIC is often performed on mixed, unengineered and rock fill layers up to 8m in thickness. Experience has shown that conventional geotechnical testing techniques, including nuclear densometer tests, penetration tests (CPTs, SPTs, DCPs) and plate load tests have great limitations in testing such fill profiles. The MASW method is a useful tool for assessing ground improvement as it addresses many of the problems associated with more conventional tests. The MASW method has been used by Black Geotechnical on ground improvement projects since February 2006. The ground improvement methods often create a very stiff raft of fill over soft natural soils that become gradually stiffer. This very stiff-soft-stiff profile is not optimal for MASW as Lamb waves can be easily introduced and it is often difficult to define the base of a soft layer when there is a gradual transition to stiffer soil. Lamb waves, modes and artifacts contribute to making the use of MASW as an absolute stiffness measurement difficult at times. Pre and post compaction MASW surveys enable the method to be used as an effective relative measure of ground improvement.
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Gravity And Magnetic Data Analysis To Detect The Basement Rock Structure At Sungai Pahang Delta Area
Authors M.N. Khairul Arifin, Mohd N. Nawawi and T.H. Zuhar ZahirThe objective of this study is to model and establish a geological structure, mainly the basement rock, using potential field analysis. Two potential field methods, i.e. gravitational field and magnetic field were used in this study. The coastal margin sedimentary basin at Sungai Pahang Delta in Pekan, Pahang was chosen as the study site. This is to identify the basement rock structure due to delta development such as fault zone evolution, basement expansion and compaction. The data were interpreted both qualitatively and quantitatively. The qualitative interpretation is based on anomalies on the contour maps, and the quantitative interpretation is based on data modeling. There is good correlation between the gravitational and the magnetic field methods since the same features are found at the same locations. The result from the magnetic field method shows that the basement rock contains extended basalt intrusion. However, the gravitational data show a more localized intrusion and the presence of a metamorphism contact zone.
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3-D Resisitivity Survey Downstream A Landfill In Brazil – Preliminary Results
A contaminated site downstream a landfill in Brazil was investigated using a 3-D resistivity imaging technique. The purpose of this investigation was to detect and delineate the contamination plume produced by the wastes and to obtain detailed information about the affected area. The data set consisted of a series of parallel electrical profile data acquired with the dipole-dipole array, and was inverted as a complete 3-D survey. This acquisition technique is less troublesome than a complete 3-D survey, and despite of yielding a poorer resistivity model, the resulting model still provide the major resistivity contrasts and enables a tridimensional picture of the main features. In this work we present depth slices and individual 2-D profiles, from the models obtained by the 2-D and 3-D least-squares smoothness constrained inversion technique. The results suggest the presence of a contamination plume and their preferential path, which is in good agreement with chemical analysis and underground water flow data. The 3-D technique reveals to be efficient in waste disposal sites investigations, and should be taken into account when choosing the investigation technique to be used in complex and contaminated sites.
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Geophysical Analysis Of The Salmon Peak Formation Near Amistad Reservoir Dam, Val Verde County, Texas, And Coahuila, Mexico, March 2006, To Aid In Piezometer Placement
Authors Gregory P. Stanton, Wade H. Kress, Andrew P. Teeple and Allan K. ClarkA reconnaissance-level geophysical study was conducted at Amistad Reservoir Dam to provide technical assistance for the horizontal and vertical placement of piezometers on the eastern embankment of the dam. The study involved an integrated approach using surface and borehole geophysical methods. In the western embankment investigation, geological and geophysical characteristics that indicate relatively large water-yielding properties of the Salmon Peak Formation were identified. The directcurrent (DC) resistivity method was selected as the surface geophysical reconnaissance technique to correlate relatively large water-yielding properties of the Salmon Peak Formation, identified from analysis of borehole geophysical logs, with variations in subsurface resistivity. The dipole-dipole array and the reciprocal Schlumberger array were selected as the most applicable DC resistivity arrays. Two resistivity units were identified in both the dipole-dipole array data and the reciprocal Schlumberger array data along DC resistivity profiles on both embankments. Resistivity unit 1 generally is of relatively
low resistivity, ranging from 45 to 150 ohm-meters compared with resistivity unit 2, which ranges from 120 to 345 ohm-meters (depending on the DC array type). The presence of mapped sinkholes in the reservoir north of the western embankment study area and the zone of increased water content (as indicated by zones of low neutron log count rates in nearby piezometers) leads to the conclusion that resistivity unit 1 is a preferential flow path where surface water from Amistad Reservoir is forced into the ground-water system (because of increased head from the reservoir). In the eastern embankment investigation, trends in the spatial distribution of sinkholes and the occurrence of weathered zones were identified from geologic descriptions of cores. The correlation of surface geophysical DC resistivity, historical lithologic data, and general trend of documented sinkholes along the eastern end of the eastern embankment profile were used to justify further exploration (drilling of piezometers) in the eastern expression of resistivity unit 1. The spatial location of the piezometers and the screened intervals were selected to best match the locations of the screened intervals of the western embankment piezometers. Six piezometers were installed on the eastern embankment and logged using borehole geophysical
techniques. Resistivity units 1 and 2 in the DC resistivity profiles generally correspond with low and high resistivity zones, respectively, on the normal and lateral resistivity logs collected in the nearby piezometers at the time of installation. Because the project was a reconnaissance-level study, the report is not a comprehensive geologic or geophysical evaluation of the study area.
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Correlation Between Geoelectric And Hydrodynamic Parameters Of Aquifers: Transversal Resistence Versus Transmissivity In Bebedouro’S Region, Southeast Of Brazil
Authors Ivan M. Carlos and Vagner R. ElisEstimates of hydrodynamic parameters from geoelectrical data settings play an important role in hydrogeology studies. In such context, correlation between transversal resistance (RT) and
Transmissivity (T) has been considered a usefu l tool for evaluation of aquifer hydrodynamic characteristics. Ten Vertical Electrical Soundings (VES) using Schlumberger configuration close to
tubular wells were carried out in Bebedouro’s region (São Paulo state, Brazil) aiming at getting RT. Through a representative average value of hydraulical conductivity (K) obtained from Adamantina Formation, it was possible to estimate T parameter that in turn allowed a RT x T relationship analyzed by linear regression with correlation coefficient R = 0.9. In order to access the reliability of such methodology, nine additional VES’s were carried out for specific points placed at the southern region of the micro basin, for which we had no available information provided by stratigraphic studies of tubular wells. Furthermore, values were also estimated for RT and T parameters plotted against results provided by the first 10 VES’s. Results were considered satisfactory validating the method applicability.
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Common Misconceptions About Capacitively-Coupled Resistivity (CCR) What It Is And How It Works
More LessCapacitively-coupled resistivity imaging systems have been available as commercial geophysical instruments for over eight years and have seen increased acceptance in near-surface engineering applications (Ball 2006), (Garman et. al. 2004). In order for a geophysicist to determine whether a capacitively-coupled resistivity meter would be appropriate for a particular application requires a fundamental understanding of the technique and its relative capabilities and limitations in relation to other near-surface imaging tools. The underlying principles of the technique are outlined in the existing literature (Kuras et. al. 2006), (Timofeev et. al. 1994). This paper is intended to point out and discuss some of the most common misconceptions about capacitively-coupled resistivity (CCR) and to review practical considerations in basic survey fundaments compared to other resistivity measuring techniques. The Geometrics OhmMapper TRN is a commonly used CCR instrument, using a dipole-dipole configuration, and will be the base of reference for this paper (Figure 1).
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Application Of Surface Geophysics For Providing A Detailed Geotehcnical Assessment Of A Large Resort Development Site In Anguilla, Bwi
Authors Sandy Nettles, Bret Jarrett and Eric C. CrossN.S. Nettles & Associates (NSN) has completed extensive geophysical investigations that have guided engineering practices for a resort community in Rendezvous Bay, located in Anguilla, BWI. Diverse technologies were utilized, including; Multi-Electrode Resistivity (MER), Continuous Resistivity Profiling (CRP), and Multichannel Analysis of Surface Waves (MASW). Resistivity
techniques allowed for differentiation of geologic units and the identification of karst features and subsurface anomalies. To further determine sub-surface density variations, MASW transects were performed. This multi-method approach provided confidence in location of anomalies that were later targeted for drilling practices. Additionally, a stagnant salt pond was mapped with MER and CRP for the purposes of determining sediment thickness overlying rock and the competency of the limestone. This provided accurate volume calculations for dredging operations, the first phase in the transformation of the hypersaline pond to a functional marine habitat. Specifications were designed for a series of horizontal flushing channels connecting the salt pond with Rendezvous Bay. Cone Penetration Testing was utilized and geologists supervised the drilling of rock cores and Standard Penetration Test Borings to investigate anomalies and calibrate the geophysics. Results have provided the geologic framework for engineers to implement a successful construction strategy for the Rendezvous Bay Resort.
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Wireless Sensor Networks In Geophysics
Authors Charles P. Oden, Gary R. Olhoeft, Dan P. Jones and Stan S. SmithA significant expense in geophysics is physically collecting data – especially data sets involving multiple field deployments. Limited site access due to hazards, weather, legal issues, etc. may also limit data collection. Consequently, many datasets have too few measurement types, too little spatial coverage, and too little temporal coverage which results in increasing uncertainty and ambiguity in our problem solutions. Wireless sensor networks are an emerging technology that addresses many of these issues. Today’s wireless sensors are small (typically a few centimeters on a side), can be left in the field for long periods of time without servicing, and are inexpensive enough to be considered disposable. Wireless sensors are a combination of several recent technological advances including inexpensive miniature sensors, low power radio telemetry, time synchronization techniques, localization techniques (spatial awareness), and energy harvesting methods. Single chip sensors are available for measuring electric, magnetic, and electromagnetic fields, temperature, pressure, mechanical displacement,
chemistry, attitude, and more. These sensors can be used in several geophysical methods including seismic, DC resistivity, induced polarization, EM induction, magnetometry, and ground penetrating radar (GPR). The small size of these sensors allows multiple types of measurements to be incorporated in a single sensor node. Examples of the wireless sensor network applications include the long term monitoring and assessment of infrastructure, investigations in ecology and environment, tracking fluids or contaminant migration, and resource and exploration studies. In this paper, we review some of the capabilities and limitations of current wireless sensor network technology.
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Exploring Masw Surveys With Random Receiver Arrays For Future Lunar Exploration
Authors Prasanta M. Yeluru, Gregory S. Baker, Choon B. Park and Larry A. TaylorUnderstanding the physical and engineering properties within the upper 30m of the Lunar subsurface will be critical as Lunar exploration advances and deployment of large structures or landing of large spacecraft on the surface becomes necessary. Advances in multi-channel seismic acquisition, either active or passive, in acquiring reliable 1-D or 2-D shear wave velocity profiles have greatly improved our ability to determine the engineering properties (e.g. Poissons ratio) of shallow subsurface, especially when using the multi-channel analysis of surface waves (MASW) technique. A new scheme of using randomly distributed geophones (likely deployed from a mortar-type device) instead of a conventional linear array is necessary for Lunar exploration because of the logistical constraints in arranging a linear or circular array robotically. This random geometry is also evaluated (a) for validity or any potential improvements in the resolution of the dispersion image and (b) as more accurate method for assessing azimuthal variations in the subsurface geology. Results indicate that the random array geometry can be used for MASW survey to produce robust dispersion curves that can be used for the subsequent analyses for the subsurface engineering parameters.
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Passive Electrical Monitoring Of Aerobic And Anaerobic Processes Using Septic Systems As An Analog
More LessUsing anaerobic and aerobic septic systems as analogs, we examined whether the passive electrical potential (SP) method can be used to detect and monitor shallow biochemical reactions. High-resolution SP surveys conducted with nonpolarizing electrodes can reliably detect potential differences as small as a few mV over relatively small areas, suggesting that the technique can find wider use in monitoring biodegradation processes, mapping effluent plumes, and identifying local preferential infiltration areas. Surface SP measurements appear to respond to changes in the oxidation-reduction potential in shallow reactors, correlating best with changes in dissolved oxygen concentration and measured electrical potential within the subsurface reactors. Among the available electrode choices, including those made of carbon, low-grade steel, stainless steel, and copper, only nonpolarizing electrodes such as the copper–copper sulfate types provide the measurement stability necessary to achieve high-resolution results.
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Seismic And Geotechnical Site Characterizations At Four Earthquake Strong Motion Sites In Washington State
Authors Recep Cakir, Timothy J. Walsh and Trevor ContrerasAs part of on going program for generating maps addressing geologic site effects in Washington, the Washington State Department of Natural Resources (DNR), Division of Geology and Earth Resources (DGER) drilled 30-meter-deep geotechnical boreholes at four strong-motion sites operated by the Pacific Northwest Seismic Network (PNSN). Invasive (soil sampling, Standard Penetration Test (SPT) and downhole seismic) and noninvasive (Multichannel Analysis of Surface Waves, (MASW)) methods were used to determine shear-wave velocity profiles, specifically for the top 100 feet of soil column, at each of these strong motion sites. The boreholes were logged for visual soil classification and SPTs, and selected soil samples were tested in the laboratory to obtain plasticity and gradation values. In addition, S-and P-waves generated at the surface were received by a 3-component geophone placed at 1-m intervals in each borehole. Then the borehole sites were later surveyed by using MASW method to estimate the Vs profiles at each borehole site. The MASW survey shows a very good correlation with the downhole S-velocity profiles. SPT blow counts are consistent with soil conditions in the Puget Sound area. Site classes E, D-E, D, C-D and C, as described in the International Building Codes (IBC 2006), were determined by using average shear-wave velocities and SPT blow count values to 30 meters (~100 feet) of soil column of the four boreholes. An updateable geospatial database incorporating shear-wave data and velocities, borehole geotechnical information (soil samples and their laboratory tests, SPT blow counts, etc.) will be generated and periodically updated. This database will directly be available through the DGER‘s interactive mapping service for end users such as federal and local government agencies, urban planning and emergency response groups and seismic networks, such as PNSN.
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Seismic Rayleigh Wave Method For Localizing And Imaging Subsurface Cavities In Extensively Exploited Districts
Authors Jon C.Q. Xu, Stephen D. Butt and Patrick J.C. RyallThis research presents recent developments using seismic Rayleigh waves to detect and image subsurface anomalies. Instead of conventional spectral analysis of surface waves (SASW) method or the multichannel analysis of surface waves (MASW) techniques, this study developed a strategy to isolate Rayleigh waves from raw field data, and apply wavelet transforms to pair-channel analysis of the Rayleigh wave data for dispersion calculation. Finally, a simple steady inversion technique was applied to yield shear velocity as a function of both depth and distance, or shear velocity field (SVF) images, for near surface section display picking. Three locations in the province of Nova Scotia, Canada, with different geological scenarios, were used for seismic investigations: moderately dipping coal seams in the Stellarton Coalfield, steeply dipping gold-bearing veins in the West Waverley Gold District and nearly horizontal strata in Liverpool. The results from the seismic surface wave technique introduced in this research can be evaluated by field observations, documents and borehole logs. The satisfactory interpretations and success of these investigations will result in engineering application for subsurface investigations.
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Investigating The Interior Of A Landfill Cell With Leachate Injection Using Electromagnetic Conductivity And Ground-Penetrating Radar Surveys
Bioreactor landfills enhance waste degradation through recirculation of leachate inside the waste mass. In this study frequency-domain electromagnetic (EM) conductivity was measured along
several profile lines before and after leachate injection at a leachate recirculation cell at the Veolia ES Orchard Hills Landfill, 15 km south of Rockford, Illinois. One profile line was located above and coincident with a leachate recirculation line (LRL). The other profiles were perpendicular to LRLs, which varied in depth from 5-15 m below the EM lines. Apparent conductivity increased along segments of the EM profile over the LRL during injection of 17.8 m3 of leachate, when measured with a Geonics EM34 at 10 and 20 m vertical dipole separations. Leachate injection appears to be nonuniform along the LRL, with larger volumes entering the waste at the beginning, middle and ends. EM values during a second experiment, however, in which a smaller leachate volume was injected, showed no change. Ground-penetrating radar (GPR) profiles, made with 25 and 50 MHz antennas, showed diffractions at the position of the LRLs (between 5 and 10 m depth) and a very strong reflector (intermediate clay cover layer or pooled leachate) at about 8-9 m depth, whereas a 100 MHz GPR profile only showed the clay cap and top of waste at approximately 2.5 m depth.
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Resisitivity And Ip 2D Surveying At An Old Landfill Site In Ribeirão Preto, São Paulo, Brazil: Acquisition Parameters Evaluation And Environmental Monitoring
More LessDue to the increasing concern with environmental protection and preservation, inadequate waste disposal areas have been receiving special attention from environmental protection agencies. Currently, the geoelectrical methods have been largely used as a non-invasive investigation methodology in affected areas by inadequate disposal of solid urban and industrial residues. The objective of this study is the evaluation of the field acquisition parameters and 2D investigations with resistivity and induced polarization (IP) methods for environmental characterization and monitoring. The study area is an old landfill site in Ribeirão Preto, São Paulo State, Brazil. The evaluation of the field acquisition parameters showed that the pole-dipole array (electrode spacing = 5 meters and investigation depth levels = 10) yields the best result (resolution image and investigation depth). The comparison between the results, resistivity and IP with dipole-dipole and pole-dipole shows the contamination in the two trenches, marked by low resistivity values (< 30 ohm.m) and medium to high IP values (15 – 50 mV/V).
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An Approach To Uxo Discrimination Via Polarizability Curvematching And Feature Extraction Applied To Polarizability Curves
More LessPolarizability curves are means of representing data from a multi-transmitter, multi-receiver Berkeley Unexploded Ordnance discriminator (BUD) sensing system. The polarizability curves contain information about the geometry and electromagnetic properties of isolated targets in the BUD vicinity. The are many ways in which polarizability data can be processed and interpreted, resulting in a classification as UXO or non-UXO object for a given set of curves. We explore a process of feature extraction, together with pattern recognition applied to resultant feature-vectors. By examining training data from known object classes, we seek features which tend to cluster together for a given object class. This can be viewed as empirically estimating probability density functions on each feature. The minimum number of classes is two: UXO and non-UXO. However, in future we envision one class for each type of UXO present in a dataset, and possibly more than one class of scrap in the case where particular non-UXO objects are known to contaminate a site. The probability density function estimates obtained are used to partition the feature space into regions, which correspond to ‘high probability of being UXO’, and ‘high probability of being non-UXO’. These probabilities are greater than some predefined threshold α. In this way, bounded regions of the feature space can be identified using hyperplanes and a simple calculation on a given feature-vector will then determine the region in which the
observation lies. Clearly, some feature-vectors will fall outside both regions. In this case we discuss some reasons why it is not immediately clear in which category the observation lies, and describe an auxiliary algorithm intended to treat this subset of observations.
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Geophysical Characterization Of The Red Lake Peatland Complex, Northern Minnesota
Authors James T. Nolan, Andrew D. Parsekian, Lee D. Slater and Paul H. GlaserThe Red Lake Peatland Complex in Northern Minnesota is one of the largest and most studied peatlands in North America (140 km2), but the logistical impediments of working in such large remote wetlands limit direct subsurface data collection to a few widely spaced samples. This mid-continent forested bog complex is comprised of three major peat landforms, each of which was surveyed using ground penetrating radar (GPR), electrical resistivity, and induced polarization (IP): (1) a raised, ombrotrophic, wooded crest; (2) a sphagnum lawn down slope of the bog crest; (3) a spring fen water track where water flows across the peat surface around ovoid wooded islands. GPR was used to obtain peat thickness and to distinguish the peat stratigraphy as a function of variable water content between organic soil horizons. Resistivity data was collected to characterize the peat thickness and structure and to image the hydrogeologic framework beneath the organic soil. The results form a novel data set of a well studied bog complex, offering new insights into the peat structure and hydrogeologic framework. These observations have implications for general models of peatland development and carbon cycling.
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A Study Of Seasonal Salinity Variation In Lake Whitney, Texas Using Continuous Resistivity Profiling
Authors John A Dunbar, Sikiru A. Amidu and Peter M. AllenLake Whitney, Texas is an example of many reservoirs whose water quality is controlled by highly variable sodium chloride loads originating from near surface evaporate deposits within the upper reaches of the contributing watershed. We investigate seasonal changes in salinity within Lake Whitney using the continuous resistivity profiling (CRP) method. From December, 2006 to October, 2007 we repeated a 30-km long profile along the axis of the reservoir six times. A 135-m long, 11-electrode, marine resistivity array was used to collect eight dipole-dipole readings at offsets from 5-120 m, at intervals of approximately 1 m along the profile. Each profile was collected in an 8 to 10 hour period to produce a “snapshot” of the salinity distribution. Starting from a well mixed and highly saline (3 ohmm/2,300 mg/L) state in early winter 2006, the reservoir became progressively fresher, due to the inflow of fresher water (4 ohm-m /1,700 mg/L) over the winter months. Spring rains, caused resistivity to rise and salinity to drop as layers of freshwater flowed out along the surface from north to south after each storm. The freshwater in these layers progressively mixed with deeper, more saline water as it moved south, raising the average resistivity of the reservoir. A second layer of cold freshwater flowed along the reservoir bottom in the north and out into mid-water depths as it moved south. The greatest contrast within the water column always occurred near the main tributary inlet and was least near the dam,
suggesting progressive downstream mixing. We conclude that the CPR method can be used to delineate the depth and lateral extent of abnormally fresh and saline regions within water reservoirs and can resolve shallow and deep zones of contrasting salinity within the water column.
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The Nmr Spin Lattice Relaxation Rate Of Hydrated Sands As A Function Of Magnetic Field
Magnetic resonance sounding can be used to locate near-surface aquifers. The nuclear magnetic resonance spin-lattice relaxation rate (R1) of the aquifer can be used to determine the porosity of the sedimentary material in the aquifer. Large variations in R1 have been reported in laboratory measurements of porosity. We believe these variations are attributable the different magnetic field strengths used in the laboratory measurements, and the sand type. The R1 of three fully hydrated quartz sands was measured and compared to that for fully hydrated glass beads as a function of applied magnetic field. R1 values increased with decreasing particle diameter for both sand and glass bead samples. R1 values also increased with decreasing magnetic field strength. The field dependent R1 data allowed the prediction of R1 at the Earth’s magnetic field. Measurable R1 differences were observed between the three natural quartz sands and glass beads. These differences can not be attributed to the geometric characteristics of the grains and porosity differences. The R1 differences can be attributed to trace paramagnetic impurities in the quartz which influence the surface relaxation component of R1. These findings will be useful in the prediction of aquifer characteristics based on nuclear magnetic resonance sounding information.
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Love Wave Propagation In Viscoelastic Media
Authors G. Vijaya Raghavendra Chakravarthy and Paul MichaelsSurface wave measurements have been used to compute the dynamic soil properties for near surface site characterization and the dynamic design of foundations. Much of this work has been
done with the Rayleigh waves which are dependent on both the shear and the compressive wave properties of the soil. Love waves, on the other hand, are sensitive only to the shear wave response of the soil. This shear only sensitivity greatly simplifies determining the damping and the stiffness of a near surface soil profile. Further, the mechanism of damping can be related to purely inertial interactions of the soil frame and the pore fluids, free from compressive factors. Traditionally, soils have been represented by elastic models. While elastic models are adequate
in representing dry or impermeable soils, they fail to account for the observed down-hole body wave dispersion in permeable, water saturated soils. To overcome this limitation, a viscoelastic model can be used. In this work, a viscoelastic representation of the Love wave propagation is derived for the forward problem. The solution to this forward problem yields the dispersion and the attenuation curves. Also computed are the complex motion-stress vectors for a vertically heterogeneous, viscoelastic medium, with the shear viscosity as a specific material property. The viscoelastic constitutive model will lead to an improved representation of Love wave propagation in permeable, water saturated soils where the concept of the effective viscosity becomes inappropriate.
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Characterization Of A Beach Revetment Using Ground Penetrating Radar And MASW
Authors Mario Carnevale and Jutta HagerA geophysical survey was performed on Nantasket Beach in Hull, Massachusetts to measure the angle of slope and depth to the bottom of a buried rock revetment. The work was commissioned to confirm that the revetment had been constructed in accordance with design specifications. Considering the difficult subsurface terrain of a beach environment, the survey methods deemed most appropriate for achieving the stated goals were multi-frequency ground penetrating radar (GPR) systems, supplemented by multi-channel active surface wave (MASW) seismic using higher resolution survey geometry. Data collection was scheduled during the lowest ocean tide level within the 8-hour low tide cycle in order to mitigate the effects of saltwater saturation of the subsurface. In order to overcome the effects of the difficult beach environment, several iterations of data processing and analysis of GPR and seismic data were performed to:
• Delineate the revetment surface,
• Identify features associated with the revetment bottom, and
• Determine the critical parameters affecting the accuracy of the interpreted results (error analysis).
An advantage of these non-invasive methods was that they produced relatively limited interference with public use of the beach, which remained open while the data were being collected.
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Some Practical Aspects Of Masw Analysis And Processing
Authors Julian Ivanov, Richard D. Miller and George TsofliasWe use multi-channel analysis of surface waves (MASW) on seismic data in an attempt to test data acquisition parameters and compare those results to reaffirm existing general theoretical recommendations and rules of thumb. Of particular interest were optimum seismic receiver spread size, minimum and maximum receiver offsets and dominant geophone frequency for best-case fundamental-mode dispersion-curve evaluation of the Rayleigh wave. Recommended MASW parameter selection criteria are tested on seismic data collected at various sites, such as desert setting, river sediments, and glacier, for which shear-wave properties were estimated. Presented MASW results demonstrate that observing optimal parameter selection can improve the resolution and quality of the fundamental-mode dispersion-curve images of the surface wave and the final 2D Vs section. After comparing the optimal parameter selection approach with the general theoretical recommendations it was concluded that the rules of thumb are s a good starting point, especially when applying the MASW method at a site with unknown seismic characteristics. However, optimal acquisition and processing MASW parameter selection can be best achieved using field site tests and is the preferred approach over theoretical recommendations. Specifically testing a selected brand of geophones, it is expected that, in general, frequencies as low as one octave and a half bellow the natural geophone frequency can be recommended used for most MASW analysis.
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Temporal Geophysical Investigations Of The Ft-2- Plume At The Wurtsmith Air Force Base, Oscoda, Michigan
Authors R. Joyce, C. Vukenkeng, E. Atekwana, E. Atekwana, D. Werkema, S. Rossbach, G. Abdel Aal, C. Davis and J. NolanThe decommissioned Wurtsmith Air Force Base former Fire Training Cell (FT-02) facility has been the focus of several geophysical investigations. After several decades of fire training exercises, significant amounts of hydrocarbons and some solvents seeped into the subsurface contaminating the vadose and saturated zones in the source area. Groundwater geochemistry studies defined a contaminant plume that was approximately 125 m wide and > 300 m long. The boundary of the plume was further defined by using GPR, SP, and resistivity techniques. The source of the geophysical anomalies was attributed to biogeochemical modifications of the contaminated zone resulting from intrinsic bioremediation. In 2007, another integrated geophysical study of the site was conducted. GPR, SP, and electrical resistivity surveys were conducted with expectations of achieving similar results as the past investigations. However, there was a marked decrease in geophysical response from all of our geophysical techniques. The GPR anomaly has migrated deeper into the subsurface, the positive SP response was significantly attenuated, and the conductive resistivity anomaly has been replaced by background resistivity values. Also, six Geoprobe cores at three different locations were collected in order to conduct laboratory microbial counts and IP measurements. We attribute the attenuation of the observed geophysical anomalies to ongoing soil vapor extraction initiated in 2001. Significant removal of the contaminant mass by the vapor extraction system altered the subsurface biogeochemical conditions and these changes were documented by the 2007 geophysical data. The results of this study show that the attenuation of the contaminant plume is detectable with geophysical methods.
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Use Of Active Source Seismic Surface Waves In Glaciology
More LessActive source seismic surface wave experiments were performed on Jakobshavn Glacier, Greenland, to evaluate the potential utility of surface wave methods on ice. A sledge hammer source striking a wooden beam, and a receiver line with twelve 28 Hz vertical geophones were used to generate and record surface wave data. We employed the Multichannel Analysis of Surface Waves (MASW) method to obtain dispersion curves and estimate shear wave velocities of firn and shallow ice. The sledge hammer source produced signal with usable frequencies in the 12 to 100 Hz range. Maximum depth of imaging was estimated to approximately 50 m. Firn shear wave velocities progressively increased from 1000 m/s near the surface to the ice velocity of 1950 m/s at around 47 m below the surface. This indicated that the firn-ice transition was at approximately 47 m below surface. We show that surface wave methods can be a viable alternative to traditional refraction surveys in determining firn velocity structure. Surface wave methods can provide continuous shear wave velocity maps of the subsurface which can aid in developing a better understanding of firn mechanical properties and mechanisms of crevasse formation.
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A Multi-Instrument Approach To Meeting Positional Data Quality Objectives
Authors Steve Saville and Nathan HarrisonAccurate and repeatable positioning is central to quality digital geophysical mapping. Varying field conditions, such as residential development, tree canopy, and terrain, often require a multiinstrument approach to collecting positional data at a given site. Although each instrument contributes to overcoming these data collection obstacles, the inability to transition between positioning instruments can undermine an otherwise successful field effort. In August 2007, Parsons conducted digital geophysical mapping within residential areas of the Former Brooksville Turret Gunnery Range, Florida. Housing, landscaping, and tree canopy posed unique challenges, and required the fluent use of Real Time Kinematic GPS, Robotic Total Stations, and
fiducial methods for positional data. This presentation will provide a brief narrative on the multiinstrument approach. We will discuss survey planning and team assignments, technical issues,
processing requirements, and the final quality of each method. We will compare each method’s ability to meet data quality objectives efficiently. Finally, we will present lessons learned on how to more effectively complete a multi-instrument approach.
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Airborne Vertical Magnetic Gradient Survey At Fort Mccoy, Wisconsin
Authors Jacob R. Sheehan, William E. Doll, T. Jeffrey Gamey and Mark W. McCartyIn October 2006, an airborne vertical magnetic gradient survey was conducted at Fort McCoy near Sparta, Wisconsin for the U.S. Army. The intent of this project was to conduct a wide area
geophysical screening survey to determine where UXO is concentrated within the 570 acre Badger Drop Zone (BDZ), a paratrooper training area. A geophysical prove-out site, consisting of nine emplaced targets and one pre-existing item distributed on two profile lines, was established to support daily quality control measurements, and to provide a benchmark for detection limits of the survey. The data acquired during this survey will assist the Fort McCoy staff and their contractors in a variety of characterization, screening-level, and removal activities associated with determination of the extent of potential UXOrelated contamination at the site.
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Combined Ground Penetrating Radar And Masw Surveys To Locate Dam Seeps
Authors Mario Carnevale and Jutta HagerMultiple-frequency ground penetrating radar (GPR) and multi-channel analysis of surface waves (MASW) methods were used at the Reichenback Pond Dam in Woodbury, Connecticut to delineate the extent of known seeps and to locate possible responsible utilities. The present dam was constructed over an earthen road stream crossing thought to contain a small culvert. MASW was used to obtain soil property data, constraints for GPR interpretations, and to detect possible shallow seep zones or utilities. The multi-frequency (100-, 200-, and 500-MHz) GPR program was implemented on the paved road on top of and along both sides of the dam. Seismic data were collected along the paved road and on its north side where the seeps were located.
Strong GPR anomalies indicated air- or water-saturated zones with localized collapse. MASW results also showed velocity anomalies in the interpreted seep zones. The strength and depth of MASW velocity anomalies were sensitive to variation in coupling media (road pavement vs. grass) and the methodology of dispersion curve analysis. Post-survey drilling supports the geophysical interpretation of seep zones related to the collapse of the older original culvert, primarily at the north toe of the dam.
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Analysis Of Surface Waves From 9-C 2-D Seismic Data
Authors Carlos Calderón-Macías and Jim SimmonsIn seismic exploration, knowledge and understanding of the near surface is paramount for recovering reflectors with a high bandwidth, and uncontaminated by shallow subsurface effects such as strong statics, surface waves and scattered noise. High quality multicomponent seismic data are obtained using a vertical and two orthogonal shear-wave vibrators as seismic sources, and recorded by threecomponent (3-C) geophones in a two-dimensional (2-D) acquisition geometry. The vertical vibrator is predominantly a compressional wave (P-wave) source, while the inline and crossline shear-wave vibrators are predominantly SV- and SH-wave sources, respectively. Surface wave dispersion curves (Rayleigh wave and Love wave) can be interpreted from phase-velocity measurements taken from the appropriate source-receiver components, and 1-D shear wave velocity profiles derived through linearized inversion. Without a priori knowledge of the velocity distribution with depth, the inverted profiles often result in unrealistic models. A simple model with relatively few parameters to solve for then constitutes the target of the inversion. An important aspect of our work is validation of the inverted shear-wave velocity profiles using multicomponent elastic forward modeling. Inversion and modeling tests show that a relatively simple shallow profile explains the observed surface-wave phase-velocity measurements. Our results indicate that use of additional information such as reflection, refraction and borehole data are needed to more accurately invert for the shallow subsurface.
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Mapping The Extent And Activity Of Tree Root Zones With Self Potential And Misse A La Masse
Authors Anton Kepic, Tristan Campbell and Christoph HinzAfter collaborating with soil scientists in studying salinity it became evident that the typical methods used by botanists and soil scientists to study the rizosphere (root-zone: Fitter and Hay, 1987; Wheatheley, 1975) appear to be somewhat crude by the standards of physical scientists. The most popular method of study is to instrument the tree and its environment with some basic non-invasive sensors (if at all), let it grow to some size, and then dig it up to begin the research. The principal instrument used in these studies is a large backhoe. This approach makes time-lapse studies difficult as the subject of the study is killed and the earth surrounding the tree is disturbed in the process. So the possibility of non-invasive monitoring the rizosphere via geophysical techniques is very appealing to the scientists who study trees.
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A Geophysical Study Of The Impact Of Agricultural Management Practices On The Hydrologic Properties Of A Texas Vertisol
Authors Sikiru A. Amidu, Kenneth N. Potter and John A. DunbarWe integrate geoelectrical measurements with in-situ soil-moisture determination using core sampling to assess changes in vadose zone properties induced by agricultural management ractices in a Texas Vertisol. Two sites were established at the USDA research station, Riesel, Texas, where the underlying soils are cultivated soil for crop production and a soil in grass pasture. Center spread multielectrode resistivity data were collected on each site along the same profiles on February 22, May 7, and September 12, 2007. Data analysis involved inversion using a rapid least-square technique and temperature corrections. The results were calibrated against the in-situ soil-moisture values to generate apparent soil-moisture sections. Using the van Genuchten pedotransfer function, we used the apparent soil-moisture data to compute apparent distribution of pressure heads in the soil. The results for successive sections were then related to compute apparent soil-moisture flux over the intervals between each field survey. Significant variations in resistivity and soil-moisture dynamics between the two sites were observed in the upper 2 m of the soil, especially within the root zone. We show that, within the limitation posed by the problem of equivalence in data interpretation, management-induced changes in
soil hydrologic properties can be characterized using the electrical resistivity method.
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Inversion Of Large Electrical Resistivity Surveys On Multiprocessor Platforms
Authors Dale F. Rucker, Marc T. Levitt, Jason Greenwood and Xianjin YangModern multi-channel resistivity instrumentation has facilitated an increased usage of electrical resistivity geophysical surveying over large and complex areas. Resistivity line lengths for near surface environmental problems commonly exceed a kilometer and 3D acquisition may be on the order of hectares. To evaluate the data through electrical resistivity inversion, however, the size of the model domain has been limited to very small problems based primarily on the memory allotment of the 32-bit Microsoft Windows-based operating systems. In this case, multiple small domains are required to model the large surveys. To overcome the domain-size limitation, the EarthImager3D code has been restructured to accommodate the latest Microsoft 64-bit operating systems (Windows Vista or Server 2003), with multiple processors and large computer memory availability. To demonstrate the increased capacity of the code, a field example is provided that shows the advantage of inverting data within a single domain compared to smaller multiple domains. The field data includes 47 lines of pole-pole resistivity profiles collected along parallel and orthogonal lines over a liquid waste disposal site in eastern Washington.
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Seismic Refraction For Monitoring Zones Of Water Table Fluctuation In A Shallow Tropical Aquifer
Authors Christopher A. Crowell, Dr. Curtis A Link and Dr. Paul NelsonFertilizer application on sugar cane fields has resulted in increased levels of nitrates entering the drainage system of the Mulgrave river basin in north Queensland, Australia. A series of refraction profiles were recorded at six locations where monitoring wells were located. Approximately six profiles were recorded at each well location from February through May 2007. We used seismic refraction to determine water table depth to sub-meter precision based on proper understanding of the water table annual zone of fluctuation and the residual air that exists in the soil within this zone. Within the annual zone of fluctuation, saturation is approximately 99%. At this saturation, refracting velocities were observed to be in the range of 600 m/s to 1000 m/s. Additionally, refraction is also observed from the 100% saturated zone which yields refraction velocities greater than 1500 m/s. Using the refraction from the less than completely saturated zone, we were able to predict water table depths in good agreement with well measurements.
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A Modern Geophysical Approach To Mapping Clay In The Subgrade – Case Study
Authors Jim Pfeiffer, Kanaan Hanna, Khamis Haramy, Roger Surdahl and Khalid MohamedThe presence of swelling clay beneath roadways poses a significant problem to road rehabilitation design and construction. Conducting precise subgrade soil investigations to determine the
location of potential clay-rich zones rapidly and nonintrusively is of great interest to the geotechnical engineer. A multi-phase program was designed to demonstrate the effectiveness of the Electromagnetic Induction (EMI) method as a state-of-practice geophysical imaging tool for mapping the presence of clay seams in the subgrade beneath roadways. The objective of this study was to compare the results from traditional subsurface soil investigation to a nonintrusive investigation using the EMI method. The results indicated that the EMI is a promising geophysical tool to compliment the current geotechnical engineering investigations approach as a value added. It is a fast, efficient, and cost effective tool for continuous mapping of spatial variations in soil conductivity of subgrade. A strong correlation between soil conductivity and the Atterburg Limits of Soils was not established; however, a qualitative evaluation of areas with increased potential for high plasticity clay content can be estimated from the EMI data. The EMI tool can be used to investigate in-situ soil behavior and to focus the soil boring programs during project site investigations, road rehabilitation, and construction.
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A Comparison Of Shear Wave Velocities Obtained From The Crosshole Seismic, Spectral Analysis Of Surface Waves And Multiple Impacts Of Surface Waves Methods
Authors Patrick K. Miller, Nils Ryden, Yajai Tinkey and Larry D. OlsonPresented herein is the comparison of the shear wave velocity results, with respect to depth, obtained from three separate test methods at a soil test site. The Crosshole Seismic (CS) test was performed utilizing three cased boreholes nominally 10 feet apart. The direct shear wave velocity was obtained from the results of the CS test. The Spectral Analysis of Surface Waves (SASW) test method and Multiple Impact of Surface Waves (MISW) test method were also performed at the same test site for comparison purposes. Neither the SASW nor MISW test methods require the installation of boreholes, thus reducing the cost of the test. SASW and MISW differ slightly from one another in the equipment used, method of data collection, and differ significantly in data processing. This paper includes a comparison and discussion of the test results, as well as backgrounds of each test method.
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Imaging Lava Tubes For Engineering Design
Authors Jim Pfeiffer, Steve Hodges, Kanaan Hanna and Khamis HaramyIn Hawaii, lava tubes are a significant concern to highway construction and maintenance projects not only for the long-term durability of the road surface, but also for the immediate safety of the construction crews and public. Prior knowledge of the location and depth of lava tubes can greatly aid in the design of engineering structures to improve safety and mitigate road degradation. This paper covers the geophysical investigation using ground penetrating radar (GPR) technique to map the lateral extent of lava tubes beneath the roadway and to determine the depth to the top of the lava tubes at two sites in Hawaii. At the first site, a detailed survey was performed over a segment of Crater Road with known lava tubes. The Federal Highway Administration (FHWA), Central Federal Lands Highway Division (CFLHD) is currently designing a remediation structure to bridge the lava tube to protect the tube from damage while increasing the load carrying capacity of the roadway. At the second site, a segment of Saddle Road was surveyed to locate lava tubes beneath the existing roadway prior to CFLHD’s planned reconstruction project. The information obtained from the GPR surveys is of great interest to the geotechnical and design engineers during site investigations, road rehabilitation and construction.
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Modeling The Emi Decay Response Of Medium And Large Uxo With Conventional And B-Field Sensors
Authors Michael W. Asten and Andrew C. DuncanWe compare the response of a conventional dB/dt EMI system (Geonics EM63) with a new system which utilizes a 3-component fluxgate B-field sensor. The B-field system has the advantage of providing decay curve information to times a factor of 5 to 10 greater than is achieved by the conventional dB/dt system. The transition from intermediate to late-time decay behavior is predicted theoretically to occur about a factor of two earlier in time for the B-field system, and this is confirmed by plotted observed data. Longer pulse times, lower transmitter frequencies, and longer decay curves are possible with the B-field system due to its wider bandwidth and lower noise at the low-frequency end of the spectrum. The decay constant for the medium and large munitions items considered here ranges from 12 to 25 msec and all decays when excited and measured with the EM63 EMI metal detector are incorrectly estimated as too small, due to the limited pulse-length and off-time intervals in the EM63 system. We propose that the improved ability of the B-field system to estimate the fundamental decay constant of a conductive permeable object will assist in UXO target discrimination, especially for situations where decay curves at earlier sample times are perturbed by ancillary scrap, or the response of
magnetic earth.
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Turning Crosshole Sonic Logs Into Tomography Images Of Defects In Drilled Shaft Foundations
Authors Yajai Tinkey, Ph.D. Olsen and Larry D. OlsonThis paper presents velocity tomograms from the horizontal Crosshole Sonic Logging (CSL), Crosshole Tomograpahy (CT) and Angled Crosshole Sonic Logging (ACSL) tests on a mock up shaft for comparisons of defect resolution. The CSL method is used to measure the speed of sound horizontally between water-filled cast-in-place access tubes. The velocity of the sound wave which travels from source to receiver in a horizontal plane determines the presence of anomalous regions (due to water or air-filled voids or soil intrusions) and therefore the quality of the concrete. For added higher resolution of shaft integrity and defects, the CT velocity imaging method is used. The CT velocity method precisely defines the size, shape, severity, depth, and location of potential defects by determining the spatial velocity distribution of shaft concrete through analysis of numerous sound wave ray paths. However, performing the CT tests can be time consuming. The ACSL test is a compromise technique between the CSL and CT test methods in terms of speed of testing and resolution of the tomogram image. This technique uses arrays of sources and receivers (in this study, 4 sources and 4 receivers) to obtain different angled ray paths. The ACSL method turns every log into a tomogram image with a fraction of time used in the CT tests.
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Determining The Length Of H And Sheet Piles Using The Parallel Seismic Method
Authors Eugenia K. Roman, Larry D. Olson and Dennis SackMany of the older bridges in the United States have no original contract documents available and about 26,000 bridges that are rated as scour critical have unknown foundation conditons. Thus, no information is available regarding the type, depth, geometry or material of these scour critical bridge foundations. The unknown bridge foundations pose a significant problem to bridge owners because of safety concerns. The Parallel Seismic (PS) method allows for easy and accurate determination of the foundation pile tip depth. The theory of the PS test method is presented herein. Several case studies for the Parallel Seismic method for determining the unknown depths of different types of foundations are summarized in this paper.
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Geophysical Surveys At Machu Picchu, Peru: Results For Landslide Hazard Investigations
Authors Melvyn Best, Peter Bobrowsky, Marten Douma, Victor Carlotto and Walter PariGeophysical methods are being used more frequently to assess slopes for landslide hazard potential, especially in areas where traditional methods such as trenching and drilling are either difficult to employ or not allowed. This paper presents the results of joint DC resistivity and EM surveys to map fractures and zones of weakness in crystalline bedrock at Machu Picchu, Peru. DC resistivity surveys were carried out along the upper 8 switchbacks leading to the sanctuary as well as across the sanctuary. EM-34 surveys were carried out along the upper 3 switchbacks and across the sanctuary. Inversion of the resistivity data located several lower resistivity zones along the switchbacks. These zones were associated with water seeping out of the rock in ditches. The water is confined to the upper switchbacks which is consistent with the disappearance of lower resistivity zones in the lower switchbacks. EM-34 results along the switchbacks, although more subtle to recognize, located several coincident zones of lower resistivity. The DC resistivity data across the sanctuary located a lower resistivity zone on the east side of the main plaza. There is presently no information on whether any of these fractures have been active in the recent past. Consequently the results from this study are still under investigation.
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Estimation Of Bedrock Depth Using The Horizontal-To-Vertical (H/V) Ambient-Noise Seismic Method
Authors John W. Lane, Eric A. White, Gregory V. Steele and James C. CanniaEstimating sediment thickness and the geometry of the bedrock surface is a key component of many hydrogeologic studies. The horizontal-to-vertical (H/V) ambient-noise seismic method is a novel, non-invasive technique that can be used to rapidly estimate the depth to bedrock. The H/V method uses a single, broad-band three-component seismometer to record ambient seismic noise. The ratio of the averaged horizontal-to-vertical frequency spectrum is used to determine the fundamental site resonance frequency, which can be interpreted using regression equations to estimate sediment thickness and depth to bedrock. The U.S. Geological Survey used the H/V seismic method during fall 2007 at 11 sites in Cape Cod, Massachusetts, and 13 sites in eastern Nebraska. In Cape Cod, H/V measurements were acquired along a 60-kilometer (km) transect between Chatham and Provincetown, where glacial sediments overlie
metamorphic rock. In Nebraska, H/V measurements were acquired along approximately 11- and 14-km transects near Firth and Oakland, respectively, where glacial sediments overlie weathered sedimentary rock. The ambient-noise seismic data from Cape Cod produced clear, easily identified resonance frequency peaks. The interpreted depth and geometry of the bedrock surface correlate well with boring data and previously published seismic refraction surveys. Conversely, the ambient-noise seismic data from eastern Nebraska produced subtle resonance frequency peaks, and correlation of the interpreted bedrock surface with bedrock depths from borings is poor, which may indicate a low acoustic impedance contrast between the weathered sedimentary rock and overlying sediments and/or the effect of wind noise on the seismic records. Our results indicate the H/V ambient-noise seismic method can be used effectively to estimate the depth to rock where there is a significant acoustic impedance contrast between the sediments and underlying rock. However, effective use of the method is challenging in the presence of gradational contacts such as gradational weathering or cementation. Further work is needed to optimize interpretation of resonance frequencies in the presence of extreme wind noise. In addition, local estimates of bedrock depth likely could be improved through development of regional or study-areaspecific regression equations relating resonance frequency to bedrock depth.
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Effects Of Spatial Data Density, Sensor Noise And Position Errors On Uxo And Clutter Target Parameters From Inversions Of Alltem Data
More LessALLTEM is a multi-axis electromagnetic induction system designed for unexploded ordnance (UXO) applications. It uses a continuous triangle-wave excitation and provides good late-time signal-to-noise ratio (SNR) especially for ferrous targets. Inversions of field data acquired in survey (moving platform) mode over the Army’s UXO Calibration Grid and Blind Test Grid at the Yuma Proving Ground (YPG), Arizona in 2006 produced polarizability moment values for many buried UXO items that were reasonable and generally repeatable for targets of the same type buried at different orientations and depths. In 2007 we finished construction of a test stand that allows us to collect data with varying spatial data density and accurate automated position control. We have studied the behavior of physics-based nonlinear inversions of ALLTEM test stand data as a function of spatial data density, sensor SNR, and position error. These studies have been performed as part of our effort to develop quantitative confidence levels for our inversions. A high confidence level in inversion-derived target parameters will be required when a target is declared to be harmless scrap metal that may safely be left in the ground. Unless high confidence can be demonstrated, regulators will likely require that targets be dug regardless of any “no-dig” classifications produced from inversions, in which case remediation costs would not be decreased. Multi-axis transmitter (Tx) and receiver (Rx) systems such as ALLTEM provide a richer data set from which to invert for the target parameters required to distinguish between clutter and UXO. Our inversions are more tolerant of sensor noise and position error than has been reported for single-axis, single-element data inversions and thus higher confidence in calculated target parameters can be achieved. This is especially important in the case of moving platform survey mode field data.
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3D-Gpr In Transportation Infrastructure Evaluation
Authors Nenad Gucunski, Carl Rascoe and Ali MaherCommonly conducted GPR surveys on transportation infrastructure have several limitations. The first limitation stems from the use of a single antenna. This limits surveying during a single pass to a single survey line. The second limitation comes from the use of a fixed frequency antenna. Therefore, if of interest is to get a high-resolution image of a medium tested, from the surface to depths of a few meters, it is necessary to use multiple antennas of different frequencies. The third major limitation represents the antenna orientation. A single oriented antenna can detect only objects in the test line direction. A new generation of GPRs, three-dimensional (3-D) GPRs, provide significant improvements in the solution of the above problems. The 3D-GPR system presented operates in the step frequency mode, in a frequency range from 140MHz to 2GHz, and utilizes an array of 31 transmitting and receiving antenna pairs with a spatial resolution of 75 mm. The surveyed medium can be presented in terms of horizontal planes at different elevations, vertical cross sections or three-dimensional images. Applications of the system in roadway and concrete bridge deck surveys are presented.
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