- Home
- Conferences
- Conference Proceedings
- Conferences
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 - 100 of 136 results
-
-
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.
-
-
-
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..
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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).
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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).
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
Fiber-Optic Distributed Temperature Sensing: A New Tool For Assessment And Monitoring Of Hydrologic Processes
Fiber-optic distributed temperature sensing (FO DTS) is an emerging technology for characterizing and monitoring a wide range of important earth processes. FO DTS utilizes laser light to
measure temperature along the entire length of standard telecommunications optical fibers. The technology can measure temperature every meter over FO cables up to 30 kilometers (km) long. Commercially available systems can measure fiber temperature as often as 4 times per minute, with thermal precision ranging from 0.1 to 0.01 °C depending on measurement integration time. In 2006, the U.S. Geological Survey initiated a project to demonstrate and evaluate DTS as a technology to support hydrologic studies. This paper demonstrates the potential of the technology to assess and monitor hydrologic processes through case-study examples of FO DTS monitoring of streamaquifer interaction on the Shenandoah River near Locke’s Mill, Virginia, and on Fish Creek, near Jackson Hole, Wyoming, and estuary-aquifer interaction on Waquoit Bay, Falmouth, Massachusetts. The ability to continuously observe temperature over large spatial scales with high spatial and temporal resolution provides a new opportunity to observe and monitor a wide range of hydrologic processes with application to other disciplines including hazards, climate-change, and ecosystem monitoring.
-
-
-
Strategies For Accurate Automated ERT Data Acquisition
Authors Douglas J. LaBrecque, Paula Adkins and William A. DailyThe use of microprocessor-controlled data-acquisition systems allows the rapid collection of electrical-resistivity and induced-polarization data. Although this provides a method for cost-effective collection of multidimensional data sets, there can be significant sources of error introduced by these acquisition systems. These errors are systematic in nature and thus may be difficult to identify. Of particular concern are errors resulting from re-use of the same electrodes for transmitting and receiving and aging of those electrodes over time. In this paper, we consider results from laboratory sand-tank experiments and field studies at a number of electrical resistivity project sites. The field studies include measurements over an eight year period during the Drift-Scale Heater Test at Yucca Mountain, Nevada. The object of these studies was to understand the ability of the site to perform over a long period of time and to test a number of
methods of mitigating both systematic and non-systematic errors for real-world applications. A number of different data strategies are being tested including the effects of varying the delay time of measurements using the same electrodes and the impact of using constant-current versus constantvoltage transmitter sources. The initial results show that the relationships between errors and measurement strategies are not always intuitive. For example, a longer delay between transmitting and receiving on a given electrode pair may not necessarily reduce the errors. In addition, electrodes show long-term changes in error levels that do not show a consistent pattern or correlation to other factors.
-
-
-
Multi-Faceted Characterization Of Variable Limestone Terrains
More LessVariations in composition and karstic features within limestone terrains have the potential to be significant geotechnical risks to development in certain areas of Western Australia (WA). Over the past 4 years, Geoforce conducted a series of geophysical investigations in WA to assist in the geotechnical assessment and risk mitigation of such areas. The key findings from the surveys discussed in this paper are: 1. Electrical Resistivity Imaging (ERI) is only suitable for imaging geotechnical units where an electrical contrast is expected between geotechnical units. In limestone terrains, this will typically be for cavity investigations or where the geotechnical units have marked changes in clay content (e.g. Site 3) or porosity and are saturated with conductive liquid, such as saline groundwater or seawater. ERI has not been effective in imaging geotechnical units in dry, sand/limestone environments. 2. Multi-channel Analysis of Surface Waves (MASW) is usually an effective tool for imaging geotechnical units primarily due to the strong correlation between material hardness and shear velocity. However, the method is lower
resolution than other geophysical approaches used and is not always able to pick subtle variations within the sedimentary layers overlying limestone. 3. Ground Penetrating Radar (GPR) works exceptionally well in imaging karstic features where the ground is sufficiently resistive and other forms of information are available to assist in the interpretation of the data (e.g. CPT’s,
drillholes or other geophysical datasets. GPR is unable to provide any useful information in the more clay-rich materials of the Pilbara so a solid understanding of the site conditions are required before recommending its use. An EM31 is a useful tool for quickly establishing whether GPR is likely to work in the upper 5m. 4. The use of a combination of geophysical methods was found to enhance the nderstanding of the subsurface in all three sites, from either the improved resolution of one method with the geotechnical information from another (e.g. GPR and MASW at Site 2) or the measuring of different physical properties (e.g. ERI and MASW at Site 3) to understand the relationship between geological units and geotechnical properties.
-
-
-
Characterization Of Complex Hydrogeology And Geology At A Large Environmental Site In New Mexico Using Advanced Borehole Geophysical Data
By Ned ClaytonAdvanced borehole and cased well geophysical logging and analysis, using technologies developed in the petroleum industry, have been performed in over 40 groundwater monitoring wells at a large environmental site in New Mexico since 1998 as part of an environmental restoration project. Applied geophysical logging technologies include magnetic resonance for bound/moveable volumetric water content and pore size distribution (uncased wells only); fully oriented, high resolution electrical resistivity imaging for geologic structure and texture (uncased wells only); epithermal neutron porosity for total volumetric water content (uncased and steel cased wells); bulk density and photoelectric factor for total porosity, water saturation and lithology evaluation (uncased and steel cased wells); array induction resistivity for water saturation and lithology evaluation (uncased wells only); neutron induced gamma ray spectroscopy for rock/sediment matrix geochemical evaluation; and natural gamma ray spectroscopy for geologic and lithologic evaluation. In addition to individual geophysical log measurements, integrated analysis (multi-log inversion) of t+H166he acquired geophysics data has been performed to generate continuous depth profiles of key formation properties, including total and effective porosity, vadose zone moisture content, water saturation, permeability, discrete fracture identification and aperture calculation, bedding and fracture orientation, formation electrical imaging showing geologic texture and grain size, rock/sediment matrix geochemistry, and lithology/mineralogy. The geophysical logs are used to guide well design (including optimal screen placement), evaluate borehole conditions, and provide a detailed in-situ characterization of the complex geology and unsaturated/saturated zone hydrogeology.
-
-
-
Geotechnical Site Characterization Of A Flood Plain By Refraction Microtremor And Seismic Refraction Methods
More LessThe objective of this study was the evaluation of quality VS models generated by refraction microtremor method (ReMi) testing 3 differents seismic sources (1 passive and 2 active ones), and its comparison with VP models generated by seismic refraction tomography, in the geotechnical site characterization of a flood plain where 2 borehole and 12 test-pits had been done in a previous geotechnical study. Nine seismic profiles were deployed with different reciever spacing (60 geophones of 10 Hz spaced 2, 1 and 0.5 meters). In each of the lines we acquired data from ambiental noise and sledgehammer hits at the beginning and the end of the seismic line to mod+H167el 3 VS profiles and one seismic refraction profile to model VP data. The ReMi and seismic refraction methods gave us good results. On the whole, both VP and VS models allowed a complete geotechnical characterization of the flood plain. All the geophysical models were compared with the geological data profiles from boreholes and test-pits and permitted a 3-D overview of the study site.
-
-
-
Detection Of Buried Timber Trestles Using Surface Waves
Authors Fernando Tallavó, Giovanni Cascante and Mahesh PandeyThis paper presents results from multi-channel analysis surface waves tests (MASW) conducted on an earth embankment to detect the location of rotten buried trestles in two different sections (A and B). In Section A, the locations of the trestles are known as well as the soil properties; thus, this section is used for calibration purposes. In Section B, the trestle locations are unknown. A seismic array of 24 geophones with a geophone spacing of 0.5 m is used. Different signal processing techniques were used for the analysis of surface waves to compute dispersion curves, power spectral density functions, distance-frequency contour plot, and wavelet transforms. Numercial and experimental results show that MASW tests were able to detect the location of buried trestles. MASW tests with a low-energy source (sledgehammer test) clearly show the location of buried trestles. Timber trestles can be detected by plotting the mean square value of the vibration energy. The effects of the trestles are also observed in the dispersion curves, the distance-frequency contour plot, and the Morlet wavelet transform. Not all source locations showed the location of timber trestles, likely because of the stronger effect of the ballast layer in this test.
-
-
-
GPS-Denied Geolocation For Geophysical Data Acquisition And Analysis
Authors David W.A. Taylor and Brian T. ClarkPrecise sensor positioning is critical to geophysical data collection and analysis. Positioning presents a special challenge in the woods, urban canyons and other areas where GPS does not perform well or at all. Efficient data acquisition, assurance of spatial coverage, and sensor data interpretation and analysis all require high-quality position data tightly correlated with sensor data. Improvements in underground feature/target characterization are critically reliant on the quality of the geolocation data. These approaches demonstrate the range of solutions which ENSCO has developed and demonstrated that may be considered for a particular application regardless of GPS coverage: Ranger – A local area radio-frequency positioning system, primarily applicable in wooded terrain. Integrated with an EM61 and a Geometrics G-858 for UXO surveying. Bloodhound – A GPS/inertial integrated system. Integrated with a Geometrics G-858 for meandering path data collection. SAINT – A high-precision (< 2 cm error) for local-area target characterization. Integrated with a Geonics EM61-HH for UXO characterization. RTOP – A super-precise (< 2 mm error) positioning system for ground-penetrating radar imaging. Integrated with a GSSI SIR-3000 for concrete imaging. There is no single GPS-denied technology for geophysics. The requirements for each application need to be understood and then matched to the available technology.
-
-
-
GPR Stratigraphy Of Fort La Presentation: Successful Target Delineation In A Highly Impacted Cultural Site
Authors Andrew L. Kozlowski, Aaron Gore, Barry Dale, Christina Rieth and Daniel MazeauFort La Presentation, a French fort built in 1749 at the confluence of the Oswegatchie and St. Lawrence Rivers in Ogdensburg, NY. The fort was destroyed by the British and rebuilt on numerous occasions prior to American occupation. Subsequent changes to the site included alteration of the original river bank, construction of a landfill, ship yard, train yard and later a business district. Overlapping the site was a petroleum storage facility that had contaminated the soil and the shallow water table. In February of 2007 initial ground penetrating radar (GPR) surveys were conducted over a 4 acre sight suspected to contain fort remains buried at depth. Surveys were completed using a GSSI 400 MHz antenna on 0.6 meter grid spacing. Initial amplitude slice maps revealed many targets including several rectangular high amplitude features at depths ranging from 1.5-2.4 meters in depth. In September, exploration trenches guided by amplitude–slice maps revealed a cobblestone surface overlain by ash, burnt timbers, faunal remains and hand wrought nails. Within the interstices of the cobblestone surface 5 French gun flints, musket balls and pottery confirm the surface to be that of one of the original structures built as part of Fort La Presentation.
-
-
-
Comparison Of Array Microtremor Survey Methods For Estimation Of Dispersion Curves In Launceston, Australia
Authors Maxime Claprood and Michael W. AstenThe geology of Launceston (Tasmania, Australia) is characterized by the presence of soft Tertiary and Quaternary sediments filling the Tamar rift valley, overlying a hard dolerite bedrock of
Jurassic age. We compare data interpreted from two microtremor (passive seismic) array processing methods at Launceston; the spatially averaged coherency (SPAC) and the frequency-wavenumber (FK) methods. We present array observations at two selected sites; GUNN Company (site GUN) located at a site with expected shallow bedrock interface, and the Detention Basin of Launceston (site DBL) inside the Tamar valley with expected deep bedrock interface. Through interpretation of SPAC data, we get a precise estimation of the shear wave velocity profile (or slowness profile) with depth, from which we derive the dispersion curve. Using FK, we estimate the shear-wave velocity and direction of propagation of the wave of most energy on the wavenumber spectra at different frequencies, also leading to the computation of the dispersion curve. At both sites GUN and DBL, we observe that SPAC analysis enables interpretation over a wider range of frequencies, while the FK method seems to overestimate the velocity at low frequency. SPAC is thus preferred for the evaluation of shear wave slowness profiles.
However, FK processing is useful for evaluating the spatial distribution of the waves direction of arrival.
-
-
-
Using Geophysics To Locate Unmarked Graves To Aid In Remediation Design And Construction At An Npl Site
More LessTetra Tech EM Inc.(Tetra Tech) was engaged by the Region 6 U.S. Environmental Protection Agency (EPA) under the Response Action Contract (RAC) program to perform a geophysical survey at the Rockwool Industries Superfund site. The purpose of the survey was to delineate the lateral extent of an old cemetery adjacent to a gulley where, for remediation purposes, a culvert was to be constructed. The cemetery was known to have unmarked graves, and some of the wooden coffins had been exposed due to erosion on the steep bank of a river immediately to the north. The geophysical survey results, if successful, would be used to guide the crew in avoiding any grave sites while placing the culvert. The survey was performed on March 1 through March 3, 2005. The Tetra Tech field crew employed a GSSI SIR 3000 ground penetrating radar system with a 400 MHz antenna and a GEM 2 terrain conductivity meter. Tetra Tech ran transects spaced 2.5 feet apart in an area measuring 25 feet by 40 feet over known grave sites to test the effectiveness of the equipment. Both the GPR depth sections and time slice plots successfully identified six known grave sites and four unmarked graves, but the GEM 2 had only limited success. Upon evaluation of the test plot, Tetra Tech continued the investigation in the area of concern near the planned placement location of the culvert. The results of the GPR survey identified four marked graves, but no additional unmarked graves were located. The GEM 2 survey, while not specifically identify individual graves, did differentiate disturbed soil in the cemetery area from undisturbed soil, so was used to conservatively delineate the boundaries of the
cemetery. The construction crew used the geophysical results to guide in the placement of the culvert, and there was no incident during construction.
-
-
-
Data Resolution Matrix And Model Resolution Matrix Of Rayleigh-Wave Inversion Using A Damped Least-Square Method
Authors Jianghai Xia, Richard D. Miller and Yixian XuEstimation of shear (S)-wave velocities by inversion of high frequency (≥ 2 Hz) Rayleigh waves has been given increasingly more attention by the near-surface geophysical community with application to a variety of near-surface geological and geophysical problems. For a given near-surface geophysical problem, it is essential to understand how well the data, calculated according to a layered-earth model, might match the observed data. It is also important to recognize that a match may only be possible for data within a certain frequency range or at specific frequencies because the sensitivity of Rayleigh-wave phase velocities due to changes in S-wave velocities varies with frequency. To provide insights into the process of inverting Rayleigh-wave phase velocities to estimate S-wave velocity structure, we introduced and discussed a data resolution matrix and a model resolution matrix of a damped least-square method. The resulting discussion indicated that each near-surface geophysical target can only be resolved using Rayleigh-wave phase velocities within specific frequency ranges and higher mode data are normally more accurately predicted than fundamental mode data because of restrictions on the data kernel of the inversion system. We proposed an inversion of data selected according to the data resolution matrix. The synthetic and real-world examples demonstrated that the proposed inversion could produce models with higher data resolution as well as higher model resolution.
-
-
-
Numerical Modeling Of Wave-Propagation In Elastic-Half-Space With Imperfections
By Gokhan InciSoil deforms under impact. If the strains are small enough (5×10-4 or less), the material approximates elastic behavior. In geotechnical engineering analysis, soil properties are assumed to be
isotropic and the state of stress is often modeled as an equivalent isotropic state. Thus, the compression wave velocity and the shear wave velocity can be used to characterize the material in the stress-strain range of mechanical waves. Shear modulus and Poisson's ratio are then estimated from these wave velocities. Elastic properties of soils are important in determining the small-strain response of soils under dynamic and static loading and are of major concern in site assessment. In the field seismic crosshole and seismic down-hole tests are performed to evaluate small-strain, elastic properties of soils. Ultrasonic testing has been used to determine small-strain, isotropic, elastic properties of soils in the laboratory. Seismic testing methods have the advantage of providing fast and reliable results. In this paper wave propagation in isotropic elastic half space is simulated with Finite Element and Finite Difference numerical models. P-wave and S-wave arrival times are compared to the theoretical arrival times and elastic properties are back-calculated. Imperfections on the surface are detected in terms of change in the wave arrival time. Errors for input versus back calculated values are provided. Finite element and finite difference methods can be used to simulate complex problems. Numerical tools can assist in the interpretation of field and laboratory test results.
-
-
-
Efficient 2D Inversion Of Long Ert Sections
More LessIn this work a new algorithm for the efficient 2D inversion of long ERT lines is introduced. The algorithm incorporates an experimental procedure to avoid calculation and storage of the entire Jacobian matrix. This approach speeds up the Jacobian matrix calculations and also reduces the required memory resources to store it. The efficient storage of the sparse Jacobian and Smoothness matrices and the efficient inversion using the LSQR method increase significantly the inversion speed. The application of the new algorithm to synthetic and real data sets resulted in reconstructed models of comparable accuracy to the standard inversion approach.
-
-
-
ERT Monitoring Of Recycled Water Injection In A Confined Aquifer
Authors Panos Tsourlos, Jung-Ho Kim, George Vargemezis and Myeong-Jong YiThis work describes the installation and measurements of an electrical resistivity tomography (ERT) system to monitor the injection of recycled water into a confined aquifer in the area of Sindos (Thessaloniki, N. Greece). The aim is to provide, through time-lapse ERT measurements and processing, geoelectrical images of rather increased volumetric sampling around and between the holes and to obtain improved understanding of the flow and transport of the injected water. The details about the general setting, the construction and installation of the ERT cables into the boreholes are explained in full. Measurements involving single and cross-hole ERT measurements in time-lapse mode were obtained and processed with a 2D inversion algorithm to produce images of the subsurface. Results depict a very good correlation between ERT images and the lithology and resistivity logs an indication of the reliability of the approach.
-
-
-
Cooperative Inversion Based On Fuzzy C-Means Cluster Analysis – Application To Field Data
Authors Hendrik Paasche, Jens Tronicke and Peter DietrichIn many near-surface geophysical applications it is now common praxis to collect co-located disparate geophysical data sets. The advantage of such multi-method based exploration strategies is the potential to reduce ambiguities and uncertainties in data analysis and interpretation. To reconstruct the underlying physical parameter distributions, usually requires the application of tomographic reconstruction techniques. To improve the reliability of the tomographic parameter models, the information content of all co-located data sets should be considered during the model-generation process. In this study, we apply a novel approach based on fuzzy c-means cluster analysis and conventional single-input data set inversion algorithms for the cooperative inversion of crosshole seismic P-wave and S-wave traveltimes. The approach results in a single zoned two-parameter model outlining the major subsurface units in terms of the P-wave and S-wave velocity fields.
-
-
-
Numerical Modelling Of Commericial GPR Antennas
Authors C. Warren and Dr. A. GiannopoulosGround Penetrating Radar (GPR) antennas are often not well described and hence modeled in the majority of GPR simulators. As a consequence results from these models do not represent reality. In this paper two detailed Finite-Difference Time-Domain (FDTD) models of commercial GPR antennas are presented. The complex geometry, material properties and feeding of the antennas are all captured in the models. The Visualisation Toolkit (VTK) format has been utilised to enable powerful three-dimensional visualisations of the complex antenna geometries, in addition to the antenna field patterns. Initial results from free-space responses (crosstalk) show good agreement between the models and data taken from the H177actual GPR systems.
-
-
-
Spatially Constrained Inversion For Quasi 3D Modeling Of AEM Data
Authors Andrea Viezzoli, Anders Vest Christiansen and Esben AukenThe spatially constrained inversion (SCI) is a robust methodology for quasi-3D modeling of geoelectrical and EM data of varying spatial density, using a 1D forward solution. It can be implemented with airborne or ground-based data, both in frequency and time domain. The airborne EM data here presented show how the SCI produces laterally smooth results with sharp layer boundaries that respect the 3D geological variations of layered settings. Information migrate horizontally through spatial constraints applied between nearest neighboring soundings, and allow to resolve layers that would be locally poorly resolved. The constraints are built using the Delaunay triangulation, which ensures automatic adaptation to data density variations. Data sets, models and spatial constraints are inverted as one system, producing layered sections with smooth horizontal variations. The SCI suppresses the elongated artifact commonly seen in horizontal maps (i.e., average resistivity, or saltwater boundary elevation maps) resulting from profile oriented data sets. Being an over-determined parameterized inversion problem, it produces a full sensitivity analysis of the output models, an essential tool for the evaluation of the results.
-
-
-
Characterizing Submarine Ground-Water Discharge Using Fiber-Optic Distributed Temperature Sensing And Marine Electrical Resistivity
More LessSubmarine ground-water discharge (SGD) contributes important solute fluxes to coastal waters. Pollutants are transported to coastal ecosystems by SGD at spatially and temporally variable rates. New approaches are needed to characterize the effects of storm-event, tidal, and seasonal forcing on SGD. Here, we evaluate the utility of two geophysical methods–fiber-optic distributed temperature sensing (FO-DTS) and marine electrical resistivity (MER)–for observing the spatial and temporal variations in SGD and the configuration of the freshwater/saltwater interface within submarine sediments. FO-DTS and MER cables were permanently installed into the estuary floor on a transect extending 50 meters offshore under Waquoit Bay, Massachusetts, at the Waquoit Bay National Estuarine Research Reserve, and nearly continuous data were collected for 4 weeks in summer 2007. Initial results indicate that the methods are extremely useful for monitoring changes in the complex estuarine environment. The FO-DTS produced time-series data at approximately 1-meter increments along the length of the fiber at approximately 29-second intervals. The temperature time-series data show that the temperature at near-shore locations appears to be dominated by a semi-diurnal (tidal) signal, whereas the temperature at off-shore locations is dominated by a diurnal signal (day/night heating and cooling). Dipole-dipole MER surveys were completed about every 50 minutes, allowing for production of high-resolution time-lapse tomograms, which provide insight into the variations of the subsurface freshwater/saltwater interface. Preliminary results from the MER data show a high-resistivity zone near the shore at low tide, indicative of SGD, and consistent with the FO-DTS results.
-
-
-
Remote Operated Vehicle Geophysical Survey Using Magnetic And Vlf Methods: Proposed Schemes For Data Processing And Interpretation
More LessAircraft geophysical investigations are recognized now as a powerful tool for geologicalgeophysical mapping, searching economic minerals, environmental studying, ecological monitoring, etc. Two main reasons limit an effective application of such conventional investigations: (a) essential impediments of performing geophysical surveys at small altitudes, (b) heightened danger for the aircraft crew, especially in the regions with a rugged topography. Remote Operated Vehicles (ROV) are free from the above-mentioned limitations. The new ROV generation – small and maneuvering vehicles – can fly at levels of few (and even one) meters over the earth’s surface (flowing the relief forms) with simultaneous performing geophysical measurements. Besides this, geophysical investigations observed at the vehicles, should have an extremely low exploitation cost (we suggest that the exploitation ratio of ROV / conventional investigations may consist of 1/20). Finally, measurements of geophysical fields at different observation levels could provide new unique geological-geophysical information. It is proposed that the most prospective geophysical integration for ROV should include measurements of magnetic and VLF electromagnetic fields. GPS (with utilization of the improved wide-band Kalman filtering) will assure an exact topogeodetic relation for the proposed observations. The nonconventional interpreting system developed for complicated environments may be successfully applied for analysis of the ROV observed geophysical data. Keywords: airborne, magnetics
-
-
-
An Overview Of Ice Profiling Using Ground Penetrating Radar (GPR)
Authors Patrick I. Finlay, Neil S. Parry, Samuel A. Proskin and Robert J. MickleWinter ice roads are built on water bodies in northern regions to transport goods and machinery to otherwise isolated mines and communities. Effectively monitoring ice thickness is one of the major factors that contribute to safe ice road travel. By continuously profiling the ice with Ground Penetrating Radar (GPR), thin areas can be detected by measuring the time it takes the electromagnetic pulse to travel to the ice-water contact, then converting this time to depth using the ice's velocity. Traditionally, for calibration purposes, an auger hole is drilled in the ice and its depth is used to back calculate the velocity of the ice. This method gives a fairly accurate indication of ice thickness and allows calibration at that location. However, changes in the ice's dielectric properties do exist and are primarily a function of temperature and the material’s composition – a mixture of water, air and ice. Therefore, with larger data sets, greater separations in latitude, and differences in the ice's composition, the ice’s physical properties are in constant flux. EBA Engineering Consultants Ltd. has developed a new radar system that can directly measure the ice's velocity while profiling. This paper looks at ice road data collected with traditional systems, discusses what mechanisms lay behind changing ice dielectrics and speculates that being able to measure real time variations in ice velocity may lead to a correlation in measuring ice strength.
-
-
-
Engineering Geophysics In Australia: Urban Case Studies From Downunder
Authors Robert J. Whiteley and Simon B StewartWithin Australia’s major coastal cities and urban areas geotechnical engineers are increasingly applying engineering geophysics for improved site characterisation in civil engineering projects and to assist with specific problems. Recent case studies from these cities illustrate the application of a variety of methods to a range of projects. Combining conventional surface geophysics, innovative borehole and underground geophysics with geotechnical methods increased innovative engineering opportunities and assisted the solution of specific design, construction and remediation problems for these civil projects.
-
-
-
A Comparative Assessment Of Several Dipole-Based Algorithms For The Extraction Of Uxo Target Parameters
Authors D.D. “Skip” Snyder, David C. George, Scott C. MacInnes and J. Torquil SmithWith funding from the Office of Naval Research (ONR), the Naval Explosive Ordnance Technology Division (NAVEODTECHDIV), the Strategic Environmental Research and Development Program (SERDP), and the Environmental Security Technology Certification Program (ESTCP), several groups have developed physics-based interpretation software for extracting target parameters from secondary EM fields induced in UXO or other small buried metallic objects. In most cases, the software uses a point dipole with a frequency- or time-dependent polarizability tensor as a model of the EM field. As part of an effort currently being funded by ESTCP to commercialize some of the emerging hardware and software technology for UXO detection and characterization, this paper presents comparative results from the application of 3 different parameter extraction algorithms for EM data based on the dipole model. Although based on a common model, there are significant differences in the respective algorithms. We highlight these differences by applying the algorithms to a common data set. The data were acquired over the Calibration Lanes at the UXO Test Site located at the Yuma Proving Grounds using a new version of the Advanced Ordnance Locator (AOL2), a state-of-the-art time-domain EMI system consisting of 3 orthogonal transmitters and an array of 9 tri-axial receivers.
-
-
-
Imaging A Shallow Paleo-Channel Using 3D Ultra-Shallow Seismic Reflection Methods
Authors Steven D. Sloan, Don W. Steeples and Georgios P. TsofliasA 3D ultra-shallow seismic-reflection survey was conducted to image a shallow paleo-channel at a field site located near Lawrence, KS. An orthogonal survey design was used, with a patch consisting of 4 receiver lines with 48 receivers each and 12 source lines with 16 source locations each. The source and receiver intervals were 0.5 m, and the source line and receiver line intervals were 2 m. The survey design resulted in a total fold of 48, covering an area of ~15.5 m x 35.5 m. Large variations in velocity were present, ranging from 300–600 m/s laterally and ~300–1600 m/s vertically. As normal moveout corrections cannot account for intersecting reflection hyperbolae due to large vertical velocity gradients, the data were processed by extracting offset-dependent subsets based on the optimum window for each reflection. The subsets were NMO corrected independently and stacked together using conventional 3D processing techniques. Despite the large lateral and vertical velocity variations, we were successful in imaging the top of the saturated zone, paleo-channel features, and bedrock located at depths of ~5, 8.2, and 14.4 m, respectively. Results of the 3D survey are in agreement with previous studies conducted at the site.
-
-
-
Investigation Of The Hydrogeological Setting Of Plitvice Lakes, Croatia
Authors Bozo Padovan, Mark Blohm, Tomo Novosel, Miroslav Andric and Damir GrgecGeophysical surveys were conducted at the Plitvice Lakes in the Plitvice Lakes National Park, Croatia to help define the geological and hydrogeological setting of the Lakes.
Plitvice Lakes is one of Croatia’s most popular tourist attractions. It was set aside as a National Park in 1949, and was granted United Nations Educational, Scientific and Cultural Organization (UNESCO) World Heritage status in 1979. The Lakes are located in an area dominated by carbonate rocks (limestones and dolomites). The limestone units are typically highly permeable (karstic). The Lakes are formed in depressions and separated by travertine barriers with a number of impressive cascade falls. A complex system of joints and faults are postulated to form barriers that impede water flow and allow the formation of the natural reservoirs. Below the Lakes, the excess water flows out to the Korana River, which sinks underground in the permeable limestone during dry periods. Three geophysical methods (shallow seismic reflection, geoelectrical tomography and time domain electromagnetic soundings) were used to map structural features and rock types to assist in interpretation of hydrogeological relations and to site future investigation boreholes. This poster paper provides the preliminary results of the geophysical investigations.
-
-
-
Assessing The Cost-Benefit Of Multi-Core Cables And Nonpolarizable Electrodes On Shallow Time-Domain Ip Surveys
Authors Daniel F.S. Maia and Guilherme P. CastilhoIt has become a common procedure to acquire electrical data for environmental surveys with multi-core cables and multi-channel readers. These systems use pre-loaded protocols that instruct the relay box to combine the electrodes in hundreds of possible arrangements. When acquiring Induced Potential (IP) data, there is always a fear of electromagnetic (EM) coupling on the cables and polarization effects on the steel electrodes. As a precaution, current cables are usually separated from the potential cables and non-polarizable electrodes are used for potential readings. This also implies that special care must be taken when writing the acquisition sequence protocols. All these precautions increase considerably the time needed to assemble and disassemble a line thus leading to greater cost and lesser production. In this work, the effects of multi-core cables and non-polarizable electrodes on shallow time-domain IP surveys are analyzed from a practical point of view. It is shown that, if the instrument is able to perform Self Potential (SP) correction before integration, the results obtained with stainless steel electrodes and multicore cables are virtually the same as those obtained with separate cables and non-polarizable electrodes.
-
-
-
Seismic Reflection And Resistivity Surveys To Map Sand Resources For New Jersey Beach Nourishment Projects
The New Jersey Geological Survey (NJGS) maps the State’s offshore geology and sand deposits by acquiring, analyzing and interpreting marine geologic and geophysical data. These data support development of a regional geologic framework that characterizes offshore sediment distribution. This framework produces a statewide assessment of offshore sand resources for beach nourishment, supports the NJGS geologic mapping program and is essential for a science-based approach to long-term resource management and contingency planning. The NJGS conducts surveys using seismic reflection methods and marine DC electrical resistivity. Geophysical data is ground-truthed with sediment vibracores. Analyses include grain size distribution, calculated interval velocity, conventional radiocarbon and amino-acid racemization (AAR) dating of sediment samples, and seismic stratigraphy. Delineating sand resources using a geologic framework permits the NJGS to identify areas strategically, obtaining detailed information where the resource potential is greatest for the least cost. This methodology enables a comprehensive assessment of sand location, quality and volume. NJGS has identified more than 274 million cubic meters (358 million cubic yards) of sand in both State and Federal waters along New Jersey's 127 miles of coastline. Data and findings are shared with the U.S. Army Corps of Engineers (USACE), NJ Department of Environmental Protection, and U.S. Department of Interior Minerals Management Service.
-
-
-
Geotechnical Parameters From Integrated Geophysical Methods: Laboratory Measurements And Regression Models
Authors Frederick Owusu-Nimo, Fred Kofi Boadu and Aboagye MenyehSeismic and electrical measurements are performed in the laboratory on unconsolidated geomaterials with well-characterized geotechnical properties. The measured seismic parameters are compressional wave velocity (Vp) and shear wave velocity (Vs), and the electrical parameters include the amplitude and phase of electrical response. Measurements are conducted on 32 samples with wide variability in mineralogical composition, texture and geotechnical properties. Each sample is saturated with fresh water and subjected to varying effective stress levels of 5, 10, 15, 20 and 25MPa for measurements of the seismic and electrical parameters. The geotechnical properties, porosity, fines content, particle size distribution, plastic and liquid limits are determined for each sample. The relationship between the geotechnical properties and geophysical parameters is investigated and regression models are developed. It is shown that porosity decreases slightly with increasing fines content to a threshold of about 15%, after which the linear decrease is sharp, for all the effective stress levels. The variation of resistivity with stress is also found to be dependent on the amount of clay and fines present in the sample. Resistivity correlated all the geotechnical properties with higher accuracy. The best prediction is for fines content with R2 of 0.93. Fines content is also found to be the best geotechnical parameter which has better relationship with both resistivity and velocity. Combinations of resistivity and velocity also predicted plastic and liquid limits reasonably. The relationships developed will be useful in the geophysical interpretation of field measurements as well as the rapid estimation of geotechnical properties in the preliminary investigation of a project.
-
-
-
Detecting Abandoned Air-Raid Shelter Using The S-Wave Seismic Reflection Method
Authors Shunichiro Ito, Takao Aizawa, Fumio Nakada and Ryosuke KitamuraA high-resolution S-wave survey was conducted over a known air-raid shelter to evaluate its effectiveness in detecting an underground void. It is a part of a government project of prevention of accidents of caving shelters. The survey used a mechanical impactor powered by an air compressor as the source and a purpose-built S-wave land streamer. The good quality of the data acquired warranted a focused processing to the depth of the target, and migrated stack and instantaneous amplitude sections show the target clearly.
-
-
-
Magnetometric Researches Used In The Archaeological Studies Of The Greek Roman Fortress Located On The Shore Of Razelm Lake
By Sorin AnghelIn Romania, geophysical methods are normally used to estimate the distribution of cultural relics, before digging. Objects of archaeological interest are usually located within a few meters of the surface. The geophysical studies were carried out within the archaeological site both in 2005 as well as in 2006.Geophysical works were conducted using Geometrics equipment (G856 proton procession magnetometer) with a 0.1nT precision, which allowed for a highly detailed local morphology of the geomagnetic field and for the mapping of the magnetic anomaly. The working technology has been chosen to enable to emphasize mainly abnormal effects produced by sources located at depths of 0-5 m. On the south side of the late Roman fortification, outside the precinct wall, an artisanal area including a furnace for manufacturing building materials dated from the late Roman period, was found as well as some Greek furnaces for manufacturing ordinary brick. The south area of the site has been studied within this research project using the magnetometrical method (Fig. 5). Geophysical studies will prove very useful for further archaeological diggings, supplying them with a more clearly defined image on the substratum situation. Keyword ancient cities, proton pocession magnetometer, geomagnetic field, gradient system
-
-
-
Inversion Of Surface Waves In Complex Structures
Authors Anouar Romdhane, Gilles Grandjean, Fayçal Réjiba and Adnand BitriSeismic techniques are nowadays widely used to image near-surface structures for both geomechanical and geological applications. However, in the context of shallow complex
structures, some limitations arise, particularly for inverting surface wave dispersion. In this paper, we introduce the full waveform inversion as an alternative to conventional MASW
(Multichannels Analysis of Surface Waves) methods typically used for subsurface prospecting. Considering 2D reference velocity models, we study the elastic wave propagation,
based on finite difference modelling in the frequency-space domain, for generating synthetic seismograms. The frequency versus phase-velocity curve, known as the dispersion curve, is afterwards computed and used to invert shear-wave velocities. Full-waveform inversion technique, based on the Born approximation, is tested using both body waves and surface waves to evaluate their respective contributions in the seismic imaging processes. The efficiency of such an inversion method compared to the classical MASW one is then evaluated.
-
-
-
Electrical Imaging Of A Triassic Fault System In Northern New Jersey
Authors Peter J. Hutchinson and Jeffrey M. DereumeContinuous vertical electrical sounding (CVES) imaged early Triassic normal faults on the southeastern side of Mount Arlington Ridge, part of the northeast-southwest trending ridges within the New Jersey Highlands physiographic province of north-central New Jersey. The site had been previously characterized with a regional normal (down to the east) fault, the Longwood Valley Fault that places undefined Proterozoic bedrock units against the sandstone/conglomerate Silurian Green Pond Formation. The sandstone/conglomerates of the older Cambrian Hardyston Formation conformably overlie the Green Pond Formation. The Hardyston with the overlying Leithsville Formation and veneer of Pleistocene-aged glacial deposits comprises most of Long Valley within the study area. CVES profiles collected normal to the Longwood Valley Fault show displacement within the Mesozoic sediments that are beneath the Pleistocene-aged glacial sediments in the contiguous valley. This previously unnamed fault system is termed the Kenvil Works Fault. Further, four or more synthetic faults exist between the Kenvil Works Fault and the Longwood Valley Fault. These faults accommodate right-rotational torsion between the two fault systems. The synthetic faults and Kenvil Works Fault System can act as a migration pathway for the movement of groundwater from the upland impermeable bedrock to the more permeable valley-fill sequences.
-
-
-
Walsh Transforms For Depth Determination Of A Finite Vertical Cylinder From Its Residual Gravity Anomaly
More LessWalsh functions, which are defined as a set of complete and orthogonal functions of nonsinusoidal waveform, have been used for estimating the top and the bottom depths of isolated vertical cylinder gravity data. Calculating the Walsh transforms for a vertical cylinder, Walsh power spectrum and its analysis proved to be affective in the depths determination. A fully interpretation scheme has been devised from Walsh transforms for the depths determination of a vertical cylinder model. Furthermore, the effect of profile length, sampling interval and noise analysis on the interpretive technique has been investigated. Spectral analysis, which is conventionally referred to the Fourier transform, has been widely utilized for geophysical interpretation. However, Walsh functions, which have only discrete amplitude of +1 and -1, can as well be used in geophysics. Thus, Walsh transform can be implemented for geophysical interpretation which is much faster and simpler than the spectral analysis. A scheme of the interpretation has been applied first to a synthetic data and then to the real data of the famous Humble Dome anomaly to evaluate its validity. The interpreted results of the target showed a good agreement with other published techniques of more commonly utilized methods.
-
-
-
Field Applicability Of Masw Data
More LessOne-dimensional multi-spectral analyses of surface waves (MASW) are used to predict subsurface shear-wave interval velocities. Shear wave velocities can also extract additional
velocity-related information such as mechanical properties of soils and rocks. In general, MASW data compare favorably to other geophysical methods for predicting interval velocities. Furthermore, comparisons to vertical seismic profiles correlate well with MASW predicted shearwave interval velocities. Over 100 one-dimensional MASW records and 30 vertical seismic profiles in 5 states were collected and compared. Surface waves saturate the geophones (5-foot spread with 5-foot hammer offset) on bedrock and dispersion curves are difficult to evaluate. Consequently, MASW-derived shear-wave velocities are elevated above those derived from down-hole vertical seismic profile methods (VSP). MASW-derived shear-wave velocities collected in areas with a veneer to thick sequences of unconsolidated soil have predicted MASW shear-wave interval velocities that compare favorably to those derived from VSP data.
-
-
-
Assessment Of Geological Conditions Of Barrage Seat Area Through Seismic Tomography: A Case Study
Authors S.L. Kapil and R. ChandraA hydro power project of 750 MW capacity is proposed on the Tawang Chu river. The Project area lying within the Higher Himalayas is located about 35 Km from Tawang, a district headquarter of Arunachal Pradesh, India. Presently, the project is under active iinvestigation. Seismic tomography was undertaken in April 2007 at one of the proposed location of barrage site, for assessment of bedrock profile and in-situ rockmass properties of barrage seat area. Three drill holes on barrage axis were utilized for taking measurements. Sparker source with TTL triggering system and high frequency active hydrophones were used for signal generation and detection respectively. Data was recorded with Terraloc MK-VI, 48-channel seismograph. More than 2000 ray measurements between the drill holes were taken and data was processed in two stages. Initially, the complete data was utilized for assessment of bedrock profile within the scanned area. In second stage, data recorded within bedrock was analysed and strong evidence of anisotropy was inferred in this data set. Accordingly, inversion was carried out with anisotropy and this reduced the RMS residuals significantly. Seismic tomography provided in-situ characteristics of bedrock and helped in avoiding some of the expensive riverbed drill holes.
-
-
-
Helicopter Magnetic Survey At The Teapot Dome Oilfield (Naval Petroleum Reserve No. 3) - A Case History
Authors G.A. Veloski, R.W. Hammack, V.W. Stamp, R. Hall and K. ColinaA helicopter magnetic survey was conducted in August 2007 over the 40.5 km2 Teapot Dome Oilfield (Naval Petroleum Reserve No. 3) near Casper, Wyoming. The primary purpose of the survey was to accurately locate wells that had been drilled there during more than 90 years of continuous oilfield operation. The survey was conducted at low altitude and with closely spaced flight lines to improve the detection of wells with weak magnetic response and to increase the resolution of closely spaced wells. The survey was conducted partly in preparation for a planned enhanced oil recovery demonstration that requires a complete well inventory with accurate locations for all existing wells. The magnetic survey was intended to identify wells that are missing from the well database and to provide accurate locations for all wells. The ability of the helicopter magnetic survey to accurately locate wells was accomplished by comparing airborne well picks with well locations from an intense ground search of a small test area. This paper describes the results of the survey.
-
-
-
A Successful Mixed Land-Underwater 3D Resistivity Survey In An Extremely Challenging Environment In Amazônia
Authors Guilherme P. Castilho and Daniel F.S. MaiaPlanning the best acquisition design for a specific objective is one of the most important phases of the whole acquisition/processing/interpretation process, mainly when it is necessary to surpass the environmental difficulties and the HSEQ issues. This work will demonstrate some of the challenges that had to be confronted in order to conclude a 3d resistivity survey through mixed terrain-underwater environment with rough topography and dense vegetation in Amazonia. It also presents the measures that had to be taken to collect a reliable resistivity dataset. Nevertheless, the survey was successful and subsequent ground-truthing confirmed the impacted areas predicted from the geophysical data.
-
-
-
Geophysical Investigations Of Earthen Dams: An Overview
Authors Lewis E. Hunter and Michael H. PowersThe Sacramento District U.S. Army Corps of Engineers (USACE) controls 16 dams in the state of California. Three of these dams were classified in the 2006 USACE Screening for Portfolio Risk Analysis as being in Class I or Class II, where the hazards associated with potential failure are considered either urgent and compelling, or urgent, respectively. These dams are Isabella and Martis Creek, both Class I, and Success Dam, identified as Class II. All three dams are earthen structures with either an impervious core or blanket on the upstream toe. Starting in 2005, the USACE teamed with the U.S. Geological Survey in acquiring geophysical data on these dams to provide geotechnical information to be used in assessing the dams and their foundations. The goal of this paper is to provide a review on the status of these surveys, one of which is complete (Success Dam), another underway (Isabella Dam), and a third (Martis Creek) where detailed surveys are planned for the spring of 2008. The techniques being applied include direct current (DC) resistivity, compressional (P) and shear (S) wave seismic reflection and refraction tomography, audio-magnetotellurics (AMT), frequency- and time-domain electromagnetics (EM and TDEM), and self potential (SP). Other techniques are continually being evaluated as project demands change.
-
-
-
Tight Location Requirements For Geophysical Investigations On Urban Sites Using RTS
Authors Sandra Takata, Mark Kick, Lester Tyrala, Martin Miele, Colin Chang and Sally LambFor geophysical surveys, the accurate location and documentation of measurement points, lines and features in densely-built areas with limited survey control and sky-view is challenging. Yet in the present day, urban sites containing numerous obstructions are more often the norm for geophysical applications. Historic site information may span generations of data ranging from as-designed drawings to generated 3-D plans. Frequently, each dataset is probably in different coordinate systems with widely differing accuracies. Using a robotic total station (RTS) theodolite for survey location/navigation control has significant advantages over conventional gridding, tick wheel, and global positioning system (GPS) techniques including:
Survey-grade X,Y,Z precision
In-field verification of positional accuracy
Operation wherever line-of-sight can be established
Data collection directly in agreed-upon or convenient coordinate systems
Locations are continuously streamed by radio-link to geophysical loggers/equipment
Remote-control RTS operation
Follow-up relocation independent of changing ground conditions
Geophysical survey and utility mapping results from five “urban” sites are presented illustrating typical location/navigation problems, collection of high locational accuracy survey data around complex structures, and considerations for survey planning, design, and reporting.
-
-
-
Geophysical Characterization Of A Levee With Dc Resistivity And Electromagnetic Measurements
A geophysical characterization of a portion of American River levees in Sacramento, California was conducted in May 2007. Targets of interest included sand lenses that
underlay the levees and the depth to a clay unit that underlies the sand. The concern is that the erosion of these sand lenses can lead to levee failure in highly populated areas of
Sacramento. DC resistivity and electromagnetic surveys were conducted over a 6 mile length of the levee on roads and bicycle and horse trails. 2-D inversions were conducted
on all the geophysical data. The OhmMapper and SuperSting surveys produced consistent inversion results that characterized the targets of interest. GEM-2 apparent resistivity data were consistent with the DC inversion results. However, the GEM-2 data could not be inverted due to large system drifts. While this would not be as large a problem in conductive terrains, it is a problem for a small induction number electromagnetic profiling system such as the GEM-2 in a resistive terrain (the sand lenses). Despite issues with the GEM-2 inversion, this geophysical investigation was successful in detection of the sand lenses and the depth to the clay zone of interest.
-
-
-
Comparison Of Airborne Magnetic And Electromagnetic Systems For Ordnance Detection And Mapping
Magnetic and electromagnetic data collected by helicopter boom-mounted systems at the same survey sites permit direct comparison of the systems as to their suitability for buried ordnance detection. The ORAGS-TEM system is an airborne electromagnetic system developed specifically for unexploded ordnance mapping and detection. Although airborne boom-mounted magnetic systems are at a more advanced stage of development than their electromagnetic counterparts, in basaltic terrain, electromagnetic systems have proven capable of detecting buried ordnance, whereas magnetic systems sometimes fail altogether. Magnetic systems use passive sensors and these can be distributed along the boom structure such that dense data can be collected with sensors spaced 1-2 m apart over a broad swath, up to 12 m wide. Current airborne electromagnetic systems are unable to match this data density. The ORAGS electromagnetic system, having only two receivers, must rely on interleaved flight lines to obtain data of a spatial density approaching that of the airborne magnetic systems. Active electromagnetic fields decay at greater rate than magnetic fields, and this constrains current electromagnetic systems to practical survey altitudes of no more than about two meters for ordnance detection. Tests at the Badlands Bombing Range indicate that in some circumstances, the signal-to-noise for the ORAGS electromagnetic system exceeds that of airborne magnetic systems.
-
-
-
Using Ground Based Geophysics To Evaluate Hydrogeologic Effects Of Subsurface Drip Irrigation Systems Used To Manage Produced Water In The Powder River Basin, Wyoming
Authors ames I Sams III, Brian A. Lipinski and Garret VeloskiThe U.S Department of Energy’s National Energy Technology Laboratory has been evaluating various geophysical methods for site characterization regarding environmental issues associated with fossil fuels including produced water management. A relatively new method of managing produced water from coal bed natural gas production is through subsurface drip irrigation. This system involves disposing the produced water near the bottom of the root zone in agricultural fields, which would provide a beneficial use of this resource. The focus of this paper is to present results from a pre-injection geophysical survey for site assessment and background data. A pre-construction survey of approximately 1.2 km2 was completed in June 2007 using a Geophex GEM-2 broadband sensor over six fields along the Powder River floodplain. Quality assurance measures included drift checks, duplicate line surveys, and repeat field surveys using the Geometrics OhmMapper instrument. Subsequent surveys will be completed once the system is installed and operational. Geophysical inversion models were completed to provide a detailed cross-section of the subsurface geoelectrical structure along each line. Preliminary interpretations reveal that the subsurface conductivity distribution correlates to geomorphologic features.
-
-
-
Imaging Dispersion Of Passive Surface Waves With Active Scheme
More LessIn passive surface-wave surveys under urban environments there is usually one surface location from which a major portion of the surface wave energy—used for the dispersion analysis—originates. This is similar to an active survey, in which exact relative coordinates of both source and receivers are known prior to data processing. Using a method that scans through all possible incoming directions of those passive surface waves, the azimuth of the responsible source point can be estimated fairly accurately, especially when a method employing an integral approach for the calculation of surface wave energy at a particular azimuth and phase velocity is incorporated. Then, along with the distance information that only needs to be estimated very roughly, the passive data set can be processed by any active scheme. Key concepts are explained using both synthetic and field data sets, with comparisons made to some of the existing methods.
-
-
-
Distinguishing Between GPR Subsurface Reflections And Surface/Air Waves At Cluttered Urban Sites
More LessAt sites where relatively deep exploration is desired for GPR, 100 MHz or lower frequencies are required. These large antenna are either unshielded, or their shielding is not 100% effective, allowing radiation to escape parallel to the earth’s surface in all directions. At typical industrial sites with linear or planar grounded structures, such as power lines, chain-link fences, railroads, and metal-sheathed buildings, reflections of the air and surface waves are common. While the experienced user can recognize many of these events on a profile, particularly those reflections returning from directly in front of, and from behind the antennas, the patterns from lateral reflectors whose distance from the survey line is not constant may be mistaken for real undulating subsurface reflectors. The early use of true CMP or expansion surveys is used to recognize which reflectors on the GPR display are actually from the subsurface. The horizontal reflections arrive at nearly constant times at all expansions regardless of their direction from the center of the CMP survey, while the true geologic reflections arrive in the expected half-hyperbola pattern. An example from Michigan is shown, where only two shallow reflectors were found to be valid using the CMP, while the profiles showed numerous other realistic apparent deep reflections.
-
-
-
Multiple Frequency Electromagnetic Response Of The Dispersive Layer
Authors Zeng Zhaofa, Liu Fengshan, Sun Jiguang and Liu CaiThe electromagnetic (EM) detection method with the frequency between Transient Electromanetic method TEM) and ground penetrating radar (GPR), has a wide potential application in engineering and environmental geophysics. The study on the method mostly based on the real dielectric and conductivity. Unfortunately the surface medium such as soil and water saturated rock is mostly frequency dispersive medium. In this paper, we simulate electromagnetic response of the near-surface layer medium using Cole-Cole model and Debye model. Our algorithm use the high density sampling filtering since it has advantages on efficiency and accuracy over linear filtering and Chave’s Gauss integration algorithm. From the simulation we can clear see different response of the dispersive layer from the non-dispersive layer which may play an important role in data inversion.
-
-
-
An Integrated Geophysical Approach For Groundwater And Seismic Hazard Management In Joshua Tree National Park, Southern California
Authors Darcy K. McPhee, Victoria E. Langenheim, Bruce A. Chuchel and Louise PellerinTwo-dimensional inversion of audiomagnetotelluric (AMT) sounding data define buried resistivity distributions that reflect subsurface geology and structure within the upper kilometer beneath Pleasant Valley, a 1-2 km-deep pull-apart basin in Joshua Tree National Park, southern California. The Park lies within the Eastern California Shear Zone just east of the San Andreas Fault, and is surrounded by developing desert communities. Understanding the subsurface in and around the Park is important for management of groundwater resources, for mitigation of seismic hazards, and for unraveling the tectonic evolution of the region. Our resistivity models, interpreted in conjunction with gravity inversions, show transitions between coarse-grained and fine-grained alluvium, resistive (> 400 ohm-m) crystalline rocks, and the locations of range-front and intra-basin faults.
-
-
-
A Quadrature Approach To Detection, Localization And Estimation Of Magnetic Dipoles
We describe a matched filter algorithm for detecting, locating and characterizing magnetic dipoles. The matched filter operates on an array of vector magnetic field measurements
at an arbitrary set of orientations and points in space. For a given dipole location, the algorithm finds a best-fit magnetic dipole moment by projecting the N-dimensional vector representing the magnetic measurements onto the three-dimensional subspace spanned by the calculated data vectors for all possible magnetic moments at that location. It then varies the dipole location to find a best global match between the calculated and measured data. This approach, which is analogous to quadrature decomposition of a signal into sine and cosine components of a given frequency, removes the need to search exhaustively through all possible magnetic moments at each trial location. The algorithm provides optimal detection of a magnetic dipole in a background of white Gaussian noise, and unbiased estimation of the location and vector moment of an isolated dipole within the spatial sampling resolution defined by the user. An application to UXO is demonstrated using a moving magnetic tensor gradiometer to detect and localize inert artillery shells. The extension of the algorithm to active EM systems is explored in theory and computer simulations.
-
-
-
VSP And Well Logs From A Shallow Test Well
Authors Joe Wong, Soo K. Miong, Laurence R. Bentley and Robert R. StewartShallow VSP and geophysical well logging surveys were undertaken in a 127 m-deep well drilled at the Rothney Astrophysical Observatory site near Priddis, Alberta. The well was drilled through interbedded sands and shales of the Tertiary Paskapoo formation. A suite of geophysical well logs (including natural gamma-ray, single-point resistance, focused-beam resistivity, density, neutronneutron, caliper, temperature, and SP) was acquired in the open hole immediately after drilling. After PVC casing was inserted into the well and grouted to the formation rocks, we obtained natural gammaray and full-waveform sonic logs. The logs were useful for delineating the sandstone and shale beds, and for providing hydrogeological information at the well site. For the VSP surveys, we used a 5.5 kg sledge hammer source with a downhole clamping 3C geophone. From the full-waveform sonic logs and VSP data, we determined P-wave velocities to lie between 1.7 to 3.0 km/s. Standard VSP processing resulted in a corridor stack of up-going reflections that correlate reasonably well with a 1-D synthetic seismogram constructed from the density and P-wave velocity logs.
-
-
-
Watershed Characterization For A Water Resource Decision Support System In Honduras
Authors Weldon W. Hammond Jr., Louis R. Manz, Ronald T. Green and Omar A. Andino CruzWatershed characterization studies in southeastern Honduras are being conducted by the Center for Water Research at the University of Texas at San Antonio (UTSA), the National Autonomous University of Honduras and several non-governmental entities. The major emphasis of these studies is the application of a Decision Support System for Village Water Resources (DSSVWR) developed as a research project at UTSA to determine sustainable water supplies in remote areas of Honduras. In order to quantify water resources available on a seasonal basis, drainage basins were delineated and will be characterized by precipitation, runoff characteristics, soil type, land use and geology. Drainage basins are being studied for potential groundwater yield from extensive Miocene ignimbrite sequences and alluvial deposits in numerous structural and erosional valleys. Two types of regional aquifers were identified: (i) ignimbrite sequences with low potential yields and (ii) excellent alluvial aquifers in valleys. Groundwater investigations included geophysical resisitivity surveys. Because of the heterogeneous nature of both the ignimbrite sequences and the alluvial deposits variations in the geoelectrical properties of these units in the subsurface can be used to interpret depth to water table. Results from these hydrologic studies will be used in the DSSVWR to estimate yields on a seasonal basis from various sources for individual watersheds in rural Honduras.
-
-
-
Submarine Slides At Finneidfjord (Norway): Geophysical Investigations
On June 20th, 1996, a submarine land failure in a fjord near the village of Finneidfjord (Northern Norway) developed into a retrogressive quick clay slide encroaching 100-150 m inland, resulting in the loss of life and significant material damage. Reports in the aftermath of the slide concluded that build up of excess pore pressure may have been the main reason for the slide, though other causes are invoked too. The geological settings at this location involve many of the processes typical for large offshore slides. As the fjord is sheltered and accessible, this location is ideal as a field laboratory for studying submarine slide hazards. Such a project for evaluating instrumentation and site investigation techniques for studying submarine slope stability was initiated in 2004 by the International Centre for Geohazards (ICG, Oslo). Initial field campaigns since 1997 have consisted of sediment coring, VHR seismic surveys, and the deployment of long term in situ instrumentation. A larger campaign is planned in 2008, including shear-wave acquisition, and, to support that campaign with land data, several geophysical investigations were carried out onshore in July 2007 in cooperation with the University of Strasbourg. The field studies have included several students to train them in field practice. Seismic, GPR and
resistivity investigations were all carried out, and preliminary results are presented.
-
-
-
Ground Truth Verification Of An Integrated Geophysical Investigation For The Assessment Of An Earthen Levee
We proposed an integrated geophysical technique to assess the vulnerability of earthen levees to flooding and earthquakes. The geophysical technique mainly consists of multi-channel surface wave dispersion measurements (MASW) using Land Streamer, capacitively-coupled resistivity (CCR) measurements, and additional multi-frequency electromagnetic (EM) survey. The effective performance of field measurements using these methods is assured because sensors are not fixed on the levee surface. The geophysical properties evaluated by these methods, resistivity and S-wave velocity, are essential to evaluate the permeability and stiffness of the levee body. We also demonstrated the usefulness of crossplots of the measured data as criteria for the assessment of levee conditions. However, the collection of ground truth data is imperative for the validation of the criteria. Consequently, we then conducted detailed field measurements at an open-cut of an earthen levee on which the integrated geophysical survey had been applied. The investigated levee, which runs along the right bank of
Chikuma River in central Japan, was damaged by a high water event in 2006. In addition, open-cut work was planned within the surveyed line to replace an old sluice. We therefore could observe the internal structure of the levee and take samples of levee materials for grain size analysis at the open-cut. In conclusion, the mapped resistivity profile was concordant with the surface survey results. Moreover, a clear relationship was recognized between grain size and measured resistivity. We interpreted the high resistivity anomalies in the levee body detected by means of surface geophysical survey as potential high-permeability zones. Actually, seepage was observed along the rear slope of the levee just in anomaly zones delineated by the integrated geophysical investigation.
-