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23rd EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 11 Apr 2010 - 15 Apr 2010
- Location: Keystone, Canada
- Published: 11 April 2010
1 - 100 of 131 results
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Not Such an Easy Target: A Student Case Study using Ground Penetrating Radar to Locate Buried Mortars at West Point
More LessOne, or possibly two, of the 12-inch coastal artillery mortars used for cadet artillery instruction between 1902 and 1931 remain buried roughly two to six meters below the surface of the northern edge of the Plain at the United States Military Academy at West Point, New York. This survey used a Sensors and Software PulseEKKO 1000 Ground Penetrating Radar (GPR), 225 MHz antennae, together with geo-referenced imagery to attempt to locate these mortars. The intrinsic value of 132 tons of buried iron, the historic value of the mortars, and sheer curiosity provided the impetus for this study. Geo-referenced aerial photography of Battery Byrne provided a starting point for the search, and we developed a data collection grid to estimate the most likely location. We collected data in conjunction with independent study classes from September 2007 through April 2008, collecting a total of 7,690 GPR traces. After processing initial data with EkkoView and EkkoMapper, we found a distinct hyperbola at Trace 386 of Line 16. We then constructed a tighter grid to characterize our point in higher resolution, but the reflection we identified may be too shallow to be the first mortar. For the second mortar, we focused on a location identified from a 2002 GPR survey, which indicated a mortar near the corner of a gravel pit on the grass of the Plain. The data indicated a small hyperbola shape in the East-West transect of Line 12, so we designed a second tighter grid to further investigate. Again, the results were not as conclusive as we had hoped. Additional research with another ground-truthing method, such as a magnetic or a gravity survey, could validate our findings. This survey has opened the way for future work. More GPR data with a different frequency would be beneficial, preferably 110 MHz to achieve greater penetration. Alternate methods of near surface geophysics would be very valuable, such as magnetic, gravity, or even seismic refraction. Additionally, a partnership with the Department of Civil Engineering could determine the costs, benefits, and feasibility of an excavation project. The West Point Historian may eventually want to erect a plaque describing the historical importance of Battery Byrne for the artillery instruction of cadets. Finally, locating these mortars would provide an interesting geophysics laboratory exercise for future West Point cadets in science and engineering classes.
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Ground Penetrating Radar: Utility/Rebar/Cable Detection and Concrete/Subgrade Debonding
Authors Neil L. Anderson, Evgeniy Torgashov and Oleg KovinGround penetrating radar (GPR) profiles acquired during seven separate field investigations are presented. The intent is simply to illustrate that GPR can be used to detect rebar, pre-tensioned tendons, deteriorated and/or detached concrete/fill, buried utilities, underground storage tanks, and buried foundations. The objective of each investigation is summarized, accompanied by brief descriptions of the nature of the target of interest. The application of GPR to the investigations described in this paper is not new. However, the presentation and illustration of multiple applications of this imaging technology in a single manuscript is somewhat unique.
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Ground Penetrating Radar as a Sentinel Device
Authors Peter J. Hutchinson and Bryan J. TeschkeGeophysical methods provide a non-destructive non-intrusive method of subsurface investigation. Oftentimes, however, the target is difficult to “see” due to lack of contrast between the target and background. This lack of contrast can be rectified through the use of a sentinel device. A series of sentinel devices were used in downtown Pittsburgh, Pennsylvania to determine potential subsidence beneath a building plaza. This sentinel strategy was performed to predict future deformation of the sidewalk and to prevent foot-traffic hazards.
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Using Shear-Wave Velocity to Detect Void-Induced Chages in Stress
By Steven SloanThe absence of geologic materials associated with subsurface anomalies such as voids creates an abrupt and distinct change in material properties. These voids can be challenging to image directly using geophysical techniques, but their effect on surrounding materials may produce physical property variations that are detectable. This has been described as the “halo” effect, where changes in density, stress, fracturing, etc. may produce a geophysical anomaly larger than the actual target. The removal of geologic material causes an increase in effective stress as the load previously borne by the removed material is transferred to the sidewalls and roof of the void. Shear-wave velocity (Vs) is directly related to stress and it is not unreasonable to suggest that localized changes in stress will result in Vs variations. Examples from seismic surface wave and reflection studies showing detectable increases in Vs coincident with zones of expected stress build up are presented.
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Joint Land and Shallow-Marine Seismic Investigations of Landslide Processes in the Bay of Trondheim, Mid-Norway
More LessThe urban development of the city of Trondheim in the last century has extended onto the near-shore areas (Figure 1). In the last 15 years, land reclamation has been intensified for construction work and building activity. Historical landslides are known to have occurred along the shore (e.g., L’Heureux et al., 2007). Damages to coastal infrastructures and loss of life resulted from these events. In one case (1888) a devastating tsunami wave struck the shoreline (Figure 1). The combination of historical landslides and urbanization has increased the concerns about the stability of the near-shore slopes. Therefore, numerous geological, geophysical and geotechnical investigations were carried out in recent years to explore in detail the stratigraphy of the fjord-valley fill and to investigate the stability both on land and in the fjord. One of the purposes of this paper is to show the ability of the shear-wave seismic method to study fjord-valley sediments from paved areas. In addition, we demonstrate the exceptionial potential for correlation between land-seismic and shallow-marine seismic data sets.
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Application or Radiomagnetotellurics on Geomorphological Studies
By B. TezkanA radiomagnetotelluric (RMT) survey is carried out to solve geomorphological studies concerning the evolutionary history of the terraces of the river Rhine in the Lower Rhine Bay next to Cologne, Germany. Geomorphological studies concern e.g. the evolutionary history of the valleys and the classic geomorphologic approach is to take drilling samples to examine the spreading of the covering sediments. The geophysical task is to map continiously the two boundaries between tertiary sands, fuvial gravel and loess. The measurements were realized using the new tensor RMT-device developed recently. Horizontal components of the magnetic and electric fields were observed in the frequency range from 10 kHz to 1MHz. Military and civilian radiostations broadcasting in this frequency range were used as transmitters. Transfer functions (e.g. apparent resistivities and phases) are determined by spectral analysis using a newly developed processing software. The observed apparent resistivities and phases were reliable and they showed a smooth frequency dependence. The data was inverted for 2D conductivity models and compared with two-dimensional inversion results of DC measurements and with existing boreholes. The good comparability indicates that radiomagnetotellurics can be optimally applied to this kind of geomorphological questions.
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Advanced Inversion Strategies using a New Geophysical Inversion and Modelling Library
Authors Thomas Günther and Carsten RückerGeophysical inverse problems often suffer ambiguity and yield fuzzy subsurface images. Often satisfactory results can only be obtained if additional information is incorporated in the inversion. The latter can be structural information about known boundaries or information about the parameters or their limits. However, this is rarely done by the available inversion software packages. We present an extremely versatile inversion and modeling framework for solving inverse problems on arbitrary geometries. Irregular meshes are used to incorporate known discontinuities. The generalized minimization scheme allows for controlling every model cell and every cell boundary individually. Moreover the subsurface can be subdivided into regions that represent different geological units or different physical properties. For each region the model transformation function can be set, e.g. for incorporating petrophysical relations, logarithmic barriers or a combination of it. The constraint type, e.g. smoothness, and the strength and characteristics can easily by varied in the course of iterations. Different joint inversion schemes are easily derived from that. By hand of a synthetic ERT study we show how the approach can be used to imagine small contrasts within a contrasted environment and to monitor small changes with time-lapse inversion.
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Borehole Flows, Hydraulic Heads, and Fracture-Zone Connection in The Potsdam Sandstone at The Altona Flat Rock Research Site in Northern New York
Authors John H. Williams, Frederick L. Paillet, David A Franzi and Edwin A RomanowiczNumerous borehole-geophysical methods are available for the characterization of fractures penetrated by boreholes but relatively few of these methods help to characterize the connections between fractures in the rock surrounding boreholes. Unfortunately, most studies in fracture-rock hydrology conclude that the characteristics of connections between locally transmissive fractures have a greater influence over aquifer-scale permeability than the local aperture of individual fractures (Long and others, 1996; LeBorgne and others, 1996; Shapiro and others, 2007). The study described here focused on the application of borehole-flow methods in the characterization of possible hydraulic connections between fracture zones penetrated by open bedrock boreholes.
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Comparison of Borehole Flow Measurements Obtained by Heat Pulse Flowmeter and Dilution Logging in a Fractured Bedrock Aquifer
Authors Frederick Paillet, John Williams and Edwin RomanowiczWe compare flow measurements made under ambient and pumping conditions in a bedrock borehole using high-resolution flow (heat pulse flowmeter) and fluid column dilution (repeat conductivity profiles after brine emplacement) methods. A second round of brine emplacement was avoided by using the fluid column conditions at the end of the ambient part of the dilution experiment as the initial condition for the pumping part of the dilution experiment. The estimates of flow by both methods yielded results that were in close agreement. The dilution method yielded direct estimates of flow based on the movement of interfaces, but logistics would have required the experiment to be repeated at two different pumping rates for most accurate results. The flowmeter yielded interval-averaged estimates of flow that agreed with the dilution results, but there was scatter of as much as 100% among the individual flow measurements. The flowmeter also required measurements under more than one pumping rate, and this was logistically much easier to accomplish than for the dilution experiment. We conclude that the methods are largely equivalent, with offsetting advantages and disadvantages for each method such that best results would be obtained using both methods in the same borehole.
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Borehole Geophysical Investigation: Seminoe Dam, WY Characterization of Internal Fracturing and Dynamic Moduli Reduction of Mass Concrete Undergoing Aar
More LessAlkali aggregate reaction (AAR) is the general term for a slowly occurring chemical reaction in which highly alkali cement paste reacts with concrete aggregate. AAR is a common problem in concrete poured prior to the 1950’s. The reaction leads to the formation of an alkali silicate gel at the interface of the aggregate and cement. This gel product is less dense than the reactants, causing expansion. The gel product also increases in volume with water. During July of 2009, five six-inch diameter boreholes with varying depths were drilled into Seminoe Dam. Down hole optical and acoustic imaging tools were utilized to locate and characterize fractures within the concrete surrounding the borehole. Data collected from sonic and density logging tools were used to calculate the in-situ dynamic modulus values of the concrete surrounding the borehole wall. Imaging data was analyzed for fracture dip, orientation and frequency. Sonic data was analyzed for the concrete’s compression and shear wave velocities. Concrete density was computed from gamma ray logging data. In-situ shear, bulk and Young’s modulus values were determined throughout the depth of the boreholes. Characterization of the fractures and in-situ dynamic modulus values of the concrete are used in comparison with past investigations of Seminoe Dam to gauge the progression and effects of AAR throughout the structure.
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Characterization of a Slim-Hole Gamma-Ray Sonde for Potash Exploration Applications in a Simple Test Pit Environment
Authors Stefani D. Whittaker, Ryan Sharma, Daniel Hallau, James P. Lewis and Robert M. CluffPrior studies of gamma-ray tools have all been focused around instruments that typically evaluate sandstone, shale, and limestone formations that are encountered in oilfield logging. For this study, a set of experiments were conducted to characterize the lateral and vertical response functions for a slim-hole gammaray sonde used in the mining industry to locate potash mineral deposits. The experiments were conducted in an indoor warehouse environment utilizing a set of large plastic tanks that were filled with light evaporite minerals (granular halite and sylvite) in differing arrangements to simulate various possible formation configurations. Measurements were taken while using a centralized slim-hole gamma ray tool in an air filled 4.5 inch plastic borehole. Sequential tests were run to establish the linearity of tool response, the radial depth of investigation, the vertical response function, and the repeatability of the measurement. Radial depth of investigation was measured using concentric radioactive rings of increasing diameter with two possible intermediary substances, air and halite. To test vertical response a column structure was built using halite as the bottom “bed” and a sylvite layer was systematically added in known quantities to acquire a response function of increasing thicknesses. Repeatability of the measurements was verified by logging several points with multiple tools of the same model for all the various experimental setups. Results were corrected for background radiation to predict the response in solid subsurface conditions without incident surface radiation seen in the experiments. The findings were also corrected for the differences between low porosity subsurface conditions and the unconsolidated granular products that were used in the simulated formation. The experimental results were surprisingly close to theoretical tool response for an oil field sonde, as well as to published specifications of major oilfield logging vendor’s tools. Consequently, gamma-ray logs collected with a slim-hole tool in shallow mineral core holes should be directly comparable to oilfield gamma-ray tools run in open-hole wellbores, once corrections for borehole size and fluid content using best practices are applied.
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Practical Focusing of Surface-Wave Inversion to Image Levees in Southern New Mexico
Authors Julian Ivanov, Richard D. Miller, Shelby Peterie and Joseph B. DunbarExisting algorithms for inversion of dispersion-curves estimated from analyzing the seismic surface-wave data provide a reasonable representation of the overall shear-wave velocity structure. However, in some cases these results may not meet the resolution requirement of the survey objectives targeting the upper portion of the subsurface section. Near-surface geophysical surveys often look for greater detail in the very near surface, such as the case for levees, while still being interested in the overall velocity structure at greater depth. The proposed method for applying surface-wave inversion revolves around applying a greater degree of focusing on the very near-surface component of the inversion model through the practical use of existing algorithms. Specifically by eliminating the low frequency portion of the dispersion-curve data and using a shallower model. The proposed inversion technique is demonstrated using the multi-channel analysis of surface waves (MASW) inversion algorithm. As a result of using this near-surface focusing approach, surface-wave velocity estimates of the levees possess greater detail and resolution. Results presented here demonstrate the potential of the proposed approach to more accurately image the very shallow subsurface top portion of other near surface MASW sites.
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Geophysical Surveys, Levee Certification Geophysical Investigations, DC Resistivity
More LessThe Yuma Area Levee system, running along the northern boundary of the city of Yuma (Arizona), trends parallel to sections of the Gila and Colorado Rivers. These Levees constructed from the surrounding earth, are composed of an assortment of sands, silts, clays, and quarried rock (which armors the river side of each levee structure). Sections of the levee system, and portions of the levee system near Walker’s Ranch have been chosen for investigation to determine structural integrity and areas susceptible to slope failure or internal erosion in the event of flooding. By using direct current resistivity (DCR), an assessment of the subsurface levee structure can be made, identifying material properties within the levee itself that indicate the presence of sands, clays, or anomalous void spaces if present. This data is used to help determine locations for levee remediation. This report discusses results from the DCR surveys performed at various locations along the levees. In general, areas of high electrical resistivity can represent locations of clean sands and gravels which may be prone to internal erosion at flood stage river levels. Areas of localized very low resistivity can indicate the presence of steel or other metallic materials such as culverts. This report provides a table of all direct current resistivity soundings and their quality of processed data. A few of the soundings revealed very high root mean square (RMS) error. These soundings will be disregarded. Direct current resistivity soundings with lower RMS error more accurately reveal areas of high resistivity sands and gravels within the levee structure. Only soundings classified as Good Data and Very Good Data will be used in evaluating the subsurface conditions when considering possible levee remediation locations.
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Time-Lapse Monitoring of the Slope Failure Process of a Model Levee
Authors Tomio Inazaki, Makoto Inoue, Yukiko Saito, Satoshi Arakane and Naoto YoshidaA half-shaped model levee 3 m high and 20 m long with a 3.5-m wide crest was time-lapse monitored over a period of four days. The purpose of the monitoring was to clarify the behavior of water migration in the levee during the deformation process. The time-lapse data included the height of the water table in the levee body measured using a water gauge array, apparent resistivity along a line set on the slope shoulder, surface temperature, and slope surface topography scanned by means of a 3D laser imaging system. Data were acquired basically at 1-hour intervals. Groundwater conditions in the levee body were controlled by infiltration from a perforated tank set at the rear side and supplemental surface watering. Surface deformation was recognized 5 hours after the surface watering, and it took another 2 hours until small slope failure occurred. Resistivity data strongly indicated that infiltration of surface water through the vadose zone and its connection with the water table in the body triggered the surface slope failure.
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A Case Study of Self-Potential Detection of Seepage at the Junction of Two Embankment Dams
This paper deals with a case study of the self-potential (S.P.) method applied to the detection of seepage occurring at the junction of two embankment dams. We took advantage of the controlled progressive emptying of the upstream reservoir to monitor changes of S.P. together with changes in water level. Seepage flow rate was also monitored. DC resistivity tomography was used to control changes in electrical resistivity. Repeated measurements in time with dual non-polarizable electrodes before the outset of the experiment showed that the repeatability of the measurements is better than 3 mV. The mapping of the electric potential showed an upstream low and a downstream high as expected. We have computed the effective electrokinetic coupling coefficient from the variation of potential with water level and flow rate. Horizontal gradients of potential were computed to display directions of preferential flow through the dam.
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Airborne Electromagnetic Surveys by The U. S. Geological Survey over Concealed Glacial Aquifers, Central United States
Authors Bruce D. Smith, Jared D. Abraham and Scott C. LundstromThe U.S. Geological Survey (USGS) over the last decade has performed several airborne electrical resistivity (helicopter electromagnetic, HEM) surveys over buried glacial features that constitute major aquifers in different regions of the central United States (Figure 1). These surveys have been conducted to map geology, contaminants, and hydrogeology for groundwater studies. Glacial deposits also can contain significant aggregate resources in the United States (Langer, 2002). This paper summarizes the USGS HEM applications in three different glacial terrains. The HEM systems applied in the surveys described here used frequency domain methods that, in electrically conductive areas may be limited to mapping depths less than 60 m. The frequency range typically is from about 100,000 Hz to 400 Hz.
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Airborne Electromagnetic Systems and their Engineering and Environmental Applications
Authors Dima Amine and Greg HodgesAirborne geophysical surveys have been used in the mining industry for over 50 years as a standard part of exploration programs (Fountain, 1998). Only recently have airborne geophysics surveys been used to help solve engineering and environmental problems.
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AEM Data for Assessing Irrigation Channel Leakage – A Meritorious Approach in an Australian Setting?
Authors Tim Munday, Mike Hatch, Andrew Fitzpatrick and David AllenGeophysical technologies, and in particular electrical and electromagnetic methods, have the potential to provide a rapid and relatively inexpensive approach to determining the location and extent of seepage along irrigation canals or channels. Although showing potential, the application of airborne electromagnetic (AEM) systems for these purposes has been very limited, in part because of the fine scale information required and also the costs associated with acquisition. However, recent developments in AEM system technologies have contributed to substantial improvements in the definition of conductivity at shallow depths and we believe these trends have made these systems a more relevant technology for the systematic mapping and detection of variations associated with irrigation infrastructure. In this paper we examine that potential through the analysis of high resolution HEM data for an irrigation system located in Victoria, Australia. Inverted data from a RESOLVE FDHEM survey along an irrigation channel were compared with an inverted ground resistivity array data set. Results demonstrated that the spatial patterns and magnitude of conductivity variations are generally comparable. The ground geophysical technique benefitted from being able to map variations at finer scales. However, there may be merit in considering the deployment of airborne mapping methods if large surveys are considered and a rapid turn-around of information is required.
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Transient Electromagnetic Mapping of Clay Units in the San Luis Valley, Colorado
Authors David V. Fitterman and V.J.S. GrauchTransient electromagnetic soundings were used to obtain information needed to refine hydrologic models of the San Luis Valley, Colorado. The soundings were able to map an aquitard called the blue clay that separates an unconfined surface aquifer from a deeper confined aquifer. The blue clay forms a conductor with an average resistivity of 6.9 ohm-m. Above the conductor are found a mixture of gray clay and sand. The gray clay has an average resistivity of 21 ohm-m, while the sand has a resistivity of greater than 100 ohm-m. The large difference in resistivity of these units makes mapping them with a surface geophysical method relatively easy. The blue clay was deposited at the bottom of Lake Alamosa which filled most of the San Luis Valley during the Pleistocene. The geometry of the blue clay is influenced by a graben on the eastern side of the valley. The depth to the blue clay is greater over the graben. Along the eastern edge of valley the blue clay appears to be truncated by faults.
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Direct and Inverse TDEM Method for Near Subsurface Resistivity Imaging
By I. MerhasinWe investigate the applicability of TDEM technology for near subsurface mapping. In the direct method, we use time domain response of a multi-layered earth to a dipole excitation based on Fréchet derivatives. Expected sensitivity of detection of a low-conducting layer is analyzed for various ground conductivities and layer depth. Our inversion method is based on Marquard technique and gives 1-D conductivity depth profile for each time sequence measurement.
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Equivalence Analysis of DC and EM Data for Layered Models using the Resolution Matrix
More LessRidge-regression inversion (Inman, 1975) is used to formulate and carry out the inversion of DC resistivity and Electromagnetic (EM) data. A by-product of this process is the resolution matrix, which is symmetric and defines the linear combinations of the parameters which have been resolved in the inversion process. Subtracting the resolution matrix from the identity matrix yields the linear combinations of the parameters which are not resolved. The implication is that the model can be varied indefinitely in these directions without affecting the fitting error. In practice, there can be a limit to the extent to which the model can be varied in these unconstrained directions. After obtaining a best fit and the resolution matrix, the model is varied in the unconstrained directions to find the point where the fitting error exceeds the best fit error by a specified amount or until the parameter variation exceeds a specified limit. Variation is done in both increasing and decreasing directions for each original parameter. For m parameters, the resulting collection of 2m+1 models and synthetic curves shows the range of models which satisfactorily fit the data and their corresponding synthetic curves. The results concur with known equivalence principles for thin surface and buried layers and the method provides a convenient means of illustrating the equivalence status of any inversion result.
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Calibration and Filtering Strategies for Frequency Domain Electromagnetic Data
Authors Burke J. Minsley, Bruce D. Smith, Richard Hammack, James I. Sams and Garret VeloskiTechniques for processing frequency-domain electromagnetic (FDEM) data that address systematic instrument errors and random noise are presented, improving the ability to invert these data for meaningful earth models that can be quantitatively interpreted. A least-squares calibration method, originally developed for airborne electromagnetic datasets, is implemented for a ground-based survey in order to address systematic instrument errors, and new insights are provided into the importance of calibration for preserving spectral relationships within the data that lead to more reliable inversions. An alternative filtering strategy based on principal component analysis, which takes advantage of the strong correlation observed in FDEM data, is introduced to help address random noise in the data without imposing somewhat arbitrary spatial smoothing.
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Agricultural Geophysics: Past, Present, and Future
Authors Barry J. Allred, Robert S. Freeland, Hamid J. Farahani and Mary E. CollinsGeophysical methods are becoming an increasingly valuable tool for agricultural applications. Agricultural geophysics investigations are commonly (although certainly not always) focused on delineating small- and/or large-scale objects/features within the soil profile (~ 0 to 2 m depth) over very large areas. The three geophysical methods predominantly employed for agricultural applications, both past and present, are resistivity, electromagnetic induction (EMI), and ground penetrating radar (GPR). Some of the more important past developments for agricultural geophysics include: soil water content monitoring using resistivity methods beginning in the 1930s and 1940s; soil salinity assessment with resistivity and EMI methods beginning in the 1960s and 1970s; updates and improvements in U.S. national program soil survey mapping using GPR beginning in the late 1970s and on into the 1980s; and for precision farming purposes, the delineation of spatial variations in soil properties with resistivity and EMI methods beginning in the 1990s. There has been significant recent advancements in agricultural geophysics, with resistivity, EMI, GPR, and other geophysical methods presently being used or evaluated for applications ranging from soil hydrologic characterization, determination of clay-pan depth, soil nutrient monitoring at confined animal feeding operation sites, crop/tree root biomass surveying, subsurface drainage system infrastructure detection, identification of subsurface flow pathways, soil compaction evaluation, etc. However, before agricultural geophysics can reach its full potential, new developments are needed, such as: expanding possible agricultural applications for resistivity, EMI, and GPR methods; greater employment of geophysical methods that have not traditionally been applied to agriculture; construction of multi-sensor geophysical equipment platforms, perhaps integrated with agricultural machinery; development of agricultural geophysics expert system computer software; etc. Achieving these future advancements in agricultural geophysics will require close collaboration between those in both the agricultural and environmental/engineering geophysics communities.
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Third Year of Subsurface Drip Irrigation Monitoring using Gem2 Electromagnetic Surveys, Powder River Basin, Wyoming
The National Energy Technology Laboratory and the U.S. Geological Survey are collaborating with BeneTerra LLC to comprehensively monitor a sub-surface drip irrigation (SDI) system at a site in the Powder River Basin (PRB) of Wyoming. Irrigation water for the SDI system is coalbed natural gas (CBNG) co-produced water. The study is being conducted at the Headgate Draw area, located approximately 17 km south of Arvada, Wyoming at the confluence of Crazy Woman Creek and the Powder River. The study site encompasses six fields and covers an approximate area of 1.2 km2 (Figure 1). The project is an integration of geophysical, geochemical, and soil science studies. The third year of a five year geophysical monitoring study is reported here.
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Applications of Self-Potential Method in Agriculture
Authors Larisa Golovko and Anatoly I. PozdnyakovElectrical geophysical methods are classified as methods measuring natural electrical potentials of the ground without introducing additional electrical field and methods utilizing artificial electrical or electromagnetic fields to measure soil electrical parameters. Method of self-potential (SP) measures the naturally existing electrical potentials in soils and “bio-potentials” in plant, which are important in agriculture. Despite growing popularity of electrical resistivity/conductivity methods in precision agriculture, method of self-potential is rarely used. The SP method is based on measuring the natural potential differences, which generally exist between any two points in the soil or plant. Electrical potential in Soil-Plant system is a combination of the natural electrical potential differences on the interfaces inside soil (between soil horizons or peds), on the interfaces inside growing plant (between different plant tissues), as well as between soil and plant. The largest electrical potential differences were observed inside soils between soil horizons drastically different in physical and chemical properties. In most soils topsoil has higher electrical potentials than subsoil. The highest potential difference between soil horizons reported for Spodosols (40-60 mV), decreasing to 20-40 mV in Alfisoils and to ~20 mV in Mollisols, and even lower in Aridisols. Maps of electrical potentials in topsoil help to reveal the micro-environments for plant growth and correspond to plant biomes in natural ecosystems. Electrical resistivity (ER) or conductivity (EC) maps are generally similar to the maps of self-potentials, but using combination of those methods brings more information about infiltration and subsurface water fluxes and aid in search for clogged drainage pipes and reclamation planning. Recent advances in geophysical equipment, such as LandMapper ERM-02 also allow non-invasively measure natural electrical potentials between soils and plants, which are very small (μV magnitude), but nevertheless can be used to study plant water and nutrient stresses and manipulated to facilitate plant growth.
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Development of Methods for Determining the Suitability of Ephemeral Streams for Produced Water Discharges
More LessWyoming’s Agricultural Use Protection Policy allows discharge of produced water from coal bed natural gas operations to ephemeral streams with irrigated lands, on the basis of water quality implied from root zone soil salinity measurements. Critics of the policy argue that the soil and water quality sampling methods used to set quality limits for produced water discharges do not accurately represent existing soil conditions or indicate the potential for soil damage that can result from contact with the sodic, brackish produced water. To improve the understanding of interactions between soil and the discharges of sodic, brackish water from CBNG production, the National Energy Technology Laboratory conducted airborne, ground, and borehole electrical conductivity surveys and optical remote sensing surveys over the Beaver Creek Watershed in the central Powder River Basin of Wyoming. The airborne electrical conductivity data were found to quickly map possible areas of high soil salinity (ECe) for the extensive sub-irrigated areas that provide forage for livestock. Hyperspectral remote sensing data can help identify surface soil minerals and vegetation susceptible to the influence of CBNG produced water and identifies evidence of other possible impacts along waterways. The combined methods are potentially useful in land and water management decisions related to salinization.
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Case History: Siting Shallow Groundwater Wells with the Aid Of Geophysics
Authors Norman R. Carlson, Paul G. Ivancie and Phil C. SirlesAlthough the Colorado Division of Wildlife’s Bellvue Fish Hatchery site is relatively small, covering approximately 30 acres, groundwater drilling results across the site are variable and unpredictable; the site includes both productive, artesian wells as well as dry wells. The site is underlain primarily by the Lykins Formation, which includes interbedded siltstones, limestones, claystones, and evaporites. In preparation for new wells, geophysical surveys were done in an attempt to better understand the subsurface with respect to groundwater production. Both transient electromagnetic (TEM) and galvanic dipole-dipole resistivity lines were run, and substantial variations in resistivity within the Lykins are evident (as might be expected from the prior drilling results). The first test well after the geophysical survey was sited to test a locally conductive zone; the well was successful and flowed artesian. Similarly, a second test in a conductive zone also flowed artesian, while a third hole, not based on the geophysical survey (but sited primarily on the basis of permits and logistical considerations) was unproductive. The geophysical data confirm the heterogeneous nature of the Lykins at this site, agrees well with downhole logging, and has been clearly useful in successfully siting groundwater production wells.
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Evaluating Chloride Contamination In Sand And Gravel Aquifers And Bedrock Fractures Using Terrain Conductivity And Very Low Frequency Geophysics
Authors W. Bradley, M.S. Tirone, L. Christopher, C.G. Covel and James E. HillierIn April 2009, dissolved chloride concentrations at a public school water supply in south-central Maine were found to exceed 400 milligrams per liter (mg/L). The Maine Maximum Contaminant Level (MCL) and Federal Drinking Water Standard for chloride (250 mg/L) had been exceeded, rendering the School’s water supply non-potable. Contaminated well water was blamed for: health risks for some of the students and employees; corrosion of pipes, pumps, plumbing fixtures, and school kitchen equipment; and other potential negative impacts to School infrastructure and associated property. School officials believed the problem originated with road salt stored at a Town facility located approximately six hundred feet from the school’s drinking water supply well. However, some Town officials blamed remnant salt-water intrusion that followed sea-level rise during the Pleistocene Era, or road salting performed by the State Department of Transportation. Therefore, an impartial and scientific investigation was needed to both solve the water supply problem and, correctly assign liability. The situation required developing and interpreting a substantial amount of geologic data, as well as safely locating and installing a new 20,000 gallons per day potable water supply before the fall School session commenced in early September. This would involve mapping and interpreting key characteristics of surficial and multiple bedrock aquifers in order to isolate the existing chloride plume from a target bedrock aquifer. We elected to design a site-specific investigation employing both shallow electro-magnetic terrain conductivity (TC), and deep geophysical Very Low Frequency (VLF)
investigations to achieve these goals.
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An Integrated Groundwater Study: Chasnigua, Honduras
Authors Catherine Skokan and David MunozA group from the Humanitarian Engineering Program at the Colorado School of Mines has employed a suite of geophysical tools to characterize subsurface water for the village of Chasnigua, Honduras. The village is small, with approximately 50 families (200 people) that rely on trucking their water to their homes. They have asked for assistance in developing water well, storage and distribtution systems. Honduras is economically one of the poorest countries in the western hemisphere, with about half the population below the poverty line. Consequently, the people do what they can to subsist on the land. This location is one with economic hardships and complex geology and hydrology. Because of the complex nature of the site and because of a lack of previous geophysical information, a suite of measurements was used. These included Magnetic and Magnetic Gradient Measurements, DC Resistivity, and Frequency Domain Electromagnetic Studies. Soil and water sampling and testing, as well as topographic mapping, augmented the geophysical data. These geophysical surveys have aided in the determination of a location for a water well in the volcanic/limestone terrain. Along with the geophysical data, an interdisciplinary team of senior level engineering students, working through the Humanitarian Engineering Program at Colorado School of Mines, cooperated with the people of Chasnigua and developed a design for the water treatment, storage and distribution system.
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Integrated Use Of Surface Geophysical Methods For Site Characterization -- A Case Study In North Kingstown, Rhode Island
A suite of complementary, non-invasive surface geophysical methods was used to assess their utility for site characterization in a pilot investigation at a former defense site in North Kingstown, Rhode Island. The methods included frequency-domain electromagnetics (FDEM), ground-penetrating radar (GPR), electrical resistivity tomography (ERT), and multi-channel analysis of surface-wave (MASW) seismic. The results of each method were compared to each other and to drive-point data from the site. FDEM was used as a reconnaissance method to assess buried utilities and anthropogenic structures; to identify near-surface changes in water chemistry related to conductive leachate from roadsalt storage; and to investigate a resistive signature possibly caused by groundwater discharge. Shallow anomalies observed in the GPR and ERT data were caused by near-surface infrastructure and were consistent with anomalies observed in the FDEM data. Several parabolic reflectors were observed in the upper part of the GPR profiles, and a fairly continuous reflector that was interpreted as bedrock could be traced across the lower part of the profiles. MASW seismic data showed a sharp break in shear wave velocity at depth, which was interpreted as the overburden/bedrock interface. The MASW profile indicates the presence of a trough in the bedrock surface in the same location where the ERT data indicate lateral variations in resistivity. Depths to bedrock interpreted from the ERT, MASW, and GPR profiles were similar and consistent with the depths of refusal identified in the direct-push wells. The interpretations of data collected using the individual methods yielded non-unique solutions with considerable uncertainty. Integrated interpretation of the electrical, electromagnetic, and seismic geophysical profiles produced a more consistent and unique estimation of depth to bedrock that is consistent with ground-truth data at the site. This test case shows that using complementary techniques that measure different properties can be more effective for site characterization than a single-method investigation.
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Estimating Groundwater Storage Changes In The Western Kansas Using Grace Data
Authors Bo Chen, Jianghai Xia, Qiuge Wang, Chao Chen, Richard D. Miller and Qing LiangThe Gravity Recovery and Climate Experiment (GRACE) delivers monthly gravity fields since it was launched in March 2002, which provides a new way to monitor the groundwater storage variations for large regions. In this study, we attempt to apply the GRACE data combined with estimated soil moisture based on the water balance approach to estimate monthly groundwater changes in the western Kansas of approximately 100,000 km2. The comparison of different Gaussian smoothing radiuses indicated that a smaller filter radius (150 km) is more appropriate for this size of the study area to get more effective gravity signals. The results are compared with in situ yearly measurements of groundwater levels and show a prominent seasonal cycle. The groundwater storage changes estimated from GRACE data agree well with the measured groundwater levels during 2003 and 2008. Both of them show a decline trend. Such observation results from GRACE data will provide regional fundamental information for water resource management.
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Spatio-Temporal Monitoring With Airborne EM Data – Still Wishful Thinking, Or A Realistic Proposition?
Authors Tim Munday, Andrew Fitzpatrick, Volmer Berens, Andrea Viezzoli and Kevin CahillAlthough the notion of spatio-temporal monitoring of natural landscapes and phenomena using multi-date airborne electromagnetic (AEM) surveys has been around for some time, examples are very limited in scope, particularly when defining vertical and lateral changes with time. We demonstrate an effective procedure for defining spatio-temporal variations in ground conductivity across a salinised floodplain in South Australia, using multi-date FDHEM data. Lateral and vertical changes in the conductivity of the floodplain have been resolved. We believe the advent of improved calibration procedures, geometry correction, calibrated broad band AEM systems and advanced inversion procedures that obviate the necessity of system calibration – recalibration, such as the holistic inversion, provide for the realistic proposition of using AEM data for the semi-quantitative and quantitative monitoring of landscape change in the subsurface. However, we emphasize the need for caution when considering observed spatial variations, stressing the importance of accounting for system investigation depth and the potential for artifacts that might be introduced from noise, system geometry and/or data interpretation procedures, when comparing data and derived conductivity models from different dates.
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Redefining The Groundwater Resource Of The Eyre Peninsula, South Australia Using AEM Data
Authors Andrew Fitzpatrick, Tim Munday, Kevin Cahill and Volmer BerensThe groundwater aquifer lens systems of the lower Eyre Peninsula are an important water supply source for Eyre Peninsula. Demand from the aquifers is near the current extraction limits and there is a need to undertake further modelling of the groundwater systems to ensure confidence in the limits determined. This paper describes the use of airborne electromagnetics to map important elements of the Quaternary and Tertiary aquifer systems in the area. TEMPEST time domain EM data were acquired over the known extent of groundwater lens systems. These data were inverted using both constrained and unconstrained techniques to define the conductivity structure in three dimensions. Hydrogeologically significant bounding surfaces were then defined, through the use of a line-by-line interpretation procedure to link borehole data with the observed ground conductivity structure.
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Groundwater Purveying Using Very Low Frequency Fracture Delineation Methods
Authors Peter J. Hutchinson, Maggie H. Beird and Matthew MitchellRandom drilling for commercially-productive groundwater wells is a haphazard method within the Pennsylvanian-aged rocks of the Appalachian Plateau Region of southwestern Pennsylvania. These rocks have low permeability and porosity and the average production well produces only enough yield for homeowner use. Often these wells are installed as an open hole to 300 feet to insure an adequate water supply for the homeowner since the well bore acts as a storage reservoir during recovery and drawdown. Three sites mapped with Very Low Frequency (VLF) methods delineated fractures with the potential to maximize bedrock production through increased fracture-induced permeability. A boring was advanced from a location at each of the three sites selected through VLF mapping. The borings penetrated fractures at the anticipated depths of between 10 and 20 meters below grade. Pump tests indicate that these three borings can produce between over 1,000l/min with little drawdown. Each of the three wells is a commercial success.
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Aquifer Characterization Using Coupled Inversion Of DC/IP And Mrs Data On A Hydrogeophysical Test-Site
Authors Thomas Günther, Raphael Dlugosch, Raphael Holland and Ugur YaramanciAmong hydrogeophysical methods, Magnetic Resonance Sounding (MRS) and Direct Current resistivity / Induced Polarization (DC/IP) measurements can be particularly interesting and useful, since the underlying parameters are related to hydraulic properties. We present a combined investigation of a well-known test site with two aquifers. The inversions for MRS and DC/IP data are combined using a structural coupling and yield improved models due to common but free boundaries. A further combination is achieved by cluster analysis of the obtained resistivity, phase and water content distribution. The approach of the coupled inversion is applied to data of the test site Schillerslage (Hannover, Germany). The simple model obtained agrees with ground truth from boreholes and laboratory as well as with other geophysical measurements.
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Comparison Of 2D And 3D Electrical Resistivity Imaging Methods To Target High-Yield Water-Bearing Vertical Fracture Zones
Authors Brent B. Waters, Robert Davis, Mac G. Morrow and Colin D. LangfordIn bedrock terrain, groundwater predominantly flows through discrete fracture zones within a low permeability bedrock matrix. Fracture zones are typically long, linear, near-vertical zones of increased fracture density found in most geologic settings. These zones are typically very narrow and are often expressed as natural topographic depressions such as straight stream valley segments, swales and sags in the land surface, or as linear tonal or vegetative alignments often referred to as lineaments or fracture traces. Often, however, fracture zones do not have surface expressions. In such cases, finding and intersecting fracture zones with a well is like finding the proverbial needle in the haystack.
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Using Airborne Geophysical Surveys To Improve Groundwater Resource Management Models
Increasingly, groundwater management requires more accurate hydrogeologic frameworks for groundwater models. These complex issues have created the demand for innovative approaches to data collection. In complicated terrains, groundwater modelers benefit from continuous high-resolution geologic maps and their related hydrogeologic-parameter estimates. The USGS and its partners have collaborated to use airborne geophysical surveys for near-continuous coverage of areas of the North Platte River valley in western Nebraska. The survey objectives were to map the aquifers and bedrock topography of the area to help improve the understanding of groundwater–surface-water relationships, leading to improved water management decisions. Frequency-domain heliborne electromagnetic surveys were completed, using a unique survey design to collect resistivity data that can be related to lithologic information to refine groundwater model inputs. To render the geophysical data useful to multidimensional groundwater models, numerical inversion is necessary to convert the measured data into a depth-dependent subsurface resistivity model. This inverted model, in conjunction with sensitivity analysis, geological ground truth (boreholes and surface geology maps), and geological interpretation, is used to characterize hydrogeologic features. Interpreted two- and three-dimensional data coverage provides the groundwater modeler with a high-resolution hydrogeologic framework and a quantitative estimate of framework uncertainty. This method of creating hydrogeologic frameworks improved the understanding of flow path orientation by redefining the location of the paleochannels and associated bedrock highs. The improved models reflect actual hydrogeology at a level of accuracy not achievable using previous data sets.
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Groundwater Evaluation Using Vtem Helicopter Electromagnetics In The South Platte Nrd, Sidney, Nebraska
Authors Jean M Legault, Paolo Berardelli, Jared Abraham, James Cannia and Kerim MartinezA VTEM time domain helicopter-borne electromagnetic survey was undertaken for groundwater evaluation in western Nebraska with the objective to map the extent of deep freshwater aquifers. The VTEM system combines near surface high resolution resistivity imaging and deep penetration making it a low cost, rapid reconnaissance mapping tool in areas with thick, conductive terrain. The survey was preceded by a synthetic computer modeling study that proved its resolution and penetration capability below 200m depth. The test survey that followed used a new X-Z component system and caesium magnetometer that covered a 165 square km region of the South Platte NRD in two short survey days. Data analysis using a variety of 1D (layered-earth) inversion and conductivity-depth imaging (CDI) tools indicate that, in spite of significant presence of man-made culture (powerlines and metallic structures), the moderately conductive Ogallala Group aquifer was successfully mapped to a known depth of 160m above the conductive White River Group Brule Formation bedrock aquitard. Simulated penetration depths in excess of 200m appear to have been easily reached, suggesting the use of VTEM to be extended into deeper, more conductive aquifers within the Natural Resource Districts of Nebraska.
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Advances In The Evaluation Of Pile And Shaft Quality
Authors Frank Rausche and Brent RobinsonFor the past half century, great efforts have been made and progress has been achieved in developing a variety of electronic testing methods for the quality control and quality assurance of deep foundations. These developments took advantage of major advances in ever more accurate and sensitive sensor manufacturing and faster and more powerful computers. The dynamic pile testing methods were the primary beneficiaries of these R&D efforts and its application has been expanded from bearing capacity assessment of driven piles to drilled shafts, micro piles and even penetrometers. In addition to soil resistance, results from construction monitoring now provide information about stresses along the pile, pile integrity and occasionally soil vibrations. Dynamic pile testing methods also include nondestructive techniques involving sonic and ultra sonic signals. Much of the recent developments involved not only ruggedizing hardware and preparation of more user friendly software, but also deriving reliable calculation procedures and presenting results in a way which is easy for the report recipient to understand. Additionally, experiences from construction sites showed that an immediate assessment of the foundation characteristics is imperative. This requirement lead to the need for easily used simulation software and workshops. Today such training events are frequently performed over the internet. This presentation summarizes several recent hardware and software developments and shows a few typical results.
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Quality Management Of Stabilized Soil Construction Using Lab And Field Seismic Testing
Authors Nathan M. Toohey, Michael A. Mooney and Nils RydenCurrent pavement design practice for stabilized soils specifies a 28-day modulus and stiffness value. There is a need to evaluate performance after 5 to 7 days to ensure efficient constructability. There is a large disconnect between quality management programs not only for design and construction, but between lab and field evaluations during construction. The difference in design and measured parameters, lab and field, for performance evaluation does not permit a direct comparison. Current quality management techniques do not permit assessment of the true performance of the pavement construction. Seismic wave based testing offers considerable potential for quality assessment of stabilized soils. Surface wave analysis can be used to assess low-strain or seismic modulus of stabilized soils in the field while travel-time analysis and free-free resonance testing can be used to estimate seismic modulus of laboratory specimens. Lab and field seismic moduli are directly related, thus permitting seismic analysis to bridge the gaps encountered by current quality management techniques. This paper presents lab and field seismic testing protocol and results which indicate its effectiveness as a combined quality management technique.
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Integrated Three Dimensional GPR And EM Study Of Three Large Water Supply Pipes
Authors Steven P. DiBenedetto and Heron R. MochnyA new 16-inch municipal water supply line is to be installed between two siphon chambers in the right-of-way (ROW) of three very large diameter (9+ft) steel water supply conduits in the northeastern United States. While excellent as-built records of the conduits were available, given the age of the infrastructure, exact surveyed locations of the large water supply pipes were unknown within the ROW, and were required during the design phase of the project in order to safely perform geotechnical borings and facilitate the routing of the installation trench for the 16-inch line. Additionally, the mapping of any underground utilities within the ROW and adjacent to an existing pump station was required for design in advance of excavation and construction activities relating to the expansion of the pump station. A geophysical survey was performed by Underground Imaging Technologies, Inc. (UIT), acting as a subcontractor to Malcolm Pirnie along the ROW in order to determine the precise location of the large water supply pipes and also the locations of any underground utilities or other subterranean features that may interfere or otherwise impact the installation of the new waterline. Multi-channel Ground Penetrating Radar (GPR), multi-sensor Time Domain Electromagnetic Induction (TDEMI) and a Ground Conductivity Electromagnetic (GCEM) survey was performed to obtain the requisite data. The geophysical survey was performed between May 19th and 22nd, 2009 and over 182,000 square feet were surveyed. The results of the geophysical survey were able to accurately determine the horizontal positions and depths of the water supply pipes throughout the investigation area, in addition to mapping the positions of utilities in the vicinity of future construction for a pump station upgrade. Several geological anomalies were detected that warrant consideration in any excavation or construction activities. Depth below ground surface of the pipes obtained via GPR was converted to elevation by subtracting from USGS 10m DEM ground surface elevation. This allowed for the construction of a fully georeferenced, elevation-based, three-dimensional digital model of the pipes within the investigation area in AutoCAD.
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Continuous Exploration Ahead Of The Tunnel Face By Tswd - Tunnel Seismic While Drilling
Authors Ewald Brückl, Werner Chwatal, Stefan Mertl and Alexander RadingerSeismic measurements using the VSP principle have been carried out for over 20 years to investigate the rock ahead of a tunnel face and made a contribution to reduce the risks during construction for conventional tunnelling, as well as for tunnelling with a Tunnel Boring Machine (TBM). However, reflecting horizons intersecting the tunnel axis obliquely cannot be imaged at their intersection with the tunnel. This circumstance imposes a major uncertainty on the prediction of the geological situation ahead of the tunnel face. A possibility to image all reflecting horizons, regardless of their orientation, at least near to their intersection with the tunnel axis is offered by continuous monitoring with the drilling head of a TBM as the seismic source (Tunnel Seismic While Drilling - TSWD). In this study we present continuous TSWD data from a gallery drilled in limestone and dolomite of the Northern Calcareous Alps, Austria. This gallery intersects a deeply incised valley, filled with sediments. The two main goals for the processing were the derivation of high signal to noise seismograms from the pilot and receiver signals and the removal of the first arrivals from the data in order to uncover reflected phases, even from reflectors very near to the TBM drilling head. Both goals were achieved satisfactorily and the main geological structure was well resolved. Geophysical issues which need further investigation are addressed. The results of our study suggest that substantial risk reduction could be achieved by continuous TSWD. However, the high production rate of modern TBMs imposes a major challenge on real time monitoring, processing and prediction.
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Geoelectrical Imaging For Detection Of Water Migration In A Bioreactor Landfill
Authors Håkan Rosqvist and Torleif DahlinIn this paper we describe field investigations of leachate recirculation at a bioreactor landfill using geoelectrical imagining technique (i.e., electrical resistivity) combined with a tracer test. The use of geoelectrical imagining techniques is an established practice for environmental investigations and monitoring of various landfill processes and in recent years also the bioreactor landfill concept has been emphasised. In the study, the electrical resistivity technique was evaluated and the possibility to detect water and gas migration in the waste mass was investigated. Results showing moisture migration through the bioreactor landfill, during leachate flushing and during a tracer test, are presented. Also results indicating the resistivity technique being useful for biogas detection are shown.
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An Evaluation Of The Potential Of The Geoelectrical Resistivity Method For Mapping Gas Migration In Landfills
Authors Håkan Rosqvist, Virginie Leroux, Torleif Dahlin, Sara Johansson and Mats SvenssonMethane is a powerful greenhouse gas and growing concern regarding global climate changes over the last years has pointed out the need to quantify and control the leaking of methane into the atmosphere. Landfill gas is regarded as one of the major sources for methane migration to the atmosphere. In this study we present research work with the objective to evaluate the use of geoelectrical resistivity to detect gas migration in landfills. Extensive field experiments were conducted at the Filborna landfill site in Helsingborg, Sweden, in August 2008. In general, the resistivity measurements showed results corresponding to results reported from previous investigations in waste. However, also large variations in resistivity were indicated. Relatively high variability and high mean resistivity in the surface-near layers clearly indicate influence on the resistivity in the upper zone of the landfill. The variability and high resistivity may partly be explained by appearance and migration of landfill gas.
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Case History: Monitoring Resin Injections With The Aid Of 4D Geophysics
Authors Justin B. Rittgers, Phil Sirles, Gianfranco Morelli and Marco OcchiGround improvement is an important practice in areas where the combined presence of expansive soils and fluctuating moisture content often result in differential heaving and settling soils and variable confining forces exerted on foundations. In fall of 2009, three-dimensional (3D) seismic pressure wave (p-wave) refraction and 3D electrical resistivity tomography (ERT) surveys were performed to determine the effectiveness of seismic refraction tomography in imaging the permeation of resin injected during ground improvement efforts within problematic soils. A test site near Piacenza, Italy was selected for this undertaking: Data were collected around the perimeter of an existing house suffering damage due to differential ground settlement. Three independent yet identical surveys were conducted using both methods, producing 3D images of the spatial distribution and variations in subsurface material properties before, during and after resin injection. The site is underlain primarily by a two to three meter thick layer of silt and clay with some sand lenses over an alluvial silty sand base layer. Prior to resin injection, substantial variations in both electrical resistivity and p-wave velocity are evident beneath the particular corner of the structure that exhibits the highest extent of damage (e.g., cracking and settling). During and after resin injections and curing, resistivities and velocities can be seen to change in the surrounding vicinity of injection points, and the magnitude of change in both data sets appears to be related to the amount of resin injected at each point. Geophysical measurements confirm the heterogeneous nature of the near-surface soil at this site, results from both methods correlate well with each other and additional field data (i.e., CPT data), and resultant 3D models are clearly useful in siting injection points as well as time-lapse monitoring the extent of resin permeation.
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Identification Of The Polaris Fault Using Lidar And Shallow Geophysical Methods
Authors Lewis E. Hunter, Michael H. Powers and Bethany L. BurtonAs part of the U.S. Army Corps of Engineers’ (USACE) Dam Safety Assurance Program, Martis Creek Dam near Truckee, CA, is under evaluation for earthquake and seepage hazards. The investigations to date have included LiDAR (Light Detection and Ranging) and a wide range of geophysical surveys. The LiDAR data led to the discovery of an important and previously unknown fault tracing very near and possibly under Martis Creek Dam. The geophysical surveys of the dam foundation area confirm evidence of the fault in the area.
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Internal Structure Of An Ilmenite Mine Waste Rock Pile Modelled From Ip Imaging And Laboratory Measurements
Authors Michel Chouteau, Rachid Intissar and Michel AubertinNickel concentrations occasionally above the allowed norm have been measured in water samples in the vicinity of the Petitpas waste rock pile at the Tio mine, Québec, Canada. In order to understand the chemical and hydrodynamic mechanisms responsible for the nickel dissolution and release in the environment a large hydrogeological/geotechnical/geophysical study was undertaken on the very large rock pile (600 m x 300 m x 150 m). Geotechnical and physical properties were measured in the laboratory on samples of waste with various moisture content and salinity. Induced polarization allowed the determination of electrical resistivities and chargeabilities that were to be used to interpret time-domain IP tomography surveys carried out on the waste rock pile. IP survey data were inverted in 2-D. The resistivity models for all survey lines show common features. From surfae to 25-30 m depth, the subsurface is resistive and show lateral changes which suggests large grain size heterogeneities and low water content; below and up to 50 m, a quasi uniform layer with resistivities in the range 50-250 ohm.m suggests fine-grained material with increased saturation. Finally below a depth of 50 m, the subsurface becomes very resistive again, indicative of coarse low-moisture content material. The chargeability model shows no structural correlation with the resistivity model. In general, chargeabilities are very large (up to 100 mV/V) and show no layering. From the laboratory and the survey results, we interpret the resistivity to be sensitive to water content and salinity while chargeability is sensitive to the metal concentration. The geoelectrical model and the interpreted hydrogeotechnical model will be useful for modeling water flow and reactive transport through the waste rock pile.
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Mapping Bedrock Topography Beneath Glacial Overburden Near Cape Horn, South America
More LessPlacer gold mining operations were carried out on several of the small islands between Tierra del Fuego and Cape Horn in the late 1800’s, just before the Klondike gold rush. As soon as the Klondike rush was announced to the world many of the miners and prospectors working in this isolated region went north. The area was quiet for nearly a hundred years before there was any renewed interest in it. This was due to the dispute between Chile and Argentina over ownership of these islands. Although the Chilean government was eventually granted ownership of these islands it is only recently that any exploration activity has occurred. A placer gold exploration program that included surface sampling, geological mapping and bulk sampling was carried out in the early 1990’s. The project looked promising but there was difficulty in unravelling the glacial history and obtaining estimates of gravel thickness for tonnage calculations. Bemex Consulting International was asked to set up a program to map the bedrock topography and estimate gravel thickness. The project was carried out in two phases. The first phase was carried out during the summer season (December) to determine if time-domain EM soundings would provide the necessary accuracy to meet the above objectives. At the end of this phase the conclusion was the Geonics EM-47 system was capable of mapping the gravel thickness and bedrock topography. The second phase was conducted the following summer (January and February) and consisted of carrying out more than two hundred 40 m x 40 m loop soundings at the site. The results of this survey were verified with a series of manholes dug to depths varying from 15 m to more than 30 m. The depth to bedrock in these holes was consisted with the 1D interpretation provided from the Interpex software.
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Earthquake Hazard Maps Of The City Of Ottawa, Canada, Using Near-Surface Geophysical And Geological Methods
The city of Ottawa, Ontario, Canada, is in an area of elevated earthquake shaking hazard and is considered to be the Canadian city third-most at risk to damage (after Vancouver and Montreal). Maps showing regional variation of Vs30, fundamental site period, and an example map of the spectral accelerations at Sa=0.2s have been completed for the city at a reconnaissance scale. These have been developed from combined geological information from ~21,000 boreholes (water wells and geotechnical borings) within the city limits as well as ~700 surface and borehole shear wave seismic measurement sites. Borehole and surface shear wave measurement techniques developed for the operational area included: surface reversed refraction and reflection sites, MASW, downhole shear wave and horizontalto- vertical spectral analyses of ambient noise. The surficial geology was subdivided into three basic units based on their geotechnical properties: (i) soft, fine-grained, post-glacial sediments, (ii) glacial till and coarse-grained, till-derived sediments, and (iii) firm Paleozoic and PreCambrian bedrock. A series of shear wave velocity-depth functions were assigned to each borehole based on interpolation from proximal geophysical sites. The resulting three-dimensional shear wave velocity database was then used to determine parameters such as Vs30 and fundamental site period. The Vs30 map of the city is subdivided in terms of the U.S. National Earthquake Hazard Reduction Program (NEHRP) zones which have been adopted by the 2005 National Building Code of Canada. Since the City of Ottawa has a large areal extent and is close to the West Quebec Seismic zone, the base accelerations for the 2% in 50 year
earthquake event vary extensively within the city boundaries. Hence an example map of the spectral accelerations at Sa=0.2s has been developed to demonstrate regional variations and the effects of NEHRP zones.
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Finding Faults Using High-Resolution Aeromagnetic Data In Great Sand Dunes National Park And Vicinity, San Luis Valley, Colorado
Authors V.J.S. Grauch, David V. Fitterman and Benjamin J. DrenthHigh-resolution aeromagnetic data reveal faults near the Great Sand Dunes National Park and Preserve (GRSA) and vicinity that offset both bedrock and sediments, even under the dunes themselves. Complicated fault patterns evident in the aeromagnetic data over the exposed range front may represent multiple-age events. The range-front and parallel faults to the west together suggest that basement steps down along high-angle faults. A prominent linear feature parallels the range front from the dunes southward (“the parallel fault”). Preliminary analysis suggests that the top of the parallel fault is about 50-70 m deep, with near-vertical dip, and offsets sediments with differing magnetic properties as well as basement rocks at greater depths. In places, it is paralleled by less prominent aeromagnetic features, which may also be faults. TEM soundings across the parallel fault indicate that sediments juxtaposed there contain abundant clay to the west and mostly sand to the east. The clay-rich sediments are underlain by eastward-shallowing sand at depth. This result suggests that the eastern limit of the confining clay in this area is fault-bounded at shallow depths and may be interfingered with sand at greater depths. These relations have implications for groundwater modeling, geologic studies, and seismic hazards.
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Airborne Full Tensor Gravity
Authors John H. Mims and James MataragioThe gravity tensor measures changes in the three dimensional gravity field along the three axes of motion, giving a nine component array of differentials. Because of symmetry and the Laplacian character of gravity, only five of the components are independent. Gravity has been used for resource exploration since the early 20th century. The first exploration gravity surveys used a ground based gradiometer that was eventually replaced with ground based gravimeters. In the late 20th century, a moving platform full tensor gradiometer was developed for use on submarines. Eventually the technology was declassified and applied to commercial resource exploration using marine and airborne acquisition. Since much of acceleration caused by the vessel motion is removed as the gradient is being measured, the gradiometer can provide a high resolution gravity image in a fraction of the time it takes for an equivalent ground gravity survey to be completed. A case study of alluvial diamond exploration provides one example of using airborne gravity gradiometry for resource exploration.
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The Falcon Airborne Gravity Gradiometer For Engineering Applications
Authors Greg Hodges, Mark H. Dransfield and Tai-chyi SheiWhile airborne gravity has been available for decades, only with the advent of airborne gravity gradiometry (AGG), and specifically the FALCON AGG installed in a helicopter, has airborne gravity measurement reached a sensitivity and spatial resolution that can be effective for a wide range of engineering applications. Survey examples and gravity models comparing fixed-wing and helicopter AGG measurements demonstrate that voids as small as 10 m, or tunnels of 4 m width can be detected.
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Airborne EM Data Complement Magnetics In An Unexpected Way
In the fall of 2008, a low-altitude airborne geophysical survey was carried out at a military installation in Australia, the primary goal of which was detection and mapping of infrastructure, buried wastes, and other buried and surface metallic objects within a 1738 hectare area. The primary survey system was the Battelle VG-16 vertical magnetic gradient system. Because the base is active, the time frame for conducting the survey was limited to a few weeks. The short time frame and the added expense of an additional system were factors against adding on an electromagnetic survey. However, the Australian Department of Defence suggested that there might be non-ferrous targets of significance that the magnetic system would not detect. Moreover, the base was located some tens of kilometers from a field of extinct volcanoes, presenting the possibility of magnetic geology in the form of mafic igneous units. Therefore, it was determined that an airborne transient electromagnetic system should be included in the project. The added electromagnetic system proved valuable, but not in the way that was expected. Concentrations of strong anomalies appeared in the magnetic data, the sources of which could be either buried debris or geological. The TEM-8 system was flown over some of the more dense concentrations of magnetic anomalies. In some of these areas the TEM data showed very few anomalies, indicating that either the VG-16 anomalies are associated with magnetic rock types, or that the metallic sources detected by the VG-16 system are too deeply buried to be detected with the TEM-8 system. A few carefully located excavations indicated that the sources of the magnetic anomaly concentrations without associated electromagnetic anomalies were localized concentrations of very magnetic iron-bearing rock.
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Mapping Epikarst In The Arbuckle-Simpson Aquifer, Southcentral Oklahoma, Using Helicopter Electromagnetic Survey Data
Authors David V. Smith, Maryla Deszcz-Pan and Bruce D. SmithThe U.S. Geological Survey has been actively using helicopter electromagnetic surveys over karstic aquifers as part of on-going research to aid in the creation of highly detailed three-dimensional geologic models. The geologic models are the basis for understanding the geohydrologic framework of the aquifers, and they provide essential information needed for groundwater models used to manage an increasingly important resource. As part of this research, the USGS has developed and applied methods for mapping epikarst, which plays an important role in groundwater recharge. A case study in the Arbuckle-Simpson aquifer in south-central Oklahoma is presented here.
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Hydrogeophysical Surveys Of The Trinity And Edwards Aquifers At Camp Bullis, Northern Bexar County, Texas, 2006
Authors Jason D. Payne, Bruce D. Smith and Allan K. ClarkIn 2002, the U.S. Geological Survey (USGS), in cooperation with the U.S. Army, began hydrogeologic studies of Camp Bullis in northern Bexar County, Texas, with mapping of hydrogeologic features and hydrostratigraphic units (Clark, 2003) at a scale of 1:24,000. In 2003, a USGS-contracted helicopter electromagnetic (HEM) resistivity and magnetic survey was flown over Camp Bullis and the adjacent Camp Stanley (Figure 1). This paper describes the integrated ground electrical and electromagnetic geophysical surveys that were conducted in 2006 in order to follow up on the previous studies and to map hydrogeologic features in more detail. The goal of the project is to better understand the hydrogeologic framework and structure of the Trinity and Edwards aquifers within the study area. The Edwards aquifer is classified as a sole-source water supply for the city of San Antonio.
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Subsurface Imaging Of Karst Geology For Energy Infrastructure Expansion
Authors John A. Mundell and Gabriel J. HebertThe development of building infrastructure on top of karst geology always presents challenges and has the potential for catastrophic failure. Recently, an electrical substation located in southern Indiana known to sit atop potentially karstic limestone was scheduled to be expanded onto an adjacent 10-acre parcel. A standard preliminary geotechnical investigation consisting of 18 soil borings with three rock cores conducted across the parcel indicated that although the bedrock was slightly to moderately fractured, it was sufficiently competent to build upon. However, the presence of several active sinkholes across the parcel led the local electrical power company to request a more thorough, geophysical investigation of the bedrock. For this project, a preliminary terrain conductivity survey was performed to yield information regarding the thin residual soils and shallow bedrock, followed by twodimensional resistivity profiling to detect any karst features deeper within the bedrock. The end result of the geophysical study gave the structural engineer and his client what they wanted - greater assurance that they had exercised diligence in their efforts to define site conditions and avoid hazards.
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Urban Geophysics: A Mapping Of Mount Bonnell Fault And Its Karstic Features In Austin, Tx
More LessAlthough most karstic regions are characterized by caves, collapsed features, and sinkholes, such features often do not have surface expressions, and their presence may go unrecorded. Central Texas and the Greater Austin metropolitan area have been built on the karstic limestone (Lower Cretaceous of Glen Rose Formation and Edwards Aquifer) in the Balcones Fault Zone (BFZ), and their growth is expanding. Near-surface karst features in the Austin area have a profound effect upon geotechnical engineering studies, such as structural foundations (residential buildings, shopping malls), utility excavations, tunnels, pavements and cut slopes. Thus the practice of geotechnical engineering is and has been a challenging proposition in the Austin area. Geophysical methods are sporadically used to estimate the locations and parameters of these karst features prior to any of these above-mentioned geotechnical studies. Opinions concerning the effectiveness of these geophysical surveys are mixed, and geophysical techniques are not generally recognized as primary tools in engineering-scale studies. However, remarkable advances in the manufacturing of geophysical instruments over the last ten years have made geophysics a viable tool for geotechnical studies of these karstic features. Data quality has been increased by the advent of continuous data collection. The data are better processed and interpreted by new and improved software packages, which produce improved sub-surface imaging and mapping. Thus integrated geophysical surveys can provide new insight into the near-surface karstic features in the Glen Rose Formation and Edwards Aquifer. I have conducted geophysical surveys (ground penetrating radar [GPR], resistivity imaging, magnetic [G-858], conductivity [EM-31] and natural potential [NP]) at three locations where the Mount Bonnell fault (MBF) is present, along the northern limiting boundary of the BFZ. Results indicate that all methods successfully imaged significant karst anomalies across the known fault locations. Integration of all these anomalies provides a much better understanding of near-surface geology defined by the caves, voids, collapsed materials, sinkholes and the fault itself.
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3D Masw Characterization Of Sinkhole: A Pilot Study At Usf Geology Park, Tampa, Fl
Authors Choon B. Park and Chris TaylorBy running three parallel and one crossing lines of conventional 2D MASW surveys followed by normal 1-D MASW inversions, a 3D characterization was attempted as a pilot study over an area of a known sinkhole 10-40 ft deep with lateral dimension smaller than 50 ft. Shear-velocity (Vs) data sets from each line were then used as constraints to calculate a cubic grid data in x (east-west), y (southnorth), and z (depth) directions by using a 3D inverse-distance-weighted (IDW) interpolation scheme. When displayed in depth-stripping mode at 5-ft depth intervals, velocity anomalies of substantially lower values than those in the ambient are recognized in the surface and depth locations that correlate fairly well with those identified in a geologic cross section previously compiled from other methods of well drilling, CPT, and GPR surveys. Properly selecting offset range during data acquisition and subsequent dispersion analysis seems critically important for the successful detection of a sinkhole.
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A Multi-Level Approach To Site Characterization C.W. Bill Young Regional Reservoir Hillsborough County, Florida
Authors Thomas L. Dobecki and Sam B. UpchurchThe C.W. Bill Young Reservoir is located in southeastern Hillsborough County (Tampa Bay Area) of Florida and is a 15.5 billion gallon, above-ground reservoir designed for temporary storage of excess surface water flow during rainy periods with the intent of recovery during dry periods. The water is held by a continuous earthen embankment that is 300-ft wide at its base with a circumference of five miles along the top. During the site selection and reservoir planning stages of the project, it was recognized that several factors would have an impact on the reservoir’s ability to retain water. Included among these are the risk of sinkholes and the presence of an abandoned phosphate strip mine underlying about one third of the 1,100 acre reservoir footprint. Each of these caused concern for both the ability of the reservoir to hold water (bottom leakage) and the ground stability beneath the embankment. The subsurface investigation included a multi-level approach to site characterization including:
• Photolinear analysis,
• Ground penetrating radar,
• Shear wave seismic refraction,
• High resolution seismic reflection, and
• Nearly 17,000 ft of soil borings
The intent of this program was to progress (going down this listing) from broad reconnaissance to successively more detailed investigations as important subsurface features became identified. The net result was identification and remediation of potential sinkhole and mining areas risks, which has resulted in a reservoir whose actual leakage volumes are less than the original design estimates.
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Wave-Energy Source For MASW?
Authors Mario Carnevale and Choon B. ParkSince its inception as a subsurface imaging technique, the multichannel analysis of surface waves (MASW) seismic method has been used in a variety of environmental and geotechnical applications. One of the more interesting applications is performing subsurface imaging in a beach environment. Although the loose and dry ground surface appears to present a formidable obstruction to the application of MASW for deep imaging, there could be an anonymous unexploited source of energy to make it happen. We look at the possibility that low frequency energy from ocean wave fronts can be introduced into seismic recordings made during MASW surveys along a beach or shoreline. Seismic data from MASW beach and shoreline surveys in Massachusetts will be examined for possible evidence of constructive or destructive interference from energy produced by ocean waves. The possible relationships of MASW survey geometry and the geography of the project settings are also examined. This study aims at evaluating the possible exploitation of ocean energy for deep MASW surveys in beach and shoreline environments.
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Roadside Passive Masw Survey - Dynamic Detection Of Source Location
More LessIn a roadside passive surface-wave survey under a typical urban setting with relatively heavy traffic and a complicated network of roads, a field record usually contains surface wave events generated from multiple source points scattered around the survey location. It is, however, those dominating energy events coming from one common surface point on the road that are used as signal in most advanced dispersion analysis methods based on the 2-D wavefield transformation. Events from other locations interfere adversely with signal events during the analysis if they take comparable energy or are largely ignored in the case of insignificant energy. A long record (e.g., 120 sec) is divided into many subsets of much shorter time of a proper length (e.g., 1 sec) and are treated as independent records of only one (or none) of a dominating event. By utilizing an advanced technique to detect fairly accurately the source location of the event, subsets are processed for their own dispersion images by using the scheme commonly used in the active MASW survey. Multiple data sets of the dispersion image are then stacked to result in an image of the highest signal-to-noise ratio (S/N) ever possible. This is demonstrated by using a field record acquired with a linear receiver array deployed along a busy street that contains events from complex source points and therefore could not be processed for any interpretable dispersion image using other methods currently available.
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Comparison Of FK And Spac Methods In Determining Dispersion Curves From Passive Surface Wave
More LessFK and SPAC are the two common approaches in determining dispersion curves from passive surface waves. To conduct a systematic comparison, we stimulate passive surface waves with randomly distributed sources and different types of arrays. A field data is also used in the comparison. The study shows that the SPAC method provides higher resolution on the dispersion image and is able to generate a dispersion curve with a larger frequency range. The FK method performs well within a limited frequency range. To reduce the uncertainty in determining dispersion curves, the combination of both methods is recommended.
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Applicability Of A Spatial Autocorrelation Method (Spac) Using A Linear Array In Comparison With Triangular And L-Shaped Arrays
Authors Koichi Hayashi and Takaho KitaWe have examined the applicability of a spatial auto-correlation (SPAC) method using a linear array in comparison with triangular and L-shaped arrays. The SPAC requires two dimensional arrays, such as a circle, a triangle and a crossing for calculating the phase-velocity of the microtremor. Theoretically, isotropic arrays, such as a circle or an equilateral triangle, are preferable in the SPAC analysis. However, the isotropic arrays required wide space and it is difficult to obtain such wide space in urban area. Recently, several theoretical and experimental studies have shown the validity of irregular arrays. Results of these studies have also implied the validity of linear arrays in which receivers are placed only on a line. The use of linear arrays will enable us to apply passive methods in urban area much easily. In this paper, we are going to examine the applicability of the linear array in terms of numerical simulation and field experiments. The result of field experiment showed that the linear array provides almost identical dispersion curves as that of two dimensional arrays although numerical simulation showed clear disadvantage of the linear array. It implies that that the sources of the microtremor are distributed randomly in space and the microtremor does not have any specific propagation direction at most of sites.
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Subsurface Tunnel Detection Using Electrical Resistivity Tomography And Seismic Refraction Tomography: A Case Study
Authors Grey I. Riddle, Craig J. Hickey and Douglas R. SchmittSeismic and electrical methods are two geophysical techniques commonly used to detect rock property changes in the subsurface. Surveys are usually carried out with sources and sensors placed at or near the earth’s surface. Various levels of data processing are applied to construct a map of the subsurface distribution of a physical property. Seismic methods are sensitive to velocity and density changes of the rock, while the electrical response is dependent upon the electrical resistivity of the rock. In this paper, we present an evaluation of using both seismic refraction and electrical imaging to locate a tunnel. Although the contrast in seismic velocity and electrical resistivity between the tunnel and its surrounding material can be large, tunnels remain difficult to detect. The difficulty primarily arises because the spatial resolution of these methods is less than or on the order of the size of the tunnels. Detection is further complicated by heterogeneity of the near surface materials within which many tunnels are constructed. In this paper, we present a case study using ERT dipole-dipole data and seismic refraction data at a tunnel site. Both seismic and electrical surveys were acquired at the same time with a lateral offset of about 3m. The results from both techniques show anomalies at the location of the tunnel. The confidence in predicting the location of the tunnel is increased by using data from both techniques.
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Geostatistical Analysis Of Borehole And Surface Wave Data A Case Study
Authors Marco de Kleine and Rik NoorlandtA Surface wave study has been executed in the center of Surinam in order to determine the depth to bedrock. The site of investigated is located in the tropical rain forest of Surina so the overburden consists of tropical oils and lateritic soil. The topography at the site is very pronounced. The survey data was combined with other types of data, i.e. boreholes, spt’s, cpt’s. The additional information was used both during the inversion and during the interpretation of the data using an iteratively approach. By combining this data with geological and geostatistcal knowledge not only insight in the thickness of the overburden was obtained but also information about the limitations of the data and the reliability of the results was determined. This additional information is relevant for the construction company who can make better cost estimates based upon this type of information.
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Revisiting SH-Wave Data Using Love-Wave Analysis
Authors Jianghai Xia, Richard D. Miller, Recep Cakir, Yinhe Luo, Yixian Xu and Chong ZengAlthough Love waves are widely analyzed in earthquake seismology, there is much less attention on utilizing Love waves than Rayleigh waves by the near-surface community. Unlike incident P and Sv waves, a plane SH wave for a series of horizontal layers refracts and reflects only SH waves, which makes the shallow SH-wave refraction method more popular to define shear (S)-wave velocity in near-surface geologic applications. For this reason, abundant SH-wave refraction data have been acquired and S-wave velocities have been determined using their first arrivals. If signals are recorded long enough, Love-wave energy can be clearly observed on SH-wave refraction data. Wave conversion may occur in an SH-wave refraction and Love-wave analysis only results in SH-wave velocities, which suggest that we may benefit from revisiting the existing SH-refraction data using multichannel analysis of Love waves (MALW). We used numerical modeling results and real-world examples to demonstrate three advantages of revisiting SH-wave data using the MALW method. Owing to a long geophone spread commonly used in SH-wave refraction survey, a sharp image of Love-wave energy can be generated, allowing better pickings for the phase velocities of Love waves. Because Love waves are independent of P-wave velocity, “mode crossing” in an image of Love-wave energy is less common than in Rayleigh-wave images. Fewer unknowns in the method MALW make dispersion curves of Love waves are simpler, which leads to more stable inversion of Love waves and reduces the degree of nonuniqueness.
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Seismic Refraction Surveys—How Many Shots Do I Need?
More LessClassical seismic refraction theory as discussed in most textbooks focuses on flat-lying or dipping layers and shows one or two shots. Most modern refraction surveys are shot with far more than two shots and use more sophisticated methods of interpretation and inversion. The use of only two shots, one on each end of a refraction spread, results in a critical lack of coverage, even for fairly simple velocity sections. This is in spite of the fact that the original section can sometimes be effectively recovered if some assumptions are made. Inversions using geophysical inverse theory in two dimensions as well as the Generalized Reciprocal Method (GRM) are applied to synthetic data generated from 2-D models and to field data examples to illustrate the importance of additional shots taken away from the spread ends (far shots) and additional shots taken in the interior of the spread (interior shots). These additional shots allow the interpreter to determine the number of layers in the section, assist in the assignment of arrivals and further constrain the velocities and (time-) depths and the elevation section. This produces a better and more reliable interpretation.
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Using Synthetic Data To Guide Processing Of Shallow Seismic Reflection Data Collected Across A High Scarp In Sw Montana
Authors Jose Pujol, Mervin J. Bartholomew, Andrew Michelson and Michael BoneWe collected shallow reflection data in SW Montana across a 5.4 m high tectonic scarp. The goal of this survey was to try to image the fault associated with the scarp, which is visible in a trench close to the seismic line. However, processing the seismic data is challenging because the height of the scarp (about 5.4 m) is comparable to the depths of the reflectors of interest. The problem is most acute for the data from the scarp area, and to find out how to proceed we generated synthetic waveforms using the actual recording geometry and topography. To generate the synthetic data we assumed that the scarp was due to a normal fault and used velocity models based in part on parameters derived from the actual shot gathers. The analysis of the synthetic data shows that the velocity model could be recovered quite well by first determining interval velocities without consideration of the station elevations and then stacking the data after application of station corrections referred to a datum elevation equal to the height of the scarp. This procedure placed horizontal reflectors correctly in time in a relative sense, although those on the low side of the scarp were shifted to a later time. However, this shift is consistent with the velocity used to generate the corrections and the difference in elevation with respect to the datum. Moreover, away from the scarp the highest and lowest elevations can be chosen as datums, which places the horizontal reflectors correctly in time. Applying this procedure to the actual data shows a clear continuous horizontal reflector on the lower side of the scarp and more disrupted reflectors on the higher side with discontinuous reflectors under the scarp. The latter correlate with the main and secondary faults mapped in the trench, but because the early portion of the seismic data was muted, it is not possible to follow this correlation close to the surface.
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Application Of Wavefield Transformation To Spectral Analysis Of Surace Wave (Sasw) Data
Authors Chun-Hung Lin and Chih-Ping LinThis paper introduces a source-to-receiver distance gather process to reconstruct the SASW data as MASW-imitating data, to which a wavefield transformation can be applied for dispersion curve analysis. Numerical simulations were performed to demonstrate its feasibility and advantages for analyzing SASW data. Furthermore, a new field testing procedure is suggested for better results when conducting surface wave testing with two or small number of recording channels. The results of this study advocate that multi-channel wavefield transformation can and should be used even though the field testing procedures may differ as restricted by the equipment capacity.
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Update On Recent Observations In Multi-Component Seismic Reflection Profiling
Authors André J-M. Pugin, Susan E. Pullan and James A. HunterExamples of multi-component shallow seismic reflection profiling from different environments in eastern Canada are presented to examine the benefits of shear wave reflection data and the latest developments in acquisition methodology, as well as our evolving understanding of the complex nature of seismic wave propagation. Examination of the wave motion through multi-component recording shows that, regardless of the source orientation, shear wave reflections may be polarized in varying directions. In “soft” soils characterized by low shear wave velocities, extremely high-resolution shear wave reflection sections can be obtained, with the highest-resolution data related to in-line or vertical components of motion. Data recorded in the transverse (SH) direction are generally somewhat lower in frequency but may be better able to penetrate into more compact (higher velocity) sediments. Multicomponent recording provides the capacity to record all data, without having to know the main shear wave polarization direction prior to data acquisition.
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Ultrasonic Velocities In Laboratory-Formed Gas Hydrate-Bearing Sediments
Authors Marisa B. Rydzy and Michael L. BatzleGas Hydrates are widely distributed in the near surface at high latitudes and many ocean bottoms. Our laboratory measurements help calibrate the seismic and well log data that are used to ascertain the in situ distribution of hydrates. Ultrasonic velocities are measured in unconsolidated sand specimen under thermobaric conditions comparable to those found in shallow oceanic or permafrost regions, i.e. in the gas hydrate stability zone. Compressional-wave (p-wave) velocity data in dry Ottawa Sand samples subjected to a confining pressure that from 2 to 20 MPa range from about 700 to 1500 m/s. Gas hydrates were then formed a partially saturated Ottawa sand sample. As expected, this hydrate formation resulted in a dramatic increase in p-wave velocities from 700 m/s in the partially water saturated sample to 2100 m/s in the hydrate-bearing specimen. The hydrate effectively cements the sand such that nine hours after entering the hydrate stability region, the recorded waveforms remained constant even as the confining pressure was increased by more than 10 MPa.
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Phase-Scanning Approach To Correct Static Error In The Surface Wave Walk-Away Method
Authors Edwin A. Obando, Choon B. Park, Nils Ryden and Peter UlriksenSynthesized surface wave records obtained from walk-away surveys normally suffer from time shift inaccuracies due to the abrupt variation in the soil stiffness characteristics which is regarded as static error effect. In this paper we present a method that uses a phase scanning procedure in frequency domain which applies the correction in a phase range from 0 to 2
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Seismic Investigation Of Underground Coal Fires; A Feasibility Study At The Southern Ute Nation Coal Fire Site, Durango, Colorado
Authors Sjoerd de Ridder, Nigel Crook, Seth S. Haines and S. Taku IdeWe conducted a near surface seismic test at a coal fire in the Southern Ute Nation near Durango, Colorado. The goal was to characterize and image the unburned coal and adjacent burned zone in order to determine the feasibility of any future seismic surveys. The field survey was preceded by a numerical study to optimize the survey design for the field test. The numerical study suggested that field experiments would rely on creating energy with sufficiently high frequencies, ideally greater than 125 Hz. Reflections or refractions from the top of the coal layer might indicate its presence or absence. Separately imaging of both the top and bottom of the coal layer or burned zone likely would be beyond the resolution of a reflection survey. Data from line 1, which overlies unburned coal at approximately 16 m depth, show useful frequency content above 100 Hz and a reflection that we interpret to originate at approximately 11 m depth. Data from line 2, which crosses the burn front and many fissures, are of lower quality with predominantly jumbled arrivals and some evidence of reflected energy at one or two shot points. It seems that neither the refraction nor reflection method is capable of imaging down to the coal layer; due in part to the presence of unexpected high-velocity layers overlying the coal. We conclude that information about the coal is obscured by a reflection from shallower layers and by chaotic arrivals generated by fissures. Based on our data, we suggest that further seismic work at the site is unlikely to successfully characterize the coal fire zone of interest.
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Multi Geometry Approach For Masw Survey
Authors Ali Nasseri-Moghaddam and Choon B. ParkThe effect of source offset distance and the geophone array length on the dispersion curves are discussed in this paper. The source offset distance was changed systematically at sites with various subsurface conditions to investigate its effect on quality of data and the corresponding dispersion curves. Further, tests were carried out at same locations with various geophone intervals to evaluate the effect of the array length on the quality of the data and dispersion curves. Active and passive data were collected and the dispersion images were combined for possible improvement in dispersion image with enhanced multimodal delineation over a broadened bandwidth. It is observed that source offsets in the range of 25% to 45% of the array length provide dispersion curves with reasonable quality. Further, collecting data with different geophone intervals (same array mid station) improves the resolution of the obtained dispersion image. Multi geometry technique is suggested to obtain better quality field data. In this approach two (or more) different geophone intervals are used with same mid station. Passive and active data at two or more offset distances are collected for each of the array geometries. Stacking the obtained dispersion images can also result in a better quality dispersion curve.
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Using Ultrasonic Coda Wave Interferometry For Monitoring Stress-Induced Changes In Concrete
More LessThe velocity of ultrasonic coda waves, the diffusive tail of ultrasonic signals, was monitored in a concrete specimen under uniaxial compression. The ultrasonic measurements were taken in two directions: parallel and perpendicular to the loading. A geophysical correlation-based approach called coda wave interferometery (CWI) was used to calculate the incremental stress-induced changes in velocities. Ultrasonic pulse velocities were also calculated using the conventional time-of-flight (TOF) approach. A comparison of TOF and CWI velocities revealed that the CWI velocities are more sensitive to the level of stress and damage within concrete, especially in low stress levels. Also, the CWI velocities measured parallel to the loading showed greater sensitivity.
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Combined Parallel Seismic And Cone Penetrometer Testing Of Existing Bridge Foundations And Levee Sheet Piles For Length And Capacity Evaluations
Authors Dennis A. Sack and Larry D. OlsonThe use of the Parallel Seismic (PS) test method has been well documented and has been shown to be effective for foundation length evaluation when used with a cased borehole adjacent to the foundation being evaluated. In addition, the use of the Cone Penetrometer Test (CPT) to evaluate soil properties without a borehole has also been well documented. Recent research, hardware development, and field testing have been conducted on a system which combines the two methods to allow fast and economical evaluation of both soil properties and foundation depth without requiring a drill rig. The combined system collects both PS and CPT data in one or two probe penetrations into the soil. The combined system can be used with a smaller, relatively low clearance CPT rig which is self-propelled and designed for use on rough site conditions. Thus, access is possible to bridge foundations that could not be tested with conventional means. The paper presents details of the principles and operations of the combined system, as well as field test data from driven pile bridge foundations as well as steel sheet
piles under levee walls in New Orleans.
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Multiple Impact Surface Waves For Determination Of Pavement System Moduli For Assessment And Design
More LessThe Multiple Impact Surface Wave (MISW) method involves the measurement and modeling of the propagation of surface waves in pavements. MISW can accurately determine not only the surface pavement thickness and low-strain elastic modulus of concrete and asphalt, but also the thicknesses and moduli of underlying base and subgrade layers. The MISW test method was used in a forensic concrete pavement investigation project and the thickness/moduli results for the concrete, base and subgrade layers are compared with Spectral Analysis of Surface Waves (SASW) results. The MISW method is able to accurately estimate the properties of base materials immediately below the much stiffer pavement layers by accounting for higher order wave modes during the inversion process in comparison to SASW results. Example results are presented of the use of MISW combined with Impact Echo (IE) data analyses to predict thickness/moduli of an asphalt pavement. Finally, a discussion is presented of the calculation of asphalt elastic moduli from MISW results for mechanistic-empirical design of asphalt pavements.
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Measurement Of Sheet Pile Length By Pile Integrity Testing And The Parallel Seismic Method
Authors Ernst Niederleithinger and Matthias FritscheThe non-destructive measurement of sheet pile lengths at existing constructions is a complex task. Low strain pile integrity testing is an easy and efficient method, but sometimes fails to give meaningful results. Statistical evaluation enhances the reliability and gives hints on length changes. Using the parallel seismic method, which has been developed for the assessment of drilled shafts and similar constructions, is an alternative possibility worth considering. Recently developed interpretation tools allow greater distances between piles and sensor boreholes compared to other methods. Two field examples show the use of both methods and some pitfalls, including ways to overcome them.
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Crosshole Sonic Logging Of Secant Pile Walls A Feasibilty Study
Authors Ernst Niederleithinger, Joram M. Amir and Markus HübnerSecant pile walls are used as permanent or temporary elements in foundations, excavations, slope stabilization, retaining walls or hydraulic barriers. In contrast to single piles, reliable non-destructive testing methods are not available so far. The reinforced secondary piles can be checked by standard crosshole sonic logging, but there is no access to the unreinforced primary piles. Experiments at construction sites using ray paths across several piles have shown encouraging results, but there have been several open questions. To evaluate the potential of cross-pile sonic logging, a real scale test model with built in flaws on two primary piles was constructed at the BAM test site. Measurements with two different instruments have been performed. In one primary pile relevant flaws could be detected. At the other one the signals showed anomalous damping, probably due to unintended delamination. The results can be used to interpret real site data.
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Quantitative Integration Of Multiple Near-Surface Geophysical Techniques For Improved Subsurface Imaging And Reduced Uncertainty In Discrete Anomaly Detection
Authors Megan E. Carr and Gregory S. BakerThe remote sensing community—in the traditionally-used connotation of satellite and airborne imagery—has been integrating multi-technique geophysical data extensively and successfully for nearly two decades to better discriminate targets, e.g., mineral deposits, specific types of vegetative land cover, etc. Currently, however, there is no quantitative methodology in place for the integration of two or more geophysical data sets collected using near-surface geophysical techniques such as Ground Penetrating Radar (GPR), Magnetic Gradiometry, and other Magnetic/EM methods. The primary objectives of this research are to investigate quantitative methodologies for integrating multi-tool surface geophysical data to improve subsurface imaging and reduce uncertainty in discrete anomaly detection. These objectives will be fulfilled by: (1) correlating multi-tool geophysical data with existing well characterized ―targets‖; (2) developing methods for quantitatively merging different geophysical data sets; and (3) testing these new methods at several different sites with varied targets (i.e., case studies). Three geophysical techniques primarily utilized in this research are: GPR, EM (ground conductivity) methods, and magnetic gradiometry. The two study sites (Cherokee Farm and the University of Tennessee Agricultural Extension Plot 4B) located within alluvial sediments along the Tennessee River will serve as case studies to verify methodologies in a terrestrial environment. A computer model will be developed that will simulate data that would be expected given various parameters such as heterogeneity of the subsurface, type of target, geophysical technique utilized, spatial sampling, etc. The simulated data sets will then be integrated together using the same methodologies as employed with data from Cherokee Farm and Plot B4 to further develop the necessary quantitative assessment scheme to determine if these merged data sets do in fact satisfy the objectives of the research.
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Correlations Between Direct Current Resistivity And Seismic Attribute Tests Across An Active Methane Hydrate Vent In Mississippi Canyon Block 118, Gulf Of Mexico
Authors Alan R. Gunnell and John A. DunbarAn active methane vent in Mississippi Canyon Block 118 (MC118), Gulf of Mexico, has been the focus of persistent research. This vent area contains both active and dormant vents as well as blocks of methane hydrate outcropping on the seafloor. It is proposed that methane hydrate blocks also form within the Hydrate Stability Zone (HSZ) beneath the vent. Through collaborative work done by the Gulf of Mexico-Hydrate Research Consortium (GOM-HRC), surficial characteristics and mound chemistry is understood, but quantifiable distributions of hydrate with the HSZ is unknown. High-frequency seismic imaging of the mound is hindered by the presence of free gas, hydrate, and biogenic carbonate blocks on the surface. A direct current resistivity (DCR) land system is adapted to function on the sea floor and to locate the sub-seafloor distributions of hydrate. Continuous resistivity profiling (CRP), totaling 26.4 km in length, is able to resolve the distribution of hydrate whereas further distinguishing between disseminated gas and hydrate. This distribution of hydrate trends along faults and fractures while disseminated methane is found within sediment pores. Through combinations of resistivity profiles and seismic attribute tests, correlations between incoherent and coherent areas beneath the vent represent gas and hydrate respectively.
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Geothermal Investigation Of Waunita Hot Springs Utilizing A Variety Of Geophysical Survey Methods And Techniques
Authors Joyce Hoopes, Gordon Johnson, Kristen Swaim and Ariel ThomasThe results of a geothermal investigation will be presented. The project, part of the Colorado School of Mines Undergraduate Geophysics curriculum, is conducted throughout a student’s senior year. The geothermal reservoir studied has surficial manifestations at Waunita Hot Springs, located in the southeastern corner of Gunnison County. The springs have been identified by the Colorado Geological Survey as a resource with potential for geothermal power generation, (Barrett and Pearl, 1978). The project goals are to better understand the geothermal reservoir and its geologic structure. To understand the fracturing system that defines and controls the reservoir, geophysical mapping of the subsurface conductivity will be presented. An image of the deeper conductivity distribution will be displayed as a result of a time domain electromagnetic survey. For imaging at shallower depths, with greater detail, the electrical methods, specifically SP and DC resistivity, were utilized. Detailed geologic maps of the area are limited; therefore, a geologic survey will be conducted along with the collection of hydrological data. A geochemical analysis of the water from the springs and temperature gradients calculated from borehole measurements will also be presented. The observations and data will be useful in assessing the geothermal potential of Waunita Hot Springs.
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Stable Parameter Estimation Method Applied To Characterization Of Plume Transport In Environmental Inverse Problems
Authors Hugo Bertete-Aguirre and Elena CherkaevThe talk discusses a geophysical environmental inverse problem of characterization of water flow model from monitoring of plume transport. We present a stable method to calibrate transport models using measurements of concentration of a chemical over time. Such observations can be used as an input for geophysical environmental inverse problems. The ability to produce realistic characterization of plume transport relies on the calibration of the parameters of the flow, which in the presented case study is described by the two dimensional advection-diffusion equation. The inverse problem of transport model calibration from inaccurate observations of contaminant concentrations is ill-posed and requires regularization. In the current work, the regularized problem is solved by an adaptive gradient minimization. Stable prediction of plume transport parameters allows to describe the dynamics and transport of solutes or suspensions within the system.
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Using Ground Penetrating Radar To Determine The Quantity Of Impounded Sediment Behind A Dam
Authors David J. Santaniello, David J. Santaniello and Allen M. GontzWe investigate the viability of ground penetrating radar (GPR) as a method to estimate the quantity of sediment stored behind the Merrimack Village Dam on the Souhegan River in southeastern New Hampshire. If the pre-dam riverbed can be imaged, the thickness and volume of the reservoir deposit can be calculated without sampling. We surveyed six cross sections with a Mala Geosciences ProEx 100 MHz GPR unit in May 2008. In a related study, topographic and bathymetric surveys were conducted in 2007, 2008, and 2009 to monitor the sediment flux associated with the removal. By 2009, these surveys measured the pre-dam riverbed in the uppermost cross sections from the dam. We compare these surveys to the interpreted GPR images to calculate a calibrated velocity through the impounded sand of 0.043 m/ns. Using this velocity, the average thickness of the sediment above the interpreted pre-dam riverbed calculated for each of the six cross sections varies between 0.81 m and 3.11 m. The estimate of the quantity of sediment stored behind the dam is ~67,000 m3 compared to a 2004 estimate of ~62,000 m3 based on probing the sediment with a steel rod to the point of refusal.
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Magnetic Prospection Of A Tumulus In The Ancient Histria Necropolis
Authors Dumitru Iouane, Sorin Anghel and Alexandra DuduNear surface geophysical investigations are employed in archaeology in order to estimate the location, depth, shape and physical properties of buried ancient structures. The geophysical study initiated in 2008 on tumuli located in the Histria necropolis was based on magnetics, the measurements being carried out with a proton precession magnetometer / gradientmeter. The networks where measurements of total magnetic field and magnetic vertical gradient were performed covered each tumulus and small adjacent areas. The magnetic measurement points situated at 2 m interval represented detailed rectangular networks. The necropolis is situated at ca 2 km north-west of Histria ancient Greek city and includes a great number of tumuli of various dimensions and trends. Previous archaeological studies evidenced different rituals of burial for the ca 1300 years of continuous inhabitation during Greek colonization and Roman / Byzantine empires. The magnetic data obtained for the tumulus analyzed in this paper, located toward the north-western limit of the Histria necropolis, suggest quite complex archaeological features, similar to those observed in the excavations. Generally, metallic artifacts, a clay layer affected by fire or active magnetic rocks employed in the buried infrastructures may represent sources of high magnetic anomalies. The magnetic total field and vertical gradient anomalies are interpreted as being here mainly due to burnt materials and buried greenshist structure (high anomalies), or to an outer stone belt made of limestone boulders (low anomalies). Key words: Histria, necropolis, tumulus, magnetic method, magnetic anomalies.
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Studies Of Electrical Characteristics Of Hukou, Hsincheng And Sanchiao Active Faults, Northern Taiwan
Authors Hsing-Chang Liu and Chieh-Hou YangTaoyuan, Hsinchu, and Taipei are three major metro areas in northern Taiwan. This study attempts to survey the resistivity structures and locations of the three active faults – Hukou Fault, Hsinchen Fault, and Sanchiao Fault – passing through the three metro areas and has thus provided resistivity imager profilings (RIP), vertical electrical soundings (VES), and audio-frequency magnetotellurics method (AMT) for this purpose. This study has examined the relationships between faults and profilings in addition to the underground resistivity and has acquired following results accordingly: 1. Both Hukou Fault and Hsincchen Fault are thrust faults wherein the hanging walls are lowly resistivity and fault footwall are highly resistivity. Discontinuous geoelectrical or lateral rapid change resistivity is shown in electrical layers, especially in the fault trace or fault zone. Anomalous bands in a homogenous layer are one of the features shown in the Hsinchen fault. In addition to a large lateral resistivity contrast shown in the Sanchiao fault, the contacts surface is very rough. 2. The advantage of RIP result has a better stability, higher resolution and less time-consuming than other resistivity sounding methods. But in the study area, surface obstacles limited the spread of some survey lines, thus the targeted depth of investigation was unattained. AMT survey can be interfered by culture EM wave; the quality of its sounding results is always severely affected, especially in the Taipei area. However, combining the AMT sounding results with the gravity result, geologic data, and formal logging information, the Sanchiao fault and the boundary between the sediment and basement of Taipei Basin can be recognized.
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3D Loop-Source Em Inversion Using Non-Linear Conjugate
Authors Mark S. Hickey and Mark E. EverettElectromagnetic (EM) exploration on land has advanced a long way, but it still needs additional refinement. A 3D inversion would make the interpretation aspect simpler for a complicated subsurface, and make EM exploration easier to implement. We have formulated a 3D inverse solution for land-based loop-source EM exploration using a non-linear conjugate gradient method. This code was developed for exploration of complex subsurface structures like those of a meteorite impact crater or of a contamination plume. A finite element forward model is used to generate predicted data. The forward model uses a finite element mesh as well as coulomb-gauged potentials to solve the governing Maxwell equations and generate data for a single frequency. The finite element forward model code also permits discretization of the subsurface into an unstructured grid, allowing element edges to coincide with the boundaries of irregular subsurface inhomogeneities. The forward model can also take into account topography and its resultant effect on the response. A quasi adjoint Green’s function approach is used to calculate the sensitivity matrix. For this presentation we will show our initial results from synthetic data as well as some preliminary results from actual field data.
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Measurement Of Seismic Local Effects And 1D Numerical Modeling At Selected Sites Affected By The 2009 Seismic Sequence Of L’Aquila
More LessStrong local effects occurred during the seismic sequence that affected the area of L’Aquila (Central Italy) in 2009, which culminated with a main shock of magnitude (Mw) 6.3 on the 6 April. Bearing in mind the magnitude, the vicinity of a regional capital to the epicentre, the presence of several historic centers and villages, which caused significant damage (IMCS max=9.5) and approximately 300 victims, among the main characteristics of this earthquake, was the variability of the recorded damages within the scale of 100 m in spite of the near field conditions and a distinct source mechanism. These local effects were measured with an array of geophones at selected sites near the city of L’Aquila. In one of the sites, located at Onna village which experienced maximum damage levels, the 1D numerical modeling allowed verifying the influence that the frequencey of the input motion has in the determination of superficial seismic effects. The numerical modeling, which was undertaken on the basis of the results from geomechanical, seismic and geoelectrical surveys, also allowed verifying that underestimation of local seismic amplification can be introduced by the current regulatory framework (Italian seismic regulatory guidance “Norme Tecniche per le Costruzioni” – D.M. of 14 January 2008) in contexts similar to that of L’Aquila.
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Solid Wastes Landfill Monitoring By Means Of Differential High-Resolution Infrared Thermography
Differential thermal imaging has been proposed to characterize the ground temperature distribution of two solid wastes landfills. The differential approach permitted to detect regions with thermal abnormalities potentially associated with either biogas leakage and migration or improper landfill settlement and management. Methods, results, limits, and potentialities of the proposed approach are discussed.
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Rayleigh-Wave Dispersion Curves For Long, Linear Arrays At A Predominantly-Gravel Site
Experimental Rayleigh-type surface wave dispersion curves were developed for a gravel site over limestone bedrock. The work was performed as part of an earthquake site-response study. The SASW, MASW, and ReMi methods were applied in linear arrays that approached 1 km in length. For the SASW method, a Vibroseis source was used. The other methods used primarily ambient noise. Dispersion curves were resolved to a minimum frequency of 1 Hz, which corresponded to a maximum wavelength of well over 1 km. Dispersion curves from the three methods were in good agreement over a broad frequency band but differed at low and high extremes. The ambient noise at the site did not appear to introduce directional bias in the passive-source survey results.
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Stream Valley Resistivity In Central Texas: Laying The Foundation For Multi-Disciplinary Research
Increasing land-use and a changing climate can drastically modify floodplain habitats along low-order streams in central Texas. Investigating stream response to these factors on the site-scale can be costly. In an effort to streamline future site-specific investigations, a near-surface geophysical method was used along Williams Creek in Axtell, Texas. A 2-D dipole-dipole resistivity reconnaissance study was employed to estimate depth to bedrock and locate buried channels in a partial-valley cross-section. Auger borings provided ground-truth along the resistivity profile, which confirmed depth to bedrock and the significance of varying resistivities. The 276 meter resistivity profile was completed across a flowing Williams Creek and a portion of its floodplain, revealing a number of different fluvial landforms. Hand-augering confirmed the presence of a coarse-grained paleochannel fill that corresponds with a high-resistivity zone (50-100 ohm-m). At one location, auger refusal at bedrock occurred 3.15 meters below ground surface, consistent with the observed change to lower resistivity values. This decrease in resistivity at the bedrock contact is associated with groundwater flow along the fissile marl bedding planes. These data suggest that resistivity and ground-truthing combined, provide a cost-effective foundation to guide future research on the effects of climate and land-use on Williams Creek.
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Near Surface Borehole Geophysical Imaging In A Highly Structural Area, Beartooth Hills, Montana
Authors Tania Mukherjee and Dr. R.R StewartUniversity of Houston conducted a student geophysical field camp at YBRA (Yellowstone Bighorn Research Association), Red Lodge Montana. The idea was to provide a detailed interpretation of the sub vertical Mississippian Madison lime stone bed beneath the YBRA camp using seismic and well logs. Several 2D seismic lines (E-W) were acquired and several logs were run in the two wells drilled in the camp.The depth of the wells are 30m and 60m , the wells were drilled then cemented and cased with PVC. SP, gamma, sonic, temperature, conductivity and sonic televiewer logs were run in the wells. Several multicomponent VSP (Vertical Seismic Profile) with different offset were also done. A shot offset of 3.5 m was selected for VSP. Both the wells were compared to see high frequency noise and shot signature. The limestone P wave velocity is about 2600 m and shale velocity is about 2800 m /s. The Vp/Vs is 2 for limestone and 1.7 for the shale unit. As there is very steep dipping reflectors, there is only little upgoing wave in the data .A VSP-NMO was also done and a corridor stack was then created. With the help of all dataset,composite plot and a quick look interpretation shows the limestone-Redbed encounter to be at 40 m and the probable dip of the bed looks to be 45° towards south.
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Groundwater Investigation In Giginyu, Nassarawa Local Government Kano State Nigeria
Authors A.U. Farouq, H.U. Suru, Bello Maruff Akande and U.A. AminuDC Vertical Electrical Soundings were carried out in 10 stations in order to determine areas with groundwater potentials. Data collected were reduced and interpreted according to profiles (profile one and profile two). The interpretation yielded two geoelectric sections of (3) geoelectric layers for profile one and four (4) geoelectric layers for profile two. The topsoil thickness ranges between 0.8 and 2.6 m with resistivity values ranging between 103 Ohm-meter and 1031.2 Ohm–meter across the study area. The topsoil is lateritic clay, sandy clay and clayey sand. The thickness of the weathered layer ranges from 3.3 m to 20 m and resistivity ranges between 11.5 Ohm-meter to 294 Ohm-meter, this indicates the aquiferous formation. Depth to aquifer ranging between 1.6 m to 15.9 m. The partially weathered/fractured basement resistivity ranges between 98 Ohm-meter to 692.4 Ohm-meter, which indicate high degree of fracture and or water saturation with thickness range between 7.2 m and 52 m. Fresh bedrock is the last layer with resistivity values ranging between 1266 Ohm-meter to 100000 Ohmmeter at all the VES points in the study area at a depth ranging between 4.1 m to 70 m. Hence, VES9 and VES10 on profile two, having highest groundwater potentials.
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Geophysical Investigations At The Chimney Rock Great House, Colorado
Authors Sarah Devriese, Michael A. Mitchell and Roxanna FraryIn conjunction with the National Forest Service, a number of different geophysical datasets were collected over the region adjoining the southwest end of the Great House at Chimney Rock, Colorado. The investigations aim to determine if the foundations for more rooms exist in this region, as early archeological sketches indicate. The following types of datasets were collected: magnetic, frequencydomain electromagnetic (FEM), DC resistivity (middle gradient and 2D dipole-dipole), and microgravity. This multipronged approach was used to provide a diverse range of data types, all of which have different physical property sensitivities. Since the expected physical property contrast between the wall foundations and possible room infill has yet to be characterized, it is difficult to determine which of the utilized methods will produce the best results. A thorough analysis of our geophysical field data along with the results gleamed from processing and inversion, will allow us to develop a meaningful interpretation, upon which recommendations for future investigations can be based. By determining whether or not the additional rooms exist, this study will help archeologists and the National Forest Service characterize the extent of the Chimney Rock Great House, plan future archeological studies, and set a basis for future geophysical investigations at the site.
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Mec Classification Parameter Selection Based On Site-Specific Munitions Characteristics
Authors Steve Saville, Nathan Harrison and Craig MurrayParsons has participated in the Environmental Security Technology Certification Program (ESTCP) unexploded ordnance (UXO) Discrimination Study at Camp Sibert, Alabama, and most recently at Camp San Luis Obispo (SLO), California. In 2008, ground truth results from Camp Sibert were used to identify commonly used target parameters from EM61-MK2 data that would improve the classification of munitions and clutter. UXA-Size (size), a parameter based on instrument response across the three major axes of an object, and a decay constant were identified as having the greatest potential for classifying the 4.2-inch mortar seed items found at Camp Sibert. A simple rule-based classification was developed based on size and decay, and the resulting receiver operating characteristic (ROC) curve showed improvement over a previous rule-based classification of the Camp Sibert ground truth results. In 2009, Parsons participated in a similar target classification study for the SLO site. Unlike Camp Sibert, which included only the 4.2-inch mortar, the SLO site included a range of munitions types: 2.36-inch rockets, 4.2-inch mortars, 60-millimeter (mm) projectiles, and 81mm projectiles. This range of munition types made application of the size and decay based classification of anomalies detected using the EM61-MK2 at Camp Sibert more challenging for the SLO site. Because of the variety of munitions types at SLO, a single size parameter could not be identified for effective classification of all munitions types from clutter. Attempts to define unique rules involving size per munitions type were not as diagnostic for the SLO data set due the wider range of size values observed for munitions and clutter at this site. The most effective rule-based classification at the SLO site was to use two sets of decay values from the EM61-MK2 data to classify the munitions and clutter.
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Self-Guiding Robotic Geophysical Surveying For Shallow Ojects In Comparison To Traditional Survey Methods
Authors Nathan Harrison, Bob Selfridge, Craig Murray and David HodoThe quality of geophysical data is a critical aspect of the digital geophysical mapping process. Human factors in geophysical mapping can affect navigation, background noise, and speed control, impacting data quality. An important issue facing MEC geophysicists is to find ways to limit these factors as a first step towards successful consistent reproducible geophysical surveying. Human data acquisition errors can be significantly improved with self-guidance/robotic technology. ESTCP and the Huntsville Innovative Technology Program funded Auburn University to develop a path-following robotic vehicle to address those problems. Parsons worked with the Innovative Technology Program to perform the first technology transfer to a contractor of the government’s semi-autonomous robotic Segway geophysical platform to a Remedial Investigation/Feasibility Study RI/FS MEC project at the former Great Salt Plains Bombing Range (GSPBR) in Alfalfa County, Oklahoma and a removal action at a former firing range within Camp Sibert, Alabama. To characterize two munitions response site’s (MRS) during the RI/FS at the Great Salt Plains, a total of 16.5 acres of transect data and 12.1 acres of grid-based data were collected between 12/1/08 and 1/12/09 using time-domain electromagnetics (TDEM). Three methods of data collection included towing either two Geonics EM61-MKII coils with a self-guiding robotic system or a small utility vehicle, or one coil operated by a person. Two of these three methods, including the selfguiding robotic system and the one coil operated by a person, were also used to geophysically map the 20 acre range at Camp Sibert. This study compares the three methods based on overall performance, including geophysical prove-outs, data quality and productivity. Site conditions and equipment problems inhibited productivity of the robotic system, however future improvements or careful site selection could make the self-guiding technology useful to UXO projects. The Great Salt Plains field tests identified system weaknesses and solutions, which were applied to the Camp Sibert project allowing for high production rates with the Segway System. The results of these projects indicate that the robotic system is a viable option for DGM on many future UXO projects.
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Multi-Channel Analysis Of Surface Waves: An Application To Montana Field Data
Authors Soumya Roy and Dr. Robert R. StewartThe multi-component (3C or 4C) seismic method is being used to more fully capture the seismic wavefield and to generate complementary P-wave and S-wave (PS) images of the subsurface. One of the complicating issues in processing PS data is the effect of receiver statics. The S-wave receiver static can be quite large due to low S-wave near-surface velocities. We are thus interested in techniques to estimate the shallow S-wave velocity (Vs) structure. The analysis of surface waves (especially Rayleigh waves) has been useful to delineate Vs in near-surface. Multi-Channel Analysis of Surface Waves (MASW) uses the dispersion properties of Rayleigh waves to create a dispersion curve (Park et al., 1998), then S-wave near-surface velocity profile (Xia et al., et al., 1999). We have applied the MASW method to seismic datasets from Elk Basin Oilfield in Bighorn Basin, Montana/Wyoming acquired by students of University of Houston. Vertical and horizontal component seismic lines are analyzed. Preliminary results show extracted S-wave velocities for vertical and horizontal component lines varying between 400-1000 m/sec.
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Ground Penetrating Radar Investigation Of Dinosaur Quarries In Morrison, Colorado
Authors Renee Francese and Orion SandovalStudents conducting the investigation are doing so through the Colorado School of Mines Undergraduate Geophysics curriculum as a senior project. Investigation has been done in Morrison, Colorado for similar purposes, however little geophysical data has been collected in the area of interest. The goal of this project is to image the dinosaur bones and model the sandstone to mudstone boundary, where the extent of dinosaur bones has been found. A quarry about 100 feet to the north of the site has been previously excavated to find large dinosaur artifacts. The director at the Morrison Museum of Natural History, Matt Mossbrucker, has reason to believe that Quarry XYZ will contain dinosaur artifacts based on geology trends, bone fragments found at the surface, and notes by Arthur Lakes (A. Hunt, M. Lockley, S.White, 2002). By experimenting with different antennas and other GPR equipment, the students will find the optimal setup to better model the geology boundaries and find large targets beneath the surface up to depths of 1015 feet. The data collected will be useful in further understanding the geology and ability to locate dinosaur artifacts in the Morrison area.
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Fracture Imaging In The Upper Kama Potash Mine Using 3-D GPR Data
More LessFracture detection and delineation is very important for salt mines operation because fracturing significantly increases the probability of failure of supporting pillars and overlaying water protective beds. Results of forward modeling studies confirmed the feasibility of georadar with a 400 MHz antenna to reliably detect the millimetric scale fracture. 3-D GPR data were acquired in the potash mine near the city of Solikamsk, Russia to evaluate the effectiveness of imaging technology to detect and delineate the fractures in heterogeneous salt rock. Continuous common-offset data were obtained at seven parallel profiles across the fracture exposed in the wall of a mine pillar. The pillar was 4.5 m thick and comprised of interbedded layers of salt rock and clay. The open millimetric scale subvertical fracture crosscuts the pillar at angle of 25°. Data were collected using commercial OKO georadar system (Logis, Russia) with a 400 MHz shielded antenna. ReflexW and OpendTect software were used for processing and interpretation of the 2-D radargrams and combined 3-D data set. The 3-D migration allowed generating a true image of subsurface structures and creating a spatial model of fractures. Using the image of known fracture as interpretation template, fracture having no surface evidence was detected.
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Laboratory Assessment Of Nano-Silver Transport In Sand Columns Using Complex Conductivity Measurements
More LessNano-materials are emerging into the global marketplace. Nanoparticles, and other throwaway nano-devices may constitute a whole new class of non-biodegradable pollutants that scientists have very little understanding of. Therefore, the production of significant quantities of nano-materials will inevitably result in the introduction of these materials to the environment with important implications for both environmental and human health. Currently there are many unanswered questions related to the release of nano-materials, their fate, transport, and transformation in the environment, and their potential toxic effects. Due to their desirable chemical–physical, electronic, and optical properties, metal nanoparticles have attracted much attention and demonstrated a wide range of applications (Kamat, 2002; Oliveira et al., 2005). Among metal nanoparticles, silver nanoparticles possess many superior properties, such as increased electrical conductivity, antimicrobial activity, catalytic effect, etc. (Kabashin et al., 2003).
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