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Near Surface Geoscience 2012 – 18th European Meeting of Environmental and Engineering Geophysics
- Conference date: 03 Sep 2012 - 05 Sep 2012
- Location: Paris, France
- ISBN: 978-90-73834-34-7
- Published: 03 September 2012
41 - 60 of 194 results
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High Resolution Electrical Resistivity Tomography in Superficial Limestones at Tournemire Site, France
Authors C. Gélis, M. Noble, J. Cabrera, H. Chauris, S. Penz and P. DesveauxDeep argillaceous formations are considered in many countries as potential host media for high-level long-life radioactive waste due their confining properties. The precise sedimentary, structural and hydrogeological characterization of such potential host sites is a key point in determining their appropriateness for the long-term deep underground disposal of radioactive waste in geological formations. The presence of faults in clay–rock formations should be carefully assessed, since these features could modify the confining properties. This study focuses on testing the potential of the electrical resistivity method to detect fault or fractured zones in the near subsurface layers above an argillaceous formation. We present in this paper results from a high-resolution electrical resistivity survey carried out at the IRSN Tournemire Experimental Platform (TEP). The electrical resistivity profile was located transversely to the fault and fractured zones location, inferred from geological data, that affect the Jurrassic formations at the TEP. Electrical resistivity data were successively acquired with 8m, 4m and 2m-electrode spacing. This multi-resolution acquisition allows to investigate the near subsurface limestones and dolomites to a depth of 100 metres. In particular, two sub vertical conductive corridors reaching the surface through higher resistive layers are correlated with fractured zones.
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Robust Acoustic Waveform Inversion from Underground Galleries to Image Strike-slip Faults in Clay-rock Formations
Authors F. Bretaudeau, C. Gelis, J. Cabrera, D. Leparoux and P. CôteDeep argillaceous formations are potential host media for high-level long-life radioactive waste due to their confining properties. In order to improve its ability to expertise possible projects of radioactive waste disposal in a geological clay-rock formation, the French Institute for Radioprotection and Nuclear Safety led various experiments in the undeground Tournemire Experimental Platform (TEP). The presence of strike-slip faults with small vertical offsets in clay-rock formations, as they are observed in the TEP, must be well assessed since they could modify the confining properties of the host rock. The TEP is composed of several galleries excavated in a 200 m thick Toacian clay-rock layer. Various studies have shown this type of fault is difficult to detected with seismic reflection from the surface or from galleries. Thus we tried to image a 10 m thick strike-slip fault with a transmission survey involving several galleries. We present here how the use of a robust adaptation of weighted acoustic full waveform inversion can provide a high resolution P-wave velocity model and revealed a much more complex structure than expected.
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CO2 Field Laboratory at Svelvik Ridge (Norway). Electrical Resistivity and Sonic Monitoring during CO2 Shallow Injection
Authors P.A. Pezard, N. Denchik, J. Paris, M. Geeraert, G. Henry, O. Jaafar, L. Baqué, S. Barry and D. NeyensThe CO2FieldLab shallow injection experiment is a mutual effort from several research groups and organizations (SINTEF, NGI, BRGM, BGS, CNRS, imaGeau and Schlumberger). The objective is to create a downhole leakage of CO2 in order to determine sensitivity of CO2 monitoring systems with respect to CO2 distribution and leakage detection. The CO2 displacement in the subsurface and at the surface was monitored with an exhaustive set of techniques. For this, the field Laboratory for monitoring CO2 migration and leakage was established in glacial deposit that forms Svelvik ridge, 50 km south of Oslo. The shallow injection experiment was conducted in fall 2011 with a monitoring plan designed to spatially and temporally monitor the expected plume development. The monitoring equipment was distributed around the 20m deep injection point of an inclined well. An integrated set of surface and downhole strategies was deployed across a 64m2 square monitoring area. The data recorded by CNRS are presented here. The CNRS techniques included: permanent downhole electrical resistivity observatory, time-lapse downhole induction and sonic logging. The CO2 plume was successfully detected and characterized by these methods even if the trajectory of migrating CO2 deviated from the monitoring predictions.
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TAU-Transformation of Time-Domain IP Data Measured Above a Hungarian Refuse Dump
Authors E. Turai, M. Dobróka, Á. Gyulai, N. Paripás and J. Somogyi Molnáre values of the time constant spectra. This method was tested over several contaminated sites. In this extended abstract we show a new interpretation result measured over a refuse dump in Hungary near Felsőtelekes. The analysis of the IP data shows that there are some very high contaminated parts in waste-rock bodies. The types of the polarization were mainly redox and metallic.
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Electrical Resistivity Monitoring on an Experimental Landfill Clayey Cover
Authors F. Genelle, C. Sirieix, J. Riss, S. Renié and P. BégassatIn France, a cover is set on the top of waste at the end of the exploitation of the landfill. The monitoring of landfill cover after closure of the site is a local problem, since its tightness must be ensured over time. Leaks in the cover allow water to infiltrate the stored waste. In order to define the ability of electrical resistivity tomography, an experimental clayey cover has been built in which defects have been intentionally made. Repeated measurements taken on this site showed that the detection of defects need to take into account the weather conditions preceding the measurements, as they affect the water content in the cover material. A statistical analysis carried out on the electrical resistivity values for all surveys at different dates has defined four clusters. Moreover, analysis performed on several cover material samples corresponding with the different clusters showed that the material was heterogeneous, because of a difference in particle size (fines content). This study has outlined, in addition to the detection of cracks, that electrical resistivity varies with the water content measured on site exponentially for each cluster.
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Electrical Resistivity Tomography and Transient Electromagnetic Survey in Luikonlahti Tailings Impoundment Area
Authors T.K.T. Huotari-Halkosaari and J.M. LerssiElectrical resistivity tomography (ERT) and transient electromagnetic (TEM) surveys were done in Luikonlahti tailings impoundment area, Eastern Finland. Purpose of the measurements were to find the structure of the tailings impoundment area and possible seepage areas. Totally 5 ERT profiles and 4 TEM profiles were measured in the tailings area. ERT and TEM measurements revealed clearly the structure of tailings impoundment. Results of the both methods agreed and coincide with the drilling results.
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Estimation of Gas Frequency Characteristics to Identify Microfault at Terra Drilling Site
Authors W.W. Parnadi, A.M. Nabeilah, A. Muis, R.P. Hutapea and T. MeidianaWe investigated the frequency characteristics of processsed GPR signals influenced by gas at a drilling site in ARTA block, Pelalawan,Riau, Indonesia. In the drilling site we found some areas with gas bubbles migrating from subsurface. This investigation was done to examine the appropriateness of this area for drilling activities. By using GPR methode we obtain radargram for 6 measurement lines. Furthermore, we calculated the frequency characteristics to find migration mechanism of the gas bubble emerging in the surface. From 9 frequency characteristics we find major differences between gas and non-gas area in subsurface enabling us to estimate gas migration mechanism. We got information of medium characteristics from two parameters, spectral bandwidth(fb) and variance σ. From aanalyzing these two frequency characteristics , we conclude that the presence of gas bubble is most likely caused by the migration of gas to the surface as the result of the existence of micro-fault. Therefore this area is classified as potential geohazard area.
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Quantifying the Volume of Potential Landslides: a Case Study
Authors F. Bahloul, T. Haenssler, D. Orlowsky, R. Elsen and S. ThorDestabilized hillsides and potential landslides can be the cause for large scale safeguarding measures at construction sites. The volume of destabilized material plays a major role in determining the amount and cost of safeguarding measures. In this case study we present the process of estimation of potential landslide volumes using geophysical methods in a geologically complex environment. The field work for this case study was carried out at potentially hazardous locations on the construction site of the railroad and highway leading from the city of Sochi, Russia to the venues of the Olympic winter games 2014.
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The Accident at Sayano-Shushenskaya Hydroelectric Power Plant (Seismologist View)
Authors V.S. Seleznev, V.M. Soloviev and A.V. LiseikinOn 17 August 2009 Sayano-Shushenskaya Hydroelectric Power Station suffered a catastrophic accident. In the “Report of technical investigation of the accident cause” as the main cause of the accident it was called “repeated appearance of additional loads of variable nature on the hydroturbine unit”. But what kind of loads, what is their source? The research presents the method, which allows to control by seismic records not only work of various sources, but also to determine parameters of their dynamic forces to the structure.
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The Influence of Electromagnetic Soil Properties on EMI and GPR Sensors in Landmine and UXO Detection
Authors J. Igel, H. Preetz, K. Takahashi and S. AltfelderElectromagnetic induction technique (EMI) has been used for landmine detection for a long time. Recently, ground-penetrating radar (GPR) is used more and more often as a stand-alone detector or in combination with EMI sensors. Both techniques are strongly influenced by electromagnetic soil properties, albeit in a different manner. There is a lack of information on electromagnetic soil properties of different soils under various conditions and on how these properties influence different detectors. We present measuring techniques and results of lab and field measurements of physical soil properties and their spatial variability on different scales. A classification system is deduced for magnetic susceptibility and its frequency dependence that can be used to predict the soil influence of tropical soils on EMI sensors and a performance map is designed for the country of Angola. Further, several dual sensors (EMI + GPR) were tested on different soils. The soil influence as predicted by geophysical field investigations and analysis of the electromagnetic soil properties and their spatial variability is in good accordance to the detector performance of the dual sensor test.
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2D-Electrical Resistivity Imaging for Sike Survey: Impact of the a Priori Information Management
Authors Y. Fargier, S. Palma Lopes, C. Fauchard, D. François and P. CôteIn France, EDF (Électricité De France) is in charge of managing the large hydraulic structure stock dedicated to producing hydroelectricity. This responsability is associated with high economical and safety issues. Electrical Resistivity Imaging (ERI) is being widely used on earth embankment dikes, either for extensive survey of large sections (a few km) or for higher resolution surveys on shorter sections (a few 100m). However, the processing of extensive longitudinal survey with conventional 2.5D software is likely to yield image artefacts. This study aims to show that a bad management of the dike complexity in the inversion process is the origin of these artifacts. To overcome this limitation, a new inversion algorithm specially created to take into account the complex behaviour of the dike is presented. This development aims at filling the gap between more classical 2D and purely 3D approaches, by optimising a compromise between acquisition cost and model reliability. Applied to real data sets this tool supplies a new understanding of the interpretation capability of the inversion results.
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Volumetric Remote Monitoring of an Earth Embankment: Part I - Geophysical – Geotechnical Property Translations
Authors C.J. Munro, J.E. Chambers, D.A. Gunn, P.B. Wilkinson, P.I. Meldrum, M. Kirkham, J. Wragg, S. Holyoake and O. KurasIn this work we describe a study where automated time-lapse electrical resistivity tomography (ALERT) monitoring technology has been installed on a section of Victorian embankment on the Great Central Railway (Nottingham, United Kingdom). Raw datasets collected by the ALERT system have been processed/filtered, and inverted to yield a 3D resistivity distribution which is temperature corrected and converted to gravimetric moisture content using a relationship established by laboratory testing. Electrical resistivity tomography monitoring has been used to characterize the internal structure of the embankment, and image moisture content changes and wetting front development at a high spatial resolution. Monitoring has been undertaken at the test site to determine seasonal temperature changes in the subsurface; these data have been used to correct for temperature effects. We fitted the resistivity data as a function of gravimetric moisture content by modifying the Waxman-Smits model. Using results from laboratory testing, a best fit is computed and used to establish a resistivity, gravimetric moisture content relationship, used to facilitate property translation from temperature corrected resistivity to gravimetric moisture content. These results indicate that ERT has potential to identify structures and processes related to instability at an early stage in their development.
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Fissure Detection in Flood Embankments using Electrical Resistivity Tomography
Authors G. Jones, P. Sentenac and M. ZielinskiFissures forming due to desiccation in clayey soils have been shown as a potential source of embankment failure during overtopping. Current methods of visually identifying fissures in flood embankments are inadequate particularly when faced with dense vegetation. The extent of fissuring cannot be discovered without the use of trenching, which is costly and destructive to the embankment structure. Electrical Resistivity Tomography (ERT) offers a non-invasive method for appraising the embankment structure. The presented study compares the use of a survey using ERT on the Thorngumbald embankment, near Kingston Upon Hull, UK, with previous laboratory studies on scale models using miniature resistivity arrays. Large scale scans across the slopes of the embankment showed areas of confirmed fissuring, while miniature arrays were used to fully map the fissures in the subsurface. The positions of surface fissures matched with those resolved from the resistivity data and the results compare favorably with those achieved in the laboratory. Additionally scans were taken across the embankment revealing serious fissuring on the landward face, the side most affected by heavy vegetation.
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Detection of Ground Movement using the Shape of Brillouin Spectrum
Authors E Buchoud, S. Blairon, G. D'urso, J.M. Henault, A. Girard, J. Mars and V. VrabieDistributed Optical Fiber Sensing systems (DOFSS) are composed by optical fibers wrapped in strain sensing cables, coupled with Brillouin interrogators. DOFSS are increasingly used for Structural Health Monitoring (SHM) as they can provide continuous strain profiles along the optical fiber localized in the structure. Raw Brillouin measurements consist in gain – frequency curves with a Lorentzian shape. Strain is generally assessed thanks to the abscissa of the maximum of the gain curve. Two new factors are introduced. They are sensitive to asymmetry and broadening of the Brillouin gain curve which can highlight strain gradient within the spatial resolution of the interrogator. These parameters could be used to detect more efficiently local events and improve instrument algorithm.
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The Robustness and General Applicability of Optimal Resistivity Surveys Designed by Maximising Model Resolution
Authors P.B. Wilkinson, J.E. Chambers, P.I. Meldrum, O. Kuras and C.J. MunroMost optimal survey design algorithms for resistivity imaging have not incorporated prior knowledge of the resistivity of the subsurface. The resulting surveys are optimal for a homogeneous earth, but little investigation has yet been carried out to test whether they are robust, i.e. that they remain optimal when applied to imaging heterogeneous subsurface resistivity distributions. This paper compares a generic survey, which is designed to maximise the estimated model resolution evenly across a homogeneous earth, with specific surveys similarly designed for a number of heterogeneous resistivity distributions. In terms of both the average estimated model resolution and the correlations between the inverted and true resistivity models, the generic and heterogeneous survey designs give near-identical results. This suggests that surveys designed using homogeneous earth approximations are robust in the presence of resistivity heterogeneities and are therefore generally applicable. Traditional dipole-dipole surveys with the same number of measurements do not give such good inverted images, and their degree of optimality (measured either by average resolution or image correlation) is less robust in the presence of heterogeneity.
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Simultaneous Inversion of Time-domain SIP Data
More LessWe developed a new inversion algorithm of time-domain SIP data in which the entire multi-channel data sets are simultaneously inverted. In the proposed algorithm, the channel numbers are incorporated as a new dimension. We define the multi-channel data sets of chargeability data as a single data vector in the space and channel domains, and similarly many chargeability distributions as a single changeability model which spans in the space-channel domain. These definitions allow us to introduce inverse model regularizations not only in the space domain but also in the channel domain. We demonstrated the performance of the proposed algorithm through numerical experiments as well as real data application; the new inversion approach can generate a reasonable chargeabilty model in the space-channel domain in which the curves of the inverted chargeability are smoothly and monotonously decaying. This performance of the proposed algorithm enables us to fully utilize the own capabilities and merits of SIP method.
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A Fast Least-squares Method for Inverse Modeling of Gravity Anomaly Profiles due Simple Geometric-shaped Structures
By K.S. EssaAn inversion technique using a fast least-squares method is developed to estimate, successively, the shape factor (q-parameter), the depth (z-parameter) and the amplitude coefficient (A-parameter) of a buried structure using normalized residual anomalies obtained from gravity data. By defining the anomaly value at the origin and the anomaly value at different points on the profile (N-value), the problem of shape factor estimation is transformed into a problem of finding a solution of a non-linear equation of the form f(q)=0. Knowing the shape factor and applying the least-squares method, the depth is estimated by solving a nonlinear equation of the form ψ(z) = 0. Finally, knowing the shape factor and the depth, the amplitude coefficient is determined in a least-squares way using a simple linear equation. This technique is applicable for a class of geometrically simple anomalous bodies, including the semi-infinite vertical cylinder, the infinitely long horizontal cylinder, and the sphere. The technique is tested and verified on a theoretical model with and without random errors. It is also successfully applied to real data from mineral exploration in India, and the interpreted shape and depth parameters are in good agreement with the known actual values.
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Modeling and Inversion of Self-potential Anomalies due to Sheet-like Bodies under the Presence of Arbitrary 2-D Resistivity Distribution
Authors P. Tsourlos, I. Giannakis, C. Papazachos and G. VargemezisVarious methods have been proposed to interpret the self-potential anomalies due to sheet-like bodies. A common point of all existing interpretation methods is the assumption that earth is geoelectrically homogeneous. We propose a non-linear inversion approach for SP anomalies which finds the optimized sheet-like body for a given arbitrarily resistivity distribution. Tests of the new technique with synthetic data suggest that it can produce more accurate and reliable results. Further, test with field data demonstrate the applicability of the scheme in real problems.
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Layered and Laterally Constrained 2D Inversion of Time Domain Induced Polarization Data
Authors G. Fiandaca, J. Ramm, E. Auken, A. Binley and A.V. ChristiansenIn a sedimentary environment, quasi-layered models often represent the actual geology more accurately than smooth minimum-structure models. We have developed a new layered and laterally constrained inversion algorithm for time domain induced polarization data. The algorithm is based on the time transform of a complex resistivity forward response and the inversion extracts the spectral information of the time domain measures in terms of the Cole-Cole parameters. The developed forward code and inversion algorithm use the full time decay of the induced polarization response, together with an accurate description of the transmitter waveform and of the receiver transfer function allowing for a quantitative interpretation of the parameters. The code has been optimized for parallel computation and the inversion time is comparable to codes inverting just for direct current resistivity. The new inversion algorithm retrieves consistent values for both the Cole-Cole parameters and the layer thicknesses and is a promising tool for identifying formation boundaries, e.g. in for discriminating sand and clay layers or pollution fans, due to the chargeability of these layers.
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Results of Geophysical Surveys to Locate Zones of Increased Fracturing of Rocks,Zones of Filtering Groundwater and to Identify Placements of Wells
Authors A.F. Volynin and A.P. PodsevalovComplex geophysical studies were conducted in the area of the settlement “Selchostechnika” for the selection of sites for placement of water wells for the monitoring observations to determine the cause of flooding of the territory and the basements of houses. The complex of methods included the method of spectral seismic profiling (SSP) (mapping areas of fractured limestone) and the method of vertical electrical sounding (VEZ) on sites allocated SSP. As a result of the work, it was found area of extensively damaged fractured limestone, within which identified two linear tectonic zones of heavy water-saturated rocks. It was specified placements of three bushes of wells (depth of wells of up to 70 m). The nine wells entirely confirmed the recommendation. It was carried out monitoring of the changing of the hydro geological regime and composition of groundwater. The applied method can be used to solve analogical problems on the areas of fractured limestone
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