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Near Surface 2006 - 12th EAGE European Meeting of Environmental and Engineering Geophysics
- Conference date: 04 Sep 2006 - 06 Sep 2006
- Location: Helsinki, Finland
- ISBN: 978-90-73781-62-7
- Published: 04 September 2006
21 - 40 of 142 results
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First Results from Thermal Tomography in the Study of Wall Structures and Archaeological Layers
Authors C. Piga, G. Ranieri and R. DeianaMasonry walls, especially those of historic buildings, are often difficult to investigate. The current approach consists of analysing small portions of the structure. The techniques employed are often invasive and in any case incapable of providing a complete picture of the variety of problems to be solved. The aim of this work is to test the effectiveness and feasibility of thermal methods suitable for assessing the conditions of masonry.
Different physical models that mimics real conditions has been designed for this purpose. A number of anomalous elements were introduced in the models, to simulate the heterogeneity of the structure.
The same method has been applied in the analysis of thermal imaging to try to reconstruct buried walls. A quasi-real scale model has been constructed also in this case.
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High-Resolution Seismic Reflection to Identify Areas with Subsidence Potential beneath U.S. 50 Highway in Eastern Reno County, Kansas
By R. D. MillerHigh-resolution seismic reflections were used to map the upper 200 m along an approximately 22 km stretch of U.S. 50 highway in Reno County, Kansas, where natural and anthropogenic salt dissolution is known to threaten ground stability. Surface subsidence in this part of Kansas can range from gradual (cm per year) to catastrophic (meter per second), representing a significant risk to public safety. The high signal-to-noise ratio and resolution of these seismic reflection data allowed detection, delineation, and evaluation of several abnormalities in the rock salt layer and overlying Permian sediments. Locations were identified where failure and associated episodes of material collapse into voids left after periodic and localized leaching of the 125 m deep, 40 m thick Permian Hutchinson Salt member were evident. Anhydrite and shale layers several meters thick within the salt are uniquely distinguishable and appear continuous for distances of several kilometers. Over a dozen unique features potentially related to subsidence risk were identified.
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Applicability and Limitations of Impact Echo in Bridge Deck Condition Monitoring
Authors P. Shokouhi, N. Gucunski and A. MaherA010 Applicability and Limitations of Impact Echo in Bridge Deck Condition Monitoring P. Shokouhi * (The University of Texas at El Paso (UTEP)) N. Gucunski (Rutgers University) & A. Maher (Rutgers University) SUMMARY Near Surface 2006 — Helsinki Finland 4 - 6 September 2006 One of the most common problems in concrete bridge decks is a corrosion-induced deck delamination. A number of nondestructive testing (NDT) techniques have been utilized to map delaminated zones in concrete bridge decks (Scott et al. 2003). Impact echo (IE) an ultrasonic seismic method has proved successful in detection of delaminations in concrete bridge decks at
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Target Prioritization in TEM Surveys for Sub-Surface UXO Investigations Using Response Amplitude, Decay Curve Slope, Signal to Noise Ratio, and Spatia
Authors D. Hall, S. MacInnes and J. DickersonTo reduce the number of false-positives in identifying UXOs and related debris for an ongoing Site Investigation, a target prioritization routine was developed based on the likelihood of a metallic source. Numerous parameters were evaluated statistically using over 2000 existing intrusive investigation results. Those showing the best ability to discriminate between metallic and non-metallic sources were incorporated into the scheme, including peak amplitude response, power-law decay slope, signal to noise ratio, and spatial match filter response. Parameters were assigned increasing numeric values based on likelihood of a metallic source, and summed to produce a target rank. Subsequent application to over 6000 new intrusive investigations revealed that the highest ranked 25% of targets were nearly five times more likely to yield a metallic source when investigated than the lowest ranked 25%. These results show that target selection routines in UXO investigations would benefit from using more parameters than just magnitude response, allowing more aggressive target identification and reduced costs by lowering the number of false positives that are investigated. Proposed refinements may further increase predictive capabilities.
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Advancements in 3D Subsurface Modeling Using Refraction Data
More LessRecent advancements in refraction data analysis have increased the ability to image geologic features, provide better presentation, and offer additional benefits from refraction results. The end product from a refraction investigation can be either a 2D image or a full 3D model, as presented here. Full 3D earth models can be used for many purposes after the geophysical survey is complete. That is, subsurface physical property data in 3D model space permits site assessment from a new perspective. For example: structural loading, seismic loading, or construction excavation requirements can be evaluated using 3D model results.
This paper presents an advanced approach to refraction data processing, presentation, and visualization, using the "Geostructural Analysis Package" (GAP). GAP incorporates several numerical modeling processes: discrete element method, particle flow code, finite differencing, and the material point method. These four numerical modeling methods have been combined and optimized for seismic applications. GAP is an innovative tool that allows better data analysis and presentation that can be used to produce 3D volumetric models for further site analysis. A set of model results from a case history are presented to demonstrate the benefit of processing refraction data using this new approach. GAP represents the newest advancement in subsurface modeling using engineering-scale seismic data.
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Using Borehole Radar to Image a Pothole in the Merensky Platinum Orebody
By P. du PisaniThe Merensky orebody (reef) in South Africa is one of the world's most important platinum resources. Potholes (slumps) in the Merensky Reef lead to significant mining losses. This paper describes for the first time how borehole radar can be used to image potholes in the Merensky Reef. Three dimensional visualization of the borehole radar data is used to delineate these structures and to improve the geological model ahead of mining.
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Crosshole Radiowave Imaging (RIM) at Eurajoki Olkiluoto, Finland
Authors E. Heikkinen, A. Korpisalo, T. Jokinen, T. Zhienbaev, A. Shuval-Sergeev, N. Popov and T. AhokasCrosshole radiowave imaging survey was conducted late in 2005 at Eurajoki Olkiluoto in Finland. Work belongs to site characterization process for spent nuclear fuel disposal into Finnish bedrock, which is run by Posiva Ltd. Crosshole radiowave imaging (RIM) was performed as a joint operation of Geological Survey of Finland and FGUNPP Geologorazvedka from Russia, using FARA-MCH tool. Pöyry Environment reviewed the results and compared the material to existing background information. The field work performed successfully between two borehole pairs at surface collar distances of 250-300 m. Recorded amplitude data were processed to resistivity images using crosshole tomographic reconstruction. The results prove that the method can be used in 100-400 m scale between boreholes to delineate and follow sulphide-bearing horizons, which are controlled by ductile and brittle geological processes in the site. Obtained results indicate that the location and geometry of resistive and conductive units in bedrock correlate rather well with data from geological mapping and geophysical logging from boreholes. The obtained projected geometry correlates also rather well with one subset of seismic 3-D reflections, and with geophysical electrical and electromagnetic results from the site.
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Monitoring Leachate Levels in Landfill Sites Using Automated Time-Lapse Electrical Resistivity Tomography (ALERT)
Authors O. Kuras, R. D. Ogilvy, J. Pritchard, P. I. Meldrum, J. E. Chambers, P. B. Wilkinson and D. LalaAutomated time-Lapse Electrical Resistivity Tomography (ALERT) is a concept that aims to provide tomographic images of landfill sites at regular intervals or on demand. The British Geological Survey has developed an ALERT system specifically for the deployment on landfills and has undertaken a research programme focussing on leachate monitoring techniques based on ERT. Simple scale experiments demonstrate the capabilities of the ALERT technique to accurately monitor liquid levels in a porous medium between wells. ALERT data provide additional control and information about inter-well properties and processes, thus contributing to an improved understanding of landfill hydrology.
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Combined Monte Carlo and Gradient Procedures Used to Optimized Solution of the Comprehensive Interpretation of Well Logs
Authors U. Woznicka, J. A. Jarzyna and A. CichyThe comprehensive interpretation of well logs is a mathematical task on a solution of a set of equations. The number of equations is determined by the number of the logs and conditions determining boundary and geological requirements. The common methods (e.g. gradient method, GRAD) are limited to cases when one global minimum occurs in the examined range of variables. Only Monte Carlo method, MC, which consists on numerous solutions obtained by random sampling of possible variables can find the global minimum of the function when other local minima are present. The MC method is time consuming, especially, in application to the well logging interpretation when enormous number of points along the depth profile should be calculated. We propose a complex method of solution combining both MC and GRAD methods. The method has been applied to the Interlog application in the GeoWin system for processing and interpretation of well logs and the field example is presented in the paper. The results confirm that the combined MC-GRAD solutions can give more information than the simple GRAD solution. Presented approach can be treated as an additional tool, especially dedicated for log analysts, for solving a set of logs difficult to interpretation.
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Correctness of the Comprehensive Interpretation of Well Logs Regarding to Geological Conditions and Calculation Methods
Authors J. A. Jarzyna and U. WoznickaA great amount of unknowns resulting from a complicated lithology and from many logs run in a borehole causes that a set of equations in the comprehensive interpretation is great and sometimes indeterminate. In real geological conditions we sometimes get solutions that are different from laboratory estimates of porosity or other parameters. Discrepancies between lab measurements and geological data on one side and results of the comprehensive interpretation of well logs on the other side were the direct reason to examine the method of optimization adopted for solution. The proposed mathematical solution in the form of combined Monte Carlo and Gradient methods works as a tool assuring interpreter that the solution is correct. The general results obtained from Interlog-GeoWin were compared to ULTRA and Petrolog systems and the agreement was satisfied.
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Geoelectric Survey of Hydraulic Experiments at the German Deep Drilling Site KTB at KM-Scale
Authors D. Laass, E. Danckwardt, G. Petzold and R. VoigtOne of the major findings of the German Continental Deep Drilling Program was the evidence of free fluids down to a depth of nearly ten kilometres. Furthermore, a series of hydraulic experiments in the pilot borehole focused on the characterization of transport processes of fluids in crystalline crust were carried out. Because of the significant differences of the electrical conductivity between the investigated fluids (natural free saline fluids and artificially inserted fresh water), geoelectrical methods are qualified for a successful detection in the kilometre scale. The Fluid Pump Test (2002/03 – production of about 22,300 cubic metres of saline formation fluids) or the Fluid Injection Test (2004/05 – injection of about 84,600 cubic metres of fresh water) clearly indicate a decreasing respectively an increasing in electrical resistivity. Inhole-logs in the open hole section (3,850 m – 4,000 m) could give a first indication (very closed to the pilot borehole) of consequence of the producing of saline formation fluids respectively of the fluid inflow displaced by injected fresh water last year. Also in greater distances to the pilot borehole, the time course of the decreasing (2003) and of the increasing of the apparent resistivity (2005) could be measured by geoelectrical combined surface-hole-experiments.
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Active and Passive Seismic at the Unstable Rock Slide of Åknes (Norway)
Authors I. Lecomte, M. Dietrich, M. Roth, O. Méric, C. Delarue and J. S. RonningThe unstable rock slope of Åknes, Western Norway, has been recently identified as a potential threat for people and infrastructure in the inner Storfjord system. The unstable part has an estimated total volume of 30 to 40 million m3 based on recent geological and geophysical mapping. It is moving with a mean rate of about 4 cm/year, but with a rate as high as 15 cm/year in some parts. Such rock slide, when hitting the water in the fjord, could generate a flood wave (tsunami) with severe consequences, as experienced in the past by the local population. During the 2005 field campaign, three seismic measurements/installations were made: 1) a refraction seismic experiment in the center of the slope to map a potential sliding plane, 2) a temporary installation of 10 seismic mini-arrays of 9 channels each for passive monitoring of seismic events and noise measurements, and 3) a permanent installation of a smaller-scale seismic network for long-time monitoring of the site with real-time data access.
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2D Inversion of the First Field Data of a New Radiomagnetotelluric Device in the Frequency Range from 10 kHz to 1 MHz
Authors B. Tezkan, A. Saraev, V. Shuman, P. Georgescu and N. B. ChristensenIn the project RMT-monitoring funded by the European Union, a new radiomagnetotelluric device has been developed which can record time series of electric and magnetic fields in a wide frequency range from 10 kHz to 1 MHz. Transfer functions are determined by spectral analysis using a newly developed processing software. A workbench program has been developed in which the transfer functions are interpreted with conductivity models based on new inversion algorithms.
The developed tensor radiomagnetotelluric device was tested in the laboratory and then applied successfully in the field to several environmental and groundwater problems in Russia, Ukraine, Denmark, Romania, and Germany.
The observed transfer functions in the field are the first ones worldwide in the frequency above 250 kHz which leads to a better resolution of the shallow structure. The new device enables quick and efficient mapping of polluted areas and supports tensor measurements allowing a 2D or 3D interpretation of the field data.
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High-Resolution S-Wave Reflection Survey in Urban Areas Using a Woven Belt Type Land Streamer
By T. InazakiHigh-resolution S-wave reflection surveying has been successfully conducted on the paved surface in large urban areas by means of a Land Streamer, which was originally developed by the author. The Land Streamer is featured by non-stretch woven belt which acts as a towing member but also as a module to mount geophone units. Whereas each geophone unit is placed on the paved surface through a metallic baseplate instead of firm planting to the ground, the Land Streamer tool provides comparatively clean data even on the pavement resistant to traffic noises. Consequently, the tool is capable of expanding the opportunity of S-wave reflection survey in the urban areas where the surface is mostly paved and cultural noise is considerably high. A series of high-resolution S-wave reflection surveys conducted at paved surfaces in large urban areas successfully delineated detailed structures of the surficial layers shallower than 60 m, and proved the wide availability of the tool to engineering, environmental applications, and earthquake disaster prevention.
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Geophysical Surveys in Prospecting of the Granite Host Rock of a Planned Radioactive Waste Disposal Site in Hungary
Authors A. Gulyás, L. Vértesy, A. Madarasi and J. KissA great amount of geophysical work was involved in the programme of final disposal of low- and intermediate-level radioactive waste in Hungary. Among others wide spectrum of geoelectric-electromagnetic methods were applied from the early stages of the project. In this poster we present the results obtained in prospecting the internal structure of the granite body either outcropping in the deep valleys, or buried under 30-60 m thick Quaternary sediments. VLF, Slingram-EM and high-frequency magnetotelluric surveys were performed to extend the detailed but were scarce information of the borehole geoelectric measurements and obtain a spatial view about the resistiv-ity distribution of the granite body, to delineate conductive zones of as possible tectonic zones, blocks etc. Regional gravity, magnetic and magnetotelluric studies were performed to delineate the granite body and for marking out regional structural lines.
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Geophysics in Constructing the Geological Model of Olkiluoto
Authors M. Paananen, T. Lehtonen and T. AhokasThe paper presents some geophysical results that have been useful in constructing the geological model of Olkiluoto. Interpretation of wide-band EM soundings, HLEM, charged potential and single-hole measurements revealed several sulphide-rich conductive zones. These zones often appear to control also the brittle deformation zones.
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Investigation of the EDZ Using High-Resolution GPR with Modulating Frequency
Authors Y. Suyama, M. Toida, K. Masumoto and S. TakeuchiThe EDZ (Excavation Damage or Disturbed Zone) is considered to be a fast transport pathway and provides a boundary condition for transport in bentonite buffers in groundwater scenarios for the geological disposal of radioactive waste. The distribution of the EDZ obtained through in-situ measurements, is important for safety assessments. High-resolution Ground Penetrating Radar (HGPR) with modulating frequency functions as a wide-angle measurement technique. It is one of the advanced techniques that can be used to investigate the EDZ of a radioactive waste disposal tunnel. Verification tests of the HGPR were carried out using a model and in-situ condition in the gallery of Tono mine in central Japan, where comprehensive techniques for investigation, analysis and assessment of the deep geological environment had been developed. In summary, it is shown that the investigation technique was able to detect underground structures with a resolution of less than 0.1m.
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Quality Control and Validation of Detailed Logging Data from Slim Boreholes
Authors E. J. Heikkinen, T. Lehtimäki and T. AhokasBorehole geophysical logging data can provide a direct link between results of large scale geophysical methods and core sample analysis. Also the in situ measurement data will focus the measured response to actual location and to the specific lithology, or overprint of alteration or deformation. This way the logging data serves as unique means to explain and control the results from a large variety of different views and scales, ranging from airborne and ground level mapping to seismic reflection surveys and electromagnetic soundings. The actual parameter information used in model interpretations is only accessible by borehole methods. Further to this, the comparison of different parameters and geological background information can lead to better understanding of processes involved in the subsurface. The presentation deals with practices of quality control and validation of slim hole logging data using different geological and sampling control data. The work includes the sample controlled conversion of measurement data to meaningful physical properties, depth matching of the data to a very good location accuracy, and computing of derivative parameters. Example data set has been produced in site characterization project of Posiva for spent nuclear fuel geological disposal in Finland.
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Geophysical Studies at the Suurpelto Construction Area
Authors T. K. T. Huotari, I. A. Suppala, H. T. Vanhala, T. Valjus, A. E. K. Ojala and J. P. PalmuIn this project geophysical, geological and geotechnical data has been collected from the Suurpelto construction site. The Suurpelto site is locating in the City of Espoo in southern Finland. The main aim of the studies is to investigate the geological history of the site and also use the data for constructional purposes. Airborne, ground as well as laboratory geophysical techniques have been used during this project. AEM measurement is fast method for outlining the highly conductive clay areas. 1D-inversion of 4-frequency AEM data was done using constrains from other Suurpelto datasets. More detailed conductivity structures were achieved from inverted ERT and ground EM data. The laboratory resistivity measurements revealed the highly conductive clays and less conductive gyttja clay sections from the drillhole samples. These sediments are the most difficult for constructional purposes.
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Municipal Waste Dump Geophysical Investigation
Authors M. Bavusi, E. Rizzo, V. Lapenna and S. PiscitelliThe proposed work is about the geophysical survey applied in three Italian waste dump (Savoia di Lucania and Pallareta in Basilicata region, Novellara in Emilia-Romagna Region). The Basilicata landfill are provided of HDPI liner while in the other one a compacted clay stratum is present at the bottom. In each site we carried out active and passive geophysical techniques: electrical resistivity tomographies (ERT), induced polarisation (IP), self potential (SP) and magnetic methods. The ERTs, inverted by using the Res2DInv software, provided information about the geometry of the waste basins where an HDPI liner is present. The IP results show high chargeability nuclei into the refuse indicated the metallic garbage cumuli. The SP signal is negative into the basins and slightly positive in the surrounding area. Moreover, the SP data show strong spikes at the borders of the basins. The SP data of Novellara waste dump (clay stratum coating) show positive values inside the basins. The magnetic method evaluates the dispersion of metallic garbage close to the waste dumps. Finally, the different acquired data allow to sketch the lateral and buried geometry of the waste basins and to infer their leachate-tight, at least where the HDPI liner is present.
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