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5th EEGS-ES Meeting
- Conference date: 06 Sep 1999 - 09 Sep 1999
- Location: Budapest, Hungary
- ISBN: 978-94-6282-119-4
- Published: 06 September 1999
61 - 80 of 196 results
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Dielectric properties of sand-clay mixtures
More LessThe interpretation of field measurements on electrical properties at high frequencies, e.g. EMR-measurements, requires detailed knowledge on relations between the electrical parameters at one hand and changes in lithology or pore filling at the other hand. Clay minerals play an important role in this subject due to their widespread occurrence and to the distinguished properties caused by electrochemical effects. In our measurements clay was used to simulate pore structures with varying internal surface. The dependence of electrical properties from pore filling and clay content was examined by changing water content. The investigations result in models quantifying the relations between lithology, pore structure and fluid content.
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Measurements of the dielectric effective permittivity applied to archaeology
Authors J. A. Canas, V. Pérez, L. G. Pujades, J. Clapés, R. Osorio, F. García and D. I. CanasArchaeological studies require high resolution radar techniques. A good knowledge of the analyzed media and conditions are necessary (material, water content and porosity) because of the influence of these conditions on the propagation and reflection of electromagnetic waves. Several in situ measurements have been performed in different archaeological places by using Ground-Penetrating Radar (GPR), allowing us to obtain the effective permittivity for several materials. Measurements were also performed in areas where different conditions of water content were observed. Wave speed variations are determined when the water content is lightly increased, mainly in porous materials. This variations seems to be caused due to a change in dielectric permittivity and conductivity of media. Several authors have carried out laboratory experiments to detect changes depending on water porosity and clay content (e.g. Robert, 1996; Saarenketo, 1996; Knoll and Knight, 1994). In this job we present the preliminary results of several measurements performed on known sites, where the exact materials of every layer and the contact depths between materials, lateral changes and water contents are well known. The analysis of the arrival times of the reflected waves on the surface, where the medium properties change, allow us to calculate the wave velocity in such a medium. Comparing the two way travel time of the reflected waves in radar records, obtained for the same material with different water contents, it is possible to obtain the different dielectric permittivities. Some of these measurements were performed on marble floor, located over a layer of concrete (which is placed over ground materials), allowing to obtain several experimental values for the dielectric permittivity of different media (several materials, water and air content). Comparing the results among them and using different models to relate the dependence of the dielectric permittivity on the porosity and saturation, it has been possible to obtain differences on the product of the water content by the porosity of the two emplacements using the simplified relation: S PΔ = Δ 2 8 1 ε , where ε is the effective value of the dielectric permittivity of the medium measured during the in situ experiences, P is the porosity of the materials and ΔS is the difference in water content in the medium.
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Contribution of the 3D display of GPR signals in noisy environment
Authors A. Rousseau, R. Baraud and D. JeantetIn order to see immediately the simultaneous variations of all the parameters of borehole acoustic signals, we made some years ago graphic softwares using a representation of our own in three dimensions (Rousseau & Jeantet, 1997). This representation proceeds from a specific projection : 1) it is orthographic, that is to say it has no vanishing point, no perspective ; 2) the z axis, which represents the amplitudes, is everywhere vertical and always directed upwards (see Fig.1). The angles between x0y plane and z axis depend on the vantage point for viewing, but parallel lines remain parallel in the x0y plane under any azimuth, which allows angle measurements as on a 2D display. This method which highlights particularly the continuous variations of the amplitudes of acoustic signals in relation to depth has provided some keys for geological interpretation such as the characterisation of fractures, delimiting crushed zones,...
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3D Ground penetrating radar applied to paleoseismology: Examples from the San Andreas fault, California, USA
Authors R. Gross, K. Holliger, G. Seitz, J. Baldwin and A. GreenOne goal of paleoseismology is to estimate future seismic hazard through an improved characterization of past fault behaviour in seismically active environments. Earthquake-related features (e.g. faults, folds and fissure fills) observed in trenches and outcrops show complex three-dimensional structures in strike-slip faulting environments. Ground penetrating radar (GPR) is a non-destructive, inexpensive technique that may allow localized paleoseismic information obtained from conventional approaches to be complemented and extrapolated. We have carried out detailed 2D and 3D GPR surveys across the active San Andreas Fault (SAF) at the Pitman Canyon and Alder Creek trench sites in California.
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Location of different soils and soil conditions using GPR
Authors J. H. Weitzel, W. Gödde and T. HesslandGPR is well known as an instrument to detect and map subsurface obstacles and general soil changes. In most cases geological and geotechnical investigations are done in addition to point out soil and geotechnical parameters. In this presentation we want to show up possibilities, advantages, limits and disadvantages using GPR for soil inspection. The case histories show up the goal and methods to examine the ground.
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Some applications of GPR to the geotechnical studies
Authors J. M. Galera, F. Peral Álvaro and A. Rodríguez SotoGPR is one of the geophysical tools which provides fullest information about the first meters of ground. For this reason, the use of this geophysical technique for geotechnical studies is getting more frequent. In this document are shown two cases of GPR use in geotechnical studies. The first one has been carried out in Barajas-Madrid Airport in order to detect voids and alterations near a service gallery of the airport. The second one has been carried out in Arguedas cross-street (Spain) in order to study the ground near the water pipes where many water leakages had been produced in a gypsum and limestone ground.
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Analysis of characteristics of slot and dipole antennas of georadar with a resistive material
More LessWhen a georadar is working in a tunnel, reflections from metallic mechanisms may be a serious interference. Therefore it is important to enlarge “front to back” ratio of antennas. A spacing between the antenna and the ground surface, which may be due to roughness of the surface, usually diminishes the front to back ratio. A placing of deformable resistive material into the spacing, as proposed by A.G.Chernokalov, increases the front to back ratio.
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Modeling of a georadar pulse reflected from underground water level
More LessCapillary rising of water smoothes a change of dielectric constant of the ground near water level. This smooth transition greatly diminish amplitudes of high frequency components of a georadar pulse, reflected from the water level. In this work we study the shape and amplitude of signals, reflected from water level in the ground. Soils with different distributions of solid particles by size are considered.
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The absorption coefficient of radio waves in sandy and clayey soils as a function of the soil moisture in the range of wavelenghts from 0.8 to 226 CM
More LessDiscovery distance of buried objects is strongly dependent upon the absorption coefficient (Q(dB/m)) of radio waves in soils. Therefore, it is necessary to know Q (dB/m) as a function of the soil moisture in a wanted range of radio waves. This paper presents generalized results of measurements of the absorption coefficient of radio waves in sandy and clayey soils as functions of the wavelength in a free space ( λ0 ) in the range from 0.8 to 226 cm for five values of the soil moisture (p (%) = 2, 4, 6, 10, 16). Samples of the soil were corresponded to sandy and clayey soils of Moscow region (Russia). The present paper is an extension of the work reported in [1,2].
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Ground penetrating radar ability to detect leaks from water pipe
Authors N. Chubinsky and A. KrampulsThe problem of detection of leaks from water pipe without digging the pipe out is of constant interest to city services. To solve this problems many different geophysical methods can be used: radiolocation, seismics, resistivity imaging etc. This paper describes numerical modeling of ground penetrating radar detection of metal pipe with a leak buried in sandy soil with various levels of water content. Relative dielectric permittivity was 5 to 30 dependent on water content. Complex dielectric permittivity was an approximation of results obtained in [1] in modeled GPR frequency range. Spatial distribution of soil water content around the leak area was considered stationary and based on the work [2]. The leak was supposed to be a linear water source along the pipe. Boundaries of areas with given value of water content were non-coaxial elliptical cylinders with their axes displaced down relative to pipe axis. The ground around the pipe in case of the leak had maximum possible water content (30%). Monostatic pulse ground penetrating radar survey was modeled by calculating signals reflected from the pipe and from subsurface dielectric inhomogeneity due to the leak. The polarization of electric field was along the pipe axis. Transmitted signal was a real GPR signal with 4 half-periods, each with duration about 4 ns. Transition coefficient conditioned by subsurface reflections was calculated in frequency domain. Then time domain signals on the receiver were found. Calculations were carried out for metal pipes of various diameter buried at depths 2-3 m, mean water content of the ground being 5%-15%. GPR survey data were simulated by adding the direct signal between transmitter and receiver and calculating received signals in points along the line perpendicular to the pipe at 20 cm steps, starting over the pipe.
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Geophysical radar techniques for the characterization of heterogeneous quarternary gravel deposits
Authors J. Tronicke, J. Heinz and E. AppelQuarternary gravel deposits build up most of the valley aquifers in central Europe and elsewhere. In order to understand and model groundwater flow and contaminant transport in these highly heterogeneous systems, a detailed geometrical image of the subsurface and the hydrogeological parameter distribution within it is needed. Geophysical radar techniques are able to identify sedimentological structures in three dimensions and to fill elements with physical parameters. Ground-penetrating radar (GPR) is a common geophysical tool to resolve sedimentary structures in unconsolidated sediments (e.g. Huggenberger, 1993). It has the potential to visualise the deposits in three dimensions (Beres, 1998). Applying 3-D GPR at a research site in the Neckar River Valley, SW Germany, we were able to get a high resolution structural image of the shallow subsurface. Sedimentological units and their spatial extension could be interpreted. Using crosshole radar tomography at the same site, made it possible to reproduce parts of certain prominent structural elements identified in the surface measurements and to fill them with geophysical parameters.
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High speed pavement investigation using G.P.R. in the “Dino e Enzo Ferrari” formula 1 autodrome – Imola (I)
Authors A. E. Bracci, E. Lucchi and R. W. MilliganSince 1993, when a new radar technique for pavement investigation was developed by Impulse Geophysics, many thousands of kilometres of data have been collected in the United Kingdom and elsewhere. The technique, in the following years, has been refined and improved with regard to data collection, processing, interpretation and easy of client use. Using a radar survey continuous thickness measurements of the construction layers, the detection of structural anomalies, moisture content and the presence of voiding in the road pavement, are readily established. An effective radar survey, therefore, offers high quality and accuracy for monitoring and scheduling road maintenance. In Italy most engineering road departments still request the traditional, locally limited, coring method to measure the thickness of bituminous and granular layers. An application of the radar technique was carried out in the “Dino e Enzo Ferrari” autodrome with the intention of integrating the 20 material core locations (see Figure 1) chosen by the Formula 1 Circuit Management Consultants, who maintained the circuit. The Ground Penetrating Impulse Radar Survey (GPR) consisted of three lane investigations placed on the right, central and left track of the road, starting and ending on the finish line. The data were collected along the three tracks using three antennae; a 500 and 900 MHz and a 2.5 GHz. The recording system used was a GSSI SIR 2. The antennae and a distance encoder were mounted behind a vehicle (see Figure 2) travelling at an average speed of about 40 kilometres/hour resulting in a sample at 20 cm intervals. Additional markers were located every 500 metres on the total length of 4,920 metres. The three antennae gave good results to the following depth: 2.5GHz = 30cm, 900MHZ = 1m, 500 MHz = 2m. During data processing, the radargrams were horizontally scaled and filtered using band-pass filtering. The processing software, WinRAS, developed by Impulse Geophysics, allowed easy and rapid tracking of the wavelets relevant to the pavement layers. Matching the two-way travel time of the radar events with the core samples, the impulse radar velocities were depth calibrated and the time cross-sections were converted into depth-sections. The combination of the results obtained using the three types of antennae gave the required resolution and penetration down to 2 metres from the surface. The average sequence of the layers, from the surface, was as follows: 4cm wearing course, 6cm asphalt, 10cm bound bituminous, 20cm granular sub-base, 40cm granular sub-base, natural gravel and sand. Using the high speed radar system, a large amount of data is normally collected, resulting in extensive paperwork if the depth cross-sections are printed in a readable size. To avoid this inconvenience and to be able to readily view the radar data, Impulse Geophysics has developed the “Roadshow” software. The Roadshow may be run on a normal Personal Computer and examples will be shown, by the authors, at the meeting. Also to be demonstrated will be a Digital Video Survey of the Circuit, recorded using 4 S-video cameras for front, rear, left and right views. Both Roadshow systems together allow engineers to view the surface and subsurface of a road from their desktop PC.
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Innovative technologies in pipe construction enabled in city centers using GPR
Authors W. Gödde, H. Weitzel and T. HesslandEconomy and safety are getting more and more important for building projects. Different circumstances can influence the success of a project. Varying in complex subsurface structures, surface conditions (traffic etc.), and organization conditions in different countries have to be considered. This presentation shows case histories measured in India and Spain and Germany.
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Radar analysis applied to cultural heritage in northern Spain
Authors J. A. Canas, D. I. Canas, V. Pérez, L. G. Pujades, J. Clapés, R. Osorio and F. GarcíaThe geo-radar (Ground Penetrating Radar, GPR) is a good prospective non-destructive tool for depths varying between some centimeters and a few meters. The GPR is a compact and portable system, with a great variety of antennas and a high resolution power, which make it very useful either in detecting and locating ground anomalies and surface structures or in detecting construction problems. Prospecting technique with GPR has improved fast in recent years due to a rising demand both in quantity and required quality. Important advantages of GPR systems are, among others, that antennas must not be necessarily contacting ground surface when working, and that they can be designed, at least theoretically, to work at a desired central frequency with appropriated band widths. Nevertheless good results will be only obtained when taking in consideration ground nature and geometry. The first studies involving electromagnetic waves are from the beginning of this century. Several works were made to find metal objects buried beneath ground’s surface, and some others trying to locate buried objects. Important work was done, during 1923 to 1928, by the Institute of Applied Geophysics of Moscow, studying the penetration of radio waves in salty soils. In the second half of this century, during the 50’s and the 60’s, Wait (1960,1962) proposed his theory of electromagnetic wave propagation. Three decades were needed to introduce the technique in Civil Engineering due, basically, to the necessity of a scale change. In this way, the usage of mono-impulses began and so did the design of georadars, appearing the Ground Penetrating Radar (GPR). In the last 25 years there has been a constant improvement of GPR. Its commercialization began in the 70’s and the First International Congress of GPR Applications was held in the U.S.A. in 1986. There have also appeared a lot of publications about GPR and its applicability has spread throughout geology, minery and civil engineering, and geotechnical and archaeological investigations as well (Ulriksen, 1982; Lorenzo, 1994; Canas et al. 1996; García, 1997).
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Properties of pulse radar echo reflected at cavity existing shallow underground
Authors K. Taketomi and K. WadaPulse type of ground penetrating radar having ns(10-9 s) order width has been widely used at the field of detecting buried objects such a pipe, cable and archaeological materials. The target usually exists in a few meters in depth of underground. In this case, difficulties to detect objects are estimation of the influence surrounding by dispersive medium and improvement of resolution for to choice the optimum parameters of transmitting waveform, the signal processing of receiving radar echo. Authors have been already reported to formaer problem and some signal processing method to the later.1),2) In this paper, we present more accurate calculation results and describe about properties of pulse type radar's echo reflected by cavity changing its parameters.
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Analysis of cross-borehole radar measurements for shallow depth investigations
Authors U. Hilbing and N. BlindowPrior to excavation in soil and rock, it is useful to know the subsurface structures and to know whether parts of the subsurface might be potentially troublesome or of different character than previously assumed. A case study for the near surface (0-20 m) application of borehole radar to groundwater and environmental problems is described. Surveys were performed with transmitter and receiver locations in cross-borehole configurations in the boreholes for the detection of soil and groundwater contaminations by organic compounds. The purpose of this work is to determine how electromagnetic tomography in its various aspects can be used to characterize light non-aqueous phase liquids (LNAPLs) in the subsurface.
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Testing of a georadar in tunnel drifting
Authors S. V. Izyumov, A. G. Chernokalov and S. V. DruchininThe radar [1] has been developed by Moscow Institute of Physics and Technology (MIPT) and joint stock company “Geological Prospecting” Rus. Ltd. Nine months, 3 days a week, the measurements of signals were carried out on the face and top of a tunnel, which is being built in Moscow. The results, obtained by the radar, has been comparing with results of borehole drilling. The ground is clay with limestone layers. Sometimes water infiltrated through thin horizontal layers. The drifting included a path below the Yauza river, at a depth 23 m. The radar uses separate transmitting and receiving antennas. Antenna have size 40×40×10 cm, distance between centers of antennas is 1.1 m. The antennas are of the slot type and have large “front to back” ratio. Due to that they are useful in tunnels, where reflections from metallic mechanisms seriously interfere to the operation of a radar. These antennas were developed in MIPT under leadership of Leschansky Yu.I. It appears that the reflections from metallic mechanisms near the face of the tunnel have unacceptable large amplitudes, in spite of large front to back ratio of the antennas. Roughness of the ground surface or spacing between the antenna and the ground diminishes the front to back ratio [2,3]. Except the metallic mechanisms, placed about 2-3 m from the face of the tunnel, cylindrical metallic part of the tunneling machine with diameter 4 m also give reflections. To increase the front to back ratio of the antennas the using of resistive material has been proposed. Several forms of resistive covering have been tested [1]. Resistive covering includes two blocks with size ~60×20×10 cm, placed on sides of the antenna in E plane, a layer with size 60×60×2÷3 cm below the antenna and a layer 60×80×5 cm above the antenna. As has been proposed by Chernokalov A.G., a layer of artificial easily deformable resistive material has been placed in the spacing between the antenna and the ground surface. That lead to diminishing of electric field in the spacing and attenuation of wave, passed through the spacing to the air. The using of this layer also diminishes a number of oscillations in radiated signal. Moreover, the using of this resistive layer enables to diminish the influence of roughness of the ground surface to the results of sounding. The inconstancy of a signal due to the roughness leads to false “objects” near the ground surface after processing of signals. With using of this resistive layer the number and amplitude of these false “objects” diminish.
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TDEM study of the spatial distribution of brines beneath the sea of Galilee, Israel
Authors M. Goldman, S. Hurwitz, H. Gvirtzman and M. EzerskyThe Sea of Galilee (Lake Kinneret), which is the major surface fresh water reservoir in Israel, suffers from severe salinization problems. In order to study a mechanism of the lake’s salinization, it is important to evaluate quantitatively the spatial distribution of saline groundwater beneath the lake’s bottom. To solve this problem a novel marine TDEM system has been developed and tested on the lake during the last few years. The results of the feasibility study survey, which have been presented in the first EEGS meeting in Torino, showed that the method facilitates an accurate delineation of the distribution of saline water within the upper 100 m of the lake subbottom sediments. However, owing to the sparse observation grid used in the first and following feasibility study surveys, the real 3-D distribution of saline ground water remained unknown. An extensive TDEM survey covering the lake with a fairly dense grid of points has been carried out during 1998. A total of 269 offshore and 33 supplementary onshore TDEM soundings were performed along six N-S and thirteen W-E profiles and at selected points both offshore and onshore along the whole coastal line (Figure a). The interpreted resistivities were calibrated with the direct salinity measurements in a few boreholes available in the vicinity of the lake and deep core probes taken from the lake bottom. Although the amount of the salinity measurements is somewhat insufficient to achieve any statistical significance of the results, the calibration data are so consistent and fit the appropriate data in other areas so well, that the resistivity maps and cross-sections shown below can be easily interpreted in terms of salinities using the following simple empirical expression: Resistivity (ohm⋅m) = 4507⋅ C (mgCl/l)-0.9083 . Based on the above relationship, resistivity value of 1 ohm-m corresponds to approximately 10,500 mgCl/l. Figures (b) thru (e) show examples of the resistivity (salinity) distribution within the subbottom sediments at different depths below the lake bottom.
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Mise Á la Masse measurements in hydrogeologyan example for a efficient, low cost geophysical method for hydrology
Authors W. Wolf and J. PichlerBy the changing of demands in hydrology due to new directions by environmental laws and several laws concerning drinking water reservoires, the importance of hydrology and hydrogeological investigations is permanently increasing. Several different geophysical methods have been developed for the prospection of mineral recources. JOANNEUM RESEARCH is looking for new methods, as well as for feasible applications of already existing methods to support hydrogeological investigations.
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Mapping of natural tracers with electrical resistivity and self-potential prospecting methods in a groundwater experimental test site
Authors V. Lapenna, V. Coviello, C. Fallico, E. Migliari, S. Piscitelli, S. Straface and V. TelescaA geophysical survey, based on electrical imaging and self-potential techniques, was carried out in a groundwater experimental test site located in Montalto Uffugo (Cosenza, Southern Italy). The aquifer concerned with the test site is controlled by a system of wells and piezometric sensors (Fig.1). From a geological point of view, the investigated area represents a valley of recent formation with alluvial, conglomeratic and sandy deposits. In particular, the direct soundings carried out in the wells area identified the presence of a thick layer of silty sand (from 11 to 40 m below the earth surface) covered by an alluvial layer (from 0 to 7 m) with the interpolation of a thin layer of clay (from 7 to 11 m). From this, we have the presence of a local shallow perched groundwater in the alluvium, sustained by the clay layer, and a deeper confined groundwater in the silty sand layer (Troisi et al., 1993).
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