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4th EEGS Meeting
- Conference date: 14 Sep 1998 - 17 Sep 1998
- Location: Barcelona , Spain
- ISBN: 978-94-6282-127-9
- Published: 14 September 1998
81 - 100 of 236 results
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Elastic moduli from sonic log with high resolution
Authors C. Pretzschner and H. LindnerThe travel time of seismic waves with frequencies up to 20 kHz is measured in borehole acoustics. Registration of the acoustic wavetrain (Fullwave Sonic-Log) allows the estimation of the dynamic elastic moduli of the formation in situ. But use of this method presupposes the traveling of longitudinal (P-) and transversal (S-) waves only as refracted waves along the borehole. In practice, the formation in the near borehole is altered or damaged by the drilling process. If the source to receiver offset (spacing) is short, as is usual in engineering, the measured results mainly reflect the velocity of this altered zone. In this case the measured arrival times will tend to be greater than those of a homogeneous formation and will depend on the penetration depth of acoustic waves through the formation (Fig. 1). Because of higher penetration depth sondes with longer spacings register the true formation velocity - by loss of structural-resolution - more exactly.
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Application of borehole log data for determination and mapping of filtration parameters
By R. SeckusThe accurate determination of the filtration parameters of thick aqueous complexes that comprise sandy and clayey beds using the traditional hydraulical tools is rather problematic. It is because under unconfined aquifer conditions values of the calculated parameters depend on both duration and intensity of pumping. Additionally, the parameters that calculated from pumping test's data characterize only a small locality. Consequently, extrapolation of the results for a larger territory requires particular approach. The application of wireline log data for this purpose could be successful if relations between the hydrogeological and geophysical parameters would be established. A correlation between permeability and formation factor in clean terrigenous formations is theoretically well known. However, presence of clay particles affects the process of conductivity that results in necessity to apply corrections while formation factor is being calculated. The empirical relationship between the corrected formation factor and permeability was derived using data of detailed hydrogeological-geophysical investigation in 28 borehole. The boreholes have penetrated approximately 200-220 m of the Upper- Middle Devonian water-bearing terrigenous complex within a well field for public water supply of Panevezys town in Central Lithuania. According to this relationship the average values of permeability and hydraulic conductivity were calculated using log data from more than 200 boreholes. As a result, maps of these parameters were compiled for the territory of the Baltic artesian basin.
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Paleoclimate reconstractions on the base of geothermal borehole data for Russian Platform
More LessCollection and analysis of temperature logs for different regions of the former USSR could be the basis for geothermal mapping of territories connected with possibility of radioactive wastes disposal investigation and for future monitoring of burial areas. Geothermal data base of the Scientific Council on Geothermal Problems of Russian Academy of Sciences includes sorne thousandes of temperature logs for different regions of the former USSR. The temperature logs have been combined from 1930 on the base of geothermal measurements in hydrogeological and oil boreholes. Not all regions are investigated quite weIl. The temperature logs quality is different for different areas. The lithological columns and hydrogeological regime description exist not for all territories.
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What is the role of well logging in environmental and engineering geophysics ?
Authors M. Ali Riahi and R. NazarianIn this paper different aspects of desirable conditions In shallow weIl logging and various corrections that one must employ to provide a good picture of geological structures for important engineering purposes like dam constructions is presented. To examine the proposed corrections electrical weIl logging data of Salman Dam site were chosen. The dam site area was located in south central part of Zagros mountain ranges, Shiraz, Iran. In this project, nine boreholes and totally six thousand meters of weIl logging experiment including temperature, normal, sp, natural gamma, caliper, gamma-gamma and a case of fluid resistivity testing were logged. The results revealed temperature anomaly of about 5C, presence of low resistivity layers, under ground hot water flow and a minor fault impression,
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Computer processing of acoustic full wavetrains recorderd with LSS device
Authors M. Bala and J. JarzynaP-wave and S-wave velocities determined from acoustic full waveforms together with density log resuIts provide unique information on elastic moduli of rocks, while the Stoneley wave slowness gives knowledge of fissuring and permeability of investigated formations. Transit interval times of P-waves, S-waves and Stoneley wave as weIl as their respective amplitude and phase spectra may be obtained using computer programs for interpretation of wavetrains.
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Seismic tomography for rock quality characterization
Authors A. E. Bracci, E. Lucchi and C. B. DyerThe tomographic survey described in this paper was carried out in Montereale Valcellina (pordenone, N-E Italy) where a dam has been under construction and the rock formation on the two sides of the valley had to be consolidated. The purpose of the geophysical study was to form an image of the velocity field over the survey region from which the conditions of the rock could be interpreted.
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Electrical resistivity tomography for petrophysical investigation
Authors A. Just, T. Küpper, D. Kürschner, J. Kulenkampff and F. JacobsDetermination of physical parameters of rock samples is essential to characterize their composition and structure. One of these parameters is electrical resistivity. Depending on porosity, resistivity of the pore fluid, saturation degree and matrix properties (esp. ore and graphite content, clay content), it thus yields information about these quantities. There are different methods for its determination as integral value over the sample (TELFORD et al. 1990 a.o.). RAUEN & SOFFEL (1995) have developed a method for the determination of transversal anisotropy. But it is not possible to estimate the spatial resistivity distribution within the core by these methods. Therefore we applied the principle of tomography. With this method we are able to detect and quantify anomalies due to fractures, cristallization of mobilisates, or spatial variations of the the pore fluid.
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Evaluation of the Police cretaceous basin using well log techniques
More LessDuring a three-year regional hydrogeological project realised in the Police Cretaceous Basin (Fig. 1) all available well-Iogging data from hydrogeological boreholes were re-interpreted (33 boreholes in total). Hydrogeological bodies defined in the Basin (Fig. 2) were identified after their geophysical properties (Fig. 3) and groundwater flow was determined in particular boreholes (Figs. 4a, b). In this way well-Iogging supported significantly other methodical approaches and yielded important data for a regional hydrogeological conclusions and implementation of a numerical model of regional groundwater flow.
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Detection of a geological barrier by electrical resistivity tomography using buried electrodes
Authors B. Ullrich and M. HeydeckeElectrical Resistivity Tomography (ERT) methods have been applied within a disturbed till complex to assist in the detection of a geological barrier on a waste deposit site. Crossborehole, single-borehole and hole-to-surface direct current (DC) electrical measurements were performed. For this studies electrodes were fixed to the well-tubes at a distance of 0.5 m to each other during casing installation. Sets of pole-pole data were aquired and inverted using a SIRT-algorithm to produce resistivity images. Due to the spacing of the electrodes the achieved image resolution and depth of investigation of these techniques are between typical values of surface surveys and logging measurements. Additionally single-borehole measurements were evaluated yielding synthetic electrical logs, simulating Laterlog 7, short norm al and long normal logging tooI measurements, respectivily. The cross-borehole and single-borehole inversion results as well as the computed synthetic logs show clear resistivity contrasts between different types of unconsolidated sediments. Resistivity changes obtained from the ERT-methods image the geological structure. In comparision with surface measurements, well logging and drilling results it helps to find a consistent modell of the geological barrier.
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Karst cavities detection investigations: a case study in Kuwait
Authors W. A. Abdullah, M. A. Mollah and N. M. Al-MutairiA thorough investigation program for the detection and delineation of karst cavities was undertaken in Al-Dhahar area, Kuwait. The investigation program included, topographical and aerial, geophysical and geotechnical and geological investigations. The investigations result indicated that the karst cavities encountered had the form of thin interconnected tunnels network. There was, in general, a good correlation between the topographical, geophysical, geological and geotechnical investigations in terms of delineating the locations and nature of karst cavities. However, the geophysical investigation presented few cases of mismatching with the other investigations. The inconsistency might be attributed to either the thin, interconnected tunnels network nature of the karst cavities or due to the incorrect presentation of the gravity contour maps,
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Application of the "impact echo method" to the detection of underground cavities part I: theory and finite element modelling
Authors Ch. Leonard, B. Piwakowski, I. Shahrour, O. Abraham and Ph. CêteThe aim of this paper is to model, by means of the finite element method (FEM), the detection of underground cavities using the "impact echo method" (IEM). The detection of holes by the IEM relies on the analysis of multiple reflections of the compression wave (echoes) between the surface and the hole. The presence of echoes in the recorded signal induces, in the frequency domain, a resonance effect which can be related to the depth of the hole. In order to enhance the performance of IEM, the signal should be analysed in a carefully chosen temporal window (so that the energy of the surface waves does not mask the relevant information). An original time-frequency analysis approach is used. It enhances the resonance frequency determination and helps "choosing an optimum temporal window of observation. The obtained results enabled us to determine the parameters which may influence the resolving power of the method and to define a theoretical thresholds of detection. The experimental verification of these results, performed in real field conditions, is presented in a second part [6].
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Application of the "impact echo method" to the detection of underground cavities part II: field experiments
Authors O. Abraham, Ph. Cötel, Ch. Leonard, B. Piwakowski and I. ShahrourThis paper presents the practical verification of the theoretical results obtained in Part 1. The "impact echo method" (IEM), is applied in order to verify the possibility of detection of holes in concrete and cavities in soiI. The advantages of IEM are its simplicity and low cost. It only requires one sensor, an impulsive seismic source and a single channel acquisition system. An original time-frequency analysis procedure which enables the automatic research of an optimum temporal window of observation is used. The joint procedure including acquisition and processing is further referred as Time Frequency Analysis of Seismie Reflection (TFASR). The field experiments were performed on sites where the positions of voids are known. In the case of concrete, the experiments were undertaken on a slab with three thicknesses (0.2m, 0.35m and 0.5m) within which some pipes of different diameters and polystyrene blocks were hidden at various depths. In the case of real underground cavities, the experiments were conducted in an "ideal" setting, because the cavities are located near the surface, in chalk. Their depth varies between 3.5 m and 8 m, and their size varies between 4 m and 12 m.
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The resistivity method in void detection
More LessThe detection of void and/or partially filled caves has been attempted using all the surface geophysical methods. However, the microgravity and the resistivity seems to be the most suitable methods, although, nowadays, the radar has a more and more important role in this domain. The resistivity method has been used by several authors, Spiegel et al. (1980), D. L. Smith (1986), Andrade Afonso (1987), Andrade Afonso et al. (1989). Spiegel et al. (1980) considered the caves as void zones using the integral equation method. to obtain the solution for the pole-dipole array. Andrade Afonso (1987) and Andrade Afonso et al. (1989), generalized this method for the dipole-dipole array. However, the method is unstable for voids close to the terrain surface. So, we tested the hypothesis of approaching, for numerical proposals, the void zones to areas of high resistivities in relation to the surrounding environment. The results obtained in an automated electric analogie test tank (2,lx1,25x1,25 m), filled with a 26 Ohmxm copper sulphate aqueous solution, and in the field (caves with known geometry) were compared with the numerical results obtained by the mentioned method and with the results obtained using numerical techriiques (A. Dey et al,1979: N. C. Smith et al., 1984 and Sasaki, 1989) suitable for continuous media. The experiment al pseudo-sections for the pole-dipole, as well as, for the dipole-dipole arrays fit very well with the numerical ones.
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Cavity detection in urban zones of mexico city
Authors R. E. Chávez, A. Tejero and J. UrbietaCavities and shallow fractures on mined regions beneath urban sites of Mexico City are a highrisk problem. Electric tomography has been applied to successively detect and map these types of structures to the western side of the city. The method developed by Loke and Barker was employed to image the real electrical distribution at depth. GPR (Ground Penetrating Radar) was also used to confirm the results obtained. The area selected possesses a high rare of population and is found in the hilly portion of the city, within the Mexican Valley. Results are very encouraging, demonstrating that a multicornponent geophysical survey help to locate and characterize areas of high risk.
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Study of voids and cavities using GPR
Authors V. Pérez Graia, L. G. Pujades, J. A. Canas, J. Clapés, R. Osorio, F. Garcia and O. CasellesGround Penetrating Radar is an excellent non-destructive tooI for ground evaluations. These studies are done in pIaces where it is important to obtain information, for example, in areas where special constructions will be built or where a special use will be performed. Holes caused by flowing water, that erodes the ground materials or by their dissolution can damage the constructions performed there. The contrast between the electromagnetic parameters of the ground materials and the air or water ones, usually existing in these cavities, causes great reflections. Radar data, in areas where a cavity is placed, shows astrong reflection, which denotes the contact between .the ground and the filling material. Also, the bottom of the cavity is usually observed. So, the presence of multiple reflections is usual in these studies. The void size to be detected mainly depends of the materiaIs, the centre frequency and the bandwidth of the antenna and the speed of the antenna movement. To determine the GPR resolution it is necessary a full study of every case: equipment employed frequencies, distribution of the profiles and a preliminary geological study. Three different examples of voids are presented. The first is a great cavity caused by the dissolution of the salt. The second is the presence of small holes in the contact of different materiaIs, caused by the flowing water through the sand existing between conglomerate layers. Finally, the last is the erosion between the tunnel facing tile and the rock of the mountain where it is located. The observed radar images are discussed.
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Detection of voids in an active open air coal mine
Authors J. L. Plata and J. RodaSeveral geophysical tests have been done with the objective of selecting the most suitable geophysical method to detect the presence of the voids produced by an old underground coal mine, where the system known as "rooms and pillars" were used. The final aim is to ensure the security conditions for people and machinery during the excavation of a new open pit mine, made to recover the coal left by the old one; many of the galleries may be nowadays collapsed by falling of the roof and swelling of the clay, but some of them can constitute cavities. The coal seams have the geometric disposition shown in fig. 1; in the actual mining system, starting from a situation like the one indicated by the line AA of fig. 1, geophysical surveys are carried out on platforms like a-a, to try and know the presence of voids inside the shadowed zone, before going on digging to reach the new situation indicated by line BB. Due to the metroIogicaI requirements of most of the different geophysical methods, measurements have to be made in absence of mining activity; another conditioning for the geophysical works is the rough topography of the surrounding area and of the mine itself, which is continuously modified, allowing a very short time to make the diagnosis for the presence of cavities. So, the main characteristics of this surveys are the detection of a group of connected voids, overlaying at several depths, with the limitations which represent the mine labours.
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Detection and characterization of near surface small karstic cavities using integrated geophysical surveys
Authors D. Rousset, P. Genthon, H. Perroud and G. SénéchalAnalyzing fluid and heat transfer in a karstic zone requires a good knowledge of reservoirs and "pipes" involved in water circulation. Exploration geophysics offers several tools to deal with such problems. The studied area, the Baget Massif, Ariège, France (tig 1) is characterized by the existence of decametric caves, acting as reservoirs and smaller features connecting them. The aim of this work is to test the ability of near surface geophysics to detect such karstic pipes. We chosed a test site where hydrological data suggest the circulation of water under the topographic surface. The studied area has been comprehensively surveyed using microgravity, high resolution seismics, radar and DC resistivity techniques. The intill of the valley is composed of recent alluvial sediments, covering the limestone bedrock.
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Using resistivity technique for locating air-filled cavities and data inversion
Authors A. Denis, N. Rahmani and D. BreysseThe presence of an underground air-filled cavity modifies the distribution of the electrical potential. One of the weak points of the resistivity method for the detection of air-filled cavities is the data processing required for quantifying depth and size of an air-filled cavity. One possible way is to use data inversion. At first, numerical computations have been undertaken to look for the major parameters influencing the measurements in an air-filled cavity detection problem with resistivity technique. Then an original inverse approach of resistivity measurements is proposed. In this approach apparent resistivity is a multivariate function, variables being the depth (H), size (X, Y, Z) and surface location (Xa). Thus we have: Pa = f (H, X, Y, Z, Xa). With numerical computations three different data bases are built. Experimental data are compared to theoretical data from the different data bases by using error criteria which allow us to get depth, size and surface location of the cavity. Finally, one example of the results obtained by this inversion approach is gi ven on real field data
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Detection of underground cavaties using radar surveys and electrical imaging
Authors G. Dittrich and B. UllrichThe investigation of the inner structures of historical buildings and their foundations is a rather sofisticated task. Because of different high amplitude disturbance sources geomagnetic surveys are not successful. Gravimetric effects of cavities and tombs inside the buildings are too low in comparison to the effects from the walls and ceilings. Only ground penetrating radar measurements and geoelectric methods have proved to be an effective tool to locate the different targets and to determine their three dimensional shape. A number of applications of these methods are widely documented in the literature. Objects of interest may he cavities, tombs, crypts, foundation structures or the condition of the walls. Classical geoelectric measurements inside of historical buildings are often difficult or impossible. In most of the cases it is necessary to drill holes to coupling the current and potential electrodes with the soil. The application of methods using the electrostatic quadrupol may overcome this problem. However, such investigations requires special measurement equipment. In the present work we integrated the high resolution GPR-measurements with three dimensional conductivity information, yielded from non-destructive geoelectrical measurements. This geoelectric examinations were carried out using special electrodes and standard measurement equipment. The target of the investigation was the detection of different subsurface structures inside the St.Trinitatis church of Meissen/Saxony.
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Geophysical detection of cavities in subsoil studies for building
By M. G. GarciaSeveral studies of cavity detection by geophysical methods, mainly with ground penetrating radar, are presented in this paper. They are in conncetion with the requirements of the construction industry (buildings, roads, urban infrastructures, etc.), environmental studies or research tests. Most of them correspond to Oviedo surroundings in the Asturias region (Northern Spain). Some types of cavities exhibit a characteristic geophysical response to local effects. I consider a classification in two general types: artificial originated cavities and natural cavities. Most of the artificial cavities can be attributed to a mining origin or infrastructures, and the correspondents to a natural origin are related to different geological contexts: cavities in cretaceous sands and karstic cavities.
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