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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
101 - 120 of 196 results
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The use of the electrical resistivity tomography in the characterisation of artificial embankments and impermeable thin diaphragms
Authors G. Morelli, G. Santarato and N. Abu-ZeidExperience gained from the construction of earthfill dams and the unpleasant disasters concerning the artificial embankments have urged scientists, engineers and public authorities to develop methods for their characterisation and monitoring. Of these methods, the indirect geophysical techniques, especially the widely known spontaneous potentials (SP) method, have been used for the identification of seepage zones within the structure of the embankment (Merkler et. al., 1989). Although the method has proved to be highly cost-effective for locating seepage zones, it can't be taken into consideration due to the lack of reliable quantitative interpretations to estimate the depth of the anomalies. Among other techniques, the potentialities of employing the highly promising Geoelectrical Resistivity Tomography (ERT) can be explored to solve this kind of problems because resistivity data can be inverted to give more reliable models. These can be very useful both in characterising the embankment's internal structure and in monitoring the continuity of impermeable diaphragms, usually constructed to prevent/minimise piping, that could result in incalculable consequences. As concerning the first problem, ERT can aid in characterising the fine structure thus leading to the identification of the presence of loose and probably permeable zones. While in the second case, a specific approach can be developed to study the diaphragms either those made of bentonite or of reinforced concrete. In this paper, we present a case study conducted over part of an earth embankment along one of the effluents of the Po River (NE ltaly). The area is characterised by a recent cover of alluvial deposits with prevailing sandy silt sediments, alternated by low permeability clay levels. The geophysical survey comprised several ERT profiles carried out both parallel and perpendicular to the embankment's main axis to accomplish a final 3D model for the embankment itself and of the impermeable bentonitic diaphragm placed just near its upstream side (Fig. 1 ).
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The improvement of slopes stability calculations precision on the basis of stresses concentration limits determinations by parameters of the rocks pulse electromagnetic emission
Authors I. Kuznetsov, M. Osykin and S. PivovarovCurrently the stability of slide-prone slopes is mainly evaluated by different analytical methods based on the derived mathematical dependencies and correlation of retraining and shifting forces acting along certain shifting surfaces. These methods reflect static of the massif and do not take into account dynamic factor, i.e. stage development of the formation in rocks, that naturally brings in an error in the results of the evaluation of the slopes stability.
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Application of geophysical methods to the geotechnical investigation of the hill slope in the centre of Vilnius
Authors R. Seckus, D. Michelevicius and K. DundulisIn the last few years interest of the application of geophysical methods for geotechnical problems solution has been growing in Lithuania. Especially it was evidently after introducing of new geophysical tools: electrical resistivity imaging and ground penetrating radar. There is one example of use of these two methods as part of geotechnical investigation carried out for evaluation of the slope stability in the centre of Vilnius city.
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Geophysical investigations for stability evaluation of blood protection dams after destructive floods in the Morava River basin (Czech Republic)
Authors J. Frolka, V. Hladík, O. Pazdírek and B. PíchaIn July 1997 the Morava river basin was hit by destructive floods which cannot be compared with any disaster in this region since 1900. The centenary water-level was exceeded and, due to unfavourable circumstances, the river was in spate for almost three weeks. In several places the flood protection dams along the river were broken or poured over and many towns and villages were flooded. After the first urgent reconstructions, the question of stability of all flood protection dams along the river had to be solved. The total length of the dams along the Morava river exceeds 400 km. The dams were originally built of local materials by farmers settled along the river in the beginning of the 20th century. Neither the composition of the dams, nor the method of foundation and soil compaction are known. At first, Povodí Moravy a.s., the administrator of the Morava river basin, decided to investigate the most exposed sections of the dams, i. e. the places where the dams were overflowed and where leakages and outflows appeared. It is obvious, that for the stability evaluation of the dams, not only the dam itself and the underlying beds, but also the foreground to a certain distance from the river had to be investigated. Non-destructive geophysical methods were chosen for the first stage of the investigation as a quick, relatively cheap and reliable investigation tool. Classical engineering-geological methods, such as borehole drilling, sampling and laboratory analyses will follow in next stages to make the interpretation more accurate and to clarify some disputable results.
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Profiling complex for quality controlled monitoring of the geotechnical environment along riverside embankments
Authors P. Salát, G. Wórum and C. UbránkovicsThe environmental target: In recent years floods all over Europe drastically increased the importance of monitoring geotechnical characteristics of loose sedimentary geological environment beneath riverside embankments. The methodological aim: The goal of the presented methodological research was to solve some important soil testing problems concerning sedimentary embankment basements. The main aim was to develop a scheme of several geophysical profiling complexes for the quality controlled recognition of some frequent soil-classes (clay, silt, sand, gravel etc.) and for the quality controlled estimation of some important geotechnical parameters (porosity, permeability, consistency, clay content, silica content as well as geometry of the layers etc.) of alluvial environment under the surface into 10 m - 30 m depth along riverside earth dams.
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Geophysical investigations on river dikes in Vietnam
Authors D. V. Tuyen, T. Canh and A. WellerSituation on river dikes A network of river dikes of a total length of more than 5000 km covers the delta of the Red River in Vietnam. The social and economic development of the region around the capital Hanoi largely depends on the safety of the dike system. Monsoon rains cause a rise of the water level of most rivers in this region up to 13 m above regular level. Every year during the rainy season, the water flow results in a strong pressure on the dikes and their fundaments. Despite of thousands of people who are engaged every year to strengthen and to repair the dikes, damages caused by seepage, slides or fractures are not exceptional. The dike network has been constructed, maintained and extended for many centuries using the locally available material. Since some dike sections are crossing old lakes, ponds or even abandoned waste dumps stability problems are unavoidable. Other sections suffer from foundation damage caused by piping. A specific problem of Vietnamese dikes is the damage caused by different species of termite population. The geophysical work on dikes aims at a better recognition of severely affected sections. A joint project between Vietnamese and German geophysicists (Weller et al., 1996) was launched to test a combination of different geophysical methods to investigate two dike sections. The technology to survey dikes in Germany is based on geoelectrical methods and penetration soundings.
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The contribute of sonic and geoelectrical prospecting techniques in the study of the Giarossa landslide (Southern Italy).
Authors S. Piscitelli, M. Gallipoli, V. Lapenna, M. Mucciarelli, A. Perrone, L. Pietro and F. SdaoIn this work we focus our attention on the Giarrossa landslide, located on Southern Apennine chain close to the western side of Potenza town (Basilicata, Italy) (Fig. 1). In past and recent years this region was interested by many landslides that damaged villages, road systems and relevant engineering buildings. In particular in the investigated area on 5 December 1976 an old and large landslide, ascribed to a rotational slide – earthflow type, was totally reactivated from the main scarp down to the underlying debris layer.
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Geophysical measurement at terrain with landslides experience with effects of raining activity in the Czech Republic in summer 1997
By J. BártaIntensive rains that occurred in the Czech Republic in summer 1997 caused heavy damage including hundreds of landslide movements, out of which around 50 had direct destroying effect on buildings and facilities. The task of geophysical measurement was to contribute to getting more detailed knowledge of geomechanical conditions in landslide areas. Geophysical measurement was carried out in several stages.
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Reconstruction of complex sections of the underground pipelines
Authors Y. I. Spector and A. E. ShchepetovThe great number of gas- and oil trunk lines in Russia are under operation more than 20 years. The results of the diagnostics of the pipelines technical state show the necessity of their repair and reconstruction. The pipelines reconstruction includes the analysis of design and technological specification, operational conditions as well as calculation of a stressed-deformed state in order to define the most loaded sections of a pipeline. As practice shows, sections of the pipelines running in the complicated engineeringgeological conditions need the reconstruction in the first turn. In soft ground, in swampy or flooded areas the filling fails and the full loss of the longitudinal stability of a pipeline takes place which provokes deflection and crushing of pipes. In order to diminish a pipeline displacement, different anchoring and strengthening devices are used. One of the means of a pipeline strengthening at the design marks is its ballasting with a mineral soil, reinforced with the geosynthetical material. The geosynthetical material is laid onto a pipeline at the trench bottom (at the design marks) and on a trench slopes, it is secured at the trench berms and is filled with the mineral soil. A soil layer is built above a trench and a width of the geosynthetics. The suggested method of calculation of a pipeline stressed-deformed state and soil holding capacity allows to determine the optimum distance between the reinforcing strips of the geosynthetics. The geosynthetical material parameters (mesh size, relative elongation, breaking load, etc.) are chosen on the basis of data of the experimental investigations of combined behaviour of the geosynthetics and the filling soil.
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Strength parameter of clay in slope
Authors E. Hoque and M. Shariful IslamAbstract: Stress-states in the field under loading condition are not unidirectional, rather the magnitude of stresses differs from one element to another. The principal stresses directions, and hence the principal strains directions, in soil mass under loaded condition rotates along the potential failure surface (e.g., slope, embankment and bearing capacity failure, etc.). Therefore, the geotechnical problems are three-dimensional in slope for which anisotropy in the design parameters should be properly accounted for all possible stress paths. When an undrained failure occurs in a slope of clay, the shear strength mobilised on a failure surface may vary with the orientation of the surface either as a result of anisotropy of the clay or as a result of reorientation of principal stresses. In order to show how these two factors, hereafter termed as anisotropy, influence the undrained strength characteristics of clay, experimental investigations were done by static laboratory element tests (such as triaxial, direct shear and unconfined compression tests).
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The research of similarity criterion of seismic and electromagnetic area observation systems in a frame of the frequency – Geometrical variant
Authors O. A. Hachay, T. A. Hinkina and V. V. BodinIn the paper [1] we had stated the theoretical principles of common area observation systems for frequency - geometrical research of complicated 3-d inhomogeneous medium, using seismic and electromagnetic fields with local excitation sources. Taking in account the common morphology of the normal field, for seismic research it had been taken a local source of vertical strength, for the electromagnetic case - vertical magnetic dipole. It is of great significance for receiving of comparing information about the structure and physical features of the medium, using both wave fields, to define the similarity criterion for observation systems. In that paper we suggest such method for defining of such criterion for constructing elastic and geoelectric 3-d model. We had elaborated two original algorithms, which use as an input information 3 components of the displacement field and three components of the alternating magnetic field.
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Superparamagnetic effect above gold and nickel deposits
Authors E. Fainberg and P. BarsukovEarly in the nineties, the effect decreasing sharply efficiency of most popular and widely used TEM (Transient Electromagnetic Method) method of electrical prospecting was described in a number of publications. Especially intensively this effect manifested itself in cases when close located or coincide transmitter and receiver loops were used. Detected process of induced current attenuation contained the component with small speed of decay which partially or fully masked the useful signal. The study of rock samples producing this effect permitted to connect the measured process with the phenomena of magnetic viscosity also known as superparamagnetic effect - SPM. SPM effect is caused by the peculiarities of magnetization dynamics of ferromagnetic particles having size of order of the first hundreds of angstrom. In rocks, SPM effect is mainly connected with availability of thin-dispersive grains of magnetite, maghemite, limonite and other minerals. After switching off external magnetic field, magnetic moments of these particles oriented in exciting field relax in course of time to chaotic state according to the logarithmic law. In TEM technology the detectors register time derivative of magnetic field and SPM effect has the decay time like ~ 1/t . The results of investigations presented in the present paper were received when studying the SPM-effects produced by subsurface samples of terrigene sediment rocks and soils bedded above gold and nickel containing ore deposits. The main objective of the investigations was to study correlation between SPM anomalies and spatial disposition of ore objects. TEM-FAST ProSystem device manufactured by AEMR Ltd. and specialized induction sensor was used. In the hollow of the sensor as a core, friable samples of investigated rocks were placed. These samples were mixture of sandy-clay deposits and coils selected from subsurficial layer at the depth smaller than 15 cm. Magnetic field with ~200 A/m magnitude was created in a sample by a pulse current flowing through the sensor’s winding. The time decay voltage induced in this winding after switching off the primary current was measured during 1000 μs. The following parameters were determined using H’(t) transient characteristic: a) superparamagnetic susceptibility χSPM characterizing the “energy” of SPM effect; b) anomaly part of H’(t) process - research parameter (d); c) integrated "energy" of IP effect (Induced Polarization) characterizing electrochemical properties of rocks. Case of histories has two examples. First example presents the data received along profile crossing gold placer deposit (Chelyabinsk region, Russia). Close correlation between χSPM and χstat distribution testifies to the fact that relation of ferromagnetic grains concentration which is under SPM state, as well as larger particles, change feebly along profile being in the limits of 1:3 - 1:4. However, these parameters don’t correlate in space with deposit zones and their nature, probably, is not connected directly with gold placers. IP effect’s distribution does not correlate with ore zones and depends on water saturation of rocks: as soon as the samples get dry, IP-effect disappears.
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Recent performance evaluations and applications of the Scintrex CG-3M Microgravimeter
Authors I. Brcic and H. O. SeigelMicrogravity surveys demand high precision measurements, despite the sometimes hostile field survey conditions, which include physical shocks and vibration, ambient temperature gradients, station instability due to natural or man-made sources, and atmospheric pressure variations. In addition to the requirement for a high level of environmental tolerance, it is desirable, for certain applications that the microgravimeter should cover a very broad range of gravity (hopefully world-wide), without the need for reset. Any reset mechanism requires extensive calibration, and may introduce errors as well. The challenge to a manufacturer of gravimeters for microgravity surveys is to design and produce an instrument which can provide 1 μGal resolution, and a standard deviation (STD) of individual measurements of better than 5 μGal, but be robust enough to function well under the usual harsh environmental conditions listed above. The CG-3M is the only field portable relative gravimeter which matches all of these features. The process of independent evaluation by end users and ultimate publication of their findings is a multi-year one. It is the objective of this paper to report on the status of the Scintrex CG-3M microgravimeter in respect of this process. In the course of so doing we will provide some details of various applications of this gravimeter, both novel and somewhat more traditional. Following applications were mentioned and the references given for the papers in which the results were published:
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Further development of the CPT method
Authors P. Draskovits, B. Magyar, J. Stickel and I. FejesIn progressive soil mechanical examination and reconnaissance geological surveys the Cone Penetrating Test (CPT) is widely applied. Special features of the geological structure of Hungary necessitated the further development of the method and the enlargement of measured physical quantities. Thus the environmental examinations gained a new too) which possesses promising perspectives due to objectiveness and in-situ applicability of the method. In the beginning, the method consisted of measurement of mechanical parameters: the cone pressure necessary for penetrating the measuring probe ending in a standardized cone into the soil, and the so-called total pressure (inside the hydraulic system). Later nuclear measuring procedures have been adopted from well logging: natural gamma, gamma-gamma and neutron-neutron intensities are measured. These nuclear measurements can be carried out even in the drilling rod. The measured parameters provide information on independent rock mechanical characteristics: cone pressure on the breaking strength on the layers penetrated, natural gamma intensity on the clay content and the neutron-neutron on the water content (more precisely on the hydrogen content). Recently we are able to measure the resistivity of the surrounding of the probe pressed down into the soil.
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A new complex method for seismic and electromagnetic research in a frame of frequency – Geometrical variant by local excitation and the results of it’s practical using
Authors O. A. Hachay, T. A. Hinkina and V. V. BodinThis method is founded on the base of a three-staged conception for alternative electromagnetic and seismic (in the dynamical variant) field interpretation for 3-d high complicated medium [1]. For it's practical realisation it had been developed such theoretical and practical results: [2,3]: 1.It had been elaborated and practical realised a new common observation system for alternating electromagnetic and seismic fields with using a local source of excitation. The choice of the excitation source type had been stated by such features: a) common geometry of the normal field, b) absence of one or more components in the field, excited in the onedimensional medium. In the case of electromagnetic field such features can be achieved by an excitation source of vertical magnetic dipole type, in the case of seismic field – by a source of vertical strength type. The fact, that the chosen excitation source is local allows to provide a regular overlapping for a given observation net for different angles of directions excitation source - heterogeneity). As the input data for the interpretation we use three components of the elastic displacement field and three components of the magnetic field as a function of space coordinates and time. The analysis of the straight problem solution for seismic and electromagnetic cases shows that a common numerical approach is realisable for both fields if we preliminary convert the electromagnetic data to the real axis and seismic data on the image axis of the complex frequency plane. And the whole interpretation process must be provided on that plane, not returning to the time domain.
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Frequency analysis of acoustic wavefield in rocks under stress
Authors A. Rozanov and S. StanchitsIn this work we present the results of frequency analysis of acoustic wavefield excited in rock blocks under uniaxial compression. This work leads up to the important problem of massif stability control during mining, for example. The problem of localizing the zones of extreme mining stresses where the fracture process is more intensive is very actual for damage prediction in mines. In order to interpret the results of observations under mining conditions correctly one should study the relation between seismic signal parameters and physical process characteristics in detail. This work is aimed to investigate the acoustic wavefield frequency changes due to the changes of rock material properties under stress. We present two results of laboratory experiments: 1. Spectrum analysis of natural radiation induced by cracks during fracture process in rock samples (acoustic emission (AE) process). 2. Spectrum analysis of ultrasonic test signals (ultrasonic test was produced for attenuation measurements during the loading of the sample ). The experimental study of the crack-forming process in rocks was carried out in High Pressure Physics Institute of Russian Academy of Science. The blocks of marble and limestone with dimensions of 500 · 500 · 1000 mm were compressed along the longest axis by the unique 50 000-ton press [1]. We mounted the piezo-transducers on the sample surfaces to register the AE signals and the ultrasonic test signals. It is well known fact that the brittle fracture process in rocks is accompanied by elastic wave radiation (AE process). So the AE process is the analogy to seismic activity in mines. Then we applied cross-spectrum and coherence function analysis, and median frequency analysis to the full waveforms of recorded signals.
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Possibilities of the laser induced plasma spectrometric measurements in the environmental prospecting
Authors A. László, B. János, N. Attila and V. LeventeThere is a spectroscopic method - suitable for field application - demonstrated by the authors which can be used to solve environmental tasks too. The excitation of the plasma was performed by a Q-switched Nd:YAG laser source for the laser induced plasma spectroscopy and on the field mode equipment (LIPS the portable laser-induced plasma spectrometer)
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Evaluation of the seismic site response using the recent earthquake swarm of Basilicata region (Southerns Appennines-Italy)
Authors G. Bais, P. P. Bruno, V. Di Fiore and A. RapollaDuring the fall of 1998, an accelerometric digital (vertical component) station has been installed in two contigous sites located at the towns of Castelluccio Inferiore (CI) and Castelluccio Superiore (CS) (Calabrian Lucan Appennines, Southern Italy), with the aim of the evaluation of the seismic site response at Castelluccio Inferiore. This area is very important because in the last centuries has been interested by large earthquakes. At present the Lucanian Appenines represent a major boundary between two distinct seismotectonic areas: the Southern Appenines, characterized by NW-SE striking active normal faulting and the Calabrian-Sicilian area with EWE-WSW striking active normal faulting. Both areas are interested by earthquakes of magnitudo up to 6-7° Richter. (Turco et al.,1990; Selvaggi et al.,1997; Kiratzi, 1994; Hyppolite et al.1994). The accelerometric station was made by a piezoelettric vertical sensor with frequency response flat in 1-100 Hz. The analogic signal was digitalized by a 16 bit A/D board and finally recorded on the mass storage of a PC.The data was collected in a time interval that allowed the recording of a considerable number of seismic events in two different sites. At the first site (CS) the power spectra is referred to the bedrock because the sensor is located on lapideus rocks (limestones), at the other site (CI) the seismic response is filtered by a 25 m thick Plio-Pleistocenic overburden constituted by shale and clay with very low seismic rigidity (vp ~ 700 m/s; ρ ~ 1.1 g/cmc).
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Regional Environmental Information System of the Little Hungarian Plain (Kisalföld)
By P. ScharekWe are to demonstrate the latest results of the geological - geophysical mapping project of the Little Hungarian Plain and to show the connection between geological/geophysical data and environmental processes. It was in fact this mapping project that was processed first in GIS in the Geological Institute of Hungary and in the Eötvös Loránd Geophysical Institute.
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Estimation of durability of chemical grout USCU as preventive measures against the liquefied subsoil
By K. MnehikoAs preventive measures against the liquefied subsoil, it is easy to improve the ground. However, It is very difficult to improve the soil underneath existing structure such as a runway. Therefore, many researchers examined how to improve. As a result, it was conclude that the chemical grouting of solution type is most effective. However, chemical grout used in Japan is limited to sodium silicate grouts except in special cases. Polymer grouts that is excellent in durability, such as acrylamide grouts, are usually not used because they pose a health risk when the polymer grouts do not combine perfectly. Although the grout material is limited to sodium silicate, many types of grout based on sodium silicate have been developed however; the durability of grouts has not yet been clarified. Recently, much importance has been attached the problem of durability of strength and impermeability of grouted sand. Concerning durability of grouted sand, this paper examined estimation the methods of the long-term strength of grouted sand. As a result, we found two estimation methods. One is extrapolation method other is Arrehenius Plot method of the same shape. Consequently, it is possible to estimate the long-term strength of grouted sand.
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