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Near Surface Geoscience 2012 – 18th European Meeting of Environmental and Engineering Geophysics
- Conference date: 03 Sep 2012 - 05 Sep 2012
- Location: Paris, France
- ISBN: 978-90-73834-34-7
- Published: 03 September 2012
101 - 120 of 194 results
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Shallow Water Integrated Geophysical Survey - A Case Study with Geological and Hydrogeological Consequences
Authors C. Grangeia and M. MatiasFresh water wetlands are usually sanctuaries to wildlife and important recharge areas for groundwater. In these areas, groundwater-surface water exchange occurs and it depends, among other factors, of local geology. Hence, management of these wetland areas should include detailed information about the local geology and hydrogeological particularities. To investigate these aspects, geophysical methods can be very a very useful tool to obtain information from concealed formations and assist in the minimization of environmental stresses. However, the use of geophysics in wetlands requires the design and construction of dedicated equipment and proper navigation and positioning techniques. The application of geophysical techniques in a sensitive wetland, Pateira de Fermentelos fresh water lagoon, is herein presented. For a successful survey equipment was specially designed and constructed, that is, a 65 m long resistivity floating multicable and a floating 24x24 m, coincident loop to be used with TEM equipment, as well as specific navigation procedures. The quality of the results show that these equipments can be used in other shallow water environments. These equipments allowed fast, efficient and accurate field operations. Modelling and interpretation of geophysical data provided most valuable information regarding geology, geological discontinuities and groundwater-surface water exchanges.
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A New Downhole, Real Time and Near Field Hydrogeophysical Observatory of Groundwater Quality
Authors J.P. Bellot, D. Neyens, P. Pezard, S. Barry, B. De Mezzo, G. Henry, O. Depraz, L. Baqué, L. Depraz and M. CherpionThe downhole imaGeau observatory provides an opportunity to deploy a vertical string of sensors probing outward into the reservoir in order to study changes over time of pore fluid electrical conductivity (hence salinity) and/or saturation. This in-situ set-up is based on near-field and high resolution (in space and time) measurements of formation electrical resistivity in aquifers. This paper presents results related to the salinization of a coastal aquifer exploited for the city of Hossegor (SW France). The subsurface measuring device (SMD) observatory has been located in the near vicinity of the city pumping station for domestic use, where increasing water salinity have been measured over the past 10 years. More than 9 months of daily probing show not only seasonal changes changes but also an heterogeneous profile of pore fluid salinity, far from the first order model expected from the Ghyben-Herzberg gravity model. These more detailed data will lead to more adequate aquifer management strategy in Hossegor. As a consequence, the technology deployed by imaGeau demonstrates to provide an answer to a series of hydrogeological issues such as salt water intrusion in coastal aquifers, pollution studies whether in a petrochemical or dump site context, or else pollution prevention or remediation.
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Integrated Geophysical Investigation Prior to Excavation in a Quarry of Milos Island, Greece
Authors G. Apostolopoulos, S. Stamataki and G. AmolohitisA preliminary geophysical investigation takes place in an area near the edge of a bentonite quarry in Milos Island run by S&B company in order to detect subsurface formations affecting mining planning and the stratigraphy in 25m depth for engineering purposes. Measurements with EM method gave the conductivity distribution in two exploration depths (3m and 6m) showing the stratigraphy and possible local features related with “linear” contouring. ERT profiles gave the same in a greater detail in a more narrow area of interest. Georadar profiles have faintly shown some features within the surface conductive layer. Finally, the stratigraphy has been detected and the area of interest with local findings has been outlined.
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Mobile Geophysical Methods Application for Establishing the Causes of Buildings Deformation
Authors M.A. Yakymchuk, S.P. Levashov, I.N. Korchagin, Y.M. Pischaniy, V.V. Prilukov and Y.M. YakymchukThe results of application of the complex of geoelectric methods of forming short-pulsed electromagnetic field (FSPEF), vertical electric-resonance (VERS) and georadar soundings in the areas of two apartment buildings in Kiev are given. It was established by geophysical studies that the appearance of cracks in the walls of problem houses are due to the man-made and natural water flows.The following conclusion is done: it is necessary in obligatory order to take into account the underground water flows when undertaking the design work for the buildings, industrial structures and objects of the transport infrastructure construction. The neglect of underground flow brings to the essential waste of time and financial resources. The finding and mapping of water flow and area of the raised soil moistening can be realized operatively by complex of used geophysical methods. This complex can be also used for solving the specific engineering-geological problems during new objects construction, as well as for regular monitoring of the engineering-geological condition of environment in areas of already constructed objects.
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Volumetric Remote Monitoring of an Earth Embankment: Part II - Visualisation and Condition Assessment
Authors J.E. Chambers, D. Gunn, P.I. Meldrum, P.B. Wilkinson, C.J. Munro, M. Kirkham, J. Wragg, O. Kuras and S. HolyoakeWe describe a study in which time-laspe electrical resistivity tomography (ERT) has been used to investigate an aged (>100 years old) section of earth embankment on an operational railway (Great Central Railway (GCR), Nottingham, UK). Monitoring has been undertaken using a permanently installed ERT array extending across the embankment from toe to toe. Part I of the study (Munro et al., 2012) describes our approach to ERT data collection and processing, including corrections for seasonal temperature changes, and the implementation of a procedure to translate time-lapse resistivity models into gravimetric moisture content. Here, in Part II of the study, we use the derived models of gravimetric moisture content to assess the internal condition of the earth embankment. These results show that this can be monitored noninvasively, and at a high spatial resolution, using ERT.
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Gravity Vertical Profiling in the Shaft Mining “Sosnica – Makoszowy”
By M. LojThe main objective of this study was to detect loosened zone in the vicinity of the rock shaft within the accuracy of the method of microgravity. The position of these zones can be one of the causes destabilization of the shaft. Rocks around the shaft undergoes weakening threatens its stability, depending on the degree of reduction in the density of rocks in the vicinity of the shaft. The solution to this problem was carried out by analyzing the results of studies of surface microgravity method and separation density complexes based on the results of gravity vertical profiling (PPGR). This paper presents the results of state farm PPGR.
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Electrical Resistivity of the Kotlin Clayey Formation: a Combined Interpretation of Physical Properties
Authors K. Titov, G. Gurin, D. Lantsova, M. Kostin and A. MarenkoIn this paper, we present an application of the resistivity model based on a modified Archie’s law (Glower et al., 2000), and accounting for a conductivity of clay material, to the Kotlin clayey formation (Vendian age, St. Petersburg, Russia). We compare theoretical prediction of the model with experimental data based on the well logging and laboratory measurements of the core porosity and granulometric composition. We found that the experimental data are in agreement with the model prediction for the case of salty formation water (about 35 g/l). This fact is in accordance with sea conditions occurring in the region in Quaternary period. Considering an abundance of sandy aquifers with fresh water in the formation, we believe that because of the salt diffusion, the formation water salinity in clayey sequences must be low in the vicinity of aquifers, and much larger in the middle of the sequences. Because the swelling pressure increases with decrease of the pore water salinity, clay with fresh water can be of high porosity. With this hypothesis we can explain an appearance of a seismic reflector at the depth of 60 m, which coincides with any lithological boundary, and which can be related to the high porosity zone.
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Subcritical Crack Growth in Sandstone in Water with Various Electrolyte Concentrations
Authors Y. Nara, R. Nakabayashi, N. Hiroyoshi, T. Yoneda, K. Kaneko, S. Murata and T. IshidaIn order to ensure the long-term integrity of structures in a rock mass such as the repositories of radioactive wastes in underground knowledge of subcritical crack growth is essential. The underground water can be fresh water or salt water with different electrolyte concentrations. However, the influence of electrolyte concentration on subcritical crack growth has not been clarified. In this study, we have measured subcritical crack growth in Berea sandstone and Shirahama sandstone in distilled water and in salt water (sodium chloride solution) with various concentrations. Specifically, we have investigated the influence of the electrolyte concentration on the relationship between the stress intensity factor and the crack velocity. It is found that the electrolyte concentration affects the relation between the stress intensity factor and the crack velocity for sandstone which contains smectite, and has little influence in sandstone which contains few clays. For the sandstone containing smectite, the crack velocity decreased and the stress intensity factor increased with increasing the electrolyte concentration because of the reduction of repulsive force on the surface of expansive clay at high electrolyte concentration. It is concluded that the rock containing expansive clay becomes more stable under salt water condition.
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New Petrophysical Model Describing the Acoustic Hysteresis
Authors J. Somogyi Molnar, A.N. Paripas, M. Dobroka and T. OrmosIn this paper a new theory is developed which describe the pressure dependence of seismic velocity and deals with acoustic hysteresis. The model is based on the idea (accepted in the literature) that the microcracks closed during pressurization do not reopen completely during depressurization. The model was applied to acoustic P wave velocity data sets measured on core samples originated from oil-drilling wells. The model parameters of the petrophysical model were determined by inversion method. During the measurements the pulse transmission technique was used. Measurements were carried out at various incremental pressures and parameters of the model were determined by linearized inversion methods. The calculated data matched accurately with measured data proving that the new rock physical model describing acoustic hysteresis applies well in practice.
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Ultradetailed Environmental Magnetic Investigations in Ukraine
Authors O. Menshov, A. Sukhorada, R. Homenko and O. KruglovThe significant and valuable results at high-resolution environmental investigations using magnetic methods are obtained in Ukraine. The ultradetailed magnetometry is the complex magnetic investigation of the geological surroundings including the magnetic survey with unlimited minuteness and studying of rock-magnetic properties and environmental magnetism including soils. The combination of the ultradetailed magnetometry with equally detailed investigations of the environmental magnetism brings the new conditions for understanding the nature of anomalous magnetic field. These data are very important at the investigations of the flanges outcrops, crystalline basement, prospecting of minerals, oil and gas exploration, agriculture, soil science, ecology. The determination of the accuracy of survey is required at the stage of selecting a rational methodical complex of magnetometry. Investigated objects were reliably identified with an accuracy above 0,5 nT. One of the most important results of the investigations is that one-time survey of the territory is enough. The magnetic characteristics decrease under the conditions of eluvial landscapes and the influence of geochemical processes of salt. The minimal values of the soil magnetism are specific for hydromorphic sites of landscapes. Often, these processes could not be fixed with visual image. In the same time, these hazards effect on the conditioning of agricultural land.
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Application of Joint Inversion and Fuzzy C-means Cluster Analysis for Road Pre-investigations
Authors K. Hellman, T. Günther and T. DahlinCollated DC resistivity and seismic profiling has become a popular method when doing pre-investigations for infrastructural projects such as roads and tunnels. The motivation behind the usage of two methods is that combined usage of both of these methods can decrease the ambiguity inherent to the individual use of these methods. Several software packages for inversion exist, but possibilities to combine several geophysical methods are limited; research algorithms that have this functionality exists and are evaluated herein. Joint inversion and fuzzy c-means cluster analysis are potentially ways to get the most of the collated data; thus enabling the methods to enforce each other is such a way that interpretation could be improved. These methods were applied on a field dataset from a pre-investigation of a new road. The joint inversion did not result in any major changes in the inverted models for this example, probably due to the very complex geology. The cluster analysis provides an additional tool for interpretation; highlighting for example a dolerite dyke, which can have strong influence on the construction and planning process.
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Damage to Foundations Produced by Swelling Soil in Smara, Morocco - Mineralogical and Geotechnical Characterization
Authors A. Kchikach, M. El Bakay, B. Toubane, A. Abdelghaffar, R. Guerin, R. Hakkou and H. BouzahzahThis paper deals with a characterization study of swelling mudstone, which is the major constituent of the stabilized layer used for the foundations of the city of Smara, in the south of Morocco. Granulometric analysis and determination of the Atterberg limits revealed that the clayey fraction of the mudstone is insufficient to explain its swelling characteristics. X-ray diffractometry, together with the examination of several samples under a scanning electron microscope, show that this property has its origins mainly in the presence of sulfate minerals (gypsum and anhydrite) contained in the mudstone matrix. In situ rigid plate tests, using loading pressures of 3, 5 and 7 bars for each studied site, allowed the swelling pressure of the Smara mudrock to be determined. The measured values vary between 2.5 and 6 bars, and should be taken into account to improve the size of the foundations in this city.
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Transmitted Wave Technique in Coal Mines
Authors A. Salnikov, O.M. Sagaidachnaya and B.A. KanareikinSeismic researches are carried out for the purpose of exposure of geological breaking zones in the extraction pillars of coal mines (realized by “NTC Vostochnii” limited company (Kemerovo) and FSUE “SNIIGGiMS” (Novosibirsk) in Kuznetsk Basin, 2010 2011). Solving this problem could result in lowering the considerable expenses which mines suffer when a breaking zone is found that wasn’t expected or has uncertain configuration. With seismic data obtained with POCA-A autonomous station (patents RU 2366981, 90223, 103937), the registered wave identification is carried out, the systems of wave hodograph curves are constructed, the seismic tomography processing of waves passing through the medium is carried out, and features of coal-bed structure and borders of its erosion are specified.
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Method, Technology and Results of Engineering-seismic Researches in Industrial and Hard to Reach Regions of Siberia
Authors V.M. Soloviev, V.S. Seleznev, I.Y. Kulakov, A.V. Liseikin and A.E. ShenmayerIn the last decades in Russia the volume of industrial and civil construction in Siberia is increased. It is connected with considerable expansion of volumes of oil-and-gas production, construction of the gas pipelines, new highways and trunk-railways. At the same time many regions of work are hard to reach areas, it is rather difficult to realize detailed geological engineering surveys there. On the most parts of Siberia territory there is extended the permafrost zone up to 100-300 meters. Within this zone there are local areas of thaw rocks extending to a depth of few meters to several tens of meters. Under such conditions the role of complex geophysical and, first of all, seismic methods essentially increases during design and building of industrial and civil objects for detailed studying of the upper part of the section structure, exploration of fault areas, low- velocity zones of thaw rocks, etc. The paper presents the materials of complex engineering-seismic researches using systems of observations, excitation sources and equipment on sites of railway tracks construction in a number of hard to reach areas of Siberia.
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Standing Wave Method in Engineering Seismology
Authors A.F. Emanov, V.S. Seleznev, A.A. Bakh and A.A. KrasnikovStanding wave field, different from other waves by coherence property in time, is always formed in closed spaces. Standing waves extraction from recorded wave fields on filtering basis by coherence in time and conversion of nonsimultaneous observations in simultaneous standing waves records in studied objects forms the basis of standing wave method. The method performs well in study of self-induced buildings vibrations. Amplitudes and phases maps of standing waves in set of natural frequencies fully characterize object and allow to determine not only seismic stability, but realize physical state diagnostics at a constructional elements level. In microzoning the standing wave method performs well as direct research method of resonant properties of section. As a result of standing wave method use we have set of section natural frequencies and vibration amplification maps. On the basis of maps of standing wave phases a resonance type is simply set. The resonances, formed as multiples between horizontal boundaries, have the same close phase on area, whereas in lenses and block mediums horizontal resonances may appear characterized by banded change of areal phase. Combination of high-accuracy study of resonant properties of areas and buildings provides a new echelon of accuracy in seismic risk assessment.
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Diagnosing of Pipeline Supports Instability using Acoustic Noise (Physical Modeling Data)
Authors YU.I. Kolesnikov, K.V. Fedin and A.A. KargapolovOn the physical modeling results the possibility of determination of pipelines natural frequencies and mode shapes using acoustic noise records is demonstrated. It is shown that this information can be used for diagnosing instability of above-ground pipeline supports. Partial and especially total support instability expanding the length of pipe segment between stable supports leads to sharply change of flexural standing wave field structure. In the places of stable supports always the nodes of standing waves are observed, but decreasing of clamping rigidity leads to change of this regularity. In particular, for a pipeline with the same length of initial segments the antinodes will be observed in the place of unstable support for the odd modes.
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Crosshole Tomographic Imaging of Velocity and Attenuation Structure
Authors A. Syahputra, F. Fatkhan, A.D. Nugraha and R. SuleCrosshole tomographic can be used for geotechnical purposes. We conducted data in the ITB campus. We used two boreholes with a distance of 19.8 m. The first one have a depth of 39 m and the second one have a depth of 19 m. Seismic wave sources were generated by impulse generator and sparker and then they were recorded by borehole hydrophone with 12 channels. Recorded first arrival time is reconstructed by using pseudo bending ray tracing method. For the tomographic inversion procedure, we started from 1-D model as initial velocity model and set up block size of 1 x 1 km2 for model parameterization. LSQR method is applied to solve the tomographic inversion solution. First, we determine velocity structure among two boreholes and then we used waveform data to invert for attenuation structure (1/Q). The input for attenuation tomographic inversion is t*. This parameter is obtained using spectral-fitting curve method. As results, velocity structure show three layers of soil including unconsolidated layer (down to 8 meters), consolidated layer (from 8 m down to 20 m), and bedrock (>20 m). High attenuation layers are observed at depths of 14 m to 24 m that may relate to water saturated condition.
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Urban Geophysical Investigations to Map Karstic Conditions for Planned Tunnel Construction, Doha, Qatar
By K. MartinezThe city of Doha is undergoing rapid expansion with extensive infrastructure development in progress. The ground conditions in Doha however are karstic, which is a major risk during construction. Cavities and sinkholes are known to exist in the Doha area in various sizes up to several hundreds of cubic meters. As part of the transport infrastructure development a series of cut and cover tunnels are planned in central Doha. Dependence on geotechnical drillings along the tunnel alignment is insufficient to fully ascertain the risks of potential cavities. As part of the geotechnical investigations geophysical surveys were conducted to identify potential cavities along the planned tunnel segments. This work presents the results of geophysical surveys carried out which consisted of electromagnetic, Multichannel Analysis of Surface Waves (MASW) and Electrical Resistivity Tomography (ERT). Resistivity and MASW surveys with good quality are able to be obtained within the urban conditions of the survey site. The Weathered Limestone is able to be mapped with the MASW method. There are occurrences of low velocity zones indicating increased likelihood of cavities at identified locations. Overall the use of these non-invasive and cost efficient methods allowed reducing the number of boreholes to be placed.
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Relations between Dead Sea Sinkholes and Faults
Authors M.G. Ezersky, S. Keydar, A. Al-Zoubi, B. Medvedev and L. EppelbaumResults of a geophysical study of the sinkhole development sites in the Dead Sea costal area in Israel and Jordan are presented. Relations between sinkhole lineaments and faults have been studied using updated Seismic Reflection methodology. It was shown that sinkhole lineaments are arranged along the salt layer edge. We suggest that superficial coastal basins where salt formed were generated by sub-vertical displacements along faults. Such suggestion would agree two major competition models of sinkhole formation: structural model, considering control of faults and second one explaining sinkholes formation along salt edge. Such model suggests that salt layer edge is conformed to faults and sinkholes are arranged simultaneously along both salt edge and faults. This model will be verified shortly by analysis of boreholes and by other reflection sections carried out in past. Note, models presented in the paper enables us also to conclude that: (1) Salt edge can be considered as an ancient shoreline existing at the stage of salt unit formation (10,000 years ago). Modern sinkholes are formed along this ancient shoreline; and (2) Buried salt layer comes out far away of the modern Dead Sea shoreline permitting its investigation from surface,
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Determination of Stream Water Movements in Karstic Zones and Boundary Fresh Water Salt Water through Geophysical Methods
Authors I. Jata, H. Reci and S. DogjaniAlbania is a reach country with underground waters such as artesian, karstic mineral water etc., which require to be identified and to be in the service of community, agriculture and the industry. In this study it is treated the use of Self Potential (SP), Charge Body and the Electrical Resistance Tomography (ERT) for hydrogeological studies. The ERT method was used for the first time in Albania for the determination of karstic water movements. The Vertical Electrical Soundings (VES) method is also used for the determination of contacts between salted water and soft water. The self potential SP method has been used by many authors to study the natural potential anomalies caused by the filtration of underground waters. Ogilvy (1965), started his work using the SP method, for hydrogeological studies. This method has been used successfully in hydrogeological studies, in combination with other geophysical methods such as resistivity, seismic and radiometric.
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