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Near Surface Geoscience 2014 - 20th European Meeting of Environmental and Engineering Geophysics
- Conference date: September 14-18, 2014
- Location: Athens, Greece
- Published: 08 September 2014
1 - 20 of 185 results
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Enhancement of SRT And ERT Interpretations Using Time-lapse Measurements and Cross-plot Analysis
More LessSummaryAccording to the 2013 ASCE report card for America’s infrastructure, dams and levees in the U.S. are in a poor to fair condition and exhibit signs of deterioration with strong risk of failure.
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Nuclear Magnetic Resonance (NMR) Logging -Lessons Learned at the USGS Cape Cod Toxic Substances Hydrology Research Site, Massachusetts
Authors C.D. Johnson, J. Sorenson, D.R. LeBlanc and J.W. LaneSummaryOver the last 30 years, advancements have been made in developing borehole geophysical tools and methods for determining aquifer hydraulic properties that control solute transport. More recent advances in technology allow for nuclear magnetic resonance (NMR) logging of small-diameter boreholes typical of environmental studies. Advantages of the NMR logging method are that (1) NMR does not use active nuclear sources to determine water content, and (2) NMR provides depth-dependent estimates of pore-size distribution that allow for the distinction between bound- and mobile-water fractions, which is not possible with active-source logs.
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Automatic Generation of Groundwater Model Hydrostratigraphy from AEM Resistivity and Boreholes
Authors P.A. Marker, N. Foged, A.V. Christiansen, E. Auken and P. Bauer-GottweinSummaryRegional hydrological models are important tools in water resources management. Model prediction uncertainty is primarily due to structural (geological) non-uniqueness which makes sampling of the structural model space necessary to estimate prediction uncertainties. Geological structures and heterogeneity, which spatially scarce borehole lithology data may overlook, are well resolved in AEM surveys. This study presents a semi-automatic sequential hydrogeophysical inversion method for the integration of AEM and borehole data into regional groundwater models in sedimentary areas, where sand/ clay distribution govern groundwater flow. The coupling between hydrological and geophysical parameters is managed using a translator function with spatially variable parameters followed by a 3D zonation. The translator function translates geophysical resistivities into clay fractions and is calibrated with observed lithological data. Principal components are computed for the translated clay fractions and geophysical resistivities. Zonation is carried out by k-means clustering on the principal components. The hydraulic parameters of the zones are determined in a hydrological model calibration using head and discharge observations. The method was applied to field data collected at a Danish field site. Our results show that a competitive hydrological model can be constructed from the AEM dataset using the automatic procedure outlined above.
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Inverting for Lithology Using Resistivity Models and Boreholes
Authors A.V. Christiansen, N. Foged and E. AukenSUMMARYWe present an automatic method for parameterization of a 3D model of the subsurface, integrating lithological information from boreholes with resistivity models through an inverse optimization, with the objective of further detailing for geological models or as direct input to groundwater models. The parameter of interest is the clay fraction, expressed as the relative length of clay-units in a depth interval. The clay fraction is obtained from lithological logs and the clay fraction from the resistivity is obtained by establishing a simple petrophysical relationship, a translator function, between resistivity and the clay fraction. Through inversion we use the lithological data and the resistivity data to determine the optimum spatially distributed translator function. Applying the translator function we get a 3D clay fraction model, which holds information from the resistivity dataset and the borehole dataset in one variable. We apply the concept to the Norsminde survey in Denmark integrating approximately 700 boreholes and more than 100,000 resistivity models from an airborne survey in the parameterization of the 3D model covering 156 km2. The final 3D model differentiates between clay materials and different high resistive materials from information held in resistivity model and borehole observations respectively
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Assessing Soil Wetness with Airborne Radiometric Data
By D. BeamishSUMMARYA valid interpretation model for UK radiometric data requires a joint assessment of both soil and bedrock variations. Although the geological bedrock (the parent material) provides a specific radiogenic level with associated radiochemical attributes, attenuation of the signal level is controlled by soil wetness in conjunction with the density and porosity of the soil cover. Peat soils, in particular, produce readily identifiable attenuation zones. Other soil types are also predicted to attenuate radiometric signal levels but at lower wetness sensitivities. The amount of water stored in the soil is of fundamental importance to agriculture
Studies of soil attenuation zones have now been undertaken using a number of modern UK radiometric data sets. Case studies are presented which highlight the procedures and results obtained. A variety of implied increases in wetness, at the scale of the airborne measurements, have been identified across a range of soil types, including those categorized as freely draining. The level of attenuation (and hence wetness scale) remains uncalibrated since ground information on wetness is not generally available at the appropriate scal
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Salt Water Intrusion Imaging at Tybaki (Greece) Using Geophysical Methods
SUMMARYA geophysical survey was conducted at Tybaki, Crete, Greece in order to support the geological and hydrogeological studies of the existing phenomenon of seawater intrusion. This survey employed seismic refraction, transient electromagnetic (TEM) and geoelectrical methods. The later, consisted of Vertical Electrical Sounding (VES) and Electrical Resistivity Tomography (ERT). The objective of this survey was to image the saltwater intrusion at this area and map possible favorable sea water pathways. We present the combined interpretation of vintage geophysical data obtained under the research project MEDIS and the ClearWater project data. At Tybaki, the geophysical survey provided images of the saltwater intrusion which is present at the north west of the basin.
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Geophysics for the Determination of Hydrological Parameters of Karst Systems in Yucatan, Mexico
Authors S. Gruber, R. Supper, A. Schiller, D. Ottowitz, J.H. Kim, A. Maqueda Estrada, M. Hendrick and P. RenardSUMMARYIn the karstic system of Yucatan, airborne geophysics as well as ground geophysics and groundwater levelling, which were performed between 2006 and 2013, led to the generation of a general groundwater model of the area between the town of Tulum and the biosphere reserve of Sian Ka’an. However, for calibration of the model, significant parameters, e.g. the geometry of the cave system, estimates on flow velocity, as well as knowledge on the hydrological properties of the karst matrix are still missing, a necessity to derive reliable modelling results. Therefore, within a small part of the conduit system, the subsurface structure was determined in detail, applying surface geoelectrical measurements of different configurations, hole-to-surface measurements, borehole logging, drilling and tracer tests. Additionally, a low cost method based on laser scanning was developed and tested to derive a 3D model of the cave shape, which was used for calibration purpose. Results coming from different methods are compared and interpreted to derive advanced knowledge about hydrological parameters of the karst system of Yucatan.
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Complex Electrical Properties of Sand-clay Mixtures and Alluvial Sediment Samples
Authors S. Inzoli, M. Giudici, M. Mele and E. RondoliniSUMMARYThe interpretation uncertainty of DC-resistivity surveys is reduced applying Spectral Induced Polarization methods. The aim of this work is to compare the complex electric resistivity behaviour, in the frequency range from 10 mHz to 100 kHz, of saturated sand-clay mixtures prepared in laboratory and alluvial muddy sands or sandy mud samples extracted from Po plain quarries (Italy). The comparison is made on the basis of the coarse-to-fine granulometric fraction ratio, defined with a cut-off diameter of 0.063 mm. Electrical analyses are conducted within a cylindrical sample-holder equipped with impolarizable potential electrodes and results are discussed in terms of magnitude and phase spectra. Large differences in the phase spectra are observed. They are interpreted in terms of mineralogical composition, especially of the fine-grained fraction, and organic matter content. In fact, the effect of water electrical conductivity on these samples is already showed by a series of systematic tests and the textural assemblage is controlled. To evaluate the contribution of sediments’ geochemical properties, data fitting through the Cole-Cole model is proposed with satisfactorily results. Since phase spectrum is quite sensitive to the fitting parameters, also a multi-objective approach that consider separately the fit of the magnitude and phase spectra has been tested.
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Fast Mapping and Analysis of Anthropogenic Noise Sources Affecting MRS Experiments
Authors J.J. Larsen, E. Dalgaard, P. Christiansen and E. AukenSummaryThe applicability of the magnetic resonance sounding (MRS) technique in urbanized areas is limited by the inherently weak signal from the subsurface water which is often deeply buried in noise from anthropogenic sources. The noise can have spatially variations on even sub-100 m scales and the signal to noise ratio of an MRS measurement can therefore be optimized by a careful choice of the exact location. In this paper we present an instrument for fast mapping and analysis of the noise conditions at a site prior to MRS experiments. The main components of the instrument are two induction receiver coils connected to amplifiers and a digital oscilloscope controlled by a PC. Analysis of the gathered data reveals the spatial distribution of the different noise components, in particular powerline harmonics and spikes. A comprehensive noise map of a test site is presented and analyzed.
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Geoelectrical Monitoring of Complex Hydrological Processes in a Riparian Wetland
Authors S.S. Uhlemann, J.P.R. Sorensen, J.E. Chambers, P.B. Wilkinson and D.C. GooddySummaryWetlands or groundwater dependent ecosystems in general provide vital habitats for diverse aquatic and terrestrial flora and fauna. Such systems usually show a highly complex hydrological regime and are very sensitive to environmental changes. Thus non-invasive methods have to be used to investigate those processes. This paper presents the application of 2D geoelectrical monitoring to such environments which is, due to its high sensitivity to changes in moisture content and pore water resistivity, aiding in improving our hydrological understanding of these systems. After correcting the resistivity data for the seasonal temperature variations, our results highlight the need to divide the alluvium into two hydrological layers showing different characteristics. While the uppermost layer shows significant responses from biogeochemical cycling, with decreasing resistivities during spring and summer, the lower part of the alluvium shows increasing resistivities due to upwelling of more resistive pore waters from the underlying gravels. These processes, and thereby also the resistivity changes, were proven by sensors at different locations and depths, showing the same results, but with higher accuracy and sampling rate.
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GPR Tomography Feasibility Study in the Process of Air-filled Voids Search in Engineering Structures
Authors M.S. Sudakova, A.Y. Kalashnikov and E.B. TerentievaSUMMARYNon-destructive testing of buildings and structures appears acutely on the agenda. The load-bearing capacity of structures apart from the concrete strength depends on the defects of the internal structure. These defects can be caused by voids of various size and origin. The GPR is known as one of the nondestructive methods of internal structure study. In some cases the conventional GPR sounding doesn’t allow solving the problem of voids’ detection. The GPR tomography can afford a better solution, eliminating the disadvantages of the sounding and offering a quantitative result: the electromagnetic waves’ velocity and amplitude values. The present paper focuses on the analysis of GPR tomography potential aimed at the search of voids of various dimensions by the example of isometric concrete structure (a construction or a bridge pillar). Mathematic modeling and in situ measurements on a pillar with a known structure, containing a void inside were carried out in order to attain the claimed objective. The paper demonstrates that the voids within the range of two wavelengths (20sm) can be successfully delineated, regardless of their position, on the basis of the following indicators: ray bending at the boundary of the void and velocity increase by more than 30%.
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Combined Analysis of Ambient Vibration HVSR and Active MASW Method
Authors F.M. Gouveia, I.F. Lopes and R.C. GomesSummaryThe well-known non-uniqueness inversion problems of dispersion curves as well as the reduced resolution at higher depths could be improved by performing a combined analysis of data sets of different types. In this study, Nakamura’s technique or HVSR technique was applied to several ambient vibration recordings performed at the surface of alluvium deposits, in order to estimate their fundamental frequency. The shear wave velocity profiles of the soil of the studied sites were previously determined using the active MASW method. The theoretical HVSR associated to each MASW profile was determined using the program ModelHVSR and compared to the experimental HVSR curves. This program was also used for the inversion of the experimental H/V curve, in order to improve the resolution of the deepest part of soil profile and identify the depth of the bedrock. Furthermore, the HVSR deduced from surface waves approximation was also computed for each profile to evaluate the reliability of the hypothesis that surface waves dominates the wavefield.
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Different Processing and Inversion Methods for Resolving Vs Profiles in Engineering Geophysics Using Surface Wave Data
Authors A. Savvaidis, G. Kritikakis, I. Papadopoulos, N. Papadopoulos, U. Dikmen, M.D. Mangriotis, P. Soupios and A. VafidisSummaryRecent advances in Seismic Codes increased the necessity in Engineering Geophysics to use surface wave analysis as a tool.
The shear wave velocity profile had to be resolved to calculate the site amplification in case of an earthquake event, necessary also for seismic hazard studies. In our approach we present the results from Surface Wave data acquired in different site in Crete Island (Greece) at strong motion sites. Passive and Active data at linear and circular geometries have been analyzed and the corresponding processing and inversion results are compared. Although one would comment that there are discrepancies on Dispersion Curve results the resulted ground profiles up to a shallow depth show considerable agreement. However, this is site dependent and in order to increase the accuracy and reliability of results one should be careful with the assignment of different modes in surface wave analysis and also combine the results provided.
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Integration of Magnetics and GPR Methods to Map Buried Tubes of a Pipeline
Authors M.A. Barsottelli-Botelho, A.R. A.S. Meneses and L.A. MesquitaSummaryIt is tested the magnetic method efficiency to detect and map buried tubes in a pipeline and also one second procedure which integrates the magnetic method with the electromagnetic method of Ground Penetrating Radar (GPR). Both geophysical methods acquire data on saturated and not saturated soils, the research uses areas where the pipeline crosses one river. The data acquisition with both geophysical methods uses profiles perpendicular to the pipelines situated at two areas, one at São Paulo and other at Bahia states, Brazil. The definition of pipe position on magnetic data map uses forward modelling in order to establish patterns of signatures of magnetic anomaly and its derivatives. The modelling illustrates approximately the response of pipes in terms of magnetic dipoles associated to cylindrical and spherical bodies. The GPR is very effective to locate the pipes and it is also able to inform the depth of the buried pipes but at saturated soils, as the ones close to the rivers, the GPR usually decreases its ability to detect the tubes and the use magnetic methods became more important. The combination of GPR with the magnetic method increase the success of mapping buried tubes of pipelines.
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Tunnel Pre-investigation - Towards a Resistivity to Rock-quality Transform
Authors S. Bazin, A.A. Pfaffhuber, H. Anschütz, G. Grøneng and C. ChristensenSummaryThe aim of our study is to assess whether resistivity may be transformable into an engineering parameter such as the Q-value and can substitute seismic investigation when not practicable. ERT has the advantage of being efficient, reliable, silent and non-destructive, therefore suitable in urban areas.
We have integrated Q-values derived from core drillings and geological logging during tunnelling and resistivity derived from surface ERT on two tunnel projects in Norway. In both cases, it is qualitatively evident that lower resistivity points towards weaker rock. Indeed, preliminary results can partially show the expected correlation where resistivity data co-align with boreholes or the tunnel.
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Geophysical Methods for the Assessment of the Ejection of Sand Due to the Liquefaction in the Mirabello Area
Authors L. Baradello, F. Accaino, S. Pepi, C. Vaccaro and D. NietoSummaryThe principal effects of the earthquake (ML 5.9) happened at May 20th, 2012 in Emilia Romagna (Northern region of Italy) were the ruptures and the ejection of sand due to the liquefaction of sand layers present in the subsurface. This study has pointed out the ability of the geophysical high resolution techniques to map the shallow subsurface extent of both fractures and, under certain conditions, the liquefied sand bodies too. In fact while Ground Penetrating Radar investigations detected the fractures in the upper part, seismic reflection profiling gets the possibility to trace back these fractures at greater depths. The results achieved in a test site, a paleo-river bed of the Reno river in Mirabello, permit geologists to obtain proper characterization of the subsurface of the damaged buildings and engineers to aid in formulating appropriate site-specific solutions.
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Detection of Water Caused Channels and Voids in Loos Soils
Authors E. Toros, Z. Pronay, P. Tildy and B. NeduczaSummary2010 was a wet year in Hungary. The heavy rains caused serious damages, especially in loose soils. Two case studies are introduced, how geophysical investigations are supplementing the geotechnical studies to detect water damages. In the first case the influence of successive rainwater on loess area was investigated, secondly the geological structures susceptible to river jetting were looked for alongside the River Danube. The research tool primarily was GPR to look for near surface water caused channels and sinkholes and carefully planned 3D resistivity measurement was used to find sandy aquiferous structures on water jet area.
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Quarry Blasts Assessment and Their Environmental Impacts on the Nearby Oil Pipelines
By A. MohamedSummaryAbstract
Ground vibrations induced by blasting in the cement quarries are one of the fundamental problems in the quarrying industry and may cause severe damage to the nearby utilities and pipelines. This research paper presents the results of ground vibration measurements induced by blasting at the National Cement Company (NCC) southeast of Helwan city, Egypt. The aim of this study is to investigate the influence of the quarry blasts on the oil pipelines of SUMED Company. The seismic refraction for compressional waves and the shear wave velocity obtained from the Multi channel Analysis of Surface Waves (MASW) are used to evaluate the closest site of the two pipelines to the quarry blasts. The results demonstrate that, the closest site of the two pipelines is of class B, according to the International Building Code (IBC) and the safe distance to avoid any environmental effects is 650 m, following the deduced Peak Particle Velocity (PPV) and Scaled Distance (SD) relationship (PPV = 440.64 × SD-1.225) in mm/s and the Air over Pressure (Air Blast) formula (Air Blast = 152.87 × SD-0.071) in dB. In the light of the prediction analysis.
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Detection of Underground Cavities and Weak Zones from Multi Channel Analysis of Surface Waves
By F.A.I. HamdiSummaryThe Multichannel analysis of ground roll dispersion data was shown to be a very effective and adaptable non-destructive tool for the detection of adverse strata and cavities within the underground of the sites for engineering projects. The two examples, which are selected, cover some of the applications of the technique in small-scale surveys to define ground conditions, which may affect civil engineering construction works.
The technique should be allied with the results of calibration boreholes drilled at selected locations along executed seismic profiles. Using this information hazardous ground conditions can be accurately described delineated and where necessary, successfully treated.
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Non-linear Ground Motion Simulation at the Sites of Atalanti Gulf Area for the Case of Real and Hypothetical Earthquakes
Authors T.I Novikova and V.K. KarastathisSummaryWe perform numerical simulation of the ground motion and liquefaction at several sites located at the coastal area of Atalanti Gulf (Greece). To incorporate region-specific geologic effects in the ground motion and liquefaction hazard estimates, subsurface information, particularly Vs and dynamic properties, are compiled and evaluated with the aid of geophysical methodologies and borehole testing respectively.
The possible non-linear soil behavior at the investigated sites is examined for three selected earthquakes. In two cases, real records, obtained from the NOA database, are used as input motion. In third case the input motion is computed using a stochastic simulation technique, for the scenario earthquake of the 1894 Atalanti main shock with M=7.0.
The results of the modelling show that in the case of an earthquake with magnitude Mw=5.4 all sites amplify the input signal to some degree. In case of Mw=6.7 earthquake almost all investigated sites will exhibit liquefaction initiation. An exception is two sites: one, where strong amplification of input motion by the shallow soft layers is expected; another one, located very close to the eastern segment of Atalanti fault, where obtained surface motion is not significantly changed through the structure. The Atalanti earthquake produces both effects liquefaction and amplification.
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