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23rd European Meeting of Environmental and Engineering Geophysics
- Conference date: September 3-7, 2017
- Location: Malmö, Sweden
- Published: 03 September 2017
81 - 100 of 157 results
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Contribution of ERI, Photogrammetry and Surface Resistivity Probe Methods for Assessing an Underground Mine Pillar
Authors L.D. Dore, Y. Fargier, S. Palma-Lopes, R.A. Antoine and C.F. FauchardSummaryNatural degradation of underground quarries is seen as a major risk management topic in France. The aim of this study is to use resistivity properties of the rock material for assessing underground quarry pillars. It focuses on a quarry pillar (located in the French city of Vendôme), on which two methods were performed. The first one consists in using ERI and photogrammetry to image the internal resistivity of the pillar ; it turns out to be both informative and difficult to carry out (because of its cost and the time it needs to be performed). The other one consists in using a small in-line Surface Resistivity Probe. It proves to be an easier but also less informative method, as it gives only surface resistivity values. Internal and surface resistivity values are well correlated. Both methods show the presence of a very conductive area on which a vertical crack is visible.
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A New Database Structure Guiding the Combination of Geophysical and Geotechnical Methods for Levee Investigation
Authors T. Dezert, S. Palma-Lopes, Y. Fargier, P. Côte and C. JodrySummaryIn this study, we introduce a new database framework for levee investigation. We are considering on an equal footing geophysical and geotechnical investigation methods in order to assist the agencies and levee managers in selecting the most relevant methods for the levees’ characterization. For this to be possible, we are taking into account the environmental constraints, the pathologies and the failure modes of the levees. The other aspect of this work is to open new ways of reflection in the research community with an important bibliographic work being carried out. We first focus on the relations between pathological physical properties and failure modes of a levee in order to identify which properties and characteristics of a levee need to be estimated. Then, we display our new database framework using the example of the Electrical Resistivity Tomography method. This work finally insists on the benefits of such a structure to propose new method investigation combinations and to provide a significant quantity of references for the research community.
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Assessment of Physical Properties of a Sea Dike Using Multichannel Analysis of Surface Waves and 3D Forward Modeling
Authors D.P. Pageot, M. Le Feuvre, D. Leparoux, Y. Capdeville and P. CôteSummarySeismic surface waves analysis methods (SWM) have been widely developed and tested in the context of subsurface characterization and have demonstrated their effectivness for sounding and monitoring purposes. Given their efficiency, SWM have been transfered to several scale of which civil engineering structures. However, at this scale, many structures may often exhibit 3D surface variations which drastically limit the efficiency of SWM application which are are mostly developed under the assumption of semi-infinite 1D layered medium without topography. Taking advantages of high-performance computing center accessibility and wave propagation modeling algorithm development, it is now possible to consider the use of a 3D elastic forward modeling algorithm in the SWM inversion process. We use a parallelized 3D elastic modeling code based on the spectral element method which allows to obtain accurate synthetic data with very low numerical dispersion and a reasonable numerical cost. In this study, we choose a sea dike as a case example. We first show that their longitudinal geometry and structure may have a significant effect on dispersion diagrams of Rayleigh waves. Then, we demonstrate the necessity of 3D elastic modeling as a forward problem for the inversion of dispersion diagrams.
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Geophysical Measurements for Seismic Microzonation of the City of Huelva, Spain
Authors A. Macau, B. Benjumea, S. Figueras, A. Gabàs, A. Roca and F.M. Alonso-ChavesSummaryOne of the targets of the ALERTES-RIM (Regional and on-site earthquake early warning system for the Ibero-Maghrebian region) project is the characterization of the seismic soil response in the city of Huelva (Spain) in order to perform site effects quantification and microzonation mapping. The aim of this work is the application of a methodology based on combination of passive and active seismic techniques in order to define soft soil layers present in the study area. In this sense, H/V spectral ratio method is used throughout the city in order to know the soil fundamental frequency. Seismic noise array technique and surface wave analysis (MASW) are performed to obtain shear-wave velocity profiles of the soft soils at the different geological setups across the city. P-wave seismic reflections present in the active seismic dataset was used to map the overburden – bedrock interface as well as to image overburden reflectors. Finally, combining all these results together with the boreholes information has allowed delineating soft soil layers topography and the bedrock geometry all over the city. All this information will be used to compute ground motion amplification due to site effects and to perform microzonation studies in the city of Huelva.
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Variation of Ultrasonic Wave Velocity with Some Engineering Properties of Limestone - A Laboratory Study in Sri Lanka
More LessSummaryMiocene limestone which covers northern and north-western coastal belt of the Island is used as a raw material for various industries but only cement and lime are being used for the construction industry. The author carried out a series of laboratory tests to find out the mechanical properties of limestone in Sri Lanka with the aim of providing literature for the construction industry. The objective of this paper is to indicate the possibility to find out the uniaxial compressive strength of porous limestone using ultrasonic wave velocity.
Borehole samples (NX) of limestone were obtained from various drilling sites in Northern Province of Sri Lanka and selected samples were prepared for different laboratory tests after visual observations. The tests were carried out according to ASTM Standards at the geotechnical and materials testing laboratories.
The range (and average result) for each property can be mentioned here as porosity 1–13.4 (6.7) %, ultrasonic P wave velocity 4739–6337 (5730) m/s and uniaxial compressive strength 11–72 (35)MPa.
Ultrasonic wave velocity indicates that limestone is highly compacted and solid. According to the compressive strength of solid limestone a few story buildings can be constructed on it after a detail investigation.
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Complex Trace Attributes of High-resolution CRS Stacked Data to Interpret the Near-Surface - The Example of Solfatara Cr
By P.P. BrunoSummaryTwo active-source, high-resolution seismic profiles were acquired in the Solfatara tuff cone in May and November 2014, with dense, wide aperture arrays which allowed recording multi-fold reflection data spanning a large range of offsets; deep penetrating refracted waves, suitable for first-arrival travel time tomography, and surface waves. The reflection profiles provide the first high-resolution seismic images of Solfatara crater, depicting a ∼400m deep asymmetrical structure filled by volcanoclastic sediments and rocks. Seismic reflection data were interpreted using trace complex attributes which clearly locate several narrow (less than 10 m thick) areas with distinctive anomalous low amplitudes in several areas within the crater. We interpreted them as fluid-filled (both gas and liquid phases) conduits created by the intersection of NE- and NW-trending sets of sub-vertical faults. The imaged degassing pathways terminate against strong-amplitude zones created by reduction of porosity that occurs at about 100 m from crater surface and generates a high impedance contrast between fluid and dry soils.
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Hydrogeological and Geophysical Characterization of Fractured Aquifer of Òdena (Barcelona, Catalunya)
Authors M. Himi, D. Rodríguez-Fernández, A. Folch, R. Lovera, C. Domènech, M. Rosell and L. RivSummaryThe results of the geophysical survey reflects the presence of heterogeneity distribution of electrical resistivity values. This allowed to delimit the geometry of the three layers, as indicated by borehole logging. At the same time, it has been possible to highlight several zones with low electrical resistivity values in the central part of some profiles. These have been considered as fractured areas. In many cases, these areas of low resistivity fractures coincide with areas where the wells have registered low values of the electrical conductivity. This fact reveals the effect as preferential flow areas that have these fractures throughout the circulation system of the contaminant.
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Development of the Electromagnetic Monitoring System under the Conditions of Urbanized Territory
By T. LaskinaSummaryThe developed electromagnetic monitoring system, adapted for the highly urbanized territory conditions, has been considered on the example of the salt deposit investigation. It can be used while exploring rock massifs, lying in the range from the surface to some hundreds of meters, with the purpose to control different geological and technogenic processes with the optimum detail level and economic efficiency.
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Identification and Characterization of Hard Rocks Weathering Profile by Electrical Resistivity Imaging
Authors A. Portal, P. Belle, F. Mathieu, P. Lachassagne and N. BrissetSummaryThis study proposes an original method for the detailed characterization of the weathering profile in hard rock (plutonic and metamorphic) contexts by electrical resistivity imaging (Electrical Resistivity Tomography —ERT). The main objective is to identify the electrical signature of the different layers constituting the weathering profile, more specifically that of the laminated layer. Location of the latter is an important issue for geological (saprolite thickness assessment) and hydrogeological (location of productive boreholes) purposes.
The dual approach presented here firstly focuses on real datasets obtained from field measurements acquired in both granitic (1 site) and metamorphic (3 sites) environments. Then, synthetic modeling, based on real data results, were performed in order to test the sensitivity of the ERT method to identify and characterize the layers of the weathering profile depending on the geometry (thickness) and the resistivity of the laminated layer and the Stratiformed Fractured Layer - SFL.
The results so obtained highlighted for the first time (i) the complex electrical signature of the weathering profile, (ii) the resistant nature of the laminated layer and (iii) a resistivity gradient at the base of the SFL.
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Research of the Increased Induced Seismicity in Complex Geoecological Monitoring of Shallow Subsurface of Ukrainian Mini
Authors O.K. Tiapkin, O.V. Kendzera and P.H. PihulevskiiSummaryThe increase of seismicity of mining territory raises danger of exogenous geological processes. The cause of increased induced seismicity of mining regions is a violation of geodynamic equilibrium and astable state of the upper layer of Earth’s crust due to intensive long-term development of mining industry with powerful explosions in mines and open pits and moving huge volumes of rock. The increase of local induced seismicity of these regions is shown on example of old-industrial region in Central Ukraine — Kryvyi Rih iron ore basin. These data significantly improved information about local tectonic earthquakes on background of seismic events of technogenically-natural origin, including the effects of powerful mining explosions. Local earthquakes with M≥4.6 may be continued with the existing intensity of mining industry with powerful explosions in this region. Therefore it’s necessary localization of modern activation areas of tectonic structures with induced seismicity for the system of complex geoecological monitoring of shallow subsurface of the region. And first of all the urgent creation of local Kryvyi Rih seismic monitoring system (with instrumental seismological observations on the base of the seismic station UK-15 and with direct link with National Centre of seismological data, Kyiv) is necessary.
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CSRMT Survey on Frozen Lake - A New Technique with an Example from the Stockholm Bypass Tunnel
Authors S. Mehta, M. Bastani, A. Malehmir and L.B. PedersenSummaryMore than 7% of the Scandinavian landmass is covered with fresh-water bodies in the form of lakes and rivers. This poses a unique challenge to carry out electromagnetic survey on shallow-water bodies for various purposes for example geotechnical investigations. Recently boat-towed RMT (radio-magnetotelluric) technique was introduced and used for measurements over the Lake Mälaren in Stockholm, Sweden. The RMT covers a wide range of frequencies (10–250 kHz) and provides good resolution for shallow subsurface studies although it lacks resolution at greater depths. Using controlled-source frequencies in the range of 1–10 kHz sufficient penetration depths can be achieved for most of the near surface targets. In this study, we present the results from the combined use of controlled-source and RMT (CSRMT) data that were obtained over frozen Lake Mälaren. The objective of this study was to map bedrock surface and fractures in the middle of the profile where using only RMT data these were not adequate. We demonstrate a new technique where CSRMT surveys were carried out over frozen-shallow-water bodies and we expect the idea to be used in the near future for other applications where moderately-resistive water bodies are present.
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Geophysical Investigations to Assess the Extent of Disturbance in Excavated Rock Faces at Hinkley Point C
Authors A.L. Stork, A.C. Butcher, J.P. Verdon, A. Koe and J-M. KendallSummaryInitial field trials to investigate the potential for seismic surveys to estimate the extent of damage caused during slope excavation and to estimate a disturbance factor show that a velocity contrast due weathering/disturbance effects in a cliff face is detectable with an active seismic survey with geophones attached to the face. Modelling results confirm the resolution of the method and the experimental set-up is being deployed to monitor excavated faces at Hinkley Point C construction site.
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Combined Application of GPR and ERT to the Detection of Voids During the Construction Phase of a Building Complex in Koz
Authors G. Vargemezis, P. Tsourlos, D. Aggelis and I. FikosSummarySeveral cavities were revealed during the excavation phase of the new building complex planned to host the regional University in the city of Kozani, Combined 3D geoelectrical and GPR geophysical methods have been applied at the foundation level prior the construction phase in order to detect voids. Initially, the foundation areas have been surveyed with dense GPR scans.
GPR data were processed and combined to form depth slices and 3D volumetric information. Targets revealed by the interpretation of radar data have been further investigated by the resistivity method which was applied in a full 3D mode at selected areas.
Evaluation of the results obtained by both methods led to the distinction of different type of structures related to possible voids or fractured areas. Locations proposed by the geophysical survey have been drilled and borehole data in most of the cases confirmed the geophysical results. This helped to better evaluate the geophysical anomalies and to increase the reliability of the interpreted data. The described approach resulted either into accelerating the construction of the buildings in areas that no geophysical anomalies were found or to redesign and to redesign construction in specific areas in which voids were detected.
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Shallow vs Structure Estimation for Seismic Site Response Using the Active MASW Method - A Case Study at the Urban Area
By E.A. ObandoSummaryThe multichannel analysis of surface wave method (MASW) was utilized to estimate the soil stiffness at the urban area of Managua, Nicaragua. A total of 24 sites distributed throughout the study area, were sampled using the active walk-away scheme. The results indicates that in most of the sampled sites the elastic bedrock appears shallower than 30 meters. From the soil-class viewpoint, based on the Vs30 criterion, the soils of the area of Managua can be grouped into soil classes C and D, that is equivalent to soil types II and III of the Nicaraguan code. It appears that, the softer soil deposits occur at the western part of the city with a marked strip in north-south direction. The stiffer soils predominate at the central part of the study area that seems to decrease eastwards. Finally, when considering a shallow local earthquake, the calculated amplification function, independently of the depth of the elastic bedrock, shows that the peak ground amplification surpasses the amplification factors suggested in the Nicaraguan Building Code. This may indicate that for shallow local earthquakes the current Nicaraguan Building Code does not reflect the actual soil amplification of the area of Managua.
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GeoBIM for Infrastructure Planning
By M. SvenssonSummaryThe GeoBIM concept makes joint interpretation of geophysics and ALL other geotechncially related data possible in a convenient way. It also makes COMMUNICATION of data and models easy using only web freeware. This means that all stakeholders get the same information at the same time, which make decisions quality assured and that the efficiency in the workflow in the interpretation and the design process is significantly improved.
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Reprocessing of Geophysical Data, Comparison with Tunneling Results from the Bergen Ring-road and Subsequent Refraction
Authors G.A. Tassis, J.S. Rønning, S. Rohdewald, T. Kirkeby and M. WåleSummaryThe Geological Survey of Norway (NGU) has reprocessed various geophysical data from the Knappe tunnel in Bergen in collaboration with the Norwegian Public Roads Administration (NPRA) and Geophysix AS, the Geophysical company that originally collected, processed and traditionally interpreted refraction seismic data along the route of the tunnel. In this work we have compared different inversion schemes of refraction seismic data to each other but also to classic interpretations, resistivity profiles, geological mapping and actual observations done after the completion of the tunnel. In connection to the results obtained in the work described above, modeling was planned and carried out to test the efficiency of refraction seismic data inversion when applied to the detection of fracture zones in Norwegian settings (abrupt velocity changes between fracture, bedrock and possible overburden layers). Our goal is not to assess the Rayfract(r) software but instead to try and identify patterns created by known models when moderately knowledgeable inversion schemes are used and in this way attempt to correlate geophysical anomalies (seismic velocities) with weak zones on real refraction seismic data and plan future studies.
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GPR Survey for the Detection of Voids in Embankment of a Highway - Case Study in EGNATIA Highway in Northern, Greece
Authors I. Fikos, G. Vargemezis, P. Tsourlos and D. AngelisSummaryHighway road monitoring by means of visual inspection has been and probably will remain standard procedure for many years. However numerous examples of sudden cracks and collapses of the pavement have shown that more efficient methodologies are essential. GPR has been used extensively for this purpose. The survey focuses on the parts of the highway over the embankments that are approaching the bridge from both ways as well as the bridge’s deck. The appearance of a small hole in the pavement of the new part of the highway, only few tenths of meter away from the western edge of the bridge called for immediate evaluation of the extent of the void and inspection for other potentially future failures. In parallel with the inspection for cracks and cavities the investigation aimed to provide insight on the construction of the pavement of the old bridge and the approaching areas and compensate for the lack of realistic cross section. The method of GPR was the ideal method for this task, since it is non-invasive, very fast and very accurate when good approximation on the material’s electromagnetic properties can be achieved ( Saarenketo and Scullion, 2000 )
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3D Ground Model Using Geophysical and Geotechnical Data - A Case Study from the Netherlands
Authors V. Minorenti, D.H.R. Brouwer and K. van KesterenSummaryThis paper intends to review and stress the benefit of analysing integrated (geophysical and geotechnical) data within in a 3D environment. Over the past years concrete efforts, both in new survey acquisition methodologies and 3D computing capabilities, have been made to overcome the limitation embedded in conventional 1D/2D techniques. The 3D CPT cone resistance model was built using the kriging interpolating algorithm between the known cone resistance data points by statistically predicting the value of the empty voxel cells via a variogram. Statistical analyses (model robustness tests and minimum input tests), were used to analyze uncertainties inherited in the model and to predict the lateral extent of these uncertainties along the units. Theoretical optimum between number of geotechnical locations and model distortions were analyzed based on differences between the resulting models and variogram analyses.
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Shear Wave Velocity Structure Derived from the Microtremor H/V Rayleigh Wave Energy Rich Part
Authors R. Yazdanfar and N. Hafezi MoghaddasSummaryIn order to derive 1D Vs profile, inversions have been done only on specific part of microtremor H/V curve. This part which is between first peak and first trough, here called as Rayleigh wave energy rich of H/V curve. Inversions were done based on the neighborhood algorithm. Some available data of site such as downhole seismic, geotechnical information, surface geology and soil texture, were used for building a robust model parameter. 1D extracted velocity profiles show good agreement with traditional geophysics and inversion of the ellipticity curve results.
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Bedrock Depth Estimations and Their Limitations - Comparison between Refraction Seismics and Geotechnical Investigations
Authors R. Behrendt, E. Lundberg, C. Juhlin, F. Zhang and T. LehtimäkiSummaryIn this study, we compared a model of bedrock depth derived from a high resolution seismic dataset to a very extensive set of geotechnical bedrock depth estimations. The results of both methods are in very good agreement on the larger scale, but also show considerable differences in some locations. These differences are usually attributed to errors in the refraction model since it has generally a lower accuracy and is affected by unresolved near-surface velocity variations. However, we found several locations where the data consistently indicate that the geotechnical sounding yielded significantly too shallow bedrock estimations. Therefore, we argue that both methods should be evaluated carefully and — wherever possible — should be combined to a comprehensive dataset. Since geotechnical investigations are one-dimensional and seismic measurements are areal, they provide complementing information that can be used to reduce errors.
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